Intercropping maize and peanut under semi-arid conditions is a zero-sum game

Context: Maize and peanut have been reported to be compatible species in intercropping with a high land use efficiency. However, little information is available at contemporary higher levels of fertilizer input and the possible importance of root plasticity for water uptake in rain-fed semi-arid condition. Objective: We aimed to quantify yield, yield components, water uptake, root plasticity and distribution of maize and peanut in dryland agriculture. Methods: A 3-year field experiment was conducted at two N input levels (N-free, without N fertilizer addition; N-farmer, N fertilizer rates were based on conventional rates used by local famers) in Liaoning province, China. Results: Maize had an average partial land equivalent ratio (pLER) of 0.73 over three years while peanut had an average pLER of 0.27. The total LER indicates no land use advantage of intercropping. Yields were unresponsive to fertilizer input. The harvest index (HI) of maize was increased by intercropping, from 0.47 to 0.52, whereas the HI of peanut was decreased from 0.39 to 0.32 over all years and N treatments. Intercropping decreased the branch numbers and increased the length of main stem and lateral branches at 1st to 3rd pairs. Roots of maize foraged in the peanut strip while roots of peanut were largely absent from the maize strip. The root length density/aboveground biomass of peanut increased 88 % in intercropping. However, contrary to expectation, total water uptake was not increased by intercrop and was not affected by N application rate. Conclusions: Under rain-fed semi-arid condition, maize/peanut intercropping does not provide land and water use advantage and the species interaction is a zero-sum game, even though peanut showed high root plasticity (88 %). A key reason for the lack of positive LER response is the reduction of HI. Low plant vigour of intercropped peanut due to water stress and shading and the elevated the branch position and the decreased branch number may be responsible for a low rate of pegging which would then result is lower HI. Implications: The results provide a testable prediction that the advantage of maize/peanut intercropping may potentially be improved by solving the HI problem of intercropped peanut, such as breeding for more shade tolerant varieties or planting the maize in narrower rows to improve the insolation of peanut. Our study is helpful for field management strategies for maize/peanut intercropping in semi-arid dryland agriculture.