Optimized planting density and nitrogen improve grain yield and water productivity in drip-fertigated maize through improved canopy function and source–sink balance

Zhenlin LaiZhenqi LiaoHao KongYiyao LiuHongtai KouKechun WangZhijun LiJunliang Fan^*

• Northwest A&F University, Xianyang, China

Balanced source-sink relations are key to achieving high maize yield and water productivity, while the maintenance of post-silking green leaf area is critical for dry matter accumulation and yield formation in maize (Zea mays L.). The underlying mechanisms of nitrogen rate and planting density effects on maize yield formation, particularly through leaf senescence and source-sink relation regulation, remain poorly understood. This study aims to explore the contributions of elucidate the respective contributions of post-silking leaf functional decline and source-sink balance to grain yield and water productivity of drip-irrigated maize. A two-year field experiment was conducted in northwest China, with three planting densities and four nitrogen rates. Nitrogen application primarily alleviated stress-induced premature leaf functional decline after silking, whereas increasing planting density significantly accelerated the loss of effective leaf function. Both high planting density and nitrogen rate significantly increased leaf area duration (LAD). Compared LD, MD and HD increased source growth by 23.0% and 19.4%, sink capacity by 23.9% and 15.2%, sink growth rate by 23.7% and 15.8%, and source-sink difference by 16.2% and 18.2% respectively, suggesting that sink limitation became the primary constraint to further yield increases under higher planting densities. The PLS-SEM analysis revealed that nitrogen application mitigated premature leaf functional decline, whereas planting density exerted a significant negative effect on leaf functional maintenance. Planting density indirectly affected LAD through leaf functional decline, accounting for 63.7% of the effect, while nitrogen rate and planting density directly influenced LAD, accounting for 75.6% of the effect. LAD had a direct impact of 90.7% on source growth parameters, which in turn increased grain yield (89.0%) and source-sink parameters (73.4%), ultimately contributing to an 81.8% direct increase in grain yield and 74.3% direct increase in water productivity. D2N3 obtained the highest grain yield, followed by D2N2, which significantly improved water productivity and irrigation water productivity. From the perspective of source-sink balance, saving water and stable yield, D2N2 was recommended. These findings contribute to a better understanding of achieving effective dense planting and high-yield cultivation in water scarce conditions.