Grassland compost amendments increase plant production without changing plant communities

Abstract

Abstract. Compost amendment to grassland is a novel strategy proposed and demonstrated to increase ecosystem carbon (C) storage. However, the effects of compost applications on biomass production and plant diversity are not well known. We assessed impacts of a one-time compost amendment over 4 yr on plant dynamics in two grazed grassland ecosystems in California: a coastal prairie and valley grassland. The valley grassland was dominated by exotic annual grasses and had significantly lower species diversity than the coastal prairie, which consisted of a mix of perennial and annual grasses and forbs. We observed large and persistent increases in aboveground biomass. Over the 4 study years, aboveground biomass from compostamended plots increased by 76% ± 21% at the valley grassland and 41% ± 21% at the coastal prairie, compared with controls. Plant N content was also greater from compost-amended plots. There were no major shifts in species richness or abundance at either grassland site. Overall, plant communities at both grasslands were relatively resistant to the compost addition, but responses of some individual species were observed. Notably at the valley grassland, the abundance of forbs decreased slightly, while the abundance of grasses increased. The abundance of two noxious weeds did not change as a result of the compost amendment. Our results suggest that a single application of composted organic matter used to sequester C provided cobenefits to grassland plant dynamics. The compost amendments produced sustained increases in plant productivity and forage production as well as plant N content without greatly affecting the diversity of these exotic annual grasslands.

Reducing climate impacts of beef production: A synthesis of life cycle assessments across management systems and global regions

“…Thus, soil amendments that contain C and nutrients and promote plant growth without large increases in soil GHG fluxes represent an important potential strategy for reducing grazed beef GHG emissions in grassland regions, although nutrient runoff challenges must be addressed (Gravuer et al, 2019). Furthermore, while one‐time applications of compost may not negatively impact some grassland plant communities (Ryals et al, 2016), nutrient addition can reduce natural grassland diversity (Bobbink et al, 1998; Suding et al, 2005), so more research on biodiversity impacts in native grasslands is necessary. It is promising that adoption of C sequestration management on grazed lands in temperate regions appears to be growing, as indicated by increased funding for and promotion of adding C‐rich organic compost in Californian and adoption of soil health programs in US beef production (CalCAN, 2019; N4E, 2018), and projections of increased global adoption rates of improved grazing management and other land‐based strategies for reducing GHG emissions, like forest and grassland protection, methane digesters, and nutrient management (ProjectDrawdown, 2020).…”

Composted manure application promotes long‐term invasion of semi‐arid rangeland by Bromus tectorum

“…), suggesting that such mixtures could potentially increase soil organic matter while having smaller effects on nutrient availability and therefore invasion (Borden and Black , Ryals et al. ).…”

“…Composted organic green waste applied to two California rangelands increased productivity of both native and introduced species without altering the relative abundance of two invasive species (Ryals et al. ). Understanding where and over what time frames organic waste amendments lead to invasion is important for predicting both the benefits and costs of this practice.…”

Supporting evidence varies for rangeland management practices that seek to improve soil properties and forage production in California

“…Applying composted organic amendments to rangeland soils is a practice increasingly promoted by government and nongovernment agencies across the state. These amendments have been shown to improve on-ranch soil C sequestration and forage quantity and quality at two sites in Northern California (Ryals et al 2014;Ryals et al 2016). In addition, a recent global meta-analysis by Gravuer et al (2019) showed that rangeland forage production and soil C increase in the first few years following application of organic amendments.…”