Saturday, 15 July 2006

Nitrogen and Irrigation Management to Improve Water Use Efficiency and Reduce Nitrate Leaching of Pepper and Tomato Crops in Florida.

Lincoln Zotarelli1, Johannes M. Scholberg1, M. D. Dukes2, and Rafael M. Carpena2. (1) Univ of Florida, Agronomy Dept, 304 Newell Hall, Gainesville, FL FL32611, (2) Univ of Florida, PO Box 110570, Gainesville, FL 32611

Most Florida soils have poor water and nutrient retention and thus are prone to nutrient leaching which combined with excessively high N-fertilizer/irrigation rates and leaching rainfall events greatly increased the risk of groundwater nitrate contamination. The specific objectives of our study were to evaluate the interactive effects of irrigation practices and fertilizer rates on yield, fertilizer requirements, fertilizer-N uptake efficiency, and N-leaching of pepper and tomato production systems. Bell peppers and tomatoes were planted on plastic mulched beds during the spring of 2005 to evaluate the interactive effects of 3 nitrogen fertilizer rates (154, 192, 288 kg N ha-1 for pepper and 166, 208 and 312 kg N ha-1 applied via weekly fertigations) and three irrigation scheduling methods. Irrigation scheduling techniques used for pepper included: MSI custom-designed Irrigation Control (QIC) system featuring time-based irrigation (up to 5 events per day) if TDR-measured soil water dropped below a critical Volumetric Water Content (VWC) value of 13%; LSI - use of commercially available “Acclima” soil moisture sensor with a VWC threshold value of 10% along with a time-based irrigation similar to the previous treatment; and FSI - “farmer” treatment with irrigation being applied at fixed daily durations of up to two hours per day. For tomato treatments were: MSUI - surface fertigation and subsurface irrigation (irrigation line was placed 15 cm below the bed surface) where subsurface irrigation was controlled by the QIC sensor with a threshold set at field capacity (~10%VWC); LSI; and FSI treatments with similar settings as described above. Leacheate volumes were measured by drainage lysimeters buried approximately 0.6 m below the bed surface and leachate was collected weekly one day prior to the next fertigation event. Composite soil samples were taken biweekly. Plant growth of pepper and tomato during the first six weeks was not significantly affected by either irrigation or N rate. For tomato, placing the irrigation line 15 cm below the irrigation line reduced leaching and thereby resulted in more efficient N-fertilizer use, and optimal plant growth was attained at intermediate N application rates. The LSI treatment did not show a significant response to N rate. Use of buried drip irrigation (MSUI) did not affect soil moisture at the soil surface compared to the use of surface applied drip irrigation (LSI), but increased VWC of lower soil layers by 2-5%. Although this did not result in excessive N leaching, it did reduce WUE. The FSI treatment showed fairly high overall VWC, resulting in excessive N leaching, and thereby increased the amount of fertilizer required for optimal yield. Increased N requirements and suboptimal yields at lower and intermediate N rates with the farmer's treatments thus were probably related to excessive N leaching below the root zone. Overall leaching amounts for pepper were 15, 27, and 60 mm, for LSI, MSI, and FSI, respectively. Nitrate leaching increased with irrigation and N rate and measured values ranged from 8 to 60 kg N ha-1. The FSI treatment had the highest N loading rates and appropriate use of soil sensor-based irrigation reduce N leaching by 33 to 67%. Overall leaching amounts for tomato were on the order of 17, 5, and 43 mm, for MSUI, LSI, and FSI respectively. Nitrate leaching increased with irrigation and N rate and measured values ranged from 3 to 60 kg N ha-1. The LSI treatment had higher residual soil N values six days after fertigation events. Increasing irrigation rates, on the other hand, resulted in dilution and/or displacement of fertilizer-N (MSI and FSI) and there by greatly reduce fertilizer use efficiency. The farmer treatment (FSI) again resulted in highest N loading rates, whereas soil sensor based irrigation reduced N leaching by 89 to 95%. Use of the farmer-based irrigation resulted in excessive leaching and therefore relatively low residual soil N values and higher fertilizer requirements. Placing the irrigation line below the fertigation line did not affected the crop yields, but it reduced nitrate leaching via improved nutrient retention in the active root zone compared to the conventional treatments. In conclusion, appropriate use of soil sensor-based irrigation allowed more efficient use of irrigation water and thereby decreasing water displacement below the active root zone. It also greatly reduced N leaching and increased N retention in the upper soil layer there by facilitating more efficient fertilizer use.

Back to 3.3B Nutrient Use Efficiency and Global Agriculture - Poster
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)