Sweet potato yield and quality as a function of phosphorus fertilization in different soils¹

Produtividade e qualidade da batata-doce em função da adubação fosfatada em diferentes solos

HIGHLIGHTS:

High sweet potato quality and yield can be obtained in soils with P concentration > 20 mg dm^-3 without P fertilization.

Soils with P concentration < 5.0 mg dm^-3 require 68 kg ha^-1 of P for maximum yield.

Replacing of exported P requires 370 g of P per Mg of sweet potato.

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.

Key words:
Ipomoea batatas (L.) Lam; sandy soil; degraded pasture; starch; reducing sugars