Nitrogen fertilizer increased litter deposition and litter N in warm-climate grasslands

Abstract

In warm-climate grasslands, litter deposition and decomposition are one of the main pathway of nutrient cycling. The application of nitrogen (N) fertilizer or the inclusion of a legume in such grasslands modifies litter characteristics and chemical composition. This study evaluated how the N supply of palisadegrass [Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster] pastures affect litter characteristics two years after seeding. Treatments were palisadegrass fertilized or not with N (150 or 0 kg N ha(-1) year(-1)) or mixed with the legume forage peanut (Arachis pintoi cv. Amarillo). The experimental period covered two consecutive rainy seasons. Nitrogen fertilization increased by 43 and 62% the existing litter mass (organic matter, OM), and by 32 and 23% the litter deposition rate compared to unfertilized palisadegrass or legume-grass mixtures, respectively. Both variables were affected by grazing cycle (GC), with low litter deposition rate (14 kg ha(-1) d(-1) OM) and existing litter mass (1390 kg ha(-1) OM) in the GC4 due to low rainfall. Nitrogen fertilized palisadegrass had greater litter N concentration (7.9 +/- 0.4 g kg(-1) OM-C:N ratio 34 +/- 2) than in monoculture or legume-grass mixtures (C:N ratios 45 and 58 +/- 2, respectively). Our results indicated that N fertilization of palisadegrass increased litter accumulation, however, N fertilization was not a key driver of the litter decomposition rate, even though it increased litter N concentration. After 2 years of establishment, the proportion of forage peanut in the litter was still low, reducing the benefits of legume inclusion to enhance litter nutrient cycling in these pastures.