Improving nitrogen management in cotton crops in sandy soils

In Brazil, nitrogen (N) fertilization of cotton crops usually occurs at the pinhead square and early flowering stages. However, in sandy soils, common N sources can increase N losses by volatilization and leaching. These disadvantages could be addressed by using controlled-release urea (CRU). This study evaluated the yield, fiber quality, and N nutrition of cotton under different N fertilization management treatments. The experiment was conducted in Presidente Bernardes-SP, Brazil, in the 2020/21 and 2021/22. The N sources were urea (46 % N); ammonium nitrate (33 % N); and sulfur-coated urea (40 % N and 8 % S). The seven treatments were: AN, ammonium nitrate as topdressing at 20, 40 and 60 DAE; UREA, conventional urea as topdressing at 20, 40 and 60 DAE; U 30 DAE, placement between rows of 100 % conventional urea at 30 days after emergence (DAE); CRU/U, placement between rows of CRU (70 % N) at sowing and topdressing UREA (30 % N) at 50 DAE; CRU 70/30, placement between rows of CRU (70 % N) at sowing and topdressing with CRU (30 % N) at 50 DAE; CRU 100 P, placement between rows of 100 % CRU at sowing; and CRU 100 T, topdressing with 100 % CRU at sowing. In 2020/21, boll number was significantly higher in UREA, whereas boll weight and fiber yield were not affected by the treatments. In 2021/22, fiber yield was higher in CRU/U, CRU 70/30, and CRU 100 T. Soil NH 4 + content at 0–20 cm was higher in CRU in 2020/21 and in U 30 DAE and CRU/U in 2021/22. Soil NO 3 - content was lower in UREA and CRU 100 T in 2021/22. Leaf N content and fiber quality were not affected by N management. CRU application combined with urea in cotton may improve boll setting late in the season when rainfall is adequate, benefiting fiber yield in sandy soils. • Controlled-release urea (CRU) fully top-dressed applied at sowing improved cotton yield. • Applying CRU at sowing at 70 % of the N rate and urea or CRU at early flowering at 30 % of the N rate improved cotton yield. • Under favorable water regimes, applying CRU in association with urea increases boll retention in the upper third of the plant. • Full early incorporated application of CRU is not recommended for sandy soil. • CRU increases NH 4 + content in sandy soil.