Soil M1-P stabilized around 55 parts per million and showed a gradual decrease after P application stopped for the two BMP systems, but M1-P steadily increased in the industry system, reaching a high of 145 ppm by the end of the study.
M1-P was positively correlated with groundwater P. Results showed that total P (TP) concentration in the groundwater for both BMP systems (BMP = 2,098 parts per billion and BMP-drip = 2,048 ppb) were 33 percent lower than the industry average of 3,090 ppb. Although the sub-drip system used almost 50 percent less water compared with the industry system, it did not offer any groundwater quality benefit.
Our results showed that adoption of UF/IFAS-recommended P rates as a BMP did not appear to reduce crop yield but improved water quality. Reductions in groundwater P observed with the BMP rates will also reduce the P loads in farm drainage.
The study was funded by the Florida Department of Agriculture and Consumer Services, the Southwest Florida Water Management District and the Southwest Florida Vegetable Growers Research and Education Fund.
Sanjay Shukla is an associate professor of agricultural and biological engineering at the Southwest Florida Research and Education Center in Immokalee. Gregory Hendricks is a post-doctoral researcher at the same center. Tom Obreza is a professor in the Soil and Water Science Department, Gainesville.