Nutrient Yield and Loss/Yield-Ratio

Nutrient yields and loss/yield-ratio were used as assessment of the grassland stands under eco-nomical and ecological vs. ecoeco-nomical aspects.

In2002, N aboveground yield of our grassland stands (Table 52) ranged from 12.9 to 15.2 g N m^-2 yr^-1. It was tendentiously higher for stand III (H. lanatus + P. lanceolata) than for any other grass-land stand.

Table 52 Nutrient removal with aboveground biomass (yield) and ratio of seepage loss to yield of experimental grassland stands I- V in 2002

Significant distinctions between stands are indicated by different letters (one way-ANOVA: dF = 5; Tukey HSD-Test; stand I-V n = 5)

^ raw data: NEßHÖVER >BEIERKUHNLEIN, unpublished

In terms of N yield, P. lanceolata dominated stand III showed the best performance of our grass-land stands in 2002. The loss/yield-ratio ranged from 0.01 to 0.03. It was lower for stand III. The stand showed the best performance in concern of N harvest and safety net function.

The mean K yield of our grassland stands ranged from 22.8 to 29.3 g K m^-2 yr^-1. Stand III and IV (H. lanatus + P. lanceolata) showed significantly higher K removals than the other grassland stands.

Stand III and IV showed best performance in concern of K harvest in 2002.

The mean yield in Mg ranged from 1.2 to 1.5 g Mg m^-2 yr^-1. Stand I (H. lanatus + A. elatius) and II (H. lanatus) showed lower Mg removals than stand III-V. The differences were significant for stand III. Stand III-V showed best performance in concern of aboveground yield for Mg in 2002.

The mean yield in Ca of our grassland stands ranged from 2.8 to 6.5 g Ca m^-2 yr^-1. Stand I and II had significantly lower Ca yields than stand III-V. Stand III appeared to be the grassland stand with the best performance in concern of N, K, Mg and Ca yield in 2002. In general, grass/herb mixtures showed better performance in nutrient yields.

Parameter I II III IV V ^Tukey

HSD F P

Yield ---[g m^-2 yr^-1

]---N 13.6 12.9 15.2 14.9 13.4 ns 2.63 0.065

K 23.6 ^b 22.8^b 29.1 ^a 29.3 ^a 24.9 ^b * 7.58 0.001

Mg 1.2 ^b 1.2 ^b 1.5 ^a 1.4 ^ab 1.3 ^{ab * 5.33 0.004}

Ca 2.9 ^c 2.8^c 6.5 ^a 5.8 ^ab 5.1 ^{b * 50.14 0.000}

Loss/yield-

ratio ---[ g m^-2 yr^-1 / g m^-2 yr^-1

]---N 0.03 0.03 0.01 0.03 0.01 ns 1.73 0.184

In 2003, the mean N yield of our grassland stands (Table 53) ranged from 7.4 to 12.2 g N m^-2 yr^-1. Stand I (A. elatius + H. lanatus) and II (H. lanatus + G. pratense) showed significantly higher N yields than stand III-V. The mean loss/yield-ratio ranged from 0.01 to 0.04. It was low for stand I.

Stand I showed the best performance in concern of N yields and safety net function in 2003.

Since loss/yield-ratio was significantly higher for stand II, the stand showed only good perform-ance in concern of N yield.

Table 53 Nutrient removal with aboveground biomass (yield) and ratio of seepage loss to yield of experimental grassland stands I-V in 2003

Significant distinctions between stands are indicated by different letters (one way-ANOVA: dF = 5; Tukey HSD-Test; stand I-V n = 5)

^ raw data: TÜNTE >BEIERKUHNLEIN, unpublished

The mean yield in K ranged from 14.6 to 21.1 g K m^-2 yr^-1. Stand I showed significantly higher K yields than stand IV (P. lanceolata + A. elatius + G. pratense) and V (P. lanceolata + A. elatius + T. offi-cinale). Stand II and III (P. lanceolata) had only tendentiously higher K yields than stand IV and V.

The mean loss/yield ratio ranged from 0.11 to 0.15. Since stand I also showed tendentiously lower loss/harvest-ratios, it had the best performance in concern of K yield and safety net func-tions in 2003.

The mean Mg yield of our grassland stands ranged from 1.1 to 1.6 g Mg m^-2 yr^-1. Stand II showed significantly higher Mg yields than the other stands. The mean loss/yield ratios ranged from 0.50 to 0.68. Due to tendentiously higher loss/yield-ratios, stand II only showed best per-formance in concern of Mg yield but not in concern of safety net functions for Mg in 2003. Stand III had lower yields, but also showed lower loss/harvest-ratios and thus, might be an alternative for stand II.

