Soil Water Dynamics after Alfalfa as Influenced by Crop Termination Technique

Abstract

AbstractBecause of their deep roots and high water demand, alfalfa (Medicago sativa L.) hay crops can reduce water available to crops following in the rotation. Recharging the soil water profile after alfalfa is, therefore, a high priority in dryland cropping systems. The objective of this study was to investigate effects of alfalfa crop termination date (late June, early August, and in spring immediately before spring wheat seeding) and method (herbicides, tillage, and herbicides plus tillage) on soil water conservation, and establishment, yield, and water use efficiency (WUE) of a following spring wheat (Triticum aestivum L.) crop. Experiments were conducted over 5 site‐years in a subhumid region of western Canada. Herbicide termination resulted in greater total water recharge and a faster rate of water recharge than treatments involving tillage. Greater efficiency of soil water recharge for herbicide termination after the first hay harvest (late June) appeared to cause deep water percolation at one site. Delaying termination until after the second hay harvest (early August) did not reduce soil water availability at spring seeding of the following wheat crop, but increased reliance on overwinter soil water recharge. Delaying herbicide treatment until spring reduced water at seeding and wheat yields in some cases. Compared with treatments involving tillage, herbicide treatments resulted in higher levels of groundcover (i.e., greater soil erosion control), higher WUE, and higher grain yields. Herbicide termination after the second hay harvest produced the most favorable overall outcome; better than the traditional approach of tillage after the first hay harvest.