Agricultural Water Demands: Preliminary Results of Silistra Case Study

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AGRICULTURAL WATER DEMANDS :

PRELIMINARY RESULTS O F S I L I S T R A CASE STUDY

I l y a V. G o u e v s k y D a v i d R. M a i d m e n t

S e p t e m b e r 1 9 7 7

Research Memoranda are interim reports on research being conducted by the ~nternational Institute for Applied Systems ~ n a l y s i s , and as such receive only limited scientific review. Views or opinions contained herein do not necessarily. represent those o f the Institute or o f the National Member Organizations supporting the Institute.

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I n t e r e s t i n w a t e r r e s o u r c e s s y s t e m s h a s been a c r i t i c a l p a r t of r e s o u r c e s and environment re- l a t e d r e s e a r c h a t IIASA s i n c e i t s i n c e p t i o n . A s demands f o r w a t e r i n c r e a s e r e l a t i v e t o s u p p l y , t h e i n t e n s i t y and e f f i c i e n c y of w a t e r r e s o u r c e s management must be d e v e l o p e d f u r t h e r . T h i s i n t u r n r e q u i r e s a n i n c r e a s e i n t h e d e g r e e of d e t a i l and s o p h i s t i c a t i o n of t h e a n a l y s i s , i n c l u d i n g economic, s o c i a l and e n v i r o n m e n t a l e v a l u a t i o n of w a t e r r e s o u r c e s development a l t e r n a t i v e s a i d e d by a p p l i c a t i o n of m a t h e m a t i c a l m o d e l l i n g t e c h n i q u e s , t o g e n e r a t e i n p u t s f o r p l a n n i n g , d e s i g n and

o p e r a t i o n a l d e c i s i o n s .

I n t h e y e a r s of 1976 and 1977 IIASA h a s

i n i t i a t e d a c o n c e n t r a t e d r e s e a r c h e f f o r t f o c u s i n g on m o d e l l i n g and f o r e c a s t i n g o f w a t e r d e m a n d s . Our i n t e r e s t i n w a t e r demands d e r i v e d i t s e l f from t h e g e n e r a l l y a c c e p t e d r e a l i z a t i o n t h a t t h e s e f u n d a m e n t a l a s p e c t s of w a t e r r e s o u r c e s management have n o t been g i v e n due c o n s i d e r a t i o n i n t h e p a s t .

T h i s p a p e r , t h e second i n t h e ILASA w a t e r demand s e r i e s and u n d e r t a k e n a t IIASA i n c o l l a b o r - a t i o n w i t h t h e B u l g a r i a n M i n i s t r y of A g r i c u l t u r e and Food I n Z u s t r y r e f l e c t s o u r d e s i r e t o d e m o n s t r a t e t h e a p p l i c a b i l i t y of t h e r e s u l t s from o u r s t u d i e s on w a t e r demand m o d e l l i n g and f o r e c a s t i n g .

The r e s u l t s p r e s e n t e d i n t h i s r e p o r t a r e of a p r e l i m i n a r y n a t u r e - and can o n l y be i n t e r p r e t e d w i t h i n t h e l i m i t a t i o n s of t h e m o d e l ' s o b j e c t i v e and i n p u t d a t a . S i n c e t h i s o b j e c t i v e and t h e s e d a t a may n o t be f u l l y r e f l e c t i v e of a c t u a l con- d i t i o n s i n t h e ~ i ' l i s t r a r e g i o n , t h e r e s u l t s of t h e model s h o u l d n o t be t a k e n a s s p e c i f i c p o l i c y recommendations f o r t h e development o f t h i s r e g i o n .

D r . J a n u s z K i n d l e r Task Leader

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ABSTRACT

Preliminary results of the Silistra Water for Irrigation Model (SWIM) for determining agricultural iater.demanas in the Silistra region of Bulgaria are presented. For various areas of irrigated and non-

irrigated land, and various volumes of water supply, SWIM uses linear programming to select the optimal combination of crop areas and production inputs so as to maximize annual net benefits from crop production in excess of target production quantities of each crop.

Both normal and dry weather conditions are examined.

The region's import-export balance is investigated for areas of irrigated land between 10,000 and 50,000 hectares and it is shown that total costs of crop production are minimized when the region is just

self-sufficient in crop production. By means of demand curves it is demonstrated that the marginal values of land and water for irrigation are greater than their unit costs of development so that it is optimal to develop irrigation to the maximum area considered by the model.

This research carried out at the ~nternational Institute for Applied Systems Analysis was partially supported with funds provided by Stiftung Volkswagen- werk and by Rockefeller Foundation grants RF75033, Allocation No. 32, and GA NES 7712. Thanks are expressed to the Bulgarian government Ministry of

Agriculture and Food Industry for providing data on the Silistra region. In developing the model, the authors have appreciated discussions with Acad. L. ~antorovich, and members of the Food & Agriculture Program and the Resources & ~nvironment Area of IIASA. Witold Sikorski provided computer programming assistance, Helen J.

Maidment drew the figures, and the text was typed by Lana Maloney.

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CONTENTS

Page

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2.2.1 Land

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2.2.2 Water

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2.2.3 Seeds

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2.2.4 Fertilizers and Pesticides

RESULTS OF APPLICATION OF THE MODEL

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i s s i t u a t e d i n t h e n o r t h - e a s t e r n p a r t of B u l g a r i a . The a g r i c u l t u r a l a c t i v i t i e s i n t h e r e g i o n a r e c o n c e n t r a t e d i n a l a r g e a g r o - i n d u s t r i a l complex c a l l e d D r u s t a r . The t e r m a g r o - i n d u s t r i a l complex m e a n s t h a t a l l i n d i v i d u a l e n t e r p r i s e s d e a l i n g w i t h c r o p p r o -

d u c t i o n and i t ' s p r o c e s s i m g a s w e l l a s w i t h l i v e s t o c k growing and p r o c e s s i n g a r e c o o r d i n a t e d by one a d m i n i s t r a t i v e body.

T h i s body i s r e s p o n s i b l ' e f o r o v e r a l l p l a n n i n g , d e v e i o p m e n t , and management of t h e complex. S i n c e t h e complex i s d e v e l o p - i n g r a p i d l y , it i s e s s e n t i a l t o choose t h e b e s t way of

d i r e c t i n g f u t u r e a g r i c u l t u r e a c t i v i t i e s and i n v e s t m e n t s . I n t h e l i s t o f problems t o be i n v e s t i g a t e d i n t h i s r e s p e c t , w a t e r r e s o u r c e s a p p e a r t o have a key r o l e . The r e a s o n i s a t l e a s t t w o f o l d :

a ) a v a s t i r r i g a t i o n development i s t o t a k e p l a c e i n t h e coming 5-10 y e a r s t o meet t h e f e e d r e q u i r e m e n t s o f meat and m i l k p r o d u c i n g l i v e s t o c k ; ~ e n c e , t o e n s u r e s t a b l e a g r i c u l t u r a l p r o d u c t i o n , a l a r g e r e l i a b l e w a t e r s u p p l y h a s t o b e

made a v a i l a b l e i n t h e r e g i o n .

b ) w a t e r r e s o u r c e s i n t h e r e g i o n a r e r a t h e r s c a r c e b e i n g l i m i t e d t o t h e b o r d e r i n g Danube r i v e r . No o t h e r r i v e r s e x i s t i n t h e r e g i o n . Ground w a t e r i s a v a i l a b l e o n l y i n s m a l l quan- t i t i e s i n d e p t h e x c e e d i n g 400 m. which makes it a n u n i m p o r t a n t r e s o u r c e .

