Straw return accompany with low nitrogen moderately promoted deep root

Grain yields of winter wheat are significantly affected by different straw and nitrogen regimes through regulating root growth and distribution in soil, especially in subsoil layers. In this study, three straw regimes used were S0 (no straw return), S1 (4500 kg ha−1 of maize straw returned), S2 (9000 kg ha−1 of maize straw returned) and four nitrogen regimes used were N0 (no nitrogen applied), N1 (150 kg ha−1 nitrogen applied), N2 (225 kg ha−1 nitrogen applied) and N3 (300 kg ha−1 nitrogen applied). Soil bulk density, soil total porosity, root length density, nitrogen efficiency and grain yield of winter wheat were measured. Straw return could not only decrease the soil bulk density and increase the soil total porosity of farming layer, but also in subsoil layers, especially at plough pan. Straw return treatments enhanced grain yield significantly, which was mainly due to the increase of 1000-kernel weight. S1N2 produced the maximum grain yield, however, S1N1 induced larger subsoil root length density and the proportion of root system in subsoil layers. Compared with S1N2, the grain yield of S1N1 decreased by 4.0%, but nitrogen partial factor productivity (PFPN) and agronomic nitrogen use efficiency (NAE) increased by 44.0% and 32.6%, respectively. Overall, this study demonstrates that suitable amount of straw returned back to field, combining with nitrogen deficiency moderately, maybe a more eco-friendly and sustainable agricultural technique in the field production.