California rice is produced on approximately
the first month of the season, when the water management between these two practices was different, indicated that K c and water use were lower in DS systems relative to WS systems when there was only one irrigation flush during this period, while two or three irrigation flushes resulted in similar values between the two systems.
California rice (Oryza sativa L.) growers typically use two forms of preplant N fertilizer: aqua NH 3 applied 7 to 10 cm below the soil surface (subsurface N) and surface-applied N. Th e rational for applying about 25% of the total N rate to the surface is to provide a readily available N source for young rice seedlings; however no research has been done to verify this. On-farm fi eld studies were conducted over a 3-yr period (12 site-years) with the specifi c objectives of determining when rice begins to use subsurface N and to compare the effi ciency of surface and subsurface applied N. Rice seedlings began accumulating subsurface N within 2 wk aft er sowing at some sites. When a portion of the N rate was applied to the surface, early season plant biomass and N uptake was higher than when all of the fertilizer-N was applied subsurface. In contrast, grain yields were higher when all of the N fertilizer was applied subsurface. Averaged across all sites, the fertilizer-N recovery effi ciency of surface-applied N was 38% compared to 53% when only subsurface N was applied. As aqua NH 3 is less expensive than NH 4 + based fertilizers and the application of surface N requires an additional fi eld operation, there is no justifi cation to recommend the practice of applying surface N fertilizer in these rice systems. Instead, all of the preplant N should be applied subsurface as aqua NH 3 .
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), but very small, effect on amylose and protein contents, with amylose being highest at the late drain date and protein being the lowest at the early drain date. Breakdown and setback were lowest for early and normal drain dates, respectively; however, no 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 significant (P < 0.05), but very small, effect on protein content. Harvesting at the earliest date (9/30) resulted in rice with higher setback and lower breakdown than at the last date (10/16) and, subsequently, the early harvested rice, when cooked, was harder, more cohesive, and absorbed less saliva in the mouth. However, the differences in texture measured by the panelists were very small and would possibly not be noticed by untrained palates. The lowest levels of the lipid oxidation products 1‐pentanol, hexanal, and nonanal occurred in rice with the lowest harvest moisture content (HMC): rice harvested on 10/13 and 10/16. Differences in levels of lipid oxidation products and branched chain hydrocarbons did not lead to significant (P > 0.05) differences in flavor. In summary, M‐202 demonstrated stable composition, physicochemical properties, flavor, and texture across drain and harvest dates.
Climate change is predicted to shift temperature regimes in most agricultural areas with temperature changes expected to impact yields of most crops, including rice. These temperature-driven effects can be classified into point stresses, where a temperature event during a sensitive stage drives a reduction in yield, or seasonal warming losses, where raised temperature is thought to increase maintenance energy demands and thereby decrease available resources for yield formation. Simultaneous estimation of the magnitude of each temperature effect on yield has not been well documented due to the inherent difficulty in separating their effects. We simultaneously quantified the magnitude of each effect for a temperate rice production system using a large data set covering multiple locations with data collected from 1995 to 2015, combined with a unique probability-based modeling approach. Point stresses, primarily cold stress during the reproductive stages (booting and flowering), were found to have the largest impact on yield (over 3 Mg/ha estimated yield losses). Contrary to previous reports, yield losses caused by increased temperatures, both seasonal and during grain-filling, were found to be small (approximately 1-2% loss per °C). Occurrences of cool temperature events during reproductive stages were found to be persistent over the study period, and within season, the likelihood of a cool temperature event increased when flowering occurred later in the season. Short and medium grain types, typically recommended for cool regions, were found to be more tolerant of cool temperatures but more sensitive to heat compared to long grain cultivars. These results suggest that for temperate rice systems, the occurrence of periodic stress events may currently overshadow the impacts of general warming temperature on crop production.
ABSTRACT. California's medium-grain rice industry experiences a wide range of head rice yield (HRY).he unit value of rice is based primarily on its head rice yield (HRY, the proportion of kernels greater than 75% of intact length; USDA-FGIS, 1994). Improving HRY is an ongoing goal for rice growers. The average moisture content of the paddy rice at harvest (HMC, expressed on a wet weight basis) influences HRY. For medium-grain rice grown in Italy, dry conditions allowed HMC to drop below about 15%, and a subsequent rain caused a significant drop in HRY (Finassi et al., 2002). However, when repeated rain events kept HMC above 20%, HRY was not influenced by HMC. In Louisiana, where rain events are common during rice maturation, long and medium grain rice experienced a significant reduction in HRY when rice dropped below 15.0% to 19.8% HMC depending on variety and year of harvest (Jodari and Lindscombe, 1996). A warmer and drier harvest season caused fissuring to begin at higher HMC than a cooler and more humid season. In two harvest seasons in Arkansas with numerous rain events, HRY was not affected by harvest moistures between 15% and 22% (Siebenmorgen et al., 1992).In California's rice production area, rain is rare and maximum HRY for medium-grain rice is obtained at high HMC. Kester et al. (1963) concluded that the highest HRY is obtained at 25% to 32% HMC. Morse et al. (1967) indicated that HRY peaks between 26% and 30% HMC. Geng et al. (1984) analyzed commercial data, and they concluded that high variability prevented them from finding a narrow range of HMC for high HRY and that HRY was maximum between 25% ±5% HMC. Commercial quality data for California medium-grain rice (D. Jones, Farmers Rice Cooperative, Sacramento, Cal., personal communication, 1999) clearly showed that HMC explains only a small portion of the variability in HRY, as described by the low regression coefficient for a second-order polynomial regression line ( fig. 1). While maximum HRY was obtained at HMCs above 20%, lots below 18% HMC had nearly the same quality, and lots above 22% moisture had HRY values of less than 50%. The data show that in commercial practice HMC was not a good predictor of HRY, and apparently there must be other variables influencing rice quality.A great deal of research beginning the 1930s showed that paddy rice kernels fissure when dried below a critical moisture content and then rehydrate because of exposure to free moisture or high humidity, (Kunze, 1993;Siebenmorgen et al., 1998;Lan et al., 1999). The fissured kernels break during milling, causing low HRY in lots with high amounts of fissured kernels. At harvest, individual kernels vary widely in moisture (Siebenmorgen et al., 1992), and if the pattern of moisture distribution varies because of varying cultural practices or weather conditions, the proportion of kernels below the critical moisture may be a better indicator of HRY than average moisture. Geng et al. (1984) indicated that cycles of drying and moisture absorption may influence quality, but they did no...
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