TO overcome t h e s e d i f f i c u l t i e s i n t e n s i v e i n v e s t i g a t i o n s have been c a r r i e d o u t i n t h i s r e g i o n o v e r t h e p a s t few y e a r s . A s a r e s u l t , a number of a l t e r n a t i v e s f o r augmenting t h e a v a i l - a b l e w a t e r s u p p l y have been p r o p o s e d . Some of them i n c l u d e c o n s t r u c t i o n of s e v e r a l r e s e r v o i r s i n v a r i o u s p a r t s of t h e r e g i o n ; o t h e r s e n v i s a g e combine u s e of pumping s t a t i o n s and r e s e r v o i r s , c o n s t r u c t i n g l o n g d i s t a n c e s a n a l s

,

e t c . The

common c h a r a c t e r i s t i c of a l l a l t e r n a t i v e s i s t h a t f i r s t l y , t h e y r e l y on Danube r i v e r w a t e r (which i s r e l i a b l e b u t w a t e r u s e i s re- s t r i c t e d by s e v e r a l i n t e r n a t i o n a l a g r e e m e n t s ) a n d s e c o n d l y , a l l of t h e a l t e r n a t i v e s are r a t h e r c o s t l y . Obviously one way of

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d e c r e a s i n g supply c o s t would be t o reduce a g r i c u l t u r a l water demands f o r i r r i g a t i o n which c o n s t i t u t e t h e major demand p a r t of t h e r e g i o n keeping a t t h e same time t h e p r o d u c t i o n t a r g e t s a t t h e d e s i r e d l e v e l . I t i s furthermore obvious t h a t reducing a g r i c u l t u r a l water demands i n v o l v e s a d d i t i o n a l c o s t s . The problem i s : a r e t h e s e c o s t s g r e a t e r than t h e supply c o s t and where i s t h e p o i n t a t which t h e water r e s o u r c e system i s i n e q u i l i b r i u m , e . g . t h e p o i n t a t which incremental c o s t of addi- t i o n a l supply i s e q u a l t o incremental b e n e f i t from demanded water?

The main o b j e c t i v e of t h e study i s t o make a thorough a n a l y s i s of f a c t o r s t h a t i n f l u e n c e both a g r i c u l t u r a l water demands and a s s o c i a t e d a g r i c u l t u r a l production t a k i n g i n t o account t h e major g o a l of t h e D r u s t a r complex, which i s t o maximize t h e t o t a l a g r i c u l t u r a l and l i v e s t o c k p r o d u c t i o n with-

i n t h e l i m i t e d r e g i o n a l r e s o u r c e s . I n t h e course of t h e study we have focused t h e main o b j e c t i v e towards providing an adequate answer t o t h e following q u e s t i o n s :

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what i s t h e amount of c r o p s a b l e t o be produced from t h e complex given v a r i o u s p o s s i b l e volumes of water supply w i t h i n t h e c o n s t r a i n t s of a v a i l a b l e r e s o u r c e s of o t h e r t y p e s : l a b o r , machinery, f e r t i l i z e r , e t c ?

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how much a r e a should be developed f o r i r r i g a t i o n and which c r o p s should be i r r i g a t e d ?

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what i s t h e export-import balance i n t h e complex i n c a s e of f a v o u r a b l e and unfavourable weather c o n d i t i o n s ?

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what i s t h e marginal p r o d u c t i v i t y of water and i r r i g a t e d land i n t h e complex i. e . how much would t h e b e n e f i t

Cor c o s t ) change i f one a d d i t i o n a l u n i t of water o r i r r i g a t e d land were provided?

The scope of t h e study i s c l o s e l y r e l a t e d t o t h e a f o r e - mentioned problems. To provide an adequate answer t o them a t

l e a s t t h r e e major a c t i v i t i e s a r e worth modelling: f e e d crop p r o d u c t i o n , non-feed c r o p production (tobacco, v e g e t a b l e s , vine- y a r d s , e t c . ) , and l i v e s t o c k production. Only t h e f i r s t a c t i v i t y , which has t h e g r e a t e s t d i r e c t impact on water r e s o u r c e s , i s p a i d a p p r o p r i a t e a t t e n t i o n i n t h e model. The non-feed c r o p production has l e s s impact on water r e s o u r c e s because of small a r e a occupied by t h e s e c r o p s and less water demands (about 1 0 % ) when compared

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w i t h f e e d c r o p o n e s . B u l g a r i a n s c i e n t i f i c o r g a n i z a t i o n s and IIASA h a v e been i n t e n s i v e l y s t u d y i n g l i v e s t o c k p r o d u c t i o n ( c a r t e r , C s a k i , and P r o p o i , 1 9 7 7 ; P r o p o i , 1 9 7 7 )

.

F o r t h i s r e a s o n t h e l i v e s t o c k f e e d r e q u i r e m e n t s are c o n s i d e r e d a s b e i n g e x t e r n a l l y s p e c i f i e d i n t h e model.

The model r e p o r t e d h e r e i n i s a p r e l i m i n a r y o n e u s i n g d a t a m a i n l y p r o v i g e d f o r u s i n a development p l a n f o r t h e complex p r e p a r e d f o r t h e B u l g a r i a n government a g e n c y Rodopaimpex by t h e c o n s u l t i n g f i r m Globe S e r v i c e s ~ n t e r n a t i o n a l . A d r a f t o f t h e r e p o r t d e s c r i b i n g t h e model was t r a n s l a t e d i n t o t h e B u l g a r i a n l a n g u a g e and r e v i e w e d i n B u l g a r i a d u r i n g August 1 9 7 7 . A s a re- s u l t , some b e t t e r d a t a w e r e o b t a i n e d and many s u g g e s t i o n s

r e c e i v e d f o r e x t e r , d i n g t h e model s t r u c t u r e t o more c l o s e l y r e p r e s e n t t h e D r u s t a r complex. On t h i s b a s i s a s e c o n d v e r s i o n of t h i s model h a s b e e n d e v e l o p e d . S i n c e t h e l a t e r v e r s i o n o m i t s some o f t h e f e a t u r e s o f t h e e a r l i e r o n e , w e h a v e d e c i d e d t o p u b l i s h t h i s c o m p l e t e d e s c r i p t i o n of t h e p r e l i m i n a r y model and i t s r e s u l t s a t t h i s t i m e and t o r e p o r t on t h e s u b s e q u e n t work on t h i s model when i t i s c o m p l e t e .

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2 . D E S C R I P T I O N O F THE MODEL 2 . 1 Overview

The - S i l i s t r a - Water f o r - I r r i g a t i o n Model

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( S W I M ) h a s been developed t o e s t i m a t e t h e amount of w a t e r needed f o r i r r i g a t i o n i n t h e D r u s t a r complex. I n t h e c o n v e n t i o n a l approach t o

e v a l u a t i n g t h e s e w a t e r demands t h e f o l l o w i n g method i s u s u a l l y employed:

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t h e a r e a t o be developed f o r i r r i g a t i o n i s s p e c i f i e d ;

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t h e a r e a of each t y p e of c r o p t o be grown w i t h i r r i g a t i o n i s d e c i d e d t a k i n g i n t o account t h e c r o p p r o d u c t i o n from n o n i r r i g a t e d l a n d ;

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c o n s i d e r i n g t h e weather c o n d i t i o n s , t h e d e p t h of w a t e r which must be i r r i g a t e d o n t o e a c h c r o p i s d e t e r m i n e d ;

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t h e t o t a l volume of water needed f o r t h e i r r i g a t e d a r e a i s found a s t h e p r o d u c t of t h e d e p t h r e q u i r e d f o r each c r o p and t h e c r o p ' s a r e a , summed o v e r a l l t h e i r r i g a t e d c r o p s .

C l e a r l y t h i s method should be a p p l i e d a number of t i m e s t o e s t i m a t e t h e e f f e c t on w a t e r demands of d i f f e r e n t assumptions c o n c e r n i n g t h e a r e a of l a n d t o be developed f o r i r r i g a t i o n ,

weather c o n d i t i o n s , c r o p p r o d u c t i o n , e t c .

