Rock phosphate combined with phosphate- solubilizing ...

4 downloads 0 Views 442KB Size Report
V.B. Giro, K. Jindo, C. Vittorazzi, R.S.S de Oliveira, G.P. Conceição, L.P. Canellas and F.L. Olivares. Núcleo de Desenvolvimento de Insumos Biológicos para ...
Rock phosphate combined with phosphatesolubilizing microorganisms and humic substance for reduction of plant phosphorus demands from single superphosphate V.B. Giro, K. Jindo, C. Vittorazzi, R.S.S de Oliveira, G.P. Conceição, L.P. Canellas and F.L. Olivares Núcleo de Desenvolvimento de Insumos Biológicos para Agricultura, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, Rio de Janeiro, Brazil.

Abstract Phosphorus (P) plays an important role in agroecosystems as a limiting nutrient for crop production because of its low soil availability and high requirements by plants at an early stage. Soluble P‐fertilizer amendments contrast with low P use efficiency in weathering tropical soils. The aim of this work was to use P‐solubilizing microorganisms (PSMs) and humic substance (HS) to enhance P solubility of natural rock phosphate (RP) of Araxá for partial replacement of single superphosphate (SSP). Two pot experiments were designed under greenhouse conditions. First, defined proportions of SSP and RP were combined in the following six treatments (T1, 0/100%; T2, 20/80%; T3, 40/60%; T4, 60/40%; T5, 80/20% and T6, 100/0% SSP/RP), using two different P‐placement methods (broadcast and deep placement). The sub‐optimal P fertilizer combination of 40% SSP + 60% RP was selected. In addition, deep placement of the P‐fertilizer combination of SSP + RP produced a better plant response for all P rates. Based on the selected proportion of SSP/RP, a second assay was performed using mixed strains of bacteria and fungi (PSM, previously selected for RP solubilization) combined with humic acid (HA). We showed that PSM + HA treatment positively stimulated root and shoot weight compared with non‐inoculated plants by 17 and 22%, respectively. Despite this biomass increase, no difference was observed in P concentration, indicating an increased P use efficiency. Overall, our findings suggest that the application of both PSM and HS with RP may be a suitable method for reduction of soluble P fertilizer demands without compromising plant yields. Keywords: humic acid, biofertilizer, organic farming, P deficiency, Acrisol INTRODUCTION Phosphorus plays an important role in agroecosystems as a limiting nutrient for crop production because of its low soil availability and high early P requirements by plants (Chien et al., 2011). However, demands for soluble P‐fertilizer sources contrast with low P use, being more critical in sesquioxide‐rich soils with high levels of active Al and Fe. In this case, large amounts of soluble sources of phosphate fertilizers are needed to overcome their high P‐fixation capacity, where P is converted into a form unavailable for plant uptake (Zhang et al., 2003). One possible approach for P supply to crops is to include integrative management practices that would increase soil organic matter and combine organic and inorganic P sources with different solubility traits in order to obtain optimal crop yield. Iglesias Jimenez et al. (1993) evaluated the effectiveness of compost as a P source compared with soluble inorganic P forms and observed an increase in plant tissue P concentration when the organic P source was used. In this case, organic matter application combined competitive adsorption effects with net mineralization of organic P that resulted in a greater residual effect on P supply. However, the use of organic sources is associated with a relatively slow mineralization process, non‐synchronized P availability and physiological requirement at    

Acta Hortic. 1146. ISHS 2016. DOI 10.17660/ActaHortic.2016.1146.8  Proc. III Int. Sym. on Organic Matter Mgt. and Compost Use in Hort.  Eds.:  M. Cayuela et al. 

63

the early phase of plant growth. By contrast, fully acidulated inorganic P fertilizers (i.e., superphosphates) that remain the major source of P application used by farmers around the world have exhibited a negative economic and ecological impact in different agriculture ecosystems (Renner, 2008). In addition, in most developing countries, superphosphates are not produced locally, and the supply to poor farmers is rather limited. These countries possess deposits of rock phosphate (RP) that can be used for direct application in agriculture, being considered as an agronomic and economically attractive alternative (Zhang et al., 2003). Selected P‐solubilizing microorganisms (PSM), technologically developed as bioinoculants (Duarah et al., 2011; Nahas, 1996; Stamford et al., 2008), can be useful to improve PR solubility. PSMs are ubiquitous inhabitants of soil, mainly represented by bacteria and fungi groups. The biomineralization activity on RP is mainly attributed to production of organic acid and subsequent lowering of pH, although other mechanisms could operate, such as exopolysaccharide production (Nahas, 1996; Oliveira et al., 2009). PSM consortiums offer the advantage of more efficient P‐solubilization capacity than single species, even comparable to soluble P sources (Braz and Nahas, 2012). Other technological approaches to increase RP solubilization involve bioreactors for confined reactions, using different carbon and/or nitrogen sources to support microbial populations and activity such as biochar (Mendes et al., 2014), agro‐industrial waste (Vassilev and Vassileva, 2003) and immobilized cell technology (Vassilev et al., 2001). The aim of present work was to assess the effect of utilization of RP as a substitute for single superphosphate (SSP) and the potential of microorganisms in the presence of humic acid (HA) on P solubilization and plant growth. Combined application of HA and PSMs have been successfully used as a new biofertilizer for different crops (Canellas et al., 2013; Canellas and Olivares, 2014; Olivares et al., 2015). It has been demonstrated that HA has a protective effect on microorganisms (Martinez‐Balmori et al., 2013), and the root exudation profile of plants treated with HA displays changes in the efflux of organic acids (Canellas et al., 2008). We initially defined the proper P ratio in a combination of SSP and RP that can potentially achieve the maximum SSP dose, evaluating as well the effect of two different types of P localization on plant growth. Subsequently, we evaluated bioinoculant, formulated with PSMs in combination with HA, as a new biological input for reduction of plant P demands in the form of SSP. MATERIALS AND METHODS Experiment design 1 Hybrid maize seeds ‘DKB 789’ were planted in plastic pots filled with yellow Acrisol, which is one of the typical tropical weathering acid soils in Brazil with low available P, low soil organic matter (SOM) content, low effective cation‐exchange capacity and high P‐fixation capacity. The chemical characteristics of the Acrisol before and after 30 days of incubation with dolomite limestone can be noted in (Table 1). The RP of Araxá (33% P2O5; particles smaller than 0.044 mm or sieve of 325 mesh) was mixed homogeneously with SSP. The mixture of SSP/RP was applied according to the recommended dose of 0.14 g of P2O5 kg‐1 Acrisol. Six treatments of the different proportion rates (SSP and RP) were set up: 1) 0% SSP + 100% RP; 2) 20% SSP + 80% RP; 3) 40% SSP + 60% RP; 4) 60% SSP+ 40% RP; 5) 80% SSP + 20% RP; 6) 100% SSP + 0% RP. In addition, other macronutrients (N and K) were applied equally to the soil. Each different treatment was performed in four replicates with randomized statistical design. The effect of the P location was also evaluated with broadcasting application and deep placement beyond the seed sowing. After 30 days under greenhouse conditions, dry weight (shoot and root), root volume (RV) and root:shoot ratio were measured. Equations of the polynomial regression model and the correlation coefficient analysis (R2) were measured with the plotting program SIGMAPLOT, based on the F test at the P