Phosphorous management

Research in 2007 and 2008 showed that surface applications of phosphorous fertilizer increased the growth of weeds and algae. In 2009 a study in Butte County sought to determine the effects of alternative phosphorous timing on rice growth, phosphorous uptake, and rice yields.

Delaying phosphorous applications until 35 days after planting (mid-tillering) provided yields comparable to applications just before planting.  Fall applications of phosphorous (just before straw incorporation) increased yields relative to controls that received no phosphorous.

Growers with phosphorous-deficient soils may need to apply more phosphorous in the fall.  For the majority of growers, who don’t have phosphorous-deficient soils, applications can be made in the fall, at planting, or after planting without negatively affecting grain yields.

Early-season algae growth in California rice fields is a widespread problem, especially as the crop is getting established. Identifying cost-effective measures to control algae with minimal environmental impact is an important goal. Thus, an important part of this research sought to determine whether delayed phosphorous applications affected water quality.

Five growers collaborated with scientists on this part of the study to compare conventional fertilizer practices (before planting) with a delayed application.  Phosphorous concentration in irrigation water was monitored at point of entry, and in-field. At harvest, growers determined yield in each field or check using their combines.

Results showed that delaying phosphorous applications by 16 to 32 days did not impact yields (but did reduce algae growth). A delayed phosphorous application may cause a water quality concern, however, if water exits a field within the first two weeks of application. Therefore, delayed phosphorous applications should be applied in conjunction with other water-holding practices to avoid potential problems.

Nitrogen research

Previous research conducted between 2005 and 2008 showed that growers could eliminate starter nitrogen and replace it with an aqua-nitrogen application of the same amount to increase nitrogen-use efficiency and rice yield.

This research continued in 2009 in grower fields on a larger scale. Results confirm previous on-farm small plot trials. Growers should apply as much of their nitrogen as possible as aqua nitrogen. Placing the nitrogen three-to-four inches below the soil surface protects it from denitrification losses, thus making it more useable to the crop. Recommendations have been developed for this practice.