Already this year I have had a couple of calls asking how to lower fertilizer costs. My guess is that these questions are largely related to the current low rice prices and growers wanting to reduce input costs in general. From a fertility perspective, here are a few strategies to help reduce input costs.
If you routinely apply a top-dress nitrogen (N) application, consider applying all the N you would normally apply as a top-dress at planting using aqua-N. We have done a lot of research on this and have seen no benefit of splitting the total N rate. If the field remains flooded early in the season, this aqua-N is efficiently used. This saves cost for two reasons. First, aqua-N is a cheaper N source than ammonium sulfate (typical top-dress N source). Second, you avoid the airplane costs associated with topdressing. I am often asked about the benefits of the sulfur (S) fund in ammonium sulfate. I have never seen S deficient rice in CA; and in the testing that I have done, the soil and plant S concentrations have always been above critical levels.
Was your field fallow last year? For the past four years we have been doing research at the Rice Experiment Station on how to manage N fertilizer in rice fields where the previous year the field was fallowed. I have written about our findings more extensively in previous articles. The bottom line is that there is more soil N available from fields which were fallowed the previous year. Thus, if you have a field coming out of fallow (and it had been in rice prior to that for several years) you can reduce N fertility rates. Our research shows that rates can be reduced by 20-40 lb N/ac.
Importantly, for both the strategies mentioned above, it is important to keep a close eye on the crop around panicle initiation (40-45 days after planting) to see if it is displaying any signs of N deficiency. This can be done with a Leaf Color Chart, a Green Seeker, or plant analysis – all of which have been discussed in previous newsletters. If the crop is showing signs of deficiency at this time, apply the top-dress of N.
Finally, test your soil. You may not need to apply phosphorus (P) and potassium (K) fertilizer. I recommend applying a balanced fertility program that balances the P and K removed from the field in harvested grain (and maybe straw) with what is applied as fertilizer. This is especially the case when soil tests are not used as it ensures an adequate supply of these nutrients. However, a decision to fertilizer with P and K can be based on a soil test. If your soil P levels are above 12 ppm (Olsen P/soil bicarbonate test), consider not applying P as these soil P levels are adequate. Similarly, if your soil K levels are above 120 ppm, you may not need to apply K fertilizer. In areas on the east side of valley – especially the red soils, higher soil K levels may be necessary.