Vegetation indexes and delineation of management zones for soybean1

ABSTRACT The delimitation of site-specific management zones may be an operational and economically feasible approach in precision agriculture. This study aimed at investigating the spatial correlations between spectral indexes sampled during different growth stages of soybean and crop yield. Soil attributes stratified in each zone and the influence of altitude were also assessed. The simple ratio index, normalized difference vegetation index and soil-adjusted vegetation index were calculated for soybean at the V6, R5 and R5.5 stages. Spatial dependence analysis via semivariogram was performed for the vegetation indexes, soybean yield and terrain elevation. The crop yield map was taken as a reference to assess the spatial agreement with the different maps generated from the spectral indexes. The average values for chemical and granulometric soil attributes were calculated and analyzed by their means among the zones delineated. The field division into two management zones, due to the combination of altitude, simple ratio index of the V6 stage and soil-adjusted vegetation index of the R5.5 stage, showed the highest agreement with the soybean yield map. Differences between the delineated zones were identified for the phosphorus, clay and silt contents.

摘要 精准农业（precision agriculture）中，定点管理分区的划定是一种兼具可操作性与经济可行性的技术路径。本研究旨在探究大豆不同生育期采集的光谱指数与作物产量之间的空间相关性，同时评估各分区内的土壤属性及海拔的影响效应。本研究针对V6、R5及R5.5生育期的大豆，计算得到简单比值指数（simple ratio index）、归一化植被指数（normalized difference vegetation index）与土壤调整植被指数（soil-adjusted vegetation index）。通过半方差函数（semivariogram）对植被指数、大豆产量及地形高程开展空间依赖性分析；以作物产量图为参照，评估其与不同光谱指数生成图的空间一致性。对划定分区内的土壤化学与颗粒组成属性的平均值进行计算并开展组间均值差异分析。结合海拔、V6生育期简单比值指数及R5.5生育期土壤调整植被指数所划定的2个管理分区，与大豆产量图的空间一致性最高。不同划定分区间的磷、黏粒及粉粒含量存在显著差异。