Forage yield and quality as affected by salt stress in different ratios of Sorghum bicolor-Bassia indica intercropping

Abstract

Salinity tolerance is presumed to be improved in the intercropping system, however, there has been inadequate evidence to scientifically prove this. In the current study, the effect of salinity was examined on forage yield and quality of sorghum and kochia in an intercropping system with different planting ratios in a two-year field trial at Shiraz University. The treatments included three salinity levels of irrigation water; 2 (non-saline as a control), 7 and 14 dS m−1 in main plots and planting ratios; sole sorghum (SS), ⅔ sorghum-⅓ kochia (S2K1), ½ sorghum-½ kochia (SK), ⅓ sorghum-⅔ kochia (S1K2) and sole kochia in subplots. The results showed that salt stress decreased forage yield of both plants, especially of sorghum. Salt stress at 14 dS m−1 reduced fresh and dry weights by 44.9% and 62.4% in sorghum, and 38.7% and 23.3% in kochia, respectively. Salinity also reduced forage quality assessed in terms of crude protein, ash, neutral detergent fiber (NDF), acid detergent fiber (ADF), and total digestible nutrients (TDN). The optimum intercropping systems did not change forage yield, but it increased forage quality via reducing ash, ADF and NDF. The optimum planting ratio was S2K1 for both sorghum and kochia, while the SK ratio was suitable for kochia only. Under non-saline conditions, the sole crop cultivation was a better system, while under saline conditions intercropping with a low density of another plant led to higher dry and fresh weights, as well as lower ash, ADF and NDF for each plant. Since kochia performed as a dominant plant, sorghum growth was considerably suppressed under the high density of kochia (i.e., S1K2), especially at 14 dS m−1 salinity level, which might have been due to high salt tolerance of kochia. Based on the findings of the current study, it could be inferred that in regions with limited freshwater, optimum planting ratio (SK in general for both plants) in an intercropping system could improve the quality of forage with no significant reduction in forage quantity.