COS 283-6 - Effects of compost amendments on rangeland soils, vegetation and microbial communities

Abstract: The health of arid lands is under increasing threat due to climate change induced shifts in precipitation and rising temperatures. For rangeland producers this threat, in combination with degraded soils due to overgrazing, has made vegetation quality and quantity difficult to predict, threatening their livelihoods as well as the food supply. Sustainable management practices are being promoted by researchers and government agencies including the use of compost, an organic material biochemically transformed by microbial communities. Compost has been shown to produce higher quality and quantity of forage, repair damaged soil structure, provide nutrients and sequester carbon in grasslands globally. However, the mechanism underlying benefits are understudied, including the potential role of microbes, which are known to be integral in nutrient cycling.


In this study we investigated soil, vegetation, and microbial community responses after food and manure compost addition to native dry grassland soils. We hypothesized that amendments would be more beneficial in colder and wetter locations as water limitations are relieved, providing more time for microbial activity and greater water and nutrient infiltration, leading to increases in productivity. Due to the specialized conditions under which compost is produced and differing sources of compost we hypothesized compost would have a distinct microbial community that would interact with the native soil microbial community, introducing new functionality and enriching native soils.


We set up field trials on three actively grazed ranches in New Mexico that encompassed a range of climatic conditions. We added manure or food compost and measured vegetation, nutrient and soil properties on treatment and control plots (n=3). We also measured microbial activity and community composition using Illumina sequencing.


After one year of treatment, plant abundance, soil properties, and microbial abundance differed with some compost additions at the coldest and wettest site but there were not differences by compost addition treatment at the other two sites. Aboveground biomass was 155% higher and infiltration rate 200% faster with compost addition than in control plots (P < 0.05). Microbial biomass also significantly increased (P < 0.05) by 28% and 51% with manure and food compost treatments, respectively, but both fungal and bacterial community composition at all three sites were not significantly different from those of control plots (P > 0.05).


This study suggests that compost additions can improve soil and vegetation for rangeland producers. Additionally, native soil microbial communities are likely better adapted to native conditions than microbial communities found in compost.