Meta-analysis of Grain Yield and N Dynamics of Legumes in Cereal Systems
One of the most significant anthropogenic alterations of the N cycle is the use of fertilizers in agriculture. The use of fertilizers stimulates plant growth but has several environmental hazards and economic costs associated with it. Using alternative N sources can not only reduce these but also help develop more sustainable farming systems. One way in which farming systems can be redesigned for the use of alternative N sources is by incorporating legumes. The aim of this meta-analysis was: (a) to investigate what variables affects the grain yield and grain N and (b) to determine which cereal farming system, intercropping or crop rotation, is the most productive. The results of this meta-analysis show that only 25% of the data showed greater cereal grain yield for intercropping than monocropping. The cereal grain yield decreased by 14% on average compared to monocropping. When looking at the combined grain yield of intercropping no significant decrease in grain yield was found but only 47% of the data showed greater grain yield for intercropping than for monocropping. 76% of the data showed greater grain yield for crop rotation than monocropping, with 7% of the data showing a doubling in grain yield. The increase in grain yield was on average 21%. For grain N 89% of the data had greater grain N in crop rotations than monocropping and 16% showed a doubling. No clear pattern was found in the variables influencing the grain yield and grain N. None of the variables significantly influenced both the treatment and control for intercropping and crop rotation for both grain yield and grain N. The findings of this meta-analysis suggest that crop rotation is a more productive and reliable farming system than intercropping in terms of grain yield and grain N.