Monitoring Nutrient Availability and Leaching Below the Root Zone in Organic Vegetable Production

Project Overview

Project Type: On-Farm Research
Funds awarded in 2008: $14,900.00
Projected End Date: 12/31/2010
Region: Southern
State: Florida
Principal Investigator:
Dr. Danielle Treadwell
University of Florida
Bee Ling Poh
University of Florida
Eric Simonne
University of Florida

Annual Reports


  • Fruits: melons
  • Vegetables: eggplant, peppers, tomatoes


  • Crop Production: irrigation, nutrient management

    Proposal abstract:

    The demand for locally grown produce is strong in Florida and certified organic vegetable growers have a hard time keeping up with market needs. High-value vegetable crops such as tomato, bell pepper, eggplant, and watermelon are well suited for the growing conditions in the Southeastern United States, especially when plasticulture is used. Typically, fertilization practices for these crops include a pre-bedding application of an approved compound fertilizer (often 8-5-5 Nature Safe), followed by fertigation events late in season using sodium nitrate (but the NOP clearly states that no more than to 20% of total N may come from this N source). The combined high risk of leaching in Florida’s sandy soil with the poor predictability of the nutrient release from the pre-plant fertilizer often results in a shortage of N and K in the middle or end of the season, thereby reducing yield and quality. Increasing the in-bed rate of the organic fertilizer is currently not an economical option. Previous efforts coordinated by the University of Florida Extension Service and supported by Southern region SARE projects have (1) improved drip-irrigation scheduling practices by showing how fast water moves through the soil profile by using soluble dye, and (2) demonstrated the usefulness of weekly petiole sap testing analyses of nitrate and potassium to monitor plant nutritional status (Hochmuth et al., 2003, 2006; Simonne et al., 2005). Yet, these two techniques alone are insufficient for managing N and K in certified organic production because (1) the rate of organic fertilizer mineralization is not known and (2) the 20% sodium nitrate restriction leaves little flexibility for rescue fertilizer applications. Other projects conducted by this group have shown that nutrient movement below the root zone may be assessed with simple drainage lysimeters. Hence, by measuring leachate parameters (volume, composition) and using sap testing results, the grower should better understand the impact of fertilizer and irrigation practices on N and K release and losses. This approach will help organic growers increase efficiency in use of expensive organic fertilizers and at the same time improve best management practices by reducing N and K losses, thus making a positive contributing to improving water quality in the Suwannee Valley area of Florida. Our hypotheses are that (1) costly certified organic fertilizer rate may be reduced without reducing productivity by improving irrigation management and (2) dual measurement of leachate electrical conductivity and plant petiole nutritional status allows for a better understanding of when nutrient shortage occurs due to insufficient fertilizer nutrient release or from nutrient leaching caused by excessive irrigation.

    Project objectives from proposal:

    Our approach is to monitor simultaneously nutrient leaching below the root zone and plant nutritional status to adjust, if needed, fertilization through drip irrigation. First, we will construct and install 10-foot long drainage lysimeters in a certified-organic vegetable field. The lysimeters will be made of a storage container and a draining container as described in Gazula et al. (2006). The storage container will be buried vertically under the collection container. The collection container will be 10-ft long, 2-ft in diameter, and installed to a 1% slope to drain into the storage container. A 5-cm-diameter schedule 40 PVC pipe cut lengthwise, and riddled with 1-cm diameter holes along the length of the pipe, and with a 6-mm thick and 1-cm long braided fiberglass wicks inserted in one hole per inch will be placed on the bottom of each collection container to break soil water tension tension and facilitate drainage. An available peristaltic pump will be used to collect leachate every 8 to 10 days. Leachate volume and electrical conductivity will be determined in the field.Raised beds will be installed exactly above the lysimers, and the crops will be grown according to the grower’s practice. At the same time, the drip-irrigation schedule will be recorded and soil moisture will be measured 6-inches away from the drip tape using a portable TDR (Simonne et al., 2007). Based on the crops grown by the cooperating grower (usually tomato and pepper in the Spring) and the certified organic fertilizer available, 2 to 4 in-bed fertilization programs will be developed and tested in the field. Two lysimeters will be installed with each fertilizer program. Beginning shortly after fertilizer incorporation, petiole sap NO3-N and K will be determined every 8 to 10 days using Cardy meters. The irrigation schedule will be adjusted based on soil moisture readings and sodium nitrate injections will be made only when EC values are high and petiole nutrient concentrations are all low.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.