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DIVISION S-8-NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Yields and Nitrogen Dynamics in a Rice–Wheat System Using Green Manure and Inorganic Fertilizer

^a Dep. of Soils, Punjab Agricultural Univ., Ludhiana 141004, Punjab, India
^b USDA-ARS, East Campus, Univ. of Nebraska, Lincoln, NE 68583 USA
^c Farm Advisory Service, Punjab Agricultural University, Kapurthala, Punjab, India

jdoran1{at}unl.edu

Integrating fertilizer N (FN) with legume green manures (GM) can foster sustainable and environmentally sound agricultural systems in subtropical, semiarid soils low in organic matter. A 4-yr replicated field experiment with irrigated rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotations was conducted on a sandy loam soil in the Punjab of India to evaluate the effects of incorporating cowpea (Vigna unguiculata L.) or sesbania (Sesbania aculeata L.) GM on crop productivity, N-use efficiency, and NO₃ leaching. Rice grain yields with pretransplant incorporation of 20 and 40 Mg GM ha^-1 (GM₂₀ and GM₄₀) ranged from 5.18 to 5.81 Mg ha^-1, which were equivalent to the 5.40 Mg ha^-1 obtained with 120 kg FN ha^-1 (FN₁₂₀). Rice yield with 60 kg FN ha^-1 (FN₆₀) and GM₂₀ was double the control yield and 6% greater than the FN₁₂₀ treatment. Nitrogen utilization by rice was greater for GM₂₀ than FN, as indicated by greater fertilizer N equivalents and an apparent N recovery by rice of 79 vs. 63%. While FN had no residual effects, residual GM produced greater wheat yields, indicating that FN applied to wheat could be reduced by 25%. Soil NO₃–N leaching to 60 cm in the rice crop was apparently used by the subsequent wheat crop, which has a deeper and more extensive rooting system. After 4 yr, use of FN₁₂₀ for both crops resulted in 35 kg of residual NO₃–N ha^-1 in the 150-cm soil profile (74% below 90 cm), whereas only 19 kg NO₃–N ha^-1 remained with GM₂₀ plus FN₆₀. Use of GM₂₀ with FN₆₀ for a rice–wheat rotation demonstrated greater yields of rice and wheat, 25 to 50% reduction in fertilizer N use, and decreased potential for groundwater NO₃ contamination.

Abbreviations: ANR, apparent N recovery • D_b, bulk density • FN, fertilizer N • FN₀, FN₆₀, FN₉₀, and FN₁₂₀ represent 0, 60, 90, and 120 kg fertilizer N ha^-1, respectively • FNE, fertilizer N equivalent • GM, legume green manure • GM₀, GM₂₀, and GM₄₀ represent 0, 20, and 40 Mg fresh weight green manure ha^-1, respectively • HI, harvest index • OC, organic C • RCBD, randomized complete block design

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