Optimizing planting pattern and nitrogen application rate improves grain yield and water use efficiency for rain-fed spring maize by promoting root growth and reducing redundant root growth

Abstract

Improving root growth is essential for enhancing the capacity of crops to acquire soil resources but redundant root growth can also limit productivity, especially in rain-fed farming areas where resources are limited. We conducted a two-year field experiment in the Loess Plateau region of China to explore the effects of different planting patterns (flat planting without film mulching; ridge–furrow plastic film mulching planting with three ridge–furrow ratios of 40:70 cm, 55:55 cm, and 70:40 cm) and nitrogen application rates (180 kg ha –1, 240 kg ha –1, and 300 kg ha –1) on the growth and activity of roots, root–shoot relationship, and grain yield and WUE of rain-fed spring maize. The planting pattern and nitrogen application rate only affected the root characteristic parameters in the shallow soil layer (0–40 m), where these parameters all increased as the ridge–furrow ratio and nitrogen application rate increased. The improvements in the root characteristic parameters were beneficial for increasing the root bleeding sap rate. The root–shoot ratio was only affected by the planting pattern. Compared with flat planting, increasing the ridge–furrow ratio enhanced the root–shoot ratio in the early growth stage, which was beneficial for allowing roots to acquire soil resources and promoting canopy establishment; however, the opposite results were observed in the late growth stage, thereby suggesting that increasing the ridge–furrow ratio promoted the distribution of dry matter to the shoots and reduced redundant root growth. The spring maize grain yield and water use efficiency were significantly positively correlated with the root characteristic parameters and the root bleeding sap rate but negatively correlated with the root–shoot ratio, thereby explaining the increases in the grain yield and water use efficiency as the ridge–furrow ratio and nitrogen application rate increased. However, there were generally no significant differences in the grain yield and water use efficiency between 240 kg ha −1 and 300 kg ha −1 under the same planting pattern. Therefore, the combination of ridge-furrow plastic film mulching planting with three ridge-furrow ratios of 70:40 cm and 240 kg ha −1 may be applied as a suitable field management practice for rain-fed spring maize production in the Loess Plateau region.