Tillage and nitrogen supply affects maize yield by regulating photosynthetic capacity, hormonal changes and grain filling in the Loess Plateau

The purpose of this research was to explore the integrative effects of tillage [rotary tillage (RT), subsoiling tillage (SST), and no-tillage (NT)] and nitrogen (N) fertilizer rate (N2, 200 kg N ha−1; N3, 300 kg N ha−1) on net photosynthetic rate (Pn), hormonal changes in grains, grain filling parameters, grain yield components, and grain yield of maize (Zea mays L.). The relationship among the yield components and grain filling parameter was also investigated. The results indicated that, on the average, tillage had no significant effect on maize yield under either N2 or N3, N rate had no significant effect on maize yield under RT and NT, only under SST, N3 increased maize grain yield significantly over N2 by 10.79%. Further on, SST with N3 enhanced Pn and promoted dry matter accumulation. The content of indole-3-acetic acid (IAA) and cytokinin (CTK) maintained a higher level over time under the SST with N3 compared with other treatments, gibberellic acid (GA) under SST with N3 had the lowest content from 21 to 28 DAP in two years. The grain filling parameter showed that SST with N3 promoted average grain filling rate and increased the weight of gradual increase period, rapid increase period, and slight increase period. It is concluded that the no-tillage with 200 kg N ha−1 is the suitable tillage as it saves tillage input, but subsoiling tillage had the advantage under 300 kg N ha−1, which improved photosynthetic rate, promoted dry matter accumulation and transport, optimized the balance of hormones, subsequently ameliorated the grain filling process, thus promoting kernels weight and ultimately increased yield.