Yield, nutritional value, and economic benefits of Atriplex nummularia Lindl. plantation in marginal dryland areas for conventional forage crops

Abstract

This study assessed: (a) the total aerial and browse biomass of Atriplex nummularia Lindl. (saltbush) on ungrazed 9, 21, and 33-month old shrubs; (b) some relevant nutritional parameters for browse: and (c) the economics benefits of saltbush plantations in terms of cost ratios of energy and protein of saltbush vs. alfalfa, Medicago sativa L., hay. Three-month old nursery-grown speedlings were hand transplanted into a furrow bottom at a spacing of 1 x 2 m in an area with shallow (1-1.1 m deep) and moderately saline (4.6 dS m -1) water table. Seven rows of about 110 plants each were established. Linear regression equations of shrub volume on total and browse biomass were estimated. Nutritional parameters were determined for 33-month old shrubs. To estimate the cost of saltbush plantation, the following scenarios were considered: (a) poorly and adequately managed plantations (10- and 30-year life-span, respectively), (b) saltbush browse yields from 1.0 to 6.5 Mg D M ha-1 year-1, and (c) two management systems (cut-and-carry for pen feeding and direct browsing). For alfalfa crop, cultivated under irrigation, the life-span was four years and the yield was 10 Mg D M ha -1 year-1 from year two onward. Costs through the life-span of the two crops were discounted at present value using a 12.0% discount rate. Browse biomass was about 0.4, 0.8, and 1.4 kg D M shrub -1 for 9-, 21-, and 33-month old shrubs, respectively, or 6.5 Mg D M ha-1 year-1 for the oldest saltbush plants, corresponding with the surviving 4,665 shrubs ha-1. Mean values of nutritional parameters were: organic matter, 74.7%; in vitro organic matter digestibility, 47.0%; ash, 25.3%; crude protein, 13.6%; Na, 5.6%; and Cl, 7.7%. Saltbush proved to be a highly productive species in areas that are marginal or unsuited for conventional crops such as alfalfa. The cost ratio saltbush/alfalfa hay for metabolizable energy and crude protein was lower than one for all the scenarios related to life-span and management systems of saltbush when saltbush yield was higher than 3.0 Mg D M ha-1 yr-1. The overall mean cost ratio saltbush/alfalfa hay for crude protein and metabolizable energy for all the scenarios was 0.22, considerably lower than that considered in our hypothesis.