Forage species composition influenced soil health in organic forage transitioning systems

Abstract

The demand for organic forage is increasing while information on appropriate forage species that influence soil properties and forage productivity is scarce. This study was conducted to understand the response of soil health to a diverse forage species in the transitioning stage of low-input organic forage systems. Soils were collected for two years after the forage establishment to analyze soil health indicators. Results showed that perennial mixtures generally had greater total nitrogen (N), mineral N, soil organic carbon (SOC), and microbial biomass carbon (MBC), while similar pH, extractable phosphorus (P), extractable potassium (K), and wet aggregate stability (WAS), compared to monocultures. Mean values of perennial mixtures vs. monocultures at 0–5 cm were 2.1 vs. 1.9 g kg−1, 21.1 vs. 16.2 mg kg−1, 21 vs. 19 g kg−1, 352 vs. 290 mg kg−1 for total N, mineral N, SOC and MBC, respectively. Among perennial mixtures, tall fescue (Schedonorus arundinaceus Schreb.)-legume mixtures showed higher pH, total N, mineral N, MBC, and soil quality index (SQI). Tall fescue-white clover (Trifolium repens L.) mixtures had highest pH (6.34 and 6.45), total N (2.09 and 1.69 g kg−1), and mineral N (25.4 and 21.3 mg kg−1) at 0–5 and 5–15 cm, respectively. The SQI in tall fescue- alfalfa (Medicago sativa L.) was higher than bermudagrass [Cynodon dactylon (L.) Pers.]- alfalfa mixture (77 vs. 71). Compared to perennials, the annual system had comparable or greater total N, mineral N, SOC, MBC, WAS, and SQI. In the 0–5 cm stratum, annual systems from two research sites had 2.01 and 2.21 g kg−1 total N, 17.9 and 29.9 mg kg−1 mineral N, 20.0 and 22.5 g kg−1 SOC, 337 and 227 mg kg−1 MBC, 72 % and 80 % for WAS, and 74 and 72 for SQI. However, the annual system had lower or comparable pH, P and K, compared to most perennial mixtures. After two-years of organic management, most treatments increased soil moisture, pH, MBC, and extractable P compared to the baseline data, while some treatments decreased SOC, mineral N, and K. This study suggested perennial mixtures, especially tall fescue-legume systems, had the greatest potential in improving soil health at the early stage of low-input organic pasture establishment. Despite the short-term management, low-input organic pastures improved some important soil properties such as moisture, pH, MBC, and extractable P. Long-term monitoring is needed to understand the full spectrum of ecosystem benefits when organic management is implemented in forage production systems.