792 Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy
Impacts of spring and summer droughts on yield and forage quality of three grasslands
Meisser M.1, Deléglise C.2, Signarbieux C.2, Vitra A.2, Mosimann E.1 and Buttler A.2
1Institute for Livestock Sciences ILS, 1725 Posieux, Switzerland; 2Laboratory of ecological systems (ECOS), WSL/EPFL, 1015 Lausanne, Switzerland; marco.meisser@agroscope.admin.ch
Abstract
An experiment was carried out on three semi-natural grasslands, characterized by contrasted climatic conditions, in order to explore the responses of herbage production and quality to drought. Drought was simulated under rain shelters, either in spring or in summer. Two factors were tested: intensity of use (intensive vs extensive) and watering regime (control vs drought). Drought reduced the dry matter production on average across sites and intensity of use by 12% during spring and by 52% in summer, without significant changes of the botanical composition. Regarding the forage quality, drought resulted in a slight decrease of crude protein content, but this response was uneven. Acid detergent fiber generally decreased, whereas water soluble carbohydrates increased. The concentrations of phosphorus were systematically lowered by water shortage. The interactive effects of drought and intensity of use were small. Although there was no consistent trend, drought impacted forage quality, but less than yield.
Keywords: rain shelter, permanent meadows, elevation gradient, nutrient content
Introduction
Drought affects forage production (yield and quality). The effects are, however, difficult to predict due to potentially very diverse environmental conditions. More specifically, the responses of grasslands to drought depend on the timing of stress (seasonality) and its severity. Management intensity is another factor that interacts with drought (Vogel et al., 2012). The objective of this study was to investigate the forage responses of different grassland types to spring and summer droughts, in interaction with two management schemes.
We hypothesised that: (1) the effects of drought are more pronounced on lowlands than highlands grasslands;
and (2) intensive management amplifies the drought impacts, compared to the extensive management.
0 20 40 60 80 100
March April May June July Aug. Sept. Oct. Nov.
Intermediate (945 m)
Spring drought
Summer drought
Sp Drought 23.04 to 18.06
mm Su Drought 18.06 to 13.08
mm
0 20 40 60 80 100
March April May June July Aug. Sept. Oct. Nov.
NJ'0GD\ÂKD
Lowland (540 m)
Spring drought
Summer drought
Sp Drought 09.04 to 04.06 nd Su Drought WRPP
0 20 40 60 80 100
March April May June July Aug. Sept. Oct. Nov.
Highland (1300 m)
Sp Drought WRmm
Su Drought WRPP
Spring drought
Summer drought
Figure 1. Timing of the drought treatments. Dates of spring (Sp) and summer (Su) droughts are given together with P ETP at each site.
Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy 793
Materials and methods
The experiment was conducted in 2015 on three permanent meadows in the Swiss Jura mountains along an elevation gradient. The more productive sites at lower and intermediate elevation (lowland, 540 m;
intermediate, 945 m) were dominated by Lolium perenne, Trifolium repens. The highest site (highland, 1,300 m) was mainly composed of Festuca rubra and Agrostis capillaris. A complete randomized block design with five replicates was set up in the three sites. Two factors were tested: watering regime (control vs drought) and intensity of use (intensive vs extensive). Drought was simulated under rain shelters, either in spring or in summer, during 8 weeks. The timing of the periods of stress was based on the seasonal dynamic of the growth (Figure 1). Control and drought plots were watered with 100%, respectively 30% of the 30-year precipitation average. The plots in the intensive management were cut at 4-week intervals, compared with 8-week intervals in the extensive management. Cutting dates were defined in order to harvest intensive and extensive plots simultaneously at the end of the drought periods. Botanical composition was determined according to the pin-point method of Daget and Poissonet (1971). The 4 m2 plots were cut by means of a motor mower. In order to assess the effects of the treatments across the whole period of drought, the dry matter (DM) of the two cuts in the intensive management were compared with one cut in the extensive one. By extension, the data on forage quality in the intensive management were obtained by weighting the nutrient content of the two harvests by their relative yield
Table 1. Effect of spring drought, intensity of use and their interactive effect on dry matter yield and forage quality of the three grasslands (lowland, intermediate and highland).1
intensive use extensive use P-value
control drought control drought watering int. use wr × int.
