The nutritive value of river saltbush (Atriplex amnicola) when grown in different concentrations of sodium chloride irrigation solution

There is little information available on the nutritive value of chenopod shrubs and how nutritive value varies among genotype and growing environments. In this experiment, the in vitro organic matter digestibility (IVOMD), crude protein (CP), acid detergent fibre (ADF), neutral detergent fibre (NDF) and ash were determined in river saltbush (Atriplex amnicola). Six different river saltbush genotypes (cloned from different geographical regions) were grown in the glasshouse and irrigated with tap water with 1 of 5 NaCl concentrations added (0, 50, 100, 200 or 400 mM). There were six replicates of each treatment (180 plants in total). Plants were harvested, dried and analysed after 8 weeks of treatment. For most measures of nutritive value including IVOMD, predicted metabolisable energy (ME), CP, ADF and NDF contents there was an interaction between genotype and NaCl treatment. IVOMD and predicted ME both decreased with higher NaCl in the irrigation solution. From a livestock production perspective, these differences were significant with predicted ME ranging from 5.4 to 8.5 MJ/kg DM across genotype and treatments. Crude protein changed but there was no significant difference associated with NaCl treatment. There was a very poor relationship between IVOMD and either ADF or NDF. This result indicates that neither ADF nor NDF should be used as a guide to nutritive value or in the selection of superior saltbush genotypes. The practical consequences of the observed variation and interactions are that selection of genotypes for improved nutritive value is possible but that plants should be screened within the environment where they will be used. The variation observed demonstrates the potential for significant improvement in both profit and livestock production if nutritive value is manipulated though selection and breeding of saltbush.