Response of root and tiller development and yield of wheat to tillage and nitrogen topdressing patterns and nitrogen application rates

Objectives Wheat production heavily relies on nitrogen application in the Huang-Huai Plains. We studied the effects of different tillage and nitrogen topdressing ways on root & tiller development of wheat in order to provide theoretical basis for maintaining stable grain yield and high nitrogen efficiency.

Methods In two consecutive planting years of 2016–2018, using the half-winterness and medium-maturity wheat cultivar ‘Aikang 58’ as the testing material, field experiments were conducted with a split-split-plot design: the main treatments were two N application rates of 240 and 180 kg/hm²; the subplots were two tillage practices of rotary and deep tillage; and the further split plots were three N topdressing patterns of broadcasting, ditching every other row and every three rows. The root growth, root vigor, culm and tillers development, grain yield and nitrogen use efficiency of winter wheat were measured and analyzed at different growth stages.

Results Secondary roots per plant, root vigor, culm and tillers per hectare, and leaf area index (LAI) at different growth stages were all reduced under reduced N application rate. Compared with those in rotary tillage, more secondary roots per plant, culm and tillers were developed, and higher root vigor and larger LAI were obtained in middle and late growing period of wheat in deep tillage. Among the three N topdressing ways, the highest secondary roots per plant, root vigor, culm and tillers and LAI were obtained in ditching every other row, the next was in broadcasting, and the lowest was in ditching every three rows. Reducing N fertilization rate decreased grain yield by 2.41%, and the partial factor productivity of nitrogen fertilizer (PFPN), the nitrogen uptake (NUE) and utilization efficiency were increased by 29.67%, 25.69% and 2.29%, respectively. Compared with those in rotary tillage, grain yield, PFPN and NUE of wheat under deep tillage were increased by 5.60%, 4.48% and 8.47%, respectively. Among the three N topdressing ways, the highest grain yields, PFPN, NUE were obtained in ditching every other rows, with 3.62%, 3.98% and 7.38% higher than those in broadcasting, and 5.93%, 6.34% and 12.93% higher than those in ditching every three rows.

Conclusions Deep tillage could increase the secondary roots per plant, root vigor and culm and tillers per unit area of soil in the middle and late growing period of wheat. The highest grain yield could be obtained with conventional nitrogen application rate (N 240 kg/hm²) combined with deep tillage (25–30 cm) and nitrogen topdressing by ditching every other row. Reducing nitrogen application rate by 25% (N 180 kg/hm²) results in grain yield reduction. However, reduced nitrogen application combined with both deep tillage and nitrogen topdressing by ditching every other row is the best practice to achieve high yield and high efficiency, with a significantly increased nitrogen use efficiency and partly decreased yield reduction from reduced nitrogen application.