Reducing nutrient loss below the root zone of drip-irrigated vegetables using low-pressure, increased irrigation time

View the project final report

• 2007 annual report
• 2008 annual report

Commodities

• Vegetables: tomatoes

Practices

• Crop Production: crop rotation, nutrient cycling, tissue analysis
• Education and Training: demonstration
• Soil Management: soil analysis

Fresh market tomatoes are grown in Florida on approximately 45,000 acres and have an annual value of about $800 million. They are mostly grown in the fall, winter or spring growing seasons under intensive irrigation and fertilizer management. Dripirrigation is rapidly gaining popularity among vegetable growers in the South Eastern United States because it allows for flexible water and fertilizer application and conserves water. Current drip-irrigation recommendations for Florida include a target irrigation volume based on historical weather data, and crop age, a fine tuning of that volume using soil moisture devices, a rule for splitting irrigation, and a method to account for rainfall. However dye tests have shown that the wetted front exceeds the root zone (12 inches) with these commendations. Lowering the amount of water discharged through drip irrigation to plant water uptake requirements may decrease leaching losses of both water and water soluble crop nutrients. Low-pressure drip irrigation system, a new concept known to have low flow rates, has also been reported to have higher water use efficiency than either overhead or drip-irrigation. With adequate modification of the low-pressure drip irrigation system, we propose to replace the current recommendation of split irrigation of 1000 gallons/acre/string/day with 750 gallons/acre/string/day using a semicontinuous low-pressure drip irrigation system that mimics crop evapotranspiration for fresh market tomato production. We also propose to lower the rate nitrogen fertilizer rate from 200 to 150 lbs/acre, thus lowering fertilizer and water inputs and their subsequent leaching losses.

The goal of this project is to reduce the risk of nutrient leaching by operating commercial drip tapes at reduced flow rates by
reducing pressure and increasing irrigation time. Objectives are to :
1. Test drip tape flow rate and uniformity of application with 6 and 12 (reference) psi of water head pressure and determine the
longest possible run with a uniformity > 90%;
2. Determine the effect of reduced flow rate on the size and shape of the wetted zone;
3. Determine the effects of fertilizer and irrigation water management on plant nutrient status, soil moisture levels, nutrients in
the soil, and fresh market tomato marketable yields when reduced-flow rates are used.