With SWIM t h e c o n v e n t i o n a l approach i s b o t h computerized and extended. One can f o l l o w t h e c o n v e n t i o n a l approach, i n which c a s e f o r a g i v e n a r e a of i r r i g a t e d l a n d S W I M d e t e r m i n e s t h e o p t i m a l c r o p d i s t r i b u t i o n f o r maximum p r o d u c t i o n on b o t h i r r i g a t e d and n o n i r r i g a t e d l a n d and t h e volume of w a t e r needed f o r i r r i g a t i o n under normal weather o r d r o u g h t c o n d i t i o n s . However, S W I M c a n a l s o o p e r a t e i n t h e o p p o s i t e d i r e c t i o n : f o r a g i v e n volume o f w a t e r a v a i l a b l e , SWIM c a n d e t e r m i n e t h e

o p t i m a l c r o p d i s t r i b u t i o n , which c r o p s a r e i r r i g a t e d , and hence t h e a r e a o f l a n d which should be developed f o r i r r i g a t i o n .

Moreover, s i n c e SWIM i s computerized, w i t h l i t t l e e x t r a c o s t i t c a n be used many t i m e s t o d e t e r m i n e t h e o p t i m a l s o l u t i o n f o r d i f f e r e n t assumptions c o n c e r n i n g i r r i g a t e d l a n d a r e a , w a t e r a v a i l a b i l i t y , weather c o n d i t i o n s , e t c .

A v e r b a l d e s c r i p t i o n of SWIM now f o l l o w s . A d e t a i l e d mathematical d e s c r i p t i o n i s g i v e n i n Appendix 2.

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In SWIM, the crop production system of the Drustar ccn;~le::

is visualized as shown in figure (2.1). The system consists of three parts: resource inputs, crop production, and crop outputs. These outputs may be used to meet the requirements of the population and livestock in the region, or they may be ex- ported to other regions within or outside the country.

From the overall viewpoint, Drustar is an agricultural-industrial complex whose primary output is from

animals: pigs, dairy cows, cattle, and sheep. Based on the

necessary diets of these animals, and the number of the different types of animals in the complex, the total amounts of feed required for livestock of each of the crop outputs may be calculated and these are considered as being externally specified

to SWIM. Likewise the requirements of the population for cooking oil and flour are externally specified. All of these requirements

are met in the solutions of SWIM. Any extra production beyond these requirements is assumed to be sold for export at internal Bulgarian prices. In case of unfavourable weather, maize grain can be imported at a price greater than that for export (for example 50% ~reater)

The objective of SWIM is to maximize the value of these exports minus the costs of all production, including %he costs of the crop outputs used within the region. All costs and prices are measured in Bulgarian Leva (1 Lv= 1 $US). The production

costs are calculated in the following way. For each crop the basic unit of production is one hectare. The amounts of the

input. resources of water, seeds, fertilizer, fuel, labor, and macl~inery needed for one hectare of crop are estimated, and their costs computed as the product of the amount of the resource and its unit cost. All other production costs which are not directly connected to the input resources (such as the cost of storage buildings, or administration) are summed up and assigned to the unit hectare of each crop as a lumped cost.

For any area of each crop the corresponding production cost can then be calculated. There are seven crops, see figure (2.1 )

,

each of which may or may not be irrigated, so SWIM considers 14 crop alternatives in all.

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INPUTS

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LAND WATER Seeds Fertilizers

hay Requirements I J

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SWIM determines the optimal area of each crop alternative so as to meet all the production requirements and maximize the objective previously stated.

SWIM is formulated and solved on the computer as a linear program. All quantities to be optimized in SWIM are included as decision variables (e.g. areas of each crop, amounts of each resource used). These variables are interrelated through a number of constraint equations which express the physical limitations of the system (e.g. sum of all crop areas must equal the total area, water used cannot exceed water available). All of these equations are linear which means that a change in one

variable leads to directly proportional changes in all the other variables related to it. SWIM currently contains 60 decision variables interrelated through 70 constraint equations involving

400 data values. It has been solved more than 50 times for the different sets of conditions described in this report.

In the following sections, the structure of SWIM is described in more detail following the scheme of Figure (2.1). In section

(2.2) the methods of calculating the amounts of resource inputs and their unit costs aregiven. Section (2.3) describes the production schedule of field operations for each crop and their cost. The crop outputs are shown in detail in section (2.4).

2.2 Input Resources 2.2.1 Land

The remaining arable land amounts to 121,600 ha of which a small

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part (about 3000 ha) must be reserved for seed production.

SWIM determines this seed area in its solution.

The main soil type of the region is Chernozem (Black Earth), which is subject to erosion in some areas. Although there are natural variations in soil structure and productivity in the district, we have no data at present on the variation in crop yields for different soil types so SWIM considers the whole

121,600 ha tobe a homogeneous block of uniform soil type and productivity. No costs of land are included in SWIM. Small amounts ofland may be needed for pasture for sheep grazing but these have not been included in SWIM.

2.2.2 Water

The Danube River is the only source of irrigation water for the region as there areno other significant rivers and ground- water is available only at great depth (400-600 metres). The climate is moderate with an average annual rainfall of 550 mm.

However the summer is hot and potential evaporation exceeds average rainfall throughout the growing season from April through September, as shown in table (2.1). Thus irrigation is necessary to ensure consistently high crop yields. Because of the rolling hills, potential for erosion, and scarcity of water resources, sprinkler irrigation is the only application method being considered in the complex. Although there will be losses in transportation and application of the irrigation water we do not have sufficiently good information to include these losses in SWIM at the present t h e . Hence the volumes of water computed are the volumes needed to be delivered to the root zone of the plants. The amounts of water needed in other parts of the agricultural-industrial complex, such as for clean-

ing and processing in animal production, are not considered separately in SWIM because it is assumed that this water will eventually be irrigated onto the land as a method of waste disposal of manure, etc.

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T a b l e 2 . 1 R a i n f a l l , E v a p ~ r a t i o n , & M o i s t u r e D e f i c i t

T a b l e 2.2 D e p t h & P e r i o d o f I r r i g a t i o n

Month R a i n f a l l (mm) E v a p o r a t i o n (mm) D e f i c i t (nun)

J a n u a r y 3 8 1 4 + 24

F e b r u a r y 3 1 20 + 1 1

March 3 3 4 2

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A p r i l 4 3 74 -3 1

May 5 2 9 8 -4 6

J u n e 7 6 1 2 2 -46

J u l y 6 5 1 4 1 -76

A u g u s t 3 6 1 3 5 -99

S e p t e m b e r 4 8 9 3 -4 5

O c t o b e r 4 4 5 4 -10

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November 3 4 2 7 + 7

December 46 1 7 + 2 9

L

Crop

L u c e r n e

M a i z e S i l a g e

Maize G r a i n

Wheat

B a r l e y

S o y b e a n s

S u n f l o w e r s

- P e r i o d I r r i g . Apr 1 5

t o J u n e 30 May 20

t o Aug 3 0 May 20

t o Aug 30 Apr 1

t o May 3 0 Apr 1

t o May 3 0 J u n e 1

t o Aug 3 0 J u n e 1

t o j u l y 3 1

T o t a l D e p t h i n D r o u g h t

64 8

408

4 0 8

1 0 8

276

155 A p r i l May J u n e J u l y A u g u s t

7 8 231 231

- -

-

_{2 2} _{6 6} _{1 0 9} _{1 4 3}

- _{2 2} _{6 6} _{1 0 9} _{1 4 3}

36 54

- - -

3 6 54

- - -

- -

4 8 7 9 1 0 3

-

4 9 80 -

T o t a l 5 4 0

3 4 0

90

9 0

2 3 0

1 2 9

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The d e p t h of w a t e r needed f o r i r r i g a t i o n by e a c h c r o p i s e s t i m a t e d where p o s s i b l e by r e f e r e n c e t o Donev ( 1 9 7 2 ) . T h i s t o t a l d e p t h i s t h e n d i v i d e d i n t o t h e d e p t h needed i n e a c h month o f t h e i r r i g a t i o n p e r i o d i n p r o p o r t i o n t o t h e d e f i c i t of r a i n - f a l l i n t h a t month. The r e s u l t s a r e g i v e n i n t a b l e ( 2 . 2 ) .

