Improving Fertilizer Guidelines for California's Changing Rice Climate, 2022


Bruce A. Linquist, UCCE rice specialist, Dept. of Plant Sciences, UC Davis

Rice production or its management can be influenced by many factors drought, late rains, water sales, fallowing. This project explores how these factors can be managed to maximize the rice crop.

N Management After Fallow

Lack of water or the sale of water has recently put many fields into a fallow state. It is generally recognized that a better rice crop is produced by a field that has been fallow compared to a field that is continuous rice. What is not specifically known is why.

This project studied rice production after a fallow period and after continuous rice. Yields were higher in fallowed fields. Two reasons have come out over the last two years work. First, higher yields may be due to reduced disease. There was less stem rot in rice after fallow compared to continuous rice. Second, fertilizer N uptake was the same between treatments; however, the fallow had a greater late season N supply from the soil (after PI). From a management perspective, this suggests that less N needs to be applied for a field coming out of fallow especially top-dress N.

No-till Planting after Fallow

When a field is fallowed, the farmer often takes advantage of the time to work and level the ground. This section of the project seeks to understand if it is possible to simply flood up these fields without any further tillage (NT). This NT approach was tested against conventional tillage (CT) on three commercial fields. Research showed that stand establishment was poorer in NT fields. Windy conditions in May probably contributed. Weed, pest and disease pressure were either similar or better in the NT treatments. Most importantly, yields were similar or higher in the NT treatments. More work will follow in this area.

Alternative N Management

2019 rains forced many growers to plant their rice before any fertilizer was applied. This was unexplored territory for growers, no recommendations were available. Research was conducted in 2020-21 and data analysis in 2022.

Aqua ammonia or urea applied to dry soil before flooding resulted in the highest yields.

If dry soil application is not possible, the next best scenario is to split the N application. A split application of 15-35-35-15% at 3-4-5-6 weeks after planting will likely give the best results. Total N rate may need to be increased compared to N applied before flooding.

Using enhanced efficiency fertilizers such as Super U, Agrotain or Agrocote, had no benefit over applying urea alone.