Effects of different irrigation and nitrogen regimes on root growth and its correlation with above-ground plant parts in high-yielding wheat under field conditions

Abstract We evaluated the effects of irrigation and nitrogen regimes on wheat root growth under high-yielding conditions in the Huanghuai wheat production area of China by performing field experiments at three locations in Henan Province. The grain yield, which was significantly affected by irrigation and nitrogen fertilization regimes, ranged from 6801 to 8340 kg ha –1 in Kaifeng, 2055 to 7190 kg ha –1 in Zhengzhou and 3711 to 6859 kg ha –1 in Wenxian. The root weight density (RWD V ) in the soil at 0–100 cm reached a maximum at the flowering stage, ranging from 115.59 to 143.49 g m –3 in Kaifeng, 39.75 to 113.85 g m –3 in Zhengzhou and 53.90 to 114.56 g m –3 in Wenxian. RWD V in the 0–40 cm soil layer accounted for 72.8–87.4% of the density in 0–100-cm-deep soil across the three locations. The irrigation significantly increased the RWD V (by 46.6% and 27.2% at the flowering stage in Zhengzhou and Wenxian, respectively). The effect of nitrogen on RWD V depended on soil water conditions. The application of N180 produced the maximum RWD V under irrigation conditions, but N0 produced the highest value under water stress conditions. Both no-irrigation and N0 treatments significantly increased the R/S, and the combined treatment (W0N0) produced the maximum R/S, which indicated that stress has a relatively strong effect on the growth of the above-ground parts of wheat plants. The grain yield was strongly, positively correlated with RWD V in the 20–40 cm and 40–60 cm soil layers but negatively correlated with RWD V in the deep soil layers. The yield components were also closely correlated with RWD V in various soil layers; in particular, the 1000-grain weight was strongly positively correlated with RWD V in most soil layers at the late stage of development in wheat. W2N240 and W2N180 treatment produced the highest grain yield and RWD V values, respectively.