Root systems and soil microbial biomass under no-tillage system

Abstract

Some root parameters such as distribution, length, diameter and dry matter are inherent to plant species. Roots can influence microbial population during vegetative cycle through the rhizodeposits and, after senescence, integrating the soil organic matter pool. Since they represent labile substrates, especially regarding nitrogen, they can determine the rate of nutrient availability to the next crop cultivated under no-tillage (NT). The root systems of two crop species: maize (Zea mays L.) cultivar Cargill 909 and soybean [Glycine max (L.) Merr.] cultivar Embrapa 59, were compared in the field, and their influence on spatial distribution of the microbial C and N in a clayey-textured Typic Hapludox cultivated for 22 years under NT, at Tibagi, State of Paraná (PR), Brazil, was determined. Digital image processing and nail-plate techniques were used to evaluate 40 plots of a 80 × 50 × 3 cm soil profile. It was observed that 36% and 30% of the maize and soybeans roots, respectively, are concentrated in the 0 to 10 cm soil layer. The percent distribution of root dry matter was similar for both crops. The maize roots presented a total of 1,324 kg C ha -1 and 58 kg N ha -1 , with higher root dry matter density and more roots in decomposition in the upper soil layer, decreasing with depth. The soybean roots (392 kg C ha -1 and 21 kg N ha -1 ) showed higher number of thinner roots and higher density per length unity compared to the maize. The maize roots enhanced microbial-C down to deeper soil layers than did the soybean roots. The microbial N presented a better correlation with the concentration of thin active roots and with roots in decomposition or in indefinite shape, possibly because of higher concentration of C and N easily assimilated by soil microorganisms. Key words: root distribution, maize, soybean, carbon, nitrogen SISTEMAS RADICULARES E BIOMASSA MICROBIANA DO SOLO SOB PLANTIO DIRETORESUMO: Parâmetros radiculares como distribuição, comprimento, diâmetro e matéria seca são inerentes a cada espécie de planta. As raízes podem influenciar a população microbiana durante o ciclo vegetativo através das rizodeposições e, após a senescência, integrando a matéria orgânica do solo. Pelo fato de representarem um substrato lábil, especialmente de nitrogênio, podem ditar o ritmo da disponibilidade de nutrientes na seqüência de culturas sob o sistema de plantio direto (SPD). A comparação dos sistemas radiculares do milho (Zea mays L.), cultivar Cargill 909 e da soja [Glycine max (L.) Merr.], cultivar Embrapa 59, e sua influência sobre a distribuição espacial do C e N microbianos foi feita em um Latossolo Vermelho-Escuro, textura argilosa, cultivado durante 22 anos sob SPD, no município de Tibagi (PR). Técnicas de processamento de imagens e de placa de pregos foram empregadas na avaliação de 40 quadrículas de um perfil de 80 × 50 × 3 cm, revelando que 36% das raízes de milho e 30% das raízes de soja estão concentradas na camada 0-10 cm do solo. A distribuição percentual no perfil do solo de matéria seca radicular ...

Soil organic carbon fraction losses upon continuous plow-based tillage and its restoration by diverse biomass-C inputs under no-till in sub-tropical and tropical regions of Brazil

“…SOC accumulation (0.60 Mg C ha −1 yr −1 in the 0-40 cm depth) under NT and resilience index for MAOC (Table 3) is relatively low at the PG site, when compared with the rate of C sequestration in the region that ranges from 0.66 Mg C ha −1 yr −1 (Pavei, 2005; 0-20 cm depth), 0.8 Mg C ha −1 yr −1 ; 0-40 cm depth), and 1.0 Mg C ha −1 yr −1 (Sá et al, 2001;0-40 cm depth;Venzke-Filho et al, 2004;0-20 cm depth). In contrast, the biodiversity and biomass-C inputs of the NT systems at the LRV site may support a continuous and higher flow of mass and energy, which releases organic compounds, accentuates soil biodiversity, and enhances on a short-term period SOC recovery (Séguy et al, 2006;Uphoff et al, 2006).…”

Soil microbiological attributes under summer/winter crops rotation in a no-tillage system

“…Another possible effect may be related to the differences on deep, density and composition of crop roots (Bordin et al 2008). Soybean has a greater number of thinner roots and higher root density per length unity than maize, and also a close correlation was found between MBC and soybean decomposing or unshapely roots, but not with maize (Venzke et al 2004). Urease and phosphatase activity had been proposed as an index of the soil potential for organic matter decomposition and indicate nitrogen and phosphorus cycling.…”

Changes in soil organic carbon during 22 years of pastures, cropping or integrated crop/livestock systems in the Brazilian Cerrado

“…Bernoux et al 2002;Groppo et al 2015), owing to the rapid decline in the mass of crop roots with depth (e.g. Venke Filho et al 2004;Caires et al 2008). In an earlier sampling of this same field experiment in 2004 (Marchão et al 2009) soil C and N concentrations were not observed to decrease with depth to 30 cm but ranged from 17 to 25 g C kg soil -1 and between 1.2 and 1.8 g N kg soil -1 in the 0-2, 2-5, 5-10, 10-20 and 20-30 cm depth intervals.…”