Least limiting water range in Spodosol and initial growth of sugarcane under soil bulk densities and salinities

ABSTRACT The impacts of agricultural mechanization and soil management on sugarcane activity may compromise the growth of plants. This study aimed to evaluate the initial growth of sugarcane (Saccharum officinarum) at soil densities under two salinity conditions, associated with the least limiting water range (LLWR), and obtain the critical density for the Spodosol. The treatments consisted of the use of five bulk densities (1.40; 1.50; 1.60; 1.70 and 1.80 Mg m-3) and two conditions of soil salinity (ECse = 0.5 and 3.0 dS m-1). Morphological variables and biomass of sugarcane plants were measured and, simultaneously, undisturbed soil samples were collected in the layers of 0.02-0.08 m to determine the water retention curve, soil resistance to penetration and the least limiting water range. In general, it was concluded that sugarcane plants has higher growth between the bulk densities of 1.50 and 1.60 Mg m-3. The salinized soil showed higher LLWR than the non-salinized soil, leading to higher shoot fresh mass at bulk densities between 1.49 and 1.66 Mg m-3. The critical bulk densities observed for the Spodosol were 1.70 Mg m-3 for the non-salinized soil and 1.77 Mg m-3 for the salinized soil.

摘要
农业机械化作业与土壤管理措施对甘蔗栽培的影响，可能会抑制植株生长。本研究旨在评估两种盐分条件下，不同土壤容重对甘蔗（Saccharum officinarum）初始生长的影响，并结合最小限制水分范围（least limiting water range, LLWR），确定灰土（Spodosol）的临界容重。试验设置5个土壤容重梯度（1.40、1.50、1.60、1.70及1.80 Mg·m⁻³）与2个土壤盐分条件（ECse=0.5和3.0 dS·m⁻¹）作为处理组。测定了甘蔗植株的形态指标与生物量；同时在0.02~0.08 m土层采集原状土样，用以测定土壤水分特征曲线、土壤穿透阻力及最小限制水分范围。总体而言，试验结果表明，当土壤容重处于1.50~1.60 Mg·m⁻³区间时，甘蔗植株生长状况更佳。盐渍化土壤的最小限制水分范围高于非盐渍化土壤，在容重1.49~1.66 Mg·m⁻³区间时，甘蔗地上部鲜重更高。本试验测得的灰土临界容重为：非盐渍化土壤1.70 Mg·m⁻³，盐渍化土壤1.77 Mg·m⁻³。