To e s t i m a t e t h e c r o p w a t e r r e q u i r e m e n t s u n d e r d r o u g h t

c o n d i t i o n s , a l l t h e i r r i g a t i o n d e p t h s a r e a r b i t r a r i l y i n c r e a s e d by 20% o v e r t h o s e f o r normal w e a t h e r c o n d i t i o n s . I t woald be r e l a t i v e l y e a s y t o modify t h e w a t e r r e q u i r e m e n t s i n SWIM t o r e f l e c t t h o s e measured i n i n d i v i d u a l y e a r s , where d a t a a r e a v a i l a b l e .

I n a l l c a s e s t h e t o t a l volume w a t e r made a v a i l a b l e was assumed t o have a u n i t c o s t f o r pumping of 0.022 Lv/cubic m e t r e .

2 . 2 . 3 Seeds

A l l s e e d s r e q u i r e d a r e assumed t o b e grown w i t h i n t h e complex on i r r i g a t e d l a n d . SWIM computes t h e a r e a of l a n d needed f o r s e e d growing p e r h e c t a r e of f i e l d c r o p p r o d u c t i o n by d i v i d i n g t h e s e e d p l a n t i n g r a t e f o r e a c h c r o p by i t s s e e d c r o p y i e l d r a t e and summing t h e r e s u l t i n g s e e d c r o p areas. Seed c r o p y i e l d s a r e assumed t o be t h e same a s t h e i r r i g a t e d f i e l d c r o p y i e l d s i n t h e c a s e of g r a i n s . The c o s t o f s e e d p r o d u c t i o n i s a s s e s s e d a s 90% c u r r e n t B u l g a r i a n p r i c e p l u s 10% f o r e i g n i m p o r t p r i c e . T h i s c o s t i n c l u d e s t h e p r o d u c t i o n , p r o c e s s i n g , and d i s t r i b u t i o n o f t h e s e e d . The d a t a used f o r s e e d p l a n t i n g r a t e s , s e e d c r o p y i e l d s , c o s t s , and s e e d a r e a , are g i v e n i n t a b l e A3.1 i n Appendix 3.

2.2.4 F e r t i l i z e r s and P e s t i c i d e s

T h r e e n u t r i e n t s must b e s u p p l i e d w i t h f e r t i l i z e r s : n i t r o g e n , phosphorus and p o t a s s i u m . The c o r r e s p o n d i n g f e r t i l i z e r s are ammonium s u l p h a t e (34% a c t i v e n i t r o g e n ) , s u p e r p h o s p h a t e (20%

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a c t i v e p h o s p h o r u s ) , and p o t a s s i u m s u l p h a t e (44.5% a c t i v e

p o t a s s i u m ) . The amount of e a c h f e r t i l i z e r needed p e r h e c t a r e . . i s c a l c u l a t e d i n t h e f o l l o w i n g way: f i r s t , t h e amount of e a c h n u t r i e n t removed by c r o p p r o d u c t i o n i s e s t i m a t e d ; n e x t , t o

compute t h e amount of n u t r i e n t s needed t o be a p p l i e d , t h e r e - moval amounts a r e m o d i f i e d t o a l l o w f o r a p p l i c a t i o n l o s s e s and t h e n a t u r a l a b i l i t y of t h e s o i l t o a b s o r b o r r e l e a s e nu- t r i e n t s ; f i n a l l y t h e amounts of f e r t i l i z e r s r e q u i r e d a r e found u s i n g t h e p r o p o r t i o n of a c t i v e n u t r i e n t i n e a c h .

S W I M c a l c u l a t e s t h e t o t a l amounts of f e r t i l i z e r s needed f o r a l l c r o p s . These t o t a l amounts must be d e c r e a s e d t o a l l o w f o r t h e n u t r i e n t v a l u e of t h e manure b e i n g s u p p l i e d t o t h e l a n d by i r r i g a t i n g a n i m a l w a s t e s . F o r 1980 c o n d i t i o n s , t h e amounts of a c t i v e n u t x - i e n t s i n t h e manure a r e t a k e n t o be 2419 t o n s n i t r o g e n ( N )

,

1738 t o n s phosphorus ( P 2 0 5 ) and 3086 t o n s of p o t a s s i u m ( K 2 0 ) ; t h e s e amounts r e p r e s e n t a b o u t a q u a r t e r of t h e t o t a l r e q u i r e m e n t s f o r n i t r o g e n and p h o s p h o r u s , and h a l f t h e t o t a l r e q u i r e m e n t f o r p o t a s s i u m ,

Where p o s s i b l e t h e f e r t i l i z e r a p p l i c a t i o n r a t e s have been compared w i t h n a t i o n a l a v e r a g e a p p l i c a t i o n r a t e s f o r B u l g a r i a , a s g i v e n i n t h e B u l g a r i a n S t a t i s t i c a l Yearbook (1975)

and found t o be n o t e x c e s s i v e . A l s o , t h e t o t a l amounts of f e r t i l i z e r s needed i n t h e complex a r e n o t e x c e s s i v e when com- p a r e d w i t h t h e t o t a l p r o d u c t i o n of f e r t i l i z e r s i n B u l g a r i a .

The f e r t i l i z e r c o s t s a r e t a k e n a s 107.10 Lv/ton f o r ammonium s u l p h a t e , 58.00 Lv/ton f o r s u p e r p h o s p h a t e , and 86.75 Lv/ton f o r p o t a s s i u m s u l p h a t e . A l l d a t a on f e r t i l i z e r quan- t i t i e s a r e g i v e n i n t a b l e A3.2 i n Appendix 3. F e r t i l i z e r a p p l i c a t i o n c o s t s a r e g i v e n t h e p r o d u c t i o n c o s t t a b l e s f o r e a c h c r o p i n Appendix 4 , c a l c u l a t e d a t 3 Lv/Ha p e r t r i p o v e r t h e f i e l d .

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A s f a r a s p e s t i c i d e s a r e c o n c e r n e d , t h e r e a r e t o o many i n d i v i d u a l c h e m i c a l s i n v o l v e d t o make a n a c c o u n t i n g f o r e a c h one s e p a r a t e l y a s i s done f o r f e r t i l i z e r s . I n s t e a d , a lumped c o s t p e r h e c t a r e i s s p e c i f i e d f o r e a c h c r o p f o r c h e m i c a l s and i s g i v e n i n t h e p r o d u c t i o n c o s t t a b l e s i n Appendix 4 .

2.2.5 F u e l

The f u e l needed by t h e f i e l d machinery i s computed on t h e b a s i s o f amounts u s e d f o r i n d i v i d u a l f i e l d o p e r a t i o n s : plowing, c u l t i v a t i o n , p l a n t i n g , and h a r v e s t i n g , a s shown i n t a b l e A3.3 of Appendix 3. For i r r i g a t e d c r o p s , t h e f u e l u s e f o r h a r v e s t - i n g i s h i g h e r t h a n f o r ' n o n i r r i g a t e d c r o p s b e c a u s e o f t h e h i g h e r y i e l d . The a v e r a g e f u e l consumption p e r h e c t a r e f o r t r a c t o r s v a r i e s from 25 t o 30 l i t r e s / h r depending on t h e c r o p . F u e l i s assumed t o c o s t 0.072 L v / l i t r e .

2.2.6 Labor

The l a b o r needed f o r f i e l d o p e r a t i o n s i s c a l c u l a t e d on t h e b a s i s of t h e number of h o u r s e a c h machine i s i n t h e f i e l d , assuming one o p e r a t o r p e r machine, a s shown i n t a b l e A3.4 o f Appendix 3 . T h i s l a b o r h a s a c o s t of 2 Lv/hour. The a d d i t i o n a l l a b o r r e q u i r e d f o r a d m i n i s t r a t i o n and s u p p o r t s e r v i c e s i s n o t d i r e c t l y computed b u t i s a s s i g n e d a c o s t of 2.82 Lv/Ha. Labor f o r i r r i g a t i o n i s i n c l u d e d i n t h e c o s t s of i r r i g a t i o n . .

