Revegetation of Retired Farmland: Response of Range Grasses to Establishment Irrigations and Microcatchment Water Harvesting

In July 1987, an experiment was initiated to evaluate the effects of water harvesting and establishment irrigations on the establishment and persistence of buffelgrass, kleingrass, and sideoats grama grass on retired farmland A density evaluation in November 1987 revealed a significant increase in percent cover of the grasses due to establishment irrigations. No significant differences were detected among water harvesting treatments or flatdisked controls. Evaluations will continue to measure any long-term effects from these treatments. INTRODUCTION The conventional wisdom of range seeding in Arizona is that seedings will be successful approximately one year out of ten. The availability of soil moisture is very critical between the time of germination and establishment of the seedlinfs (1,2). In most years, precipitation will not keep the top centimeter of soil moist long enough to allow the seedlings to become established (2). on retired farmland, a history of irrigation may have added salts to the soil which will reduce the availability of soil moisture to the plants (3). Clay soils can further complicate the problem, because clays have a large surface area and will tenaciously hold water (4). Microcatchment water harvesting has improved the survival and productivity of perennial plants in the desert range (5). This test was initiated to gain more insight into this problem, and to develop methods for improving the chances of establishing range grasses on retired farmland. MATERIALS AND METHODS The site at Three Points Test Area is a farm in the Avra Valley purchased by the City of Tucson and retired for a water transfer. The soil, a Valencia sandy loam, was last farmed in 1984. Tumbleweed (Salsola kali) has domimated the site since retirement. In July 1987, the site was disked twice, plowed, and disked. The water harvesting treatments were 40 -inch beds and 80 -inch wide water harvesting microcatchments. Each microcatchment was formed with a pair of road grader blades welded together into a "V" shape. The blades formed an 80 -inch wide, Vshaped ditch that is only 3 -4 inches deep in the middle of the "V ". The idea was to concentrate rainwater at the bottom of the "V", to improve the chances of getting at least a few seedlings established. The 40 -inch beds were also considered rainwater harvesting microcatchments, since they concentrated rainwater in the furrows. Some type of furrow is needed because many farms have sloped, furrow irrigation systems and could not be flat -irrigated without difficulty.