Organic material decomposition and nutrient dynamics in a mulch system enriched with leguminous trees in the Amazon

Abstract

SUMMARYThe new techniques proposed for agriculture in the Amazon region include rotational fallow systems enriched with leguminous trees and the replacement of biomass burning by mulching. Decomposition and nutrient release from mulch were studied using fine-mesh litterbags with five different leguminous species and the natural fallow vegetation as control. Samples from each treatment were analyzed for total C, N, P, K, Ca, Mg, lignin, cellulose content and soluble polyphenol at different sampling times over the course of one year. The decomposition rate constant varied with species and time. Weight loss from the decomposed litter bag material after 96 days was 30.1 % for Acacia angustissima, 32.7 % for Sclerolobium paniculatum, 33.9 % for Iinga edulis and the Fallow vegetation, 45.2 % for Acacia mangium and 63.6 % for Clitoria racemosa. Immobilization of N and P was observed in all studied treatments. Nitrogen mineralization was negatively correlated with phenol, C-to-N ratio, lignin + phenol/N ratio, and phenol/phosphorus ratios and with N content in the litterbag material. After 362 days of field incubation, an average (of all treatments), 3.3 % K, 32.2 % Ca and 22.4 % Mg remained in the mulch. Results confirm that low quality and high amount of organic C as mulch application are limiting for the quantity of energy available for microorganisms and increase the nutrient immobilization for biomass decomposition, which results in competition for nutrients with the crop plants. As novas técnicas propostas para a agricultura na Amazônia incluem sistema de rotação de capoeira enriquecido com árvores leguminosas e transformando a queima da biomassa em cobertura morta sobre o solo. A decomposição e a liberação de nutrientes da cobertura morta foram estudadas usando sacos de liteira com malha fina que continham cinco tratamentos com diferentes espécies de leguminosas em comparação a um tratamentocontrole com vegetação natural. As amostras para cada tratamento foram analisadas para conteúdos de C total, N, P, K, Ca, Mg, lignina, celulose e polifenóis solúveis em diferentes tempos de amostragem durante um ano. A razão constante de decomposição variou com a espécie e com o tempo. A perda de massa nos sacos de decomposição foi de 30,1 % para Acacia angustissima, de 32,7 % para Sclerolobium paniculatum, de 33,9 % para Inga edulis e para a vegetação secundária, de 45,2 % para Acacia mangium e de 63,6 % para Clitoria racemosa. Foi observada imobilização de N e P em todos os tratamentos, sendo a mineralização do N negativamente correlacionada com o fenol, razão C/N, razão (lignina + fenol)/N, razão fenol/P e o conteúdo de N nos sacos de liteira. Depois de 362 dias de incubação no campo, 3,3 % de K, 32,2 % de Ca e 22,4 % de Mg permaneceram no material em decomposição. Os resultados evidenciaram que a baixa qualidade mineral e a alta quantidade de carbono orgânico e aplicado como cobertura morta podem limitar a quantidade de energia disponível para os microrganismos resultando em uma competição por nutrientes com as plantas agr...

Decomposition and Nutrient Release Dynamics of Shoot Phytomass of Cover Crops in the Recôncavo Baiano

“…This result shows how easily this element is released during the decomposition process. Rapid release of K from plant tissues during the decomposition process is well known (Giacomini et al, 2003;Cattanio et al, 2008;Teixeira et al, 2011). Among the micronutrients, in general, Mn, Zn, and Fe had the highest average t 1/2 , suggesting lower release rates than B and Cu.…”

“…This is because K is not a structural component of any plant compound (Lupwayi et al, 2006;Gama-Rodrigues et al, 2007) and most of this element in plant tissue (up to 70 %) is in a water soluble form (Giacomini et al, 2003). The mineralization of K depends on the concentrations of C and phenolic compounds during the incubation period (Cattanio et al, 2008). Considering the storage potential of K (Table 2) and the average t 1/2 observed for this element (Figure 5), in only six days, the K content released by the species would be the following: GRAS (154 kg ha ).…”

Leaves Material Decomposition from Leguminous Trees in an Enriched Fallow

“…Blair et al (1990) found in litterbags containing mixed residues that there were significantly greater initial releases of N and lower subsequent N immobilization than predicted, and they suggest that it resulted from differences in the decomposer community originated from the mixtures of varied litter resource quality. In the same way, Handayanto et al (1997), Kuo andSainju (1998), Zimmer (2002) and Cattanio et al (2008) showed that soil N-mineralization rate of prunings could be manipulated by mixing different quality materials. Different organic materials decompose at contrasting rates because they are decomposed differentially by catabolic enzymes produced by saprophytic organisms (Linkins et al 1984).…”

“…If burning is to be abandoned, then the synchronization of nutrient release from organic material and nutrient uptake by plants (Addiscott et al 1991, Myers et al 1994, accompanying the competition between plant and microorganisms for nutrients (Cattanio et al 2008), will be the core problem in applied tropical soil biology research. Yield losses in field trials of the SHIFT project have shown that yield losses in mulch practices are evident as compared to burned treatments (Kato et al 1999).…”

“…Soluble C, which includes metabolic and storage C, is of high quality and is primarily responsible for promoting microbial growth and activity. Large amounts of soluble C but little soluble N and P in decomposing plant residues induce net immobilization (Cattanio et al 2008). The challenge resides in sustaining crop production while maintaining soil fertility through supply and efficient management of organic residues (Isaac et al 2000).…”