LEACHING AND WATER-FLOW PATTERNS IN EVERY-FURROW AND ALTERNATE-FURROWIRRIGATION

Deep water percolation and chemical leaching is a recognized environme ntal problem with furrow irrigation. Alternate furrow irrigation (AFI) was hypothesized as a method to increase water-use efficiency and dec rease chemical leaching compared with every-furrow irrigation (EFI). T he SWMS_2D finite-element model was used to investigate water and CaCl 2 movement in EFI and AFI with furrow-placed or ridge-placed fertilize r bands. Model simulations were conducted for a Crook loamy sand (mixe d, mesic, Ustic Torripsamment) and a Nunn clay loam (fine, montmorillo nitic, mesic Aridic Argiustoll). Water isolation zones occurred with A FI and EFI that contributed little to overall profile drainage. The so il water contents after infiltration and redistribution were more unif orm for EFI than for AFI for both soils. Water distribution was more u niform with AFI in the clay loam than in the loamy sand. Chemical move ment was least with AFI and CaCl2 placement under the nonirrigated fur row. The greatest chemical leaching was predicted with furrow placemen t of CaCl2 and EFI. Results with CaCl2 suggest soluble chemicals or fe rtilizers placed under the nonirrigated furrow in loamy sand may not b e available for plant uptake because the soil did not wet during irrig ation. With either form of furrow irrigation, placement of a fertilize r in the ridge rather than in the furrow would decrease leaching of th e fertilizer and keep the fertilizer in the root zone.