Alden D. Smartt

Cultivar and Previous Crop Effects on Methane Emissions From Drill-Seeded, Delayed-Flood Rice Production on a Silt-Loam Soil

Abstract The effects of cultural practices on drill-seeded delayed-flood rice (Oryza sativa L.) production on methane (CH4) emissions are not well quantified. In Arkansas, rice is produced predominantly on loamy soils following soybean (Glycine max L.) as the previous crop, and hybrid rice has replaced a large percentage of pure-line cultivars in the past decade. Therefore, research was conducted during the 2012 growing season to assess the effects of previous crop (rice or soybean) and cultivar (standard-stature, semi-dwarf, and hybrid) on CH4 emissions on a silt-loam soil. A 30-cm-diameter chamber-based method was used to determine fluxes during the 2012 growing season. When soybean was the previous crop, fluxes were generally lower (P < 0.05) until heading, after which all fluxes decreased until flood release. Seasonal emissions differed based on previous crop and cultivar (P < 0.05). Area- and yield-scaled growing season emissions from rice following soybean were less (127 kg CH4-C ha−1; 13.7 kg CH4-C (mg grain)−1) than when rice followed rice (184 kg CH4-C ha−1; 20.5 kg CH4-C (mg grain)−1). Hybrid rice emitted less (111 kg CH4-C ha−1; 11.1 kg CH4-C (mg grain)−1) than semi-dwarf (169 CH4-C ha−1; 18.3 kg CH4-C (mg grain)−1) or standard-stature rice (186 kg CH4-C ha−1; 21.9 kg CH4-C (mg grain)−1), which did not differ. Thus, results indicated decreased emissions when soybean was the previous crop and when the hybrid cultivar was grown. The incorporation of factors known to influence CH4 emissions (i.e., previous crop, cultivar, and yield) will improve estimates of the carbon footprint of rice.

Previous Crop and Cultivar Effects on Methane Emissions from Drill-Seeded, Delayed-Flood Rice Grown on a Clay Soil

Due to anaerobic conditions that develop in soils under flooded-rice (Oryza sativa L.) production, along with the global extent of rice production, it is estimated that rice cultivation is responsible for 11% of global anthropogenic methane (CH4) emissions. In order to adequately estimate CH4 emissions, it is important to include data representing the range of environmental, climatic, and cultural factors occurring in rice production, particularly from Arkansas, the leading rice-producing state in the US, and from clay soils. The objective of this study was to determine the effects of previous crop (i.e., rice or soybean (Glycine max L.)) and cultivar (i.e., Cheniere (pure-line, semidwarf), CLXL745 (hybrid), and Taggart (pure-line, standard-stature)) on CH4 fluxes and emissions from rice grown on a Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts) in eastern Arkansas. Rice following rice as a previous crop generally had greater () fluxes than rice following soybean, resulting in growing season emissions () of 19.6 and 7.0 kg CH4-C ha−1, respectively. The resulting emissions from CLXL745 (10.2 kg CH4-C ha−1) were less () than those from Cheniere or Taggart (15.5 and 14.2 kg CH4-C ha−1, resp.), which did not differ. Results of this study indicate that common Arkansas practices, such as growing rice in rotation with soybean and planting hybrid cultivars, may result in reduced CH4 emissions relative to continuous rice rotations and pure-line cultivars, respectively.

Nitrogen Source Effects on Methane Emissions From Drill-Seeded, Delayed-Flood Rice Production

ABSTRACT Rice (Oryza sativa L.) cultivation is unique compared with the production of most other upland row crops in that rice is typically produced under flooded-soil conditions, which can result in net emissions of methane (CH4). Nutrient applications for optimum production, specifically nitrogen (N), which can be organic or inorganic sources, are carefully managed in rice production. However, how nutrient-source effects on CH4 emissions from rice production may interact with other known factors affecting CH4 emissions, such as previous crop/crop rotation and soil texture, are poorly understood, particularly in the midsouthern United States where rice production is concentrated. The objective of this study was to evaluate CH4 fluxes and season-long emissions as affected by fertilizer-N source (i.e., ammonium sulfate [AS], pelletized poultry litter [PPL] + urea, and urea only) and previous crop in rotation (i.e., soybean [Glycine max L.] or rice) from rice production on a clayey Epiaquert and a silt-loam Albaqualf in the Lower Mississippi River Delta region of eastern Arkansas. Methane fluxes, measured using 30-cm-diameter, enclosed-headspace chambers, peaked near heading for all treatments, with PPL + urea resulting in greater (P < 0.05) peak fluxes than for the other fertilizer-N sources from both soil textures. Methane fluxes were consistently numerically lower from the clay soil throughout the growing season than from the silt-loam soil. Methane emissions from AS were, on average, 21% lower (P < 0.05) than from PPL + urea or urea only, which did not differ, from the silt-loam soil. Methane emissions were 60% lower (P < 0.05) when soybean was the previous crop compared with rice on the clay soil, but were unaffected (P > 0.05) by previous crop on the silt-loam soil. Results clearly indicate that the choice of fertilizer-N source for certain soil textures, specifically AS application to a silt-loam soil, has the potential to mitigate CH4 emissions and reduce the large, negatively perceived, C footprint associated with rice production.

Methane Emissions from Rice Production in the United States — A Review of Controlling Factors and Summary of Research

Flooded rice (Oryza sativa L.) cultivation has been identified as one of the leading global agricultural sources of anthropogenic methane (CH4) emissions. Furthermore, it has been estimated that global rice production is responsible for 11% of total anthropogenic CH4 emissions. Considering that CH4 has a global warming potential that is approximately 25 times more potent, on a mass basis, than carbon dioxide (CO2) and rice production is globally extensive and concentrated in several mid-southern and southern states and Cal‐ ifornia, the purpose of this review is two-fold: (i) discuss the factors known to control CH4 production in the soil and transport to the atmosphere from rice cultivation and (ii) summarize the historic and recent research conducted on CH4 emissions from rice pro‐ duction in the temperate United States. Though some knowledge has been gained, there is much more that still needs to be learned and understood regarding CH4 emissions from rice production in the United States, its contribution to climate change, and poten‐ tial mitigation strategies. Extending the current knowledge base surrounding CH4 emis‐ sions from rice cultivation will help regulatory bodies, such as the Environmental Protection Agency, refine greenhouse gas emissions factors to combat the potential nega‐ tive effects of climate change.