Managing Irrigated Corn with Diminished Well Capacity

Limited irrigation research was initiated under sprinkler irrigation in western Kansas at the Tribune Unit, Southwest Research-Extension Center in the spring of 2006. The objectives were to determine optimal plant population and grain yield benefit for corn from preplant irrigation when in-season well capacity is diminished because of depletion of the Ogallala Aquifer. The study was a factorial design of preplant irrigation (0 and 75 mm), well capacities (2.5, 3.8, and 5 mm day^-1 capacity), and plant population (55,000, 68,000, and 80,000 plants ha^-1). The irrigation treatments were whole plots and the plant populations were subplots. Preplant irrigation increased grain yields an average of 0.8 Mg ha^-1. Grain yields increased 15% when well capacity was increased from 2.5 to 5.0 mm day^-1. The yield increase was due to increased seed weight and number of seeds ear^-1. Preplant irrigation increased the number of seeds ear^-1 but had little impact on seed weight. The optimum plant population varied with irrigation level. With the lowest well capacity and without preplant irrigation, a plant population of 55,000 plants ha^-1 was adequate. However, if preplant irrigation was applied, then a higher plant population (68,000 plants ha^-1) increased yields even at the lowest well capacity. When well capacity increased to 3.8 mm day^-1, then 68,000 plants ha^-1 were required to optimize yields without preplant irrigation and 80,000 plants ha^-1 with preplant irrigation. With a well capacity of 5 mm day^-1, a plant population of 80,000 plants ha^-1 provided greater yields with or without preplant irrigation. Preplant irrigation is a viable practice when in-season well capacity cannot fully meet crop needs. Plant populations should be adjusted for irrigation level considering both well capacity and preplant irrigation.