Root development and soil carbon stocks of tropical pastures managed under different grazing intensities

Abstract

Grasslands may act as a carbon (C) sink or C source depending on how they are managed. Soil C stocks, root biomass, root length, root length density and soil organic C concentrations were assessed on pastures of elephant grass (Pennisetum purpureum) managed under different post-grazing stubble heights and signal grass (Brachiaria decumbens) managed under different stocking rates. Soil samples were collected in 20-cm layers down to 1-m soil depth. Neither stubble height nor stocking rate had any significant effects on root parameters. Both the root system and C stocks declined in both pastures with increasing soil depth. Root biomass in the 0-20 cm layer contained 2.84 and 2.04 t C/ha, declining to 0.39 and 0.64 t C/ha at 80-100 cm for elephant grass and signal grass, respectively. Signal grass had greater root development deeper in the soil than elephant grass pastures, possibly due to its greater tolerance of Al toxicity and acidity. Total soil C stocks were greater for signal grass than for elephant grass (358 vs. 214 t C/ha, respectively). ResumenLas pasturas pueden actuar como reservorio o fuente de carbono (C), dependiendo de la forma de manejo. En el trabajo se evaluaron las reservas de C y la concentración de C orgánico en el suelo, la biomasa y longitud radiculares y la densidad de la longitud de las raíces en pasturas de pasto elefante (Pennisetum purpureum) pastoreado a diferentes alturas y de pasto braquiaria (Brachiaria decumbens) manejado con diferentes cargas animal. Las muestras de suelo fueron tomadas cada 20 cm hasta 1 m de profundidad. La altura del pasto elefante ni la carga animal en braquiaria afectaron los parámetros de raíz y suelo evaluados. En ambas pasturas, tanto el sistema radicular como la reserva de C disminuyeron con el incremento de la profundidad en el suelo. En pasto elefante la biomasa radicular entre 0 y 20 cm contenía 2.84 t/ha de C y entre 80 y 100 cm contenía 0.39 t/ha. En pasto braquiaria estos contenidos eran, respectivamente, 2.04 t/ha y 0.64 t/ha. Este último pasto presentó un mayor desarrollo radicular a través del perfil del suelo que el pasto elefante, posiblemente por su mayor tolerancia a acidez del suelo y toxicidad por aluminio. La reserva total de C en el suelo fue mayor en pasto braquiaria (358 t C/ha) que en pasto elefante (214 t C/ha).

Soil microbiological properties and available nitrogen for corn in monoculture and intercropped with forage

“…These results indicate the benefits of integrating this forage with corn, with increases of 13% in TOC and 9% in TN in the uppermost soil layer, when compared to sole U. humidicola. Corn fertilization may have increased forage root development -which, in some species, can reach up to 4 Mg ha -1 in the 0.00-0.40-m layer (Saraiva et al, 2014) -and affected soil TOC and TN. Moreover, under NT systems, corn roots, which are more concentrated in surface soil layers (Silva et al, 2000), together with the deposition of plant residues, may have also contributed to increases in TOC and TN.…”

Cover crops affect on soil organic matter fractions under no till system

“…In NTS, the absence of soil movement in association with crop rotation and above-ground dry matter may contribute to increase the LC in the first layer (0-5 cm depth) of soil depth. As reported by Saraiva et al (2014), the highest carbon stocks in the soil surface (0-5 cm depth) is due to the deposition of cover crops in association with the root system concentrated into the first layers of soil. Nevertheless, it is possible to observe that in NTS, the fertilization in the seeding row with deposition of fertilizer in 8 cm depth promotes higher concentration of roots in this depth due to the nutrients placed, this fact increased the SOM in 5-10 cm depth as it was possible to observe in this research, this way, no significant difference was observed between 0-5 cm and 5-10 cm depth (Fig 3).…”

Dynamics of soil microbiological attributes under integrated production systems, continuous pasture, and native cerrado

“…In the 0.10-0.20 and 0.20-0.30-m soil layers, during the rainy season of February 2014, the levels of MBC were also higher in the ICLS, when compared with the ICLFS and native cerrado. This could be a consequence of the increased root development of Urochloa sp., which can reach 4 Mg ha -1 down to 0.40-m depth (Saraiva et al, 2014). Plant residues from eucalyptus release toxic compounds that can inhibit the growth of microbial biomass and its adaptation to the plant rhizosphere (Behera & Sahani, 2003;Araújo et al, 2010).…”