Draining Rice by Growth Stages A computer program Paul Counce, Earl Vories, Terry Siebenmorgen, Mike Popp, Vetress Thompson and Brad Watkins Introduction The current recommendations for terminating rice irrigation in Arkansas and Mississippi were developed from our research (Counce et al., 1990; 1993). Subsequent research results by other scientists have confirmed our findings (Grigg et al., 2000; McCauley and Way, 2002). Due to the large number of soil types for which the rice crop may have different responses to draining, however, potential water savings have only been partially realized. Farmers are wasting water by maintaining a flood for too long in many situations. This costs the aquifers water and the farmers money. Despite convincing evidence cited above that rice can be drained for harvest 2 weeks after 50% heading (when panicles emerge) farmers have been reluctant to practice this. Part of the reluctance lies with an inadequate frame of reference for understanding, in a practical way, how the rice crop uses water and how the soils supply that need after draining the rice field. Also, farmers need to know when to drain for harvest whereas current extension recommendations relate to time to cease irrigation. To reduce labor costs, farmers want to know when they can safely drain their rice fields since levee gates must be removed at draining to reduce labor. Also, for no-till rice production, appropriate draining of rice fields is critical since rutting leads to termination of the no-till practice to repair ruts and reform land. Consequently, appropriate rice draining is a linchpin for no-till rice production. Mr. Terry Gray said: “the key to no-till is no red, the key to no red rice is no ruts, and the key to no ruts is early draining”. Rationale A simple, field-specific computer program has been developed which utilizes four different information systems and data sets. The information system is the rice growth staging system (Counce et al., 2000). The rice growth staging system was developed to allow meaningful communication about rice farming practices and research results. The growth staging system also improves timing of management practices. The use of the rice growth staging system allows reproductive development of the rice crop to be timed with DD50 rather than simply days after 50% heading as is presently done (Keisling et al., 1984). The data sets are (1) a database for timing between the reproductive growth stages (Clements et al., 2003, Watson et al., 2005); (2) water availability dataset consisting of (a) the NRCS soil information for available water in soils; and (b) further published data for water held between field capacity and saturation (which is available to rice crop but not to most other crop plants); (3) a historical weather dataset to allow computation of timing in combination with the database for timing between reproductive stages of development (see graph for example with Drew rice); and (4) a water use database for the rice crop at different reproductive stages of development (Lage et al., 2003; Renaud et al., 2000). These calculations are combined in a cell within a spreadsheet with four site-specific inputs. The simple program provides the frame of reference. Significance Rice requires large amounts of water and, in turn, rice production and processing contribute greatly to many communities in the rice producing states. Furthermore, competing water demands conflict with other water users. Improved utilization of water for rice production could thereby increase the water available for other uses. Implementation of this research in Arkansas alone could result in savings of 3 million acre inches of water per year. This, in turn, could reduce depletion of aquifers, lower pumping costs to farmers, and reduce tillage costs associated with rutted soil conditions. The water use savings available to farmers in each situation have been substantial ($23/acre in some cases) and other ramifications of this work such as increased soybean yields make earlier draining of rice an attractive option for many growers (Popp et al., 2004). The Program See the spreadsheet below for one example of Wells rice on a Stuttgart silt loam. The program works by putting together four information sets (described in the Rationale) inside of an Excel spreadsheet. Available water at draining is calculated for a particular soil (yellow highlight), the projected water use from maturity to each reproductive growth stage is calculated (Orange highlight) and the growth stage at which draining will be safe (blue highlight). s R9 occurs when all grains which reached the R6 stage reach R8 = all filled grains are brown Anthesis Caryopsis expansion Grain Filling Grain Dry Down End of Grain Filling R-Stage Progression For Drew Rice Research in 2005 To calculate the safe stage of growth for draining a rice field using the program, several inputs are needed. Two field experiments are being conducted this year. The rooting depth for the soil at the Stuttgart site is 4 inches. The program inputs include soil type, rooting depth, 50% heading date (for historical weather data) and cultivar. One assumption embedded within the model is that water use will be maximum based on published water use data for rice. This assumption is made to assure adequate water to meet the crop’s needs after draining. One field experiment was established at Stuttgart at the Rice Research and Extension Center and another experiment was established at Gillett. The rice cultivar at Stuttgart is Wells. There are two treatments in the experiment at Stuttgart: (1) Draining at 28 days after heading and (2) Draining by the growth stage as determined by the program. The program projected the safe stage of growth for draining the rice at Stuttgart was R8 (one brown seed on the main stem panicle). The rice at present is not quite at R3 and 50% heading. The rice cultivar at the Gillett experiment is Francis. We utilize metal frames to create a drained rice field within a flooded rice field. There are three treatments: (1) Drain as the field would normally be drained (approximately 30 days after heading), (2) Drain by growth stage as determined by the growth stage program, and (3) A second control with the frame around the rice as in Treatment 2 without draining prior to draining the entire field. The rooting depth at the Gillett field is 8 inches compared to 4 inches at the Stuttgart field. At the Gillett field the predicted safe stage of growth for draining rice is R6. The rice at was at 50% heading on July 23. The present stage of development is R4. We continue to discuss ways to improve the program with a number of cooperating farmers. The program provides a comprehensive way to consider decisions on rice draining. Our goal is to allow rice producers to save money without reducing rice yield or quality. References Clements, J., T. Siebenmorgen and P.A. Counce Relationship of thermal units during grain filling to rice kernel development. pp In R.J. Norman and J.-F. Meullenet, Eds., Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 504. Counce, P.A., T.C. Keisling and A.J. Mitchell A uniform, objective and adaptive system for expressing rice development. Crop Science 40: Counce, P.A., T.J. Siebenmorgen, E.D. Vories and D.J. Pitt Time of draining and harvest effects on rice grain yield and quality. Journal of Production Agriculture 3: Counce, P.A., T.J. Siebenmorgen and E.D. Vories Post-heading irrigation management effects on rice grain yield and milling quality. University of Arkansas, Agricultural Experiment Station, Fayetteville, Arkansas. Bulletin 940. Grigg, B.C., C.A. Beyrouty, R.J. Norman, E.E. Gbur, M.G. Hanson and B.R. Wells Rice responses to changes in floodwater and N timing in southern USA. Field Crops Research 66: Keisling, T. C., Wells, B. R. and Davis, G. L., Rice management decision aids based upon thermal time base 50 0 F. Arkansas Cooperative Extension Service Technical Bulletin No. 1. Lage, M., A. Bamouh, M. Karrou and M. El Mourid Estimation of rice evapotranspiraton using a rice microlysimeter technique and comparison with FAO Penman-Monteith and Pan evaporation methods under Moroccan conditions. Agronomie 23: McCauley, G.N. and M.O. Way Drain and harvest timing affects on rice grain drying and whole-milled grain. Field Crops Research 74: Popp, M., P. Manning, P. Counce and T. Keisling Rice soybean rotations: opportunities for enhancing whole farm profits or water savings. Agricultural Systems (In review) Renaud, F., J.A. Ferguson, H.D. Scott and D.M. Miller Estimation of seasonal rice evapotranspiration. pp In R.J. Norman and C.A. Beyrouty, Eds., Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 476. Watson, N.T, P.A. Counce and T.J. Siebenmorgen Growth Stages of 12 Rice Cultivars (Oryza sativa L.) Expressed in DD50 Thermal Heat Units. pp In R.J. Norman, J.-F. Meullenet, and K.A.K Moldenhauer, Eds., Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 529.