减氮对华南地区甜玉米大豆间作系统产量稳定性的影响

在广东省广州市华南农业大学试验中心，通过大田定位试验（2013年秋-2017年秋5年9季）对比了两种施氮水平减量施氮（300 kg·hm^-2，N1）和常规施氮（360 kg·hm^-2，N2）]、4种种植模式甜玉米单作（SS）、甜玉米//大豆2：3间作（S2B3）、甜玉米//大豆2：4间作（S2B4）、大豆单作（SB）]的甜玉米、大豆及系统产量的动态变化，采用W²（Wricke''s ecovalence，生态价值指数）、变异系数（CV）和可持续指数（SYI）评价了产量的时间稳定性，旨在为华南地区一年2熟制甜玉米产区地力保育和绿色生产提供科学依据。结果表明：1）各处理甜玉米、大豆和系统总产量呈现明显的生产季节动态变化，不同年季、种植模式对甜玉米、大豆和系统总产量均有极显著影响，施氮水平仅显著影响甜玉米的产量。2）所有间作处理甜玉米的相对产量均高于单作，间作系统的实际产量损失指数（AYLs）均大于零，表明甜玉米//大豆间作能稳定地保持间作优势且显著提高了土地利用效率。3）不同处理甜玉米产量的W²、CV和SYI均没有显著差异，但单作大豆的W²值显著高于间作，单作大豆的产量稳定性低于间作大豆。种植模式对系统总产量稳定性有显著影响，且间作大豆提高了其稳定性。4）间作大豆显著提高了土壤地力贡献率，S2B3和S2B4的平均地力贡献率分别为75.07%和74.27%，比SS分别高30.29和29.47个百分点。5）与单作甜玉米相比，9季甜玉米//大豆间作显著提高了土壤pH，缓解了长期大量施氮导致的土壤酸化对地力的影响。连续减量施氮没有影响甜玉米//大豆间作系统土壤有机质和全量养分含量，300 kg·hm^-2的施氮量能够满足甜玉米和大豆对氮素的需要。减量施氮与间作大豆是华南甜玉米产区资源高效利用、系统产量稳定的可持续绿色生产模式。

Effect of nitrogen reduction on yield stability of sweet maize//soybean intercropping system in South China

The increasing demand for fresh sweet maize (Zea mays L. saccharata) in southern China has prioritized the need to find solutions to the environmental pollution caused by its continuous production and excessive use of chemical nitrogen fertilizers. A promising method for improving crop production and environmental conditions is to intercrop sweet maize with legumes and to reduce nitrogen fertilization. In this paper, a field experiment was conducted at the Experimental Center of South China Agriculture University for a total of 9 cropping season in five years (2013-2017) to investigate the dynamic changes of maize//soybean intercropping and system yields in sweet maize farmlands in South China under two nitrogen levelsreduced nitrogen dose of 300 kg·hm^-2 (N1) and conventional nitrogen dose of 360 kg·hm^-2 (N2)] and four cropping patternssole sweet maize (SS), sweet maize//soybean intercropping with sweet maize to soybean line ratios of 2:3 (S2B3) and 2:4 (S2B4), sole soybean (SB)]. This study analyzed the dynamic change of land equivalent ratio and actual yield loss index, and evaluated the stability of system yield by W² (Wricke''s ecovalence), CV (coefficient of variation) and SYI (sustainability index), and aimed to explore the effects of reduced nitrogen application on the time stability of sweet maize//soybean intercropping system in South China. Results showed that:1) the yields of sweet maize, soybean, and the total system under different treatments showed obvious seasonal dynamic changes and were significantly affected by cropping and planting patterns. Nitrogen application levels only significantly affected the yield of sweet maize. 2) The relative yield of sweet maize under all intercropping treatments was higher than that under monocropping, and the actual yield loss index (AYLs) of the intercropping system was greater than zero, indicating that sweet maize//soybean intercropping could maintain the intercropping advantage stably and significantly improving land use efficiency. 3) There were no significant differences in W², CV and SYI of sweet maize among different treatments, but the W²value of monocropping soybean was significantly higher than that of the intercropping patterns, and the yield stability of monocropping soybean was lower than that of intercropping soybean. Planting pattern had a significant effect on the stability of the total yield of the system, and intercropping soybean increased the stability of the total yield of the system. 4) Nitrogen fixation of intercropping soybean significantly increased the soil fertility contribution rate. The soil fertility contribution rate of S2B3 and S2B4 were 75.07% and 74.27%, respectively, which were 30.29 and 29.47 percentage points higher than that of SS, respectively. 5) Compared with monocropping sweet maize, sweet maize//soybean intercropping in 9 seasons significantly increased soil pH and alleviated the effect of soil acidification induced by a large amount of nitrogen application on soil fertility for a long time. The soil organic matter and total nutrient content in the sweet maize//soybean intercropping system were not affected by continuous reduced nitrogen application, and 300 kg∙hm^-2 could meet the needs of sweet maize and soybean for nitrogen. Reducing nitrogen application and intercropping soybean are sustainable and green production models for efficient utilization of resources and stable system yield in sweet maize producing areas in South China.