2.2.7 Machinery

To d e t e r m i n e t h e number of machines, s u c h a s t r a c t o r s , which w i l l be needed i n t h e complex, t h e c r i t i c a l p e r i o d i n t h e s c h e d u l e of f i e l d o p e r a t i o n s must b e known when a l l of t h e a v a i l a b l e machines a r e b e i n g used. The s c h e d u l e of f i e l d o p e r a t i o n s i s shown i n f i g u r e ( 2 . 2 ) . SWIM d e t e r m i n e s t h e

number o f t r a c t o r s , combine h a r v e s t e r s , and s i l a g e c h o p p e r s i n t h e f o l l o w i n g way. Allowing f o r some l o s t t i m e d u e t o bad w e a t h e r d u r i n g t h e c r i t i c a l p e r i o d , and a 1 0 hour working d a y , t h e number of working h o u r s i s known. The area p e r h o u r which a machine c a n c o v e r i s a l s o known; h e n c e , t h e area which c a n

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be c o v e r e d by o n e machine d u r i n g t h e c r i t i c a l p e r i o d c a n be computed, and o n c e t h e c r o p d i s t r i b u t i o n i s f i x e d , t h e number o f m a c h i n e s may be d e t e r m i n e d .

F o r t r a c t o r s , t h e c r i t i c a l p e r i o d o c c u r s d u r i n g s p r i n g c u l t i v a t i o n from 20 March t o 20 A p r i l , f o r combine h a r v e s t e r s i t o c c u r s d u r i n g t h e soybean-maize h a r v e s t from 20 September t o 30 O c t o b e r , and f o r s i l a g e c h o p p e r s it o c c u r s d u r i n g t h e m a i z e s i l a g e h a r v e s t i n J u l y .

To d e t e r m i n e t h e nwvber o f c e n t e r - p i v o t i r r i g a t i o n s p r i n k - l e r s , t h e c r i t i c a l p e r i o d i s i n J u n e when l u c e r n e , maize g r a i n , maize s i l a g e , and s o y b e a n s c o u l d be i r r i g a t e d . I t i s assumed t h a t ope s p r i n k l e r c a n i r r i g a t e 52 h e c t a r e s d u r i n g t h i s p e r i o d , s o t h e number o f s p r i n k l e r s c a n b e found from t h e c r o p a r e a s . I n t h e c a s e of wheat and b a r l e y i t i s assumed t h a t i f t h e s e

a r e i r r i g a t e d t h e same s p r i n k l e r s c a n be u s e d a s f o r m a i z e g r a i n and s i l a g e , and s o y b e a n s . I f i n s u f f i c i e n t s p r i n k l e r s a r e a v a i l - a b l e t h e n t h e y m u s t be p u r c h a s e d e s p e c i a l l y f o r wheat and b a r l e y . L i k e w i s e , t h e s p r i n k l e r s needed f o r i r r i g a t i n g l u c e r n e c a n a l s o b e u s e d t o i r r i g a t e s u n f l o w e r s .

The c o s t s o f m a c h i n e r y o t h e r t h a n i r r i g a t i o n s p r i n k l e r s a r e g i v e n f o r e a c h c r o p i n t h e p r o d u c t i o n c o s t t a b l e s i n

Appendix 4 . The f i x e d c o s t s a r e b a s e d on c a p i t a l c o s t s o f t h e m a c h i n e s , d e p r e c i a t e d o v e r t h e i r working l i f e ; t h e v a r i a b l e

c o s t s a r e c a l c u l a t e d t o a c c o u n t f o r m a i n t e n a n c e and l u b r i c a t i o n . The c a p i t a l c o s t o f d e v e l o p i n g i r r i g a t e d l a n d i s t a k e n a s

20'00Leva/Ha, which i s d e p r e c i a t e d o v e r 40 y e a r s t o g i v e 50 Leva/Ha i n e a c h y e a r . The d e p r e c i a t e d c a p i t a l c o s t o f i r r i g a t i o n s p r i n k - l e r s i s a l s o t a k e n a s 50 Leva/Ha. The v a r i a b l e c o s t s o f i r r i g a - t i o n i n c l u d e t h e c o s t o f l a b o r and m a i n t e n a n c e o f t h e e q u i p m e n t . 2 . 3 Crow P r o d u c t i o n and Outwuts

2.3.1 P r o d u c t i o n C o s t s

Moving now t o t h e c e n t r a l box o f f i g u r e ( 2 . 1 ) , t h e c r o p p r o d u c t i o n s c h e d u l e and c o s t s a r e d e s c r i b e d . Only o n e y e a r o f c r o p p r o d u c t i o n i s c o n s i d e r e d . A t p r e s e n t , SWIM d o e s n o t ex- p l i c i t l y a c c o u n t f o r c r o p r o t a t i o n from y e a r t o y e a r , o r d o u b l e

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c r o p p i n g w i t h i n one y e a r , b u t t h e s e r e f i n e m e n t s c o u l d b e i n - c l u d e d i f n e c e s s a r y . The s c h e d u l e o f f i e l d o p e r a t i o n s f o r a l l c r o p s i s shown i n f i g u r e ( 2 . 2 ) . While l u c e r n e i s t h e o n l y

p e r e n n i a l c r o p c o n s i d e r e d , w h e a t and b a r l e y a r e p l a n t e d i n t h e autumn f o r h a r v e s t t h e f o l l o w i n g summer. A l l o t h e r c r o p s a r e p l a n t e d a n d h a r v e s t e d w i t h i n o n e g r o w i n g s e a s o n . The c r o p p r o d u c t i o n c o s t s p e r h e c t a r e f o r e a c h c r o p , b o t h i r r i g a t e d and n o n i r r i g a t e d a r e g i v e n i n Appendix 4 .

L u c e r n e i s assumed t o be grown o n l y f o r h a y and i s r e p l a n t e d e v e r y t h r e e y e a r s . A c c c r d i n g l y , t h e c o s t s a s s o c i a t e d w i t h p l a n t - i n g h a v e b e e n d e p r e c i a t e d i n a s t r a i g h t l i n e f a s h i o n o v e r t h i s p e r i o d . No a l l o w a n c e h a s b e e n made f o r t h e a b i l i t y t o s u p p l y n i t r o g e n o f t h e l e g u m e s , l u c e r n e a n d s o y b e a n s , e x c e p t t h a t n o n i t r o g e n f e r t i l i z e r s a r e r e q u i r e d f o r them. Maize i s grown b o t h f o r f o d d e r a s s i l a g e , and g r a i n . When m a i z e i s h a r v e s t e d a s g r a i n it i s assumed t h a t t h e s t a l k s a r e plowed b a c k ' i n t o t h e s o i l ; f o r wheat and b a r l e y , l i k e w i s e , it i s assumed t h a t t h e s t r a w i s n o t h a r v e s t e d .

2 . 3 . 2 Crop Y i e l d s

Crop y i e l d s a r e t h e most s e n s i t i v e p a r a m e t e r s o f SWIM. The r e l a t i o n b e t w e e n c r o p y i e l d , w e a t h e r , a n d i r r i g a t i o n i s c e n t r a l t o a n y a n a l y s i s o f i r r i g a t i o n . The y i e l d s u s e d i n SWIM u n d e r n o r m a l w e a t h e r c o n d i t i o n s a r e b a s e d where p o s s i b l e o n a v e r a g e y i e l d s o b t a i n e d i n t h e D r u s t a r complex, a s shown i n t a b l e ( 2 . 3 ) . When t h e c r o p s a r e n o t grown w i t h i r r i g a t i o n a t p r e s e n t i n t h e r e g i o n , t h e i n c r e a s e i n y i e l d d u e t o i r r i g a t i o n c a n o n l y be assumed. F o r s u c h c r o p s , where n o b e t t e r d a t a a r e a v a i l a b l e , t h e i n c r e a s e i n y i e l d t y p i c a l f o r B u l g a r i a a s a whole h a s b e e n a d o p t e d .

