Strategies of supplemental irrigation and modified planting densities to improve the root growth and lodging resistance of maize (Zea mays L.) under the ridge-furrow rainfall harvesting system

In the semi-arid area of northwest China, a ridge-furrow rainfall harvesting (RFRH) system and supplementary irrigation techniques have been implemented to increase crop yields. However, the effects of supplementary irrigation and planting density on maize root growth and lodging resistance under the RFRH system are unknown. Therefore, we conducted field trials implementing three planting densities (Low: 52,500 plants ha−1; Medium: 75,000 plants ha−1; High: 97,500 plants ha−1) and four irrigation modes (NI: no irrigation; IV: irrigation at the 11-leaf stage; IS: irrigation at the silking stage; and IVS: irrigation at the 11-leaf and silking stages) under the RFRH system. The results showed that the average root length density (RLD) and root surface area density (RSD) in the 0-100 cm soil layers increased at the silking and dough stages under medium and high densities compared with low density. However, the root weight under high density significantly decreased compared with that under low density. Increased planting density significantly increased ear height and the ear height coefficient, leading to an increased probability of maize lodging. The root and stalk lodging rates under high density were higher than those under low and medium densities. Compared with NI treatment, at the dough stage, the average RLD and RSD increased in all irrigation treatments; supplementary irrigation also increased the root weight and root shoot ratio. The results showed that the grain yield under IS and IVS treatments significantly increased compared with that under NI treatment. The total lodging rate under IVS treatment was 41.2% higher than that under IS treatment. Therefore, the IS treatment under medium density achieved a higher grain yield (13.2 t ha−1) and reduced maize lodging, which could be a suitable planting model in semi-arid areas.