Utilization and fate of phosphorus of different sources applied to cohesive soil of Amazonian periphery

ABSTRACT In the Amazonian region, P is often a primary factor limiting sustainable agrosystems. We compared the efficiencies of local aluminous phosphate (ALP) and single superphosphate (SSP) under a cover of leguminous residues to determine the fate of P sources in an Amazonian soil with hardsetting characteristics. The experiment followed a randomized block design with four replications and the following treatments: ALPU, i.e. ALP plus urea (U); ALPL, i.e., ALP plus leucaena (L); SSPU, i.e., SSP plus urea; SSPL, i.e., SSP plus leucaena; and BS, i.e., bare soil (without residues). To assess the residual values of the P sources, we used a sequence of crops consisting of maize, cowpea and cassava. Both ALP and SSP exhibited low P efficiency in BS. The greatest amounts of P and N uptake in the plots where P sources and leucaena residues were added, as in those covered with leucaena residue, resulted in higher productivity levels. These differences are important for the adoption of beneficial soil management practices and the use of P sources to enhance efficiency in tropical soils. The use of residues increased the P use efficiency of both P sources, as it enhanced the uptake of both N and soluble P. The replacement of SSP with ALP may be advantageous in the second year of planting with high-demand crops, but the P of the SSP retained in the minus soluble fractions may be available if the SSP is used in P-depleting crops combined with no-tillage underneath a mulch of residues.

摘要 在亚马逊地区，磷（P）通常是制约可持续农业生态系统的核心限制因子。本研究以具有硬结特性的亚马逊土壤为供试对象，设置豆科残体覆盖模式，对比了本地含铝磷酸盐（ALP）与过磷酸钙（SSP）的肥效，以明确两种磷源在该土壤中的养分归趋。试验采用随机区组设计，设置4次重复，共包含5组处理：ALPU组（即含铝磷酸盐配施尿素(U)）、ALPL组（即含铝磷酸盐配施银合欢(L)残体）、SSPU组（即过磷酸钙配施尿素）、SSPL组（即过磷酸钙配施银合欢残体）以及BS组（即裸土，无残体覆盖）。为评估两种磷源的残效值，本试验设置了玉米-豇豆-木薯的连作序列。结果显示，在裸土处理组中，含铝磷酸盐与过磷酸钙均表现出较低的磷利用效率。在施加磷源并配施银合欢残体，或仅覆盖银合欢残体的处理小区中，植株对磷与氮的吸收量最高，对应的作物生产力水平也显著提升。上述差异对于在热带土壤中推行合理的土壤管理措施、优化磷源使用以提升肥效具有重要指导价值。残体覆盖可同时促进植株对氮与可溶性磷的吸收，进而提升两种磷源的磷利用效率。在第二年种植高需肥作物时，以含铝磷酸盐替代过磷酸钙或具备应用优势；而若在耗磷型作物中结合残体覆盖免耕模式施用，过磷酸钙留存于难溶性组分中的磷素也可被有效活化利用。