Zhang Yuanhong, Xu Zonggui, Li Jun, Wang Rui
College of Agronomy, Northwest A&F University, Yangling, China.
Key Laboratory of Crop Physi-ecology and Tillage Science in Northwestern Loess Plateau, Ministry of Agriculture, Yangling, China.
Front Plant Sci. 2021 Nov 12;12:752606. doi: 10.3389/fpls.2021.752606. eCollection 2021.
Increasing planting density is an effective strategy for improving maize productivity, but grain yield does not increase linearly with the increase in plant density, especially in semiarid environments. However, how planting density regulates the integrated utilization of key input resources (i.e., radiation, water, and nutrients) to affect maize production is not clear. To evaluate the effects of planting density and cultivar on maize canopy structure, photosynthetic characteristics, yield, and resource use efficiency, we conducted a successive field experiment from 2013 to 2018 in Heyang County (Shaanxi Province, China) using three different cultivars [i.e., Yuyu22 (C1), Zhengdan958 (C2), and Xianyu335 (C3)] at four planting densities [i.e., 52,500 (D1), 67,500 (D2), 82,500 (D3), and 97,500 (D4) plants ha]. Increasing planting density significantly increased the leaf area index (LAI) and the amount of intercepted photosynthetically active radiation (IPAR), thereby promoting plant growth and crop productivity. However, increased planting density reduced plant photosynthetic capacity [net photosynthetic rate (Pn)], stomatal conductance (Gc), and leaf chlorophyll content. These alterations constitute key mechanisms underlying the decline in crop productivity and yield stability at high planting density. Although improved planting density increased IPAR, it did not promote higher resource use efficiency. Compared with the D1 treatment, the grain yield, precipitation use efficiency (PUE), radiation use efficiency (RUE), and nitrogen use efficiency (NUE) increased by 5.6-12.5%, 2.8-7.1%, and -2.1 to 1.6% in D2, D3, and D4 treatments, respectively. These showed that pursuing too high planting density is not a desirable strategy in the rainfed farming system of semiarid environments. In addition, density-tolerant cultivars (C2 and C3) showed better canopy structure and photosynthetic capacity and recorded higher yield stability and resource use efficiency. Together, these results suggest that growing density-tolerant cultivars at moderate planting density could serve as a promising approach for stabilizing grain yield and realizing the sustainable development of agriculture in semiarid regions.
增加种植密度是提高玉米产量的有效策略，但籽粒产量并非随种植密度的增加呈线性增长，尤其是在半干旱环境中。然而，种植密度如何调节关键投入资源（即辐射、水和养分）的综合利用以影响玉米生产尚不清楚。为了评估种植密度和品种对玉米冠层结构、光合特性、产量和资源利用效率的影响，我们于2013年至2018年在中国陕西省合阳县进行了连续田间试验，使用三个不同品种[即豫玉22（C1）、郑单958（C2）和先玉335（C3）]，设置了四个种植密度[即52500（D1）、67500（D2）、82500（D3）和97500（D4）株/公顷]。增加种植密度显著提高了叶面积指数（LAI）和光合有效辐射截获量（IPAR），从而促进了植株生长和作物产量。然而，种植密度的增加降低了植株的光合能力[净光合速率（Pn）]、气孔导度（Gc）和叶片叶绿素含量。这些变化是高种植密度下作物产量下降和产量稳定性降低的关键机制。虽然提高种植密度增加了IPAR，但并未提高资源利用效率。与D1处理相比，D2、D3和D4处理的籽粒产量、降水利用效率（PUE）、辐射利用效率（RUE）和氮素利用效率（NUE）分别提高了5.6 - 12.5%、2.8 - 7.1%和 - 2.1至1.6%。这些结果表明，在半干旱环境的雨养农作系统中，追求过高的种植密度并非理想策略。此外，耐密品种（C2和C3）表现出更好的冠层结构和光合能力，产量稳定性和资源利用效率更高。总之，这些结果表明，在中等种植密度下种植耐密品种可能是稳定半干旱地区籽粒产量和实现农业可持续发展的一种有前景的方法。