I n t h e c a s e o f t h e d e c r e a s e i n y i e l d i n r e s p o n s e t o d r o u g h t , p e r c e n t a g e s o f d e c r e a s e i n y i e l d u s e d w e r e c h o s e n a s f o l l o w s : m a i z e , 5 0 % ; s o y b e a n s a n d s u n f l o w e r s , 3 0 % ; w h e a t , b a r l e y , and

l u c e r n e , 1 5 % . Wheat, b a r l e y , a n d , l u c e r n e a r e more d r o u g h t - r e s i s t a n t b e c a u s e t h e y are i n t h e g r o u n d o v e r t h e w i n t e r a n d t h e m o i s t u r e a b s o r b e d by t h e s o i l d u r i n g t h a t t i m e i s n o t l o s t t h r o u g h c u l t i v a t i o n i n t h e s p r i n g . Maize h a s a l a r g e r e s p o n s e

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Table 2.3 Crop Yields (in Tons/Ha) Crop

Lucerne

Maize Silage Maize Grain Wheat

Barley Soybeans Sunflowers

Y

Irrigated

10.6

5 0 . 0

8.6

3.7

3.6

2.7

2 . 2 Nonirrigated

Drought 5.1

1 4 . 0

2 . 3 5

2 . 7 2

2 . 6 3

1 . 0 5

1.4

Normal 6.0

2 8 . 0

4.7

3.2

3 . 1

1.5 2.0

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to drought because it has a large amount- of vegetative growth and small roots. The yield of irrigated crops during drought is assumed not to change because the loss in rainfall is made up by adding 20% more irrigation water.

2.3.3 Processing

The crops harvested from the field can be processed into a number of outputs. Since the requirements for feeding livestock are expressed in terms of processed outputs, SWIM has some processing activities included within it. The fodder crops, lucerne hay and maize silage are not processed off the farmland.

Wheat may be milled for flour in which case 78% of the grain becomes flour and 14% becomes wheat bran which is fed to livestock. Both soybeans and sunflowers are crushed and the oil is extracted. The residual is livestock meal which comprises 75%

by weight of the soybean grain and 41% of the sunflowerL seeds.

Maize and barley must be milled before being fed to pigs but there are no significant weight losses in this process.

2.3.4 Requirements for Population and Livestock -

The requirements of population for crop outputs are taken as 40,000 tons of flour and 8,400 tons of cooking oil for 1980.

The requirements for livestock for 1980 conditions are calculated on the basis of the diet of each animal and the estimated number of animals in the complex. The numbers of animals assumed are:

23,760 breeding sows; 434,404 pigs raised for slaughter; 24,000 dairy cows with associated calves and heifers; and 80,000 ewes.

The corresponding feed requirements assumed by SWIM are: 174,100 tons of maize grain, 327,000 tons of maize silage; 37,380 tons of soybean or sunflower meal; 117,100 tons of lucerne hay; and 2805 tons of wheat bran. These values for amounts of feed requirements can easily be changed in SWIM if necessary. It is assumed that 1.1 ton of barley grain can substitute for 1 ton of maize grain.

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Maximization of production is a goal of the agricultural- industrial complex. Once the livestock and population feed requirements are met, SWIM exports extra production of maize, wheat, and barley grain at internal Bulgarian prices of 113, 114, and 101 Leva/ton, respectively. In case of unfavorable weather conditions when the production requirements as specified in the previous section cannot be met, maize grain can be imported to the region at a price of 170 Leva/ton.

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3. RESULTS OF APPLICATION OF THE MODEL

When the capital investment required to develop theDrustar agricultural-industrial complex is considered, a significant part of this investment must be devoted to the development of irrigated land and the water supply facilities needed for this irrigation.

SWIM is applied to measure the benefits and water demands of various levels of irrigation development, both under normal weather conditions and under drought conditions. Two basic de- cisions are investigated:

-

How much land should be developed for irrigation?

-

How much water should be made availablefor irrigation?

The major results of these investigations are summarized in this section while the details are tabulated in Appendix 1.

3.1 Land for Irrigation

Of the 121,600 ha of arable land considered in SWIM, it is expected that between 25,000 and 40,000 hectares will be developed for irrigation by 1980, the year for which SWIM is applied. The range of development from 10,000 ha to 50,000 ha of irrigated land is investigated in 5,000 ha steps by repet- itively running SWIM on the computer, with each computer run having a different amount of irrigated land available. All

water needed is assumed to be available. Two series of computer runs were performed, one for normal weather conditions and

another for drought weather conditions. In each run, SWIM determines the optimal crop distribution on both irrigated and nonirrigated land to maximize production while also meeting the minimum production requirements for livestock and population.

The results for various levels of irrigated land development are shown in figures (3.1) to (3.8)

.

3.1

.I

Water Demands -

In figure (3.1), the volume of water needed, or water demand, for irrigation is plotted for both normal weather and drought conditions. For drought conditions, about 3900 cubic

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m e t r e s p e r h e c t a r e (390 mm) a r e r e q u i r e d , which i s a n i n c r e a s e of between 25% and 55% o v e r t h e w a t e r demand i n normal w e a t h e r c o n d i t i o n s as shown i n f i g u r e ( 3 . 2 ) . I n SWIM, t h e c r o p w a t e r r e q u i r e m e n t s are i n c r e a s e d by 2 0 % f o r d r o u g h t c o n d i t i o n s and i t a p p e a r s from f i g u r e ( 3 . 2 ) t h a t f o r l a r g e a r e a s o f i r r i g a t i o n t h e w a t e r demands i n c r e a s e by a l i t t l e more t h a n 2 0 % , b e c a u s e d i f f e r e n t c r o p s a r e b e i n g i r r i g a t e d .

3.1.2 Crop D i s t r i b u t i o n

The d i s t r i b u t i o n of: c r o p s grown f o r d i f f e r e n t a r e a s o f i r r i g a t i o n u n d e r normal w e a t h e r and d r o u g h t c o n d i t i o n s a r e shown i n f i g u r e s ( 3 . 3 ) , and ( 3 . 4 ) , r e s p e c t i v e l y . I n t h e s e f i g u r e s t h e v e r t i c a l a x i s r e p r e s e n t s t h e t o t a l a r a b l e l a n d and t h e h o r i z o n t a l a x i s t h e amount of t h i s l a n d which i s i r r i g a t e d . The 45' l i n e b e g i n n i n g a t t h e o r i g i n i s t h e boundary between i r r i g a t e d and n o n i r r i g a t e d l a n d . The area o f e a c h c r o p grown f o r a g i v e n a r e a of i r r i g a t e d l a n d i s p l o t t e d c u m u l a t i v e l y i n a v e r t i c a l d i r e c t i o n , b e g i n n i n g a t t h e bottom w i t h t h e s e e d s a r e a , which i s always i r r i g a t e d , c o n t i n u i n g w i t h t h e i r r i g a t e d c r o p s , and t h e n t h e n o n i r r i g a t e d c r o p s . I n some c a s e s , one

c r o p may be grown p a r t i a l l y i r r i g a t e d and p a r t i a l l y n o n i r r i g a t e d e . g . maize s i l a g e f o r 10,000 ha i r r i g a t e d l a n d i n f i g u r e ( 3 . 3 )

.

By l o o k i n g from l e f t t o r i g h t a c r o s s e a c h f i g u r e , t h e change i n t h e c r o p d i s t r i b u t i o n a s more l a n d i s i r r i g a t e d c a n be o b s e r v e d . I n normal w e a t h e r c o n d i t i o n s , soybeans i s t h e f i r s t c r o p i r r i g a t e d , f o l l o w e d by maize g r a i n once soybeans a r e c o m p l e t e l y i r r i g a t e d .

A v e r y i m p o r t a n t f e a t u r e of t h e r e s u l t s , which i s t h e sub- s t i t u t i o n o f w a t e r f o r l a n d , c a n b e o b s e r v e d by comparing t h e t o t a l a r e a s o f s o y b e a n s i n f i g u r e ( 3 . 3 ) f o r 10,000 and 15,000 h a of i r r i g a t e d l a n d . These a r e a s a r e 19925 ha and 15883 h a , re- s p e c t i v e l y . I n b o t h c a s e s t h e t o t a l p r o d u c t i o n i n t o n s o f soy- b e a n s i s t h e same b u t b e c a u s e a g r e a t e r p r o p o r t i o n o f t h e c r o p i s grown u n d e r i r r i g a t i o n i n t h e second c a s e , where it g i v e s a h i g h e r y i e l d , t h e t o t a l l a n d a r e a o c c u p i e d by s o y b e a n s d e c r e a s e s , t h u s l e a v i n g more l a n d a v a i l a b l e f o r growing o t h e r c r o p s w i t h - o u t i r r i g a t i o n . Hence w a t e r and c a p i t a l i n v e s t m e n t i n i r r i g a t i o n a r e b e i n g s u b s t i t u t e d f o r a r a b l e l a n d t o grow t h e same amount of

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soybeans. T h i s i s a key f e a t u r e of t h e o p e r a t i o n of S W I M and i t u n d e r l i e s a l l t h e r e s u l t s which f o l l o w .

