Rhizobial Inoculation and Molybdenum Fertilization in Peanut Crops Grown in a No Tillage System After 20 Years of Pasture

ABSTRACT: Peanut (Arachis hypogea) is an important legume grain consumed by humans and utilized for effective nutrient cycling in a diverse cropping system. Areas that have been cultivated with perennial pasture for decades may have nutritional deficiencies and lack a sufficient population of atmospheric nitrogen-fixing bacteria. Molybdenum is an essential micronutrient that is part of the enzyme nitrogenase contained within symbiotic Bradyrhizobium bacteria, which are responsible for fixing nitrogen in legumes. Our objective was to evaluate the effects of application of Mo at different rates and a rhizobial inoculant on peanut growth characteristics. The experiment was conducted in the 2009/2010 growing season in a no-tillage cropping system following 20-year use as pasture [Urochloa brizantha (Syn. Brachiaria brizantha)]. The experimental design was a randomized complete block with four replicates. The main plots were characterized by peanut inoculation with Bradyrhizobium inoculant or without, and the split plots were characterized by different rates of molybdenum (0, 50, 100, and 200 g ha-1) applied to leaves in the form of ammonium molybdate. The nutritional status of plants, nodulation (number of nodules and nodule dry matter per plant), nitrogenase activity, and nitrogenase specific activity were evaluated at 45 and 64 days after emergence (DAE). The yield components and kernel yield were evaluated at the end of the growing season. Nitrogenase enzyme activity at 64 DAE approximately doubled, and the number of pods per plant was greater with inoculation than without, both of which led to greater yields of pods and kernels. In long-term pasture areas, inoculation and molybdenum fertilization greater than the currently recommended rate appear to be necessary to increase pod and kernel yield per hectare of peanut when managed under no-tillage.摘要：花生（Arachis hypogea）是一类重要的食用豆科谷物，可在多样化种植系统中有效促进养分循环。长期种植多年生牧草数十年的地块往往存在养分匮乏问题，且大气固氮菌种群数量不足。钼是一种必需微量营养素，是共生慢生根瘤菌（Bradyrhizobium）体内固氮酶的组成成分，该类菌负责豆科作物的固氮作用。本研究旨在评估不同施钼量与根瘤菌接种剂对花生生长性状的影响。试验于2009/2010生长季开展，设置于已作为牧场使用20年的免耕种植系统中，供试牧场原生植被为多枝臂形草（Urochloa brizantha，曾用名Brachiaria brizantha）。试验采用随机完全区组设计，设置4次重复。主处理为花生接种慢生根瘤菌接种剂与不接种处理，裂区设置为以钼酸铵为喷施剂型的不同施钼量梯度（0、50、100、200 g·ha⁻¹）。分别于出苗后45天（DAE）与64天（DAE）测定植株营养状况、结瘤指标（单株结瘤数与根瘤干重）、固氮酶活性及固氮酶比活性；于生长季末测定产量构成因素与籽仁产量。结果显示，出苗后64天时的固氮酶活性提升约一倍；接种根瘤菌处理的单株荚果数高于未接种处理，二者共同促成了更高的荚果与籽仁产量。在长期牧场开垦的免耕种植区域中，接种根瘤菌与施用超过当前推荐用量的钼肥，似乎是提升花生公顷荚果与籽仁产量的必要措施。