Effect of nitrogen application rate under organic and conventional systems on rice (Oryza sativa L.) growth, grain yield, soil properties, and greenhouse gas emissions

Authors: LI, XIUFEN - Texas A&M Agrilife; JIANG, JING - Texas A&M Agrilife; GUO, JINGQI - Texas A&M Agrilife; McClung, Anna; CHEN, KUN - University Of Connecticut; VELARCA, MARIANA VALDEZ - Texas A&M Agrilife; Torbert, Henry - Allen; DOU, FUGEN - Texas A&M Agrilife

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2022
Publication Date: 7/5/2022
Citation: Li, X., Jiang, J., Guo, J., McClung, A.M., Chen, K., Velarca, M., Torbert Iii, H.A., Dou, F. 2022. Effect of nitrogen application rate under organic and conventional systems on rice (Oryza sativa L.) growth, grain yield, soil properties, and greenhouse gas emissions. Journal of Plant Nutrition. https://doi.org/10.1080/01904167.2022.2093746.
DOI: https://doi.org/10.1080/01904167.2022.2093746

Interpretive Summary: Organic crop production prohibits the use of synthetic agricultural chemicals for nutrient management and pest control. As a result, yield potential under organic systems is generally lower than conventional management. This greenhouse study was conducted to determine the response of rice yield and plant growth factors to nitrogen (N) fertilizer inputs under organic and conventional systems with the aim to identify the optimum fertilizer rate. Six rates (0, 50, 100, 150, 200, and 250 kg ha-1) of N were applied using an organic certified soil amendment, Nature Safe (13-0-0) in the organic system and using urea (46-0-0) fertilizer in the conventional system were evaluated using one hybrid cultivar. Because the organic fertilizer is released slowly, the entire rate was applied prior to planting whereas the total amount of urea fertilizer was applied as a three-way split (post emergence, tillering, and prior to heading). The plants were evaluated for rice tiller number, plant height, plant total fresh and dry biomass, grain yield, harvest index, number of panicles, and 1,000-grain weight. In addition, at three times during the growing season, soil inorganic N , plant available N, dissolved organic carbon, dissolved organic N, total dissolved N, pH, electrical conductivity, and soil total microbial biomass were determined to test the potential relationships between soil parameters and agronomic traits. Although the same amount of N was applied in the two systems, the organic fertilizer resulted in greater tiller production whereas the synthetic fertilizer resulted in greater plant height in response to increasing N rate. At the optimum N rate, grain yield of organic managed rice was 93% of conventional rice. Methane emissions, and important greenhouse gas, peaked during the reproductive growth phase. In summary, this study provided important information regarding the optimum fertilizer rates that will maximize yield while minimizing input costs for organic rice growers and greenhouse gas emissions.

Technical Abstract: The use of appropriate nitrogen (N) rates is important to optimize organic rice yield potential while minimizing environmental impact and input costs. A greenhouse experiment was conducted to identify the optimal N rate for organic and conventional rice and determine its effects on rice yield, soil properties, and greenhouse gas emissions. Six N rates (0, 50, 100, 150, 200, and 250 kg ha_1) and two cropping systems (organic, conventional) were included in this study. Plant dry biomass, panicle number, and yield of onventional rice linearly increased with increasing N rate from 0 to 250 kg ha_1, whereas those of organic rice increased significantly with increasing N rate until 200 kg ha_1. Conventional rice had a gnificantly taller plant, whereas organic rice had a significantly greater tiller number. At the optimal N rate, the panicle number and yield of organic rice were 77.3% and 92.7% of those of conventional rice, respectively. CO2 and CH4 emissions peaked at the reproductive stage, whereas N2O emissions peaked at the vegetative stage. Global warming potential (GWP) increased with increasing N rate and peaked at 200 and 250 kg N ha_1, espectively, in the organic and conventional system; however, greenhouse gas intensity (GHGI) was not affected by N rate in both systems. Of the measured soil parameters, total microbial biomass (TMB) was significantly correlated to plant growth, yield, and GWP. Our study indicated that the optimal N rate was 200 kg ha_1 for organic rice and 250 kg ha_1 or higher for conventional rice to approach yield potential.