Grazing Intensity and Nitrogen Fertilization Affect Litter Responses in ‘Tifton 85’ Bermudagrass Pastures: II. Decomposition and Nitrogen Mineralization

Abstract

In many grassland ecosystems, nutrient cycling via plant litter is important for plant growth and persistence. Understanding dynamics of litter decomposition and nutrient release under different management practices is critical to understanding nutrient cycling in grasslands, but this topic has received relatively little attention in C4 grass pastures. The objective of this study was to determine the effects of grazing intensity (defined as postgraze stubble height, SH) and N fertilization on litter decomposition and N release in ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures. Three levels of SH (8, 16, 24 cm) were compared at the same interval between grazing events (28 d) and amount of N fertilization (250 kg N ha−1 yr−1). Three levels of N fertilization (50, 150, and 250 kg N ha−1 yr−1) were compared when SH (24 cm) and regrowth interval were constant (28 d). Loss of litter mass was most rapid early in the decomposition period. Pasture SH had no effect on decomposition of litter mass, but increasing N fertilization increased decomposition rate. Immobilization of litter N began almost immediately after placement in the field regardless of treatment, did not reach its maximum for up to 60 d, and lasted more than 128 d for most treatments. Increasing SH and N fertilization increased N immobilization in plant litter. Nitrogen immobilization in bermudagrass litter occurs across a wide range of pasture management practices, impacting N availability for plant growth.

Seasonal patterns in decomposition and nutrient release from East African savanna grasses grown under contrasting nutrient conditions

“…For example, the N-enriched litter lost the highest amount of biomass C (65%) and had significantly higher rate of decomposition in the second (wet) decomposition phase (11%). These findings agree with previous observations (Liu et al, 2011;Lupwayi and Haque, 1999) that N fertilization increases biomass decomposition, but suggest that factors other than litter N concentration accelerate decomposition in N-enriched litter. An example of such a factor is an increase in C lability resulting from N enrichment (Peyraud and Astigarraga, 1998), which is a result of N promoting growth of succulent herbage with a low cell wall content (Waite, 1970).…”

“…Dubeux et al (2006) suggested that higher tissue C:N ratios indicate lower N concentration in tissues rather than changes in C concentrations. The decrease in litter N over the study period contrasted with the findings of several previous studies (Deshmukh, 1985;Dubeux et al, 2006;Hamadi et al, 2000;Liu et al, 2011), which reported increased nitrogen masses over the study period. The 68-75% N and 73-83% P of the initial mass released by the end of our 20-week study were higher than the 20-30% N and 60% P mineralization reported by Dubeux et al (2006) for 18-week incubation in sub-tropical Florida, USA.…”

“…The findings were also comparable to 36-55% Cynodon dactylon (L.) Pers. (Bermuda grass) organic matter loss reported by Liu et al (2011) within 18 weeks of incubation in Florida.…”

Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities

“…This process can become continuous, since sources of nutrients have varying C:N ratios and lignin contents, releasing nutrients at different rates, i.e., days, weeks, or even years. Different defoliation frequencies and intensities, which influence the formation of new tissues, may also affect C and N cycling due to their effects on the biochemical composition of residues (Parsons & Congdon, 2008), N concentrations in the tissues (Liu et al, 2011), and soil microbial population and diversity (Zhou et al, 2010).…”

Nutrient cycling in tropical pasture ecosystems

“…The net mineralization after 128 days of incubation was ~ 250 g kg -1 of the total N. Increasing stocking rates and N fertilization levels resulted in faster litter turnover and greater nutrient release. Liu et al (2011b) observed that increasing post-graze stubble height from 8 to 16 cm did not affect litter decomposition in Tifton 85 pastures; however, increasing N fertilization levels from 50 to 250 kg ha -1 yr -1 increased litter decomposition.…”