DM (Mg ha-1)
lowland 4.09 3.62 5.74 5.86 0.973 <0.001 0.672
intermediate 5.30 4.36 7.32 5.91 0.002 <0.001 0.469
highland 3.85 3.65 4.01 3.82 0.157 0.209 0.968
CP in DM (g kg-1)
lowland 152 159 89 88 0.360 <0.001 0.326
intermediate 157 146 88 86 0.083 <0.001 0.227
highland 145 138 111 106 0.045 <0.001 0.733
ADF in DM (g kg-1)
lowland 284 277 333 325 0.233 <0.001 0.956
intermediate 273 269 345 319 0.014 <0.001 0.052
highland 270 270 323 318 0.342 <0.001 0.399
WSC in DM (g kg-1)
lowland 135 141 167 187 0.303 0.006 0.575
intermediate 140 173 165 190 0.000 0.002 0.529
highland 175 192 127 140 0.009 <0.001 0.612
P in DM (g kg-1)
lowland 3.2 3.2 1.8 1.7 0.636 <0.001 0.657
intermediate 4.0 3.6 2.7 2.2 <0.001 <0.001 0.620
highland 3.2 3.0 2.8 2.5 0.003 <0.001 0.481
1 DM = dry matter; CP = crude protein; ADF = acid detergent fiber; WSC = water soluble carbohydrates; P = phosphorus.
794 Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy
Results and discussion
During the spring drought, forage production was solely impacted in the intermediate site (Table 1).
The lowland site was hit end of April by heavy rainfall, so that there was no real stress effect (soil under the shelters became wet). In the highland site, the grass growth was sustained even with only 30% of the
‘normal’ precipitation. The relatively low evapotranspiration and, to a lesser extent, the clay soil could explain the absence of effect. Regarding forage quality, the values for the three sites were similar within each management intensity, in line with the comparable stage of maturity. Not surprisingly, the intensity of use had a strong influence on all parameters. Although to a lower extent than management, drought had an effect: crude protein (CP) and acid detergent fiber (ADF) tended to decrease; water soluble carbohydrates (WSC) increased and plant phosphorus (P) decreased.
There were no changes in the proportion of the main plant species at the end of the spring drought (data not shown), suggesting that the variations in forage quality caused by drought were mainly related to
‘direct’ effects on the plants (i.e. changes in chemical composition and morphology) but also to side effects on plant nutrition (e.g. lower soil NO3- concentrations under drought; data not shown).
The summer drought reduced DM yield by about 50% in the three sites (Table 2). The importance of the summer losses must be tempered by the fact that only a small part of the annual forage is produced
Table 2. Effect of summer drought, intensity of use and their interactive effect on dry matter yield and forage quality of the three grasslands (lowland, intermediate and highland).1
intensive use extensive use P-value
control drought control drought watering int. use wr × int.
DM (Mg ha-1)
lowland 1.45 0.81 1.06 0.58 <0.001 0.006 0.432
intermediate 3.51 2.32 2.11 0.33 <0.001 <0.001 0.050
highland 0.36 0.18 0.61 0.30 <0.001 0.001 0.123
CP in DM (g kg-1)
lowland 159 157 128 128 0.783 <0.001 0.701
intermediate 195 182 164 178 0.899 0.001 0.007
highland 184 167 157 152 0.020 <0.001 0.188
ADF in DM (g kg-1)
lowland 250 244 254 241 0.043 0.923 0.453
intermediate 254 253 286 225 <0.001 0.676 <0.001
highland 220 231 230 238 0.043 0.069 0.690
WSC in DM (g kg-1)
lowland 129 144 155 169 0.042 0.002 0.955
intermediate 84 100 78 107 <0.001 0.905 0.114
highland 172 153 184 193 0.669 0.034 0.213
P in DM (g kg-1)
lowland 3.0 2.6 2.2 1.8 0.006 <0.001 0.776
intermediate 5.2 4.9 3.7 2.3 <0.001 <0.001 <0.001
highland 3.7 3.3 3.5 3.0 0.002 0.051 0.702
1 DM = dry matter; CP = crude protein; ADF = acid detergent fiber; WSC = water soluble carbohydrates; P = phosphorus.
Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy 795 during this period. There were no consistent effects of drought on CP and especially ADF. Interactive effects were observed in the intermediate site: responses to drought differed between the management schemes, with especially an important decrease of ADF in the extensive plots. Given the relative stability of NDF (data not shown), it can be assumed that the decrease of ADF has been counterbalanced by an increase of hemicellulose.
Conclusions
The relative reduction in yield caused by the drought was more pronounced in summer than in spring.
Our results did not reveal a clear pattern of responses for nutrients, unless for WSC and P. Drought had the most impact on the intermediate site, whereas the site in the highlands was the less affected.
This experiment suggests that drought has direct and indirect effects (i.e. on soil nutrient availability), interacting in a complex way on forage quality.
References
Buxton D.R. (1996) Quality-related characteristics of forage as influenced by plant environment and agronomic factors. Anim. Feed Sci. Tech. 59, 37-49.
Daget P., Poissonet J. (1971) Analyse phytologique des prairies, critères d’application. Ann. Agron. 22, 5-41.
Vogel A., Scherer-Lorenzen M., Weigelt A. (2012) Grassland resistance and resilience after drought depends on management intensity and species richness. PLoS ONE 7, 1-10.
