Study of P Nutrient Soil Test Calibration in Determining P Fertilization Recommendations Shallots in Ultisol Soil

The P calibration test was carried out from March 2015 to January 2016, the selected location was in Kentrong Village, Malangsari Village, Cipanas, Lebak, Banten Province. The research objective was to determine the recommendation for P fertilization of shallot plants in Ultisols using soil testing, with a single location approach. The study used a split-plot design with 5 replications.The main plot treatment was the soil P nutrient status, namely 0X, 1 / 4X, 1 / 2X, 3 / 4X, and X, where X is half the value of nutrient absorption P of 1033.3 kg P ha⁻¹. The P application used phosphoric acid (H₃PO₄), the dosages of each level were 0, 258.3, 516.65, 775, and 1033.3 kg P ha⁻¹, equivalent to 0, 0.97, 1.94, 2.9, and 3.87 kg P plot⁻¹. Fertilization of P in subplots using SP-36, the doses of P fertilizer for subplots were 0, 591.6, 1183.3, 1774.9, and 2366.6 kg P₂O₅ ha⁻¹, equivalent to 0, 0.44, 0.89, 1.33, and 1.77 kg P₂O₅ plot⁻¹. The results showed that the interval limits for the availability of P nutrients extracted with Truog for very low, low, medium, high and very high classifications were <1, 1 - <9, 9 - <28, ≥ 28 ppm P. Maximum requirement for P fertilizer for shallot plants in ultisol soils in low and medium nutrient availability classes are 1850 kg P₂O₅ ha⁻¹ and 1310 kg P₂O₅ ha-¹. The optimum requirement for P fertilizer is 1315 kg P₂O₅ ha⁻¹ and 765 kg P₂O₅ ha⁻¹