Submitted to: Encyclopedia of Water Science
Publication Type: Popular publication
Publication Acceptance Date: 10/7/2002
Publication Date: 3/1/2003
Citation: Ayars, J.E. 2003. Preplant irrigation. Encyclopedia of Water Science. On line publication, March 2003, pg. 498-501. Interpretive Summary: Irrigation is the process of supplying supplemental water necessary for plant growth and development by one of several application techniques, e.g., microirrigation, surface irrigation, sprinkler irrigation, subirrigation (by raising a shallow water table), and subsurface irrigation. It is used primarily in arid and semi-arid areas of the world but also in humid areas to supplement rainfall. In this context water is applied after the crop is planted and growth begun. Pre-plant irrigation is the application of water to a field during a fallow period between crops. The goal may be to replenish soil water to met future requirements for plant growth and development. Other identified for pre-plant irrigation include; germination, salinity management, fumigation, weed control, and fertilizer placement. The depth and timing of the application to meet the afore-mentioned uses will depend on; the irrigation water quality, the existing stored soil water, the soil salinity, the crop rotation, the crop salt tolerance, and the depth to shallow ground water.
Technical Abstract: Pre-plant irrigation is application of water during a fallow period in arid and semi-arid irrigated areas and may be used for germination of crops and weeds, salinity control, fumigation, and fertilizer management. In the San Joaquin Valley (SJV) pre-plant irrigation brings the soil water content up to field capacity while leaching excess salt from the root zone. Deep seeded crops can be planted to moisture and germinated without additional irrigation, a common practice for planting cotton in the SJV. Organic producers will use pre-plant irrigation to germinate weeds that can be then disked and killed prior to planting. Root zone salinity management is critical in arid irrigated areas and pre-plant irrigation with 150 mm of low salinity water is generally adequate to remove any salt accumulation. The total pre-plant irrigation depth for soil water management will depend on the previous crop and the rooting depth. An application of 150 to 300 mm of water will refill the depleted soil water with out excess deep percolation losses. Any type of irrigation system can be used but deep percolation losses are a consideration when making the selection. Systems with inherently poor distribution uniformities will require good management to minimize deep percolation loss, e.g. furrow irrigation.