Organomineral phosphate fertilizer from sugarcane byproduct and its effects on soil phosphorus availability and sugarcane yield

Highlights

• Application of FC enhanced PUE in the CLY soil, regardless of the mineral P source.

• Highest P contents in sugarcane were: SDY > CLY, TSP > control, and +FC > −FC.

• P in the labile and moderately labile fractions decreased with FC application.

• Al/Fe-bound species decreased 9, 24 and 3% in RPR, TSP and control, when +FC.

Abstract

The recycling of agricultural by-products to produce organomineral fertilizers and using them as soil amendments to improve soil physical and chemical characteristics is a feasible disposal solution for the sugarcane industry. This study aimed to evaluate the agronomic performance of a bio-based phosphate (P) fertilizer produced from mineral phosphates (Gafsa rock phosphate and TSP) and filter cake (FC) in two distinct soils varying in their particle sizes, namely clayey (CLY) and sandy loam (SDY). Biological tests were carried out to determine the performance of the OF for sugarcane production against commercial P sources. The addition of filter cake (+FC) was responsible for an increase in yield when compared to soils that did not receive it (−FC), yet similar sugarcane production for either soil was obtained. Phosphorus use efficiency (PUE) was ~10% higher in CLY under TSP +FC compared to phosphate rock (RPR) −FC. On the basis of our P fractionation data, the addition of FC decreased P concentrations in the more labile P fractions. Phosphorus X-rays Absorption Near Edge Structure (XANES) analysis indicated that even though P was predominantly associated with Fe- and Al-(hydr)oxides, application of FC led to a change in P speciation, causing a shift from Fe-bound P in the soil that did not receive filter cake into Al-bound P, and to an increase in P associated to organic compounds in the soil receiving this amendment. Our findings showed that PUE and dry matter yield of sugarcane can be increased in weathered soils when organic and inorganic P sources are combined to supply this element.

Introduction

Among all plant macronutrients, phosphorus (P) is arguably the one presenting the lowest use efficiency in terms of crop production. Plant availability of P is largely affected by soil texture and mineralogy, application strategy and P source (Baligar and Bennett, 1986). An insufficient P supply not only limits economically acceptable yields and the inputs of other nutrients, particularly N, that is used less effectively, but it also threatens food security for a growing world population (FAO, 2008).

In highly weathered agricultural soils of the tropics, crop production is positively related to P fertilization. In these soils, the average P application rate is of the order of 25 kg ha⁻¹, in comparison to 12 kg ha⁻¹, the average world application rate (Lu and Tian, 2017). The increasing demand for food, led by the ever-growing world population, represents an important driving force for P fertilization rates to continue to rise, with the immediate consequence of this being the depletion of P reserves on an unprecedented rate (Cordell and Neset, 2014; Jarvie et al., 2015). Because of this, the demand for P fertilizers is currently a big worldwide concern, especially in tropical agricultural soils, where P availability is severely restricted due to their generally high P sorption capacity (PSC) (Abdala et al., 2012, Abdala et al., 2018; Novais et al., 2007; Rodrigues et al., 2016). Therefore, P-fertilizer efficiency is generally low, usually sitting around 10–20% in the short term (Chien et al., 2009).

Research efforts have been made to reduce the P footprint by using less synthetic P fertilizers (Caione et al., 2015; Vasconcelos et al., 2017; Withers et al., 2018). This in turn has triggered the search for alternative P sources, usually wastes generated in agricultural operations, which can act not only as a source of this nutrient but also controlling P release, to produce more sustainable whereas agronomically efficient P fertilizers (Ahlgren et al., 2013; Alavi et al., 2017; Caione et al., 2015; Dotaniya and Datta, 2014). Particular attention has been drawn to the recycling of agricultural residues for fertilizer production as it represents an alternative to the highly soluble, high cost-effective traditional P fertilizers (Vasconcelos et al., 2017; Withers et al., 2018). Bio-based P fertilizers not only provide P among other nutrients to plants but may well act as a source of organic matter, besides representing a way of refraining to further explore existing and new P reserves.

The sugar-energy sector has for long been using by-products generated in the industrial process as soil amendments to increase sugarcane yield, by improving soil physical and chemical characteristics (Dotaniya and Datta, 2014; Vasconcelos et al., 2017). Among these by-products is the material obtained from the purification of the sugarcane broth by a filter press, termed filter cake (FC). Subsequently, the FC is open-air composted in order to drop the C:N ratio and is usually mixed with mineral nutrient sources to serve as a fertilizer. The FC is usually applied with phosphate fertilizers at the bottom furrow prior to sugarcane planting as an attempt to increase P use efficiency (PUE) by the crop (Caione et al., 2015).

Research has shown that the combined use of organic and mineral materials to supply P in soils with a high PSC is a feasible way to enhance PUE by plants (Caione et al., 2015; Withers et al., 2018). These studies suggest that the adoption of less soluble P sources, such as rock phosphate, and the application of composted organic materials may increase crop yield as a consequence of reducing soil P fixation capacity (Dotaniya and Datta, 2014; Eghball et al., 1996; Singh et al., 1988), thus improving P acquisition by plants. Trials conducted inside commercial sugarcane areas proved that the association of inorganic P sources and FC has increased crop yields (Vasconcelos et al., 2017). Other studies relying on the associated use of mineral and organic P sources for sugarcane showed that it not only increased crop yield, but also sugar accumulation (Caione et al., 2015).

One way of gaining insight into the reactivity of an element in soils is by obtaining information on the chemical forms it is presented in that medium. The chemical associations of P with other elements abundant in soil environments, e.g., Al, Fe, Si, Ca, etc.… largely influence P dynamics and thus its availability to plants. The procedure proposed by Hedley et al. (1982) to fractionate P allows the quantification of different operationally defined pools, measuring concomitantly the inorganic and organic P in distinct fractions, increasing the recalcitrance of the pools according to the extractant strength. This technique can predict P availability for plant uptake (Cross and Schlesinger, 1995). However, its isolated use limits a more in-deep assessment of environmental aspects of P management. Synchrotron-based K-edge XANES spectroscopy has for long been used for chemical speciation studies of P in soils (Beauchemin et al., 2003; Hesterberg et al., 1999) because it represents a successful means for directly determining the chemical species of this element present in a sample. Besides, this technique also offers some advantages over its conventional counterparts as little or virtually no sample preparation and chemical treatment prior to the analysis is required (Vogel et al., 2018). Because P K-edge XANES provides the actual chemical state of the absorber element, it can be used to indicate whether the element is bound to a mineral surface or associated to an organic compound (Kruse et al., 2015).

The aim of this study was to evaluate how the associated use of mineral P sources with an organic material, i.e., filter cake, performs in terms of sugarcane yield in relation to commercial P sources. A pot experiment was therefore set out using different inorganic P fertilizers sources amended with FC, and sugarcane production was evaluated by the end of each harvest and PUE at the end of the experiment. It was also our objective to determine how P was partitioned and what chemical P species were left in the soils receiving the different treatments, to which we used sequential chemical fractionation (SCF) of soil P in association with P-XANES spectroscopy, respectively.