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

Abstract

There is a need to investigate and identify locally available organic substrates with acidifying potential, which can be used as an additive in rock phosphate (RP)-organic material composting mixtures. This paper reviews attempts to increase P availability in the context of smallholder, low-input and organic farming, and presents a case study from Central India that used a participatory approach to address P deficiency issues in cotton-based organic systems. Study was conducted from 2010 to 2014 through 61 on-farm trials and investigated the agronomic effectiveness of buttermilk-acidulated RP compost. The application of buttermilk-acidulated RP manure resulted in higher yields of cotton in all field trials and higher yields of soybean in all but one field trials. While on majority of the farms (18 out of 28), wheat yields increased with the application of buttermilk-acidulated RP compost, a quarter of the field trials (7 out of 28) exhibited yields lower than farmers’ practices. The study showed that it was possible to develop a locally adoptable solution to an agronomic constraint using locally available resources including the indigenous knowhow. Buttermilk proved to be an effective acidulating agent that can be added to RP-amended compost.

Technical Efficiencies and Yield Variability Are Comparable Across Organic and Conventional Farms

“…The organic cotton farmers are suggested to use balanced nutrient management, including region-specific crop rotation, intercropping with pulses, the recycling of crop residues, and the use of compost and FYM. To complement the nutrient supply, other sources such as de-oiled castor (Ricinus communis) cake and powdered rock phosphate are also recommended [14]. Pest management primarily relies on preventive measures, such as selecting robust cotton varieties [15], maintaining a diverse crop rotation, and intercropping with maize and pigeon pea or okra (Abelmoschus esculentus) as trap crops.…”

Agronomic Suitability of Biologically Produced PARP as a Source of Phosphorus for Maize Production

“…PAPRs may offer an economic means [3] of enhancing the agronomic effectiveness of indigenous PR sources that may otherwise be unsuited for direct application.…”

“…This deficiency is more severe in the high rainfall (800 -1200 mm) regions of the country (Region III) where predominant soils are the highly weathered Oxisols and Ultisols with high phosphorous fixing capacities [2]. Although judicious application of inorganic P fertilizers is recognized as the most