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Fertility management considerations for 2022 DR. BRUCE LINQUIST CALIFORNIA UCCE Rice Specialist balinquist@ucdavis.edu With input prices increasing, it is more important than ever to manage fertilizers in the most economically feasible way possible. Here are several things to consider when making fertility decisions. First, aqua-ammonia is the cheapest and most efficient nitrogen source for California rice growers. When applying N, apply as much as possible in this form. Second, do not plan to top-dress, but apply enough N preplant for an average yield. At panicle initiation, access your crop to see if it needs additional N. Third, in 2021, we analyzed soil data from 83 rice fields (in 28 fields we also analyzed leaf samples) around the Sacramento Valley. Importantly, no soil or leaf samples were deficient for either sulfur or zinc. Many growers apply these nutrients routinely. Skipping these applications (i.e. applying urea instead of ammonium sulfate) may help reduce costs; however, if in question, it would be good to take your own soil samples. In previous years, aqua-ammonia has not always been available. The best option for replacing it is to use urea. Urea (liquid or granular) works equally well if applied preplant and is put several inches below the soil surface. Liquid urea is hard on the pump, so make sure to clean out your pump very well at the end of the season. If you are applying the N after planting, you need a split application for best results. Due to reduced N-use efficiency, the total rate may need to be increased by 5% to 10%. I suggest putting on the starter N (plus P and K) about three weeks after planting. This should represent about 15% to 20% of your total N rate. The rest of the N should be applied at four (30%), five (30%) and six (20%) weeks after planting. In our survey of rice field soils, we found many growers are under applying phosphorus (P). A typical rate was 40 pounds per acre, which is enough P to replace the P in the harvested rice grain of a field that had an 80 cwt/acre yield. Yields are usually well above this now and straw removal is also more common. If your field is yielding 100 cwt/acre, you need to apply 50 pounds per acre to replace the P removed in the grain. Add an additional 5-10 pounds per acre if you are baling rice straw. Finally, many fields did not get flooded this winter, due to water limitations. Furthermore, the October rains prevented straw incorporation in many fields. If there is still a lot of straw in the field at the start of land preparation due to poor winter decomposition, early season N may need to be increased. This is one area where I suggest adding a higher N rate in the starter fertilizer (as opposed to increasing aqua-ammonia N rate) and tilling the starter fertilizer in with the straw.
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RICE FARMING
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FEBRUARY 2022
Phosphorus and potassium DR. RONNIE LEVY LOUISIANA Extension Rice Specialist Louisiana State University RLevy@agcenter.lsu.edu With the high cost of fertilizer, don’t forget the importance of phosphorus (P) and
potassium (K). Phosphorus is a constituent of nucleic acids and is needed for several plant-essential processes, including photosynthesis, respiration, energy storage and energy transfer among others. Rice removes P from the soil as an orthophosphate ion, primarily H2PO4- or HPO4-2. Fertilizer P is always expressed as a percent P2O5 equivalent and on a fertilizer label is located as the second number (example: 0-46-0). Soil test P and soil test-based fertilizer recommendations can be reported as either P2O5 equivalent or P. Convert P to P2O5 equivalent by dividing by 0.44. Convert P2O5 equivalent to P by multiplying by 0.44. Soil P is most available to plants in soils with a pH around 6.5. Typically, plant available P is decreased as a soil becomes more alkaline or acidic. When a rice soil is flooded and becomes anaerobic (no oxygen), the pH of the soil migrates towards neutrality over time regardless of the initial pH. Therefore, in most cases P becomes more available to rice after permanent flood establishment. Rice takes up approximately 0.0086 pounds of P2O5 (0.02 pounds of P) per pound of dry rice harvested. Approximately 75% of the P taken up is contained in the harvested grain. Potassium is needed to regulate normal metabolic processes in the plant including photosynthesis and protein synthesis as well as maintaining plant osmotic pressure. Deficiencies of K in rice have been related to increased disease incidence — typically brown spot, stem rot and blast. Rice takes up K in the ionic (K+) form.
Phosphorus is a constituent of nucleic acids and is needed for several plant-essential processes, including photosynthesis, respiration, energy storage and energy transfer. RICEFARMING.COM
