N supply and pre-cropping benefits to triticale from three legumes in rainfed and irrigated Mediterranean crop rotations
2019
Oliveira, Miguel | Castro, Carlos | Coutinho, Joao | Trindade, Henrique
Including pulses in crop rotations can improve the productivity of subsequent crops due to increased soil available N and other agronomic benefits. However, the magnitude of this effect can vary with environmental conditions, agricultural management practices and legume genotypes. We aimed to measure the N supply and pre-crop benefits from pulses introduced in different crop rotations with cereals in a Mediterranean climate. Two three-year field trials were set with non N-fertilized fodder triticale (× Triticosecale ‘Alter’) as a monoculture, and in rotation with irrigated cowpea (Vigna unguiculata’ Fradel’) as replacement of summer fallow, or rainfed faba bean (Vicia faba ‘Favel’) or pea (Pisum sativum ‘Grisel’) as ‘break’ crops. Two legume residue managements were tested: incorporation into the soil and removal from the system. Triticale monocultures with three levels of synthetic N fertilization were included for estimation of N-fertilizer equivalence from rainfed pulse pre-crops. Yields and N contents were measured for each plant fraction and crop, including weeds. Biologically fixed N was estimated by an N-difference method and residual fixed N (RFN) was calculated. Cowpea fixed between 62–127 kg N ha−1 and provided up to 61 kg N ha−1 to soil as RFN. Faba bean and pea fixed between 0–72 kg N ha−1 but RFN was negative overall, as low as −52 kg N ha−1. However, the apparent N benefit of these ‘break’ crops was largely positive (up to 70 kg N ha−1) in comparison with the reference crop (triticale). Agricultural intensification with irrigated cowpea did not affect the productivity of subsequent cereal, likely due to a combined effect of low residue mineralization potential of its residues, and to increased nitrate leaching and weed infestation in cereal. However, the overall productivity of the agroecosystem was increased with minimal inputs. Rainfed faba bean and pea improved cereal productivity similarly, but only when grown in wet conditions with no weed control (30–59% yield increase, equivalent to 72–153 kg fertilizer-N ha−1). Removal of legume residue did not affect the productivity of subsequent cereal. This study identifies cowpea as a suitable crop for sustainable intensification in Mediterranean conditions.
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