Randall Mutters

Methane pool and flux dynamics in a rice field following straw incorporation

Concerns for air quality have led to legislation restricting rice straw burning in some parts of the world. Consequently, growers must dispose of large amounts of residual rice straw by incorporation into the soil, which may have large effects on CH4 emissions from those fields. Our objective was to characterize how this recent change in management has affected overall CH4 emissions in a California rice field and establish relationships between organic matter availability, CH4 pool sizes and CH4 fluxes. Closed chamber measurements were used to monitor diurnal and post drain fluxes, to describe the seasonal pattern of CH4 emissions and estimate total CH4 fluxes on a large on-farm field trial during the 1997 growing season. Soil redox, temperature and plant growth and yield were also monitored. To establish relationships between CH4 pool sizes and fluxes, soil interstitial CH4 concentrations were monitored in the field and available organic matter in the spring was estimated with a laboratory incubation. Redox values in the soil were found to be 50 mV lower in plots in which straw had been incorporated (−275 mV) than those in which it had been burned (−225 mV). No significant treatment differences were seen in total soil organic matter contents in the spring. However, available organic matter was 1.5 times higher in straw incorporated than straw burned plots. Methane emissions peaked between 22.00 and 23.00 h on two different diurnal sampling dates. Methane emission after draining was about 10% of the flooded period total. A 5-fold increase in total CH4 emissions over the rice growing season was observed in plots in which rice straw had been incorporated each fall for 4 yr. Total cumulative CH4 flux, 1 May–1 October 1997, was 8.87 g C m−2 in incorporated, winter flooded plots; 9.52 g C m−2 in incorporated, non-winter flooded plots; 1.63 g C m−2 in burned, winter flooded plots; and 2.25 g C m−2 in burned, non-winter flooded plots. Soil CH4 concentrations at 10–15 cm depth was strongly associated with emissions to the atmosphere (r=0.89). A model developed by Nouchi et al. (1994) [Nouchi, I., Hosono, T., Aodi, K., Minami, K., 1994. Seasonal variation in methane flux from rice paddies associated with methane concentration in soil water, rice biomass and temperature and its modeling. Plant and Soil 161, 195-208.] which could predict the CH4 flux based on soil CH4 concentrations and temperature was fit to our data. The model was very successful at predicting flux rates and cumulative fluxes because conductance (CH4 flux divided by CH4 concentration in soil water) was highly correlated with soil temperature (r=0.88) throughout the period of high CH4 emissions. Organic matter availability and CH4 pool and flux dynamics were altered by straw incorporation practices as evidenced by increased conductance at the same interstitial CH4 concentration and increased emissions per unit available organic matter in rice straw incorporated plots.

Effects of drain and harvest dates on rice sensory and physicochemical properties

ABSTRACT Timing of field draining and harvesting of rice with meteorological conditions can allow growers to foster conditions for high head rice yield (HRY). The effects of timing of draining and harvesting on rice sensory and physicochemical properties are not well understood. The objective of this study was to determine the effects of varying drain and harvest dates on the sensory and physicochemical properties of M-202 grown in California under controlled field conditions. Drain date had a significant (P 0.05) differences in texture were measured as a result of these parameters being low. Drain date did not affect the volatile composition or flavor of the rice. Harvest date had no effect (P > 0.05) on amylose content and a sig...

Impact of Storage of Freshly Harvested Paddy Rice on Milled White Rice Flavor

ABSTRACT Between harvest and the start of drying, paddy rice may be held for more than 24 hr at moisture contents ranging from 16% to >26%. Microbes found on the freshly harvested rice grow under these conditions and produce a wide variety of volatile compounds that impact the flavor/aroma of the white rice obtained after drying and milling of the paddy rice. The contents of 10 volatile microbial metabolites were compared in white rice obtained from paddy rice harvested at differing moisture contents and immediately dried (0 hr) or held for 48 hr before drying. No increases in volatile microbial metabolite levels were observed in white rice obtained from paddy rice that was stored at 17–21% moisture contents for 48 hr. In white rice from paddy rice stored at ≥24% moisture content, 3-methyl-butanol, 2-methyl-butanol, acetic acid, 2,3- butandiol, and ethyl hexadecanoate increased markedly with time. Also in these samples, as determined by a descriptive panel, sour/silage and alfalfa/grassy/green bean flavor...

Seasonal losses of dissolved organic carbon and total dissolved solids from rice production systems in northern California.

Water quality concerns have arisen related to rice (Oryza sativa L.) field drain water, which has the potential to contribute large amounts of dissolved organic carbon (DOC) and total dissolved solids (TDS) to the Sacramento River. Field-scale losses of DOC or TDS have yet to be quantified. The objectives of this study were to evaluate the seasonal concentrations of DOC and TDS in rice field drain water and irrigation canals, quantify seasonal fluxes and flow-weighted (FW) concentrations of DOC and TDS, and determine the main drivers of DOC and TDS fluxes. Two rice fields with different straw management practices (incorporation vs. burning) were monitored at each of four locations in the Sacramento Valley. Fluxes of DOC ranged from 3.7 to 34.6 kg ha(-1) during the growing season (GS) and from 0 to 202 kg ha(-1) during the winter season (WS). Straw management had a significant interaction effect with season, as the greatest DOC concentrations were observed during winter flooding of straw incorporated fields. Fluxes and concentrations of TDS were not significantly affected by either straw management or season. Total seasonal water flux accounted for 90 and 88% of the variability in DOC flux during the GS and WS, respectively. Peak DOC concentrations occurred at the onset of drainflow; therefore, changes in irrigation management may reduce peak DOC concentrations and thereby DOC losses. However, the timing of peak DOC concentrations from rice fields suggest that rice field drainage water is not the cause of peak DOC concentrations in the Sacramento River.

