ABSTRACT

Sandy soil is typically poor in organic matter. When areas with sandy soil are used for pasture prior to soybean cultivation, the availability of nitrogen (N) for plants is limited even further. Our objective was to evaluate if inoculation combined with N fertilization increases N content in the soil and N supply to soybean plants in post-pasture and post-soybean areas. Four experiments were conducted in degraded post-pasture and post-soybean areas in a sandy soil (Rhodustult), between 2016 and 2018, in Brazil. Treatments used a combination of inoculant (zero, 4, 8 and 12 rates ha⁻¹) and mineral N (0, 25, 50, and 100 kg ha⁻¹) with four replicates. It was using the soybean cultivar TMG 7062 IPRO. The post-soybean area had higher N content in the soil than the post-pasture area; 33, 32, and 21% for total N, microbial biomass nitrogen (MBN), and inorganic nitrogen (IN), respectively. Soybean shoots from the post-soybean area also had greater accumulations of N (86 kg ha⁻¹ of N). Increased N fertilization linearly raised levels of N in the soil (total N, MBN, and IN). In both areas, the effect of inoculation was restricted by the increase of total N in the soil. Inoculation combined with moderate rates of N in soybeans (50 kg ha⁻¹) increased levels of N in the soil and N supply to plants in post-pasture areas. In post-soybean areas, inoculation alone fulfilled the N soybean need.

摘要

沙质土壤通常缺乏有机质。如果在种植大豆之前将沙质土壤区域用作牧场，则植物的氮 (N) 可用性将进一步受到限制。我们的目标是评估接种结合施氮肥是否会增加土壤中的氮含量以及牧草后和大豆后地区大豆植株的氮供应。2016 年至 2018 年，在巴西沙质土壤 (Rhodustult) 中的退化后牧场和后大豆区进行了四项实验。使用接种剂（零、4、8 和 12 比率 ha ^-1）和矿物氮（0、25、50 和 100 kg ha ^{-1）的组合进行处理}) 重复四次。它使用的是大豆品种 TMG 7062 IPRO。后大豆区土壤氮含量高于后牧区；总氮、微生物生物量氮 (MBN) 和无机氮 (IN) 分别为 33、32 和 21%。后大豆区的大豆芽也有更多的 N 积累（86 kg ha ^-1 N）。增加施氮量会线性提高土壤中的 N 水平（总 N、MBN 和 IN）。在这两个地区，接种的效果都受到土壤中总氮增加的限制。接种与大豆（50 kg ha ^-1）中适度的氮含量相结合，增加了土壤中的氮含量和放牧后地区植物的氮供应。在后大豆区，仅接种就满足了 N 大豆的需要。