|Soil Fertility and Fertilizer
Project Leader and Principal UC Investigators
Chris van Kessel,professor, Dept. of Agronomy and Range Science, UC Davis
This project is evaluating the impact of grower cultural practices on
nutrient cycling. The goal is to develop improved fertility management
guidelines for rice growers.
The first objective of this study is to identify needed changes in fertility management following legislated reductions in rice straw. More than 100 rice growers were surveyed during 2003 annual rice grower meetings. Highlights include:
Growers expressed support for continued research on straw management and nutrient availability. Specific areas mentioned were improved nitrogen timing and rate recommendations; expanding research to additional nutrients such as zinc and phosphorous; increasing the number of field trials across soil types; correlating soil nutrient availability and leaf tissue results with fertilizer recommendations; and tying site-specific fertility management to grower yield monitoring.
Complete survey results can be viewed online at the Cooperative Extension rice web site-http://agronomy.ucdavis.edu/uccerice/NEWS/FertilityMgtSurvey2003.pdf.
Researchers also conducted nitrogen fertility trials with 15 growers in 38 fields throughout the Sacramento Valley. The trials consisted of extensive soil and plant sampling and monitoring of three different nitrogen rates across a variety of soils utilizing different management practices. While there was an apparent overall trend of yield increasing with nitrogen rate, it was not statistically significant. When three-year field histories were factored in, it became clear that those fields with a history of residue incorporation had significantly greater yields with reduced fertilizer than those that were managed with burning or baling.
According to current soil fertility guidelines, more than half those fields were phosphorous deficient. Yet no deficiency was observed in midseason tissue samples, suggesting that soil guidelines need to be reevaluated. These results are in line with previous straw management research at the Rice Experiment Station and in Maxwell but should be viewed cautiously since they have been gathered from only one year's worth of study.
The second major objective of this study was to examine liming in relation to yields, soil tilth and effect on weed pressure. Liming trials began in 2002 at two grower-managed sites in the Sacramento Valley.
Researchers designed the liming trials, which will last three growing seasons, with extensive pre-application sampling and multiple liming rates applied at different points in time to reflect grower practices. Thus far, the results indicate that liming has no appreciable effect on straw or grain yields, head rice production or mid-season plant growth parameters under standard fertilizer and herbicide applications.
There was a significant reduction in ricefield bulrush following liming. This effect appears to be additive over time, suggesting that liming may impact the weed seed bank.
Additionally, preliminary data suggest that liming significantly alters the force required for tillage and thus may result in reduced tillage requirements.
Cost efficiency calculations for lime use in rice production will be included in the final report from this study in 2004.