Don May

Response of Processing and Fresh-market Onions to Drip Irrigation

The response of yield to surface-and-subsurface drip irrigation was investigated for both processing onions and fresh-market onions. Irrigation treatments consisted of water applications ranging fro 60% to 120% of a baseline amount for both irrigation methods. Data collected were applied water, yield, soluble solids (processing onions), canopy coverage, canopy temperature, and soil moisture content. Results showed a linear increase in total yield with increasing amounts of applied water for both processing and fresh-market onions. However, for the fresh-market onions, little change in yield occurred for the medium and repack grades. No differences in the yield-applied water relationships were found between surface-and-subsurface drip irrigation.

Effect of Subsurface Drip Irrigation on Processing Tomatoes Yield, Water Table Depth, and Soil Salinity

This study evaluated the potential of subsurface drip irrigation of processing tomatoes for reducing subsurface drainage and controlling soil salinity, and for increasing farm profits in areas affected by saline, shallow ground water. Subsurface drip irrigation systems were installed in three fields of fine-textured, salt-affected soil along the west side of the San Joaquin Valley. No subsurface drainage systems were installed in these fields. Yield and quality of processing tomato of the drip systems were compared with sprinkler irrigation systems used in the remainder of the fields. Yield increases of 12.90 Mg/ha to 22.62 Mg/ha were found for the drip systems compared to the sprinkler systems with similar amounts of applied water. Solids content of the drip-irrigated processing tomato were acceptable. Response of water table levels during drip irrigation showed that properly managed drip systems could reduce percolation below the root zone. Yields of the drip systems were similar over a range of soil salinity levels in the soil profile.

Salinity Control with Drip Irrigation

Drip irrigation has the potential of increased yield under saline soil conditions. Factors affecting root zone soil salinity under drip irrigation include the salinity of the irrigation water, amount of applied water, soil hydraulic characteristics, placement of drip lines relative to plant rows, subsurface vs. surface drip lines, and under saline, shallow ground water conditions, the ground water depth and salinity. The salt pattern reflects the water flow patterns under drip irrigation. The key to profitable drip irrigation under saline conditions is adequate salinity control by leaching salts from the root zone. Under drip irrigation, highly concentrated leaching, called localized leaching, occurs near drip lines. Leaching decreases with horizontal distance from drip lines. Larger amounts of applied water increase the volume of leached soil near drip lines. Salts accumulate above subsurface drip lines, which requires rainfall or sprinkle irrigation for leaching. The water balance method of estimating leaching fractions is inappropriate for drip irrigation and underestimates the actual leaching fractions. Water applications equal to crop evapotranspiration provide adequate localized leaching.

Response of Onion to Drip Irrigation

The effect on onion yield of different water applications applied with drip irrigation was investigated for onions. In 2002, both surface and subsurface drip irrigation were used with water applications ranging from 60 to 120% of the potential ET for both fresh-market and processing onions. The 2005 and 2006 experiments used surface drip irrigation on fresh-market onions with water applications ranging from 80 to 160% of the potential ET. Root and soil water distributions around drip lines were also determined. Results showed that onion yield increased with increasing applied water indicating that water applications based on the potential ET were insufficient for maximum yield. Most of the roots occurred in the top 200 mm of the soil profile. However, the 160% treatment resulted in considerable wetting below the zone of high root density, indicating considerable deep percolation and lower irrigation efficiency compared to the smaller water applications.

Drip Irrigation of Tomatoes and Cotton in Saline Soil

A study in a commercial field evaluated the response of processing tomato and cotton to drip irrigation under shallow, saline ground water conditions at depths less than 1 m using a randomized block experiment with four irrigation treatments of different water applications for both crops. Measurements included crop yield and quality, soil salinity, soil water content, soil water potential, and canopy coverage. Results showed drip irrigation of processing tomato to be highly profitable under these conditions; however yield decreased as applied water decreased. No yield response of cotton to applied water occurred indicating that as applied water decreased, cotton uptake of the shallow ground water increased. While a water balance showed no field-wide leaching, salinity data clearly showed salt leaching around the drip lines.