By comparing f i g u r e s ( 3 . 3 ) and ( 3 . 4 )

,

i t c a n be s e e n t h a t d i f f e r e n t c r o p s a r e grown under i r r i g a t i o n i n d r o u g h t c o n d i t i o n s a s compared t o normal weather c o n d i t i o n s . I n a d r o u g h t , maize s i l a g e i s i r r i g a t e d f i r s t i n s t e a d of soybeans, f o l l o w e d by maize g r a i n , and t h e n soybeans f o r l a r g e a r e a s of i r r i g a t e d l a n d .

The r e a s o n t h a t maize i s i r r i g a t e d f i r s t i s t h a t t h i s c r o p i s t h e most s e n s i t i v e t o d r o u g h t (50% l o s s i n n o n i r r i g a t e d y i e l d ) compared w i t h soybeans and s u n f l o w e r s (30% l o s s i n n o n i r r i g a t e d y e i l d ) , and l u c e r n e , wheat, and b a r l e y (15% l o s s i n n o n i r r i g a t e d y i e l d ) . The l o s s e s i n y i e l d o f n o n i r r i g a t e d s u n f l o w e r s , wheat and l u c e r n e mean t h a t l a r g e r a r e a s of t h e s e c r o p s a r e r e q u i r e d t o grow t h e p r o d u c t i o n r e q u i r e m e n t s i n d r o u g h t c o n d i t i o n s . For lower i r r i g a t e d a r e a i n d r o u g h t c o n d i t i o n s , a s m a l l a r e a of

b a r l e y i s grown a s a s u b s t i t u t e f o r maize g r a i n i n f e e d i n g l i v e - s t o c k . I n normal weather c o n d i t i o n s , t h e y i e l d of m a i z e k . g r a i n

( 4 . 7 t o n / h a ) i s much h i g h e r t h a n t h a t of b a r l e y (3.1 t o n s / h a )

,

s o t h a t i t i s more p r o d u c t i v e t o grow maize g r a i n t h a n b a r l e y , and b a r l e y d o e s n o t appear i n t h e c r o p d i s t r i b u t i o n .

3.1.3 I m p o r t s and E x p o r t s

I f t h e p r o d u c t i o n from t h e complex i s n o t s u f f i c i e n t t o meet t h e l i v e s t o c k r e q u i r e m e n t s , SWIM may import maize g r a i n from o u t - s i d e t h e complex i n s u f f i c i e n t q u a n t i t i e s t o a l l o w t h e r e q u i r e m e n t s t o be m e t b u t a t a v e r y h i g h p r i c e (170 Lv/ton compared w i t h t h e normal p r i c e 113 L v / t o n ) . C o n v e r s e l y , when t h e r e i s a p r o d u c t i o n s u r p l u s , S W I M can e x p o r t maize g r a i n , wheat, b a r l e y from t h e r e g i o n .

The b a l a n c e of i m p o r t s and e x p o r t s i s g i v e n i n f i g u r e ( 3 . 5 ) , which d e m o n s t r a t e s t h a t it r e q u i r e s v e r y l i t t l e i r r i g a t i o n (6,890 h a ) f o r t h e r e g i o n t o become s e l f - s u f f i c i e n t (no i m p o r t s o r e x p o r t s ) i n normal weather c o n d i t i o n s b u t i n d r o u g h t c o n d i t i o n s a much l a r g e r a r e a of i r r i g a t e d l a n d (32,750 h a ) i s r e q u i r e d t o a c h i e v e s e l f - s u f f i c i e n c y . F i g u r e (3.6), which h a s a r a t h e r u n u s u a l s h a p e , shows t h e c o r r e s p o n d i n g t o t a l p r o d u c t i o n c o s t s , i n c l u d i n g t h e c o s t s of i m p o r t s . Under d r o u g h t c o n d i t i o n s t h e minimum t o t a l c o s t s (Lv 21.7 m i l l i o n ) a r e a t t a i n e d j u s t a t t h e p o i n t of s e l f - s u f f i c i e n c y . I f

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l e s s l a n d i s i r r i g a t e d , t o t a l c o s t s r i s e b e c a u s e o f t h e c o s t of imported maize which o u t w e i g h s t h e s a v i n g s made by i r r i g a t i n g l e s s l a n d . Even i f i m p o r t e d maize were p r i c e d a t t h e e x p o r t p r i c e o f 113 Lv/ton t h e t o t a l c o s t would s t i l l r i s e s l o w l y i f l e s s l a n d i s i r r i g a t e d , assuming t h e same amounts of i m p o r t s a r e r e a u i r e d .

S i n c e i m p o r t s a r e n o t r e q u i r e d u n d e r normal w e a t h e r con- d i t i o n s , t h e t o t a l c o s t c u r v e i s c o n t i n u a l l y r i s i n g a s more l a n d i s i r r i g a t e d and t h e p r o d u c t i o n s u r p l u s i s e x p o r t e d . Another s t r i k i n g f e a t u r e o f f i g u r e ( 3 . 6 ) i s t h a t t o t a l pro- d u c t i o n c o s t s a r e v e r y s i m i l a r under b o t h w e a t h e r c o n d i t i o n s when t h e a r e a o f i r r i g a t e d l a n d i s g r e a t e r t h a n t h a t needed f o r s e l f - s u f f i c i e n c y . Of c o u r s e , t h e d i f f e r e n c e i s t h a t i n normal w e a t h e r c o n d i t i o n s , e x p o r t s a r e much l a r g e r i n t h i s r a n g e of

i r r i g a t e d l a n d development.

To d e t e r m i n e w h e t h e r i t i s economic t o d e v e l o p more i r r i - g a t e d l a n d t h a n t h a t n e e d e d t o a c h i e v e s e l f - s u f f i c i e n c y , t h e v a l u e of t h e s u r p l u s p r o d u c t i o n which c a n be e x p o r t e d s h o u l d be com- p a r e d t o t h e e x t r a c o s t s n e c e s s a r y t o produce t h i s s u r p l u s . These e x t r a p r o d u c t i o n c o s t s c a n be found by s u b t r a c t i n g t h e t o t a l p r o d u c t i o n c o s t t o a c h i e v e s e l f - s u f f i c i e n c y from t h e t o t a l p r o d u c t i o n c o s t s when more l a n d i s i r r i g a t e d t o produce e x p o r t s . The n e t v a l u e , o r n e t b e n e f i t , of e x p o r t s i s t h e n found by sub- t r a c t i n g t h e s e e x t r a p r o d u c t i o n c o s t s from t h e v a l u e ~ f t h e ex- p o r t s , and i s p l o t t e d i n f i g u r e ( 3 . 7 ) , which shows t h a t t h e n e t v a l u e o f e x p o r t s c o n t i n u a l l y i n c r e a s e s , i n a l i n e a r f a s h i o n , a s more l a n d i s i r r i g a t e d . The b e n e f i t - c o s t r a t i o , which i s t h e v a l u e o f e x p o r t s d i v i d e d by t h e e x t r a p r o d u c t i o n c o s t s , i s f a i r l y c o n s t a n t a t 2.0 f o r normal w e a t h e r c o n d i t i o n s and 2.4 i n d r o u g h t c o n d i t i o n s .

