Green Fallow for the Central Great Plains

Abstract

AbstractUse of fallow to store soil water is a common practice in semiarid regions. In the central Great Plains, the most common dryland cropping system is winter wheat (Triticum aestivum L.)‐fallow. Stubble mulching involving tillage is the predominant weed‐control practice during the 14‐mo fallow period. As a result of tillage, soil organic matter content has declined 40 to 70% since the early 1900s. This decline has called for development of cropping practices that control soil erosion and increase soil organic matter. Green fallow is the practice of growing a legume during the time period not devoted to crop production. Water is a major limiting factor for crop production in the central Plains, and water use by the legume could reduce grain yields. Field studies were conducted near Tribune, KS, from 1990 to 1994 to evaluate green fallow in the central Great Plains. The objectives were to (i) evaluate the production potential of several dryland forage legumes, (ii) quantify the water use of dryland legumes as a function of growth period, and (iii) measure the effects of legume growth on grain yield of subsequent crops. Of 11 legume species evaluated, hairy vetch (Vicia villosa Roth) and yellow sweetclover (Melilotus officinalis Lam.) were the most promising in terms of biomass production and weed control. Hairy vetch was planted in a green fallow system and allowed to grow for selected periods of time. In all cases, green fallow depleted soil water and reduced grain yield of subsequent crops. Allowing hairy vetch growth throughout the fallow period reduced soil water by up to 178 mm and reduced grain yield by 42 to 83%. For every millimeter of soil water depletion by vetch, grain yields decreased by 15 kg ha−1. Although green fallow is too detrimental to subsequent crop yields to be recommended in the central Great Plains, dryland legumes may have potential as forage crops.