Soil Biological Activity Contributing to Phosphorus Availability in Vertisols under Long-Term Organic and Conventional Agricultural Management

Abstract

Mobilization of unavailable phosphorus (P) to plant available P is a prerequisite to sustain crop productivity. Although most of the agricultural soils have sufficient amounts of phosphorus, low availability of native soil P remains a key limiting factor to increasing crop productivity. Solubilization and mineralization of applied and native P to plant available form is mediated through a number of biological and biochemical processes that are strongly influenced by soil carbon/organic matter, besides other biotic and abiotic factors. Soils rich in organic matter are expected to have higher P availability potentially due to higher biological activity. In conventional agricultural systems mineral fertilizers are used to supply P for plant growth, whereas organic systems largely rely on inputs of organic origin. The soils under organic management are supposed to be biologically more active and thus possess a higher capability to mobilize native or applied P. In this study we compared biological activity in soil of a long-term farming systems comparison field trial in vertisols under a subtropical (semi-arid) environment. Soil samples were collected from plots under 7 years of organic and conventional management at five different time points in soybean (Glycine max) -wheat (Triticum aestivum) crop sequence including the crop growth stages of reproductive significance. Upon analysis of various soil biological properties such as dehydrogenase, β-glucosidase, acid and alkaline phosphatase activities, microbial respiration, substrate induced respiration, soil microbial biomass carbon, organically managed soils were found to be biologically more active particularly at R2 stage in soybean and panicle initiation stage in wheat. We also determined the synergies between these biological parameters by using the methodology of principle component analysis. At all sampling points, P availability in organic and conventional systems was comparable. Our findings clearly indicate that owing to higher biological activity, organic systems possess equal capabilities of supplying P for crop growth as are conventional systems with inputs of mineral P fertilizers.

Evaluation of physicochemical properties and enzymatic activity of organic substrates during four crop cycles in soilless containers

“…The values of the ACP activity found in this study are within the optimal ranges of phosphatase activity published by Bhat et al (2017). mediated soil processes, as reported by Stott, Andrews, Liebig, Wienhold, and Karlen (2010).…”

“…The values for the DHA activity in the substrates evaluated in this study are greater than those reported by Bhat et al (2017) for soils under organic production. Figure 4b presents the results of ACP activity (μg pnitrophenol g soil −1 hr −1 ) (10 evaluations).…”

“…The values for the DHA activity in the substrates evaluated in this study are greater than those reported by Bhat et al. (2017) for soils under organic production.…”

“…Furthermore, Cunha‐Queda, Ribeiro, Ramos, and Cabral (2007) reported that low activity of β‐GLU in the final stages of composting is one consequence of the decrease in available organic substrates. The values of β‐GLU activity in this study were greater than those reported by several previously cited authors for soil under organic management (Bhat et al., 2017; Cordovil et al., 2017; de Almeida et al., 2015). …”

Partial Acidulation of Rock Phosphate for Increased Productivity in Organic and Smallholder Farming

“…A smaller proportion of soil P is in the microbial biomass and can play a major role in P availability when the turnover time is short [22]. For instance, the rate of microbial P cycling is generally greater in organically managed soils compared to conventional soils because of greater manure additions in organic systems [15,23]. Since, plants can only take up orthophosphate ions (H 2 PO 4…”