Nutrient cycling in sugarcane. I. Plant recovery of N from single or split urea (15N) application

Abstract

A fiel experiment was established, on a Podzolic Red-yellow soil in Goiana, PE, Brazil, with three tretments: 1) no nitrogen; 2) 60 kg/ha of ¹⁵N at planting time and, 3) 20 kg/ha of ¹⁵N at planting time plus 40 kg/ha of N three months later. Each plot had nine rows, 10 m long, and received liming plus 120 kg/ha of P₂O₅ and 100 kg/ha of K₂O. In each plot receiving N, urea with 10,2% of ¹⁵N atom excess was added to two subplots, 1,25 by 1,25 m each. Nitrogen derived from fertilizer (Ndff) and total N in green and dry leaves, stalks and roots were determined 3, 6, 11 and 16 months after planting. Neither dry matter production nor N content in the different plant parts varied significantly among treatments, in any of the four sampling periods. At harvest time, cane production was 130 t/ha and N uptake was 250 kg/ha. Less than 10% of the N was derived from the fertilizer and absorved during the first three months of the growing period, Ndff percentages in the plants were proportional to ¹⁵N application rates, resulting in fertilizer efficiencies of about 40%. Different plant parts had different percentages of Nddf.