3.1.4 Value of I r r i u a t e d Land

While it m i g h t b e e x p e c t e d t h a t t h e c o s t of d e v e l o p i n g e a c h new u n i t ( h e c t a r e ) o f l a n d f o r i r r i g a t i o n would n o t change g r e a t l y w i t h t h e scale of development, the v a l u e o f e a c h new u n i t o f i r r i g a t e d l a n d m i g h t change q u i t e c o n s i d e r a b l y w i t h t h e s c a l e of development. I n t u i t i v e l y , it seems c l e a r t h a t t h e f i r s t

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u n i t s of i r r i g a t e d l a n d w i l l have t h e g r e a t e s t v a l u e , a s

measured by e x t r a p r o d u c t i o n , b e c a u s e t h e c r o p s g i v i n g t h e b e s t r e s p o n s e t o w a t e r c a n b e i r r i g a t e d . A s more l a n d i s i r r i g a t e d , l e s s r e s p o n s i v e c r o p s a r e i n c l u d e d s o t h a t v a l u e of e a c h new u n i t , o r m a r g i n a l v a l u e , of i r r i g a t e d l a n d d e c r e a s e s w i t h t h e

s c a l e of i r r i g a t i o n development. . ( T h i s m a r g i n a l v a l u e i s t h e shadow p r i c e of t h e c o n s t r a i n t on i r r i g a t e d l a n d i n SWIM.) I n t h e economics of s u p p l y and demand, t h e o p t i m a l s c a l e of i r r i g a t e d l a n d development o c c u r s when t h e c o s t of d e v e l o p i n g e a c h new u n i t of i r r i g a t e d l a n d i s e q u a l t o t h a t u n i t ' s m a r g i n a l v a l u e .

F i g u r e ( 3 . 8 ) s h o w s t h e demand c u r v e f o r i r r i g a t e d l a n d which i s t h e change i n t h e m a r g i n s 1 v a l u e o f i r r i g a t e d l a n d w i t h t h e scale of i r r i g a t e d l a n d development, f o r normal w e a t h e r and

d r o u g h t c o n d i t i o n s . A s e x p e c t e d , t h e m a r g i n a l v a l u e of i r r i g a t e d l a n d i n d r o u g h t c o n d i t i o n s i s much h i g h e r t h a n i n normal w e a t h e r c o n d i t i o n s . I n f i g u r e ( 3 . 8 ) e a c h demand c u r v e i s composed of h o r i z o n t a l s e g m e n t s , where t h e m a r g i n a l v a l u e d o e s n o t c h a n g e w i t h t h e a r e a of i r r i g a t e d l a n d , and i n c l i n e d se9ments ( d a s h e d ) i n which t h e r e a r e c o n s i d e r a b l e d i f f e r e n c e s i n m a r g i n a l v a l u e . I n t h e s o l u t i o n s of SWIM, t h e h o r i z o n t a l segments o c c u r when e a c h new h e c t a r e of l a n d i s b e i n g u s e d t o i r r i g a t e t h e same c r o p as t h e p r e v i o u s h e c t a r e , w h i l e t h e i n c l i n e d segments o c c u r when a new c r o p b e g i n s t o b e i r r i g a t e d , o r when s e l f - s u f f i c i e n c y i s a t t a i n e d . A c t u a l l y , i f a l l p o s s i b l e a r e a s of i r r i g a t e d l a n d had been e v a l u a t e d , t h e d a s h e d segments would b e v e r t i c a l , a n d

l o c a t e d a t t h e e x a c t p o i n t where a new c r o p b e g i n s t o b e i r r i g a t e d . The c o s t o f i r r i g a t e d l a n d development of 1 0 3 . 2 5 Lv/ha,

which i s assumed i n SWIM i s a l s o p l o t t e d i n F i g u r e ( 3 . 8 ) . S i n c e t h i s c o s t l i n e a l w a y s l i e s below t h e demand c u r v e s , it may b e c o n c l u d e d t h a t t h e m a r g i n a l v a l u e of i r r i g a t e d l a n d i s a l w a y s g r e a t e r t h a n t h e u n i t c o s t o f d e v e l o p i n g it w i t h i n t h e r a n g e o f a r e a c o n s i d e r e d and t h e a c c u r a c y o f SWIM.

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3.2 Water For I r r i q a t i o n

I n s e c t i o n (3.11, t h e a r e a of i r r i g a t e d l a n d i s c o n s i d e r e d a s t h e l i m i t i n g r e s o u r c e w i t h a l l w a t e r demands a b l e t o be m e t ; i n t h i s s e c t i o n , w a t e r i s c o n s i d e r e d a s t h e l i m i t i n g r e s o u r c e w i t h up t o 40,000 ha a v a i l a b l e f o r i r r i g a t i o n development.

Two s e r i e s of computer r u n s were performed, one f o r normal w e a t h e r c o n d i t i o n s and one f o r d r o u g h t c o n d i t i o n s . I n e a c h

s e r i e s , t h e f i r s t computer r u n was made assuming a l l of t h e

o p t i m a l amount of w a t e r demanded f o r 40,000 h a of i r r i g a t e d l a n d i s a v a i l a b l e . I t s h o u l d be n o t e d t h a t t h i s o p t i m a l amount i s

6 3

h i g h e r f o r d r o u g h t c o n d i t i o n s (159.26 x 10 m ) t h a n f o r normal 6 3

w e a t h e r c o n d i t i o n s (122.64 x 10 m ) . Succeeding r u n s w e r e t h e n made l i m i t i n g t h e a v a i l a b l e w a t e r t o l o % , 2 0 % ,

...,

90% of t h e o p t i m a l amount.

I t i s found t h a t i t i s n o t economical t o d e v e l o p a l l of t h e 40,000 ha of i r r i g a t e d l a n d when t h e w a t e r demanded i s n o t a v a i l a b l e , f i g u r e ( 3 . 9 ) . A s e x p e c t e d , f o r a g i v e n amount of w a t e r a v a i l a b l e , t h e o p t i m a l a r e a of i r r i g a t e d l a n d i s l e s s i n t h e c a s e of d r o u g h t c o n d i t i o n s t h a n i n normal w e a t h e r c o n d i t i o n s b e c a u s e t h e c r o p w a t e r r e q u i r e m e n t s a r e h i g h e r i n a d r o u g h t .

The c o r r e s p o n d i n g c r o p d i s t r i b u t i o n s a r e shown i n f i g u r e s ( 3 . 1 0 ) and (3.11 ) (which c a n be compared w i t h f i i g u r e s ( 3 . 3 ) and ( 3 . 4 ) , r e s p e c t i v e l y ) . The d i s t r i b u t i o n f o r normal w e a t h e r con- d i t i o n s , f i g u r e ( 3 . 1 0 ) , i s v e r y s i m i l a r t o t h a t d i s c u s s e d p r e - v i o u s l y , f i g u r e ( 3 . 3 ) . F o r d r o u g h t c o n d i t i o n s , f i g u r e ( 3 . 1 1 )

,

t h e s o l u t i o n i s i d e n t i c a l t o t h e p r e v i o u s c a s e , f i g u r e ( 3 . 4 ) f o r sun£ lo:vers, l a c e r n e , wheat, and maize s i l a g e , b u t non- i r r i g a t e d b a r l e y assumes a more i m p o r t a n t r o l e a s a s u b s t i t u t e f o r maize g r a i n i n l i v e s t o c k f e e d .

The amount of a v a i l a b l e w a t e r and p r o d u c t i o n c o s t n e c e s s a r y t o r e a c h s e l f - s u f f i c i e n c y i n t h e complex c a n be found from t h e b a l a n c e o f i m p o r t s and e x p o r t s a s i n s e c t i o n ( 3 . 1 . 3 ) . F i g u r e

( 3 . 1 2 ) shows t h a t t h i s p r o d u c t i o n c o s t i s t h e minimum a t t a i n a b l e f o r t h e r a n g e of w a t e r a v a i l a b i l i t y c o n s i d e r e d .

The demand c u r v e f o r w a t e r c a n b e d e v e l o p e d u s i n g t h e same method d e s c r i b e d i n s e c t i o n ( 3 . 1 . 4 ) f o r i r r i g a t e d l a n d . A s