Parameter I II III IV V ^Tukey

HSD F P

Yield ---[g m^-2 yr^-1

]---N 12.2 ^a 11.7^a 7.8 ^b 7.4 ^b 7.6 ^{b ** 10.75 0.000}

K 21.1 ^a 20.1 ^ab 17.1 ^abc 14.6 ^c 15.6 ^b * 6.51 0.002

Mg 1.2^b 1.6 ^a 1.3 ^b 1.1 ^b 1.1 ^{b * 8.24 0.000}

Ca 3.0 ^b 6.0 ^a 6.5 ^a 4.9 ^a 4.9 ^{a * 9.65 0.000}

Loss/yield-

ratio ---[ g m^-2 yr^-1 / g m^-2 yr^-1

]---N _0.02 ^b _0.08 ^a _0.01 ^b _0.04 ^ab _0.02 ^b * 4.02 0.015

K 0.11 0.14 0.14 0.15 0.14 ^ns 1.62 0.207

Mg 0.68 0.65 0.50 0.53 0.55 ^ns 0.73 0.581

Ca 0.92 ^a 0.59 ^b 0.35 ^b 0.46 ^b 0.42 ^b *** 13.69 0.000

The mean yield in Ca ranged from 3.0 to 6.5 g Ca m^-2 yr^-1. Stand I showed significantly lower Ca yields than stand II-V. Stand III showed the highest Ca yields with harvest. The mean loss/yield-ratio ranged from 0.35 to 0.92. It was tendentiously lower in stand III. Hence, stand III showed the best performance in concern of yield and safety net functions for Ca in 2002.

In 2003, the best performance in concern of yield and safety net function differed from 2002. In concern of N and K, highly productive grassland stand I took over best performance, whereas stand III appeared to be the stand with the best performance in concern of Mg and Ca yields as well as safety net function in 2003. In general, grass/herb mixtures showed better performance in nutrient yields and safety net functions for Mg and Ca.

DIERSCHKE >BRIEMLE (2002) gave average aboveground K yields of extensively used grass-lands of 12 g K m^-2 yr^-1 for a two-cut regime at compensation fertilization. LFL (2003) gave aboveground yields of 9.5 to 11.5 g K m^-2 yr^-1. Since 79 to 80 % of accumulated K was found in aboveground biomass (Appendix, Table III), K yields of our grassland stands were rated high for both years. Stand I (H. lanatus + A. elatius) and II (H. lanatus) showed tendentiously higher allocation of K to aboveground biomass than the other grassland stands in both years (83 to 84 %).

Lower K yields of stand I and II compared to stand III-V hint at implications of P. lanceolata species traits. Higher K yields of stand I (A. elatius + H. lanatus) in 2003 were due to H. lanatus detritus inputs.

The net K losses of stand III-V were lower than in stand I and II in 2003. This difference was mostly due to higher K yields for stand I and II despite higher KUEbm. This finding clearly illus-trates the limitation of biomass production and hence base cation yields by availability of N.

LFL (2003) gave 0.1 g Mg m^-2 yr^-1 as mean aboveground yields of extensive grasslands under a two- cut regime. Aboveground Mg accounted for 40 % of accumulated Mg in 2002 and de-creased to 36 % in 2003 (Appendix, Table XIV). Mg accumulation in our grassland stands was rated very high. Analogous to N, and K accumulation, stand III and IV (H. lanatus + P. lanceolata) had higher Mg accumulation in biomass in 2002. This finding hints at functional complementary in concern of Mg accumulation between H. lanatus and P. lanceolata to some extent. In 2003, no differences between the grassland stands in concern of Mg accumulation were found. This was mostly due to a higher biomass production of stands with high MgUEbm.

In 2003, stand IV (P. lanceolata + A. elatius + G. pratense) and V (P. lanceolata + A. elatius + T. officinale) showed slight sequestration of Mg and only slight losses under stand I (A. elatius + H. lanatus) and III (P. lanceolata) and considerable losses under stand II (H. lanatus + G. pratense). In comparison to stand I, higher Mg fluxes under stand II were likely due to higher seepage fluxes (Figure 26) and higher biomass contents of Mg²⁺ in G. pratense (Appendix Table XVI).

LFL (2003) gave 3.5 to 4.3 g Ca m^-2 yr^-1 as mean aboveground yield in extensive grasslands un-der two-cut regimes. Aboveground Ca accounted for 76 % of total Ca accumulation in 2002 and for 72 % in 2003 (Appendix, Table XIV). Ca accumulation in aboveground biomass of our grassland stands was rated very high. Stand II also had significantly higher Ca accumulation (80 % Castand) than any other stand in 2003. In 2002, stands containing H. lanatus and P. lanceolata (III-V) showed higher Ca accumulation than stand I and II. This finding suggests belowground comple-mentary in concern of Ca acquisition for both species analogous to N and K accumulation. In 2003, P. lanceolata monoculture (stand III) showed the highest Ca accumulation. Stand IV and V showed lower Ca accumulation in aboveground biomass, likely due to lower contribution of P.

lanceolata to stand biomass. Whereas, stand I also showed low Ca accumulation in 2003, despite of change in dominance patterns, the upcoming of G. pratense in stand II (H. lanatus + G. pratense) and the dominance of P. lanceolata in stand III increased the Ca accumulation considerably.

Despite of tendentiously higher Ca fluxes with seepage, the net losses of Ca were lower in stand I (A. elatius + H. lanatus) in 2003. This was due to significantly lower Ca yields in biomass. In general, grass species showed low Ca contents with implications on Ca accumulation - yields and fluxes in stand grass dominated stands.

3.1.6.3 Assessment of Grassland Stands in Respect of Nutrient Yields and