Sweet potato yield and quality as a function of phosphorus fertilization in different soils

ABSTRACT Phosphorus (P) is an essential nutrient for growth and yield of sweet potatoes; in sandy soils, sweet potato yield and quality may be limited by application of low P doses, mainly in degraded areas. The objective of this work was to evaluate the effect of P doses on yield and quality of sweet potato root tubers grown in tropical sandy soils with different initial P availabilities: 23.2 mg dm-3 (high P - crop rotation) and 3.7 mg dm-3 (low P - post degraded pasture). Two experiments were carried out in a randomized block design, with four replicates. The treatments consisted of P doses (0, 22, 44, 88, and 176 kg ha-1) applied to the planting bed. Tuber yield, number and mean weight of tubers, P concentration in leaves and tubers, exported P, as well as the percentage of starch, reducing sugars, total sugars, and sucrose in the tubers were evaluated. P concentration in the soil was evaluated at the end of the experiment. In the area with high P availability (> 20 mg dm-3 - resin), increasing P doses did not increase root tuber yield and decreased root starch concentrations. In the area with low P availability (< 3.7 mg dm-3 - resin), root tuber yield and starch concentration peaked when applying 68 and 33 kg ha-1 of P, respectively. In areas after degraded pasture, with low initial soil P concentration, P fertilization for sweet potato crops should be carried out with a P dose of 68 kg ha-1. In areas with crop rotation and adequate soil P concentration, P fertilization should be carried out to replace the amount of P exported by the harvested root tubers to avoid decreases in soil fertility.

摘要 磷（Phosphorus, P）是甘薯生长与产量形成的必需营养元素；在砂质土壤中，尤其是退化地块，低磷施用量可能限制甘薯的产量与品质。本研究旨在评估不同初始有效磷水平的热带砂质土壤中，施磷量对甘薯块根产量与品质的影响：初始有效磷水平分别为23.2 mg dm⁻³（高磷地块，采用作物轮作制度）和3.7 mg dm⁻³（低磷地块，退化牧场恢复后）。
本研究设置两个随机区组设计试验，各设置4次重复。处理组为施用于种植床的磷素施用量（0、22、44、88和176 kg ha⁻¹）。测定指标包括块根产量、块根数量与平均单重、叶片与块根中的磷浓度、磷素携出量，以及块根中的淀粉、还原糖、总糖与蔗糖的百分含量。试验结束后测定土壤磷素浓度。
结果显示：在初始树脂法提取有效磷含量较高（>20 mg dm⁻³）的地块，增加施磷量未提升块根产量，反而降低了块根淀粉的百分含量；在初始树脂法提取有效磷含量较低（<3.7 mg dm⁻³）的退化牧场恢复地块，块根产量与淀粉百分含量分别在施磷68 kg ha⁻¹和33 kg ha⁻¹时达到峰值。
研究结论：在退化牧场开垦且初始土壤磷素含量较低的地块，甘薯施肥应采用68 kg ha⁻¹的磷素施用量；而在采用作物轮作制度且土壤磷素含量充足的地块，施磷量应替换为收获块根所携出的磷素总量，以避免土壤肥力下降。