Robust increases of land equivalent ratio with temporal niche differentiation: A meta-quantile regression

Intercropping has been shown to be land use efficient, but there is a large variation in the land equivalent ratio (LER) among studies. We used quantile regression to estimate the effect of temporal niche differentiation and its interaction with other key characteristics of intercropping, i.e., crop type combination, N fertilizer, relative density, and intercropping pattern, using data from the intercropping literature. Quantile regression characterizes the entire distribution of the response metric by estimating quantiles of this distribution. This method gives a comprehensive characterization of the diversity of the response in the population. In this study, the effect of temporal niche differentiation on the LER was positive and significant across all quantiles (10, 15, …, 85, 90%). The response of the LER to temporal niche differentiation was similar in C₃ –C₃ and C₃ –C₄ intercrops except at low quantiles (below 20%), where a stronger response was found in C₃ –C₄ than in C₃ –C₃ intercrops. There was a negative effect of N fertilizer on the LER in the absence of temporal niche differentiation at all tested quantiles. At low LER (quantiles