EFFECT OF WEATHER AND RICE MOISTURE AT HARVEST ON MILLING QUALITY OF CALIFORNIA MEDIUM-GRAIN RICE

California’s medium-grain rice industry experiences a wide range of head rice yield (HRY). Average moisture of a representative paddy rice sample is the commercially used predictor of optimum harvest date to achieve high HRY. A two-year field study demonstrated that average rice moisture alone is not an adequate predictor of HRY. The history of rice moisture caused by varying meteorological conditions was needed to predict rice quality. Under typical calm conditions in California, daytime relative humidity is low and at night humidity increases, exposing rice to dew. During this meteorological pattern, HRY could be predicted by assuming that all kernels that dried below 15% moisture during the day would rehydrate at night and fissure, resulting in lost HRY. Harvest weather is also characterized by occasional episodes of dry north wind, lasting several days. These periods have insufficiently long rehydration periods to completely fissure kernels that dropped below 15% moisture, and actual HRY was much above predicted HRY. HRY dropped significantly during periods of dry north winds; however, rice value (government loan value minus drying costs) did not drop significantly during the windy period because the lower loan value was offset by lower drying costs. After the windy period ended, rice was again subject to nighttime dew and regained moisture, resulting in a large reduction in HRY and value. A combination of the range of individual kernel moisture at harvest and history of rice moisture influenced by weather conditions explained a great deal of the total HRY variation experienced by the California rice industry.

Effect of liming and fertilization on sulfur availability, mobility, and uptake in cultivated soils of South Carolina

We studied the sulfur status of 32 Coastal Plain and 34 Piedmont soils (Ultisols) under cultivation in South Carolina to assess the impact of changing patterns of sulfur input into the soil system. Through growth-chamber and field research we reevaluated the influence of liming and fertilization on soil and plant sulfur performance, with emphasis on the effect of time on soil sulfur movement and availability and on plant sulfur concentration, total uptake, and rate of uptake. The available sulfur content of these soils appeared to be sufficient for crop needs. The acetate extractable SO4-S varied from 19 ppm in the A horizon to 139 ppm in the B horizon of Coastal Plain soils and from 23 ppm in the A horizon to 126 ppm in the B horizon of Piedmont soils. Soil sulfur increased with increasing clay content and decreasing pH values, which explains why sulfur accumulated in the acid and clayey B horizons of these soils. A 1% clay increment was associated with an SO4-S increase of 1 ppm in the A horizon and 3.1 ppm in the B horizon of Coastal Plain soils and 1.4 ppm in the A horizon and 4.2 ppm in the B horizon of Piedmont soils. A pH unit increment was related to an SO4-S decrease of 15 ppm in the A horizon and 72 ppm in the B horizon of Coastal Plain soils and 23 ppm in the A horizon and 117 ppm in the B horizon of Piedmont soils. The growth-chamber study with corn (Zea mays) showed that in the unlimed soil, dry weights of shoots and roots were highest with a sulfur rate of 40 kg/ha, 8 ppm of SO4-S in the soil and sulfur concentrations of 0.19% in the shoots and 0.41% in the roots. Root length doubled with sulfur application. In the limed soil, shoot growth peaked with a sulfur rate of 20 kg/ha, 8.4 ppm of SO4-S in the soil, and a sulfur concentration of 0.13% in the shoots and 0.16% in the roots. Soil sulfur, plant growth, and sulfur uptake by soybeans increased significantly when liming with the recommended amount. Overliming had a detrimental effect on all these parameters. The field study with soybeans (Glycine max) demonstrated that while sulfur concentration decreased and then increased with plant age, total sulfur uptake increased, and the rate of sulfur accumulation in the shoots also increased, peaking between the 12th and 16th weeks in the limed soil and between the 16th and 20th weeks in the unlimed soil. Overliming soybeans in the field did not have the detrimental effect on soil sulfur and sulfur uptake observed in the growth-chamber study.

Nutrients and sediments in surface runoff water from direct-seeded rice fields: implications for nutrient budgets and water quality.

Nutrient losses from rice fields can have economic and environmental consequences. Little is known about nutrient losses in surface runoff waters from direct-seeded rice systems, which are common in the United States and increasingly more so in Asia. The objectives of this research were to quantify nutrient losses from California rice fields in surface runoff waters and to determine when and under what conditions losses are greatest. Research was conducted in 10 rice fields varying in residue (burned or incorporated) and water management over a 2-yr period. Concentrations of NH-N and NO-N in runoff water across sites, seasons, and management practices averaged <0.1 mg N L. Runoff water PO-P concentration averaged 0.14 mg L and was not affected by season or straw management practices. However, P fluxes were higher in the winter when rice straw was burned (2.59 kg ha) as opposed to incorporated (0.44 kg ha). Average seasonal runoff water K concentrations did not vary with season and straw management, although they were highest at the onset of the winter season. Average total suspended solids (TSS) concentrations did not vary by season but were highest during the winter in the straw-incorporated fields (46 mg L). Rice fields were sinks for K (4.9 kg K ha) during the growing season. Fields were not significant sources of nutrients or TSS during the growing season; however, during the winter fallow they could be sources of NH-N, P, K, and TSS, especially as water fluxes from fields increased.

Preventing Off-Odor Development in Undried Rice

Laboratory and fields studies demonstrated that undried rice has significant potential for developing off-odors as measured by ethanol formation. Rice held at moistures above 22% to 24% is particularly subject to the microbial activity that causes formation of volatile organic compounds. The potential for off-odor formation in California medium grain rice can be reduced by harvesting at lower moisture contents, without reducing grower’s monetary return. Aeration of wet rice and rapid drying can be used to reduce off odor development for rice types that must be harvested at high moisture.