Controlled release urea improved crop yields and mitigated nitrate leaching under cotton-garlic intercropping system in a 4-year field trial

Nitrogen fertilization is important for improving crop yields, but excessive amounts lead to high N losses through nitrate (NO 3 − -N) leaching. Controlled-release urea (CRU) has been shown to increase crop yields, yet the long term effects of CRU on soil NO 3 − -N distribution are not well known. A 4-year field experiment applied 50% (100 kg ha −1 ), 100% (200 kg ha −1 ) and 150% (300 kg ha −1 ) of the local practice N rates with CRU and urea was conducted under cotton-garlic intercropping system in Shandong Province, China. The linear increase in garlic yield and curvilinear increase in cotton yield indicates that crop yields increased as the input N rate increased with both urea and CRU while exceeded N application decreased cotton yields. The successive release of N from CRU permitted the meeting of the full N requirements of crops grown. Consequently, the lint cotton yield of CRU treatments was increased by 5.2%-17.3%, and garlic bulb yield increased by 2.0%-7.4%, compared with urea treatment. Although the CRU100% supplied one-third less N than Urea150%, the CRU100% produced −0.6%-5.6% more cotton, and −4.0%-2.6% more garlic than Urea150%. The NO 3 − -N contents of CRU treatments were augmented in 0–40 cm soil, but the opposite trend was found in 60–100 cm soil. The organic matter and total N contents in 0–40 cm profile were increased with CRU fertilization over 4-year fertilization. However, no prominent difference of available P and K contents in 0–20 cm soil was observed between CRU and urea treatments. Thus a one-third decrease in the recommended N application rate of urea is possible with CRU while maintaining crops yield, decreasing NO 3 − -N leaching to deep soil layer and preserving the soil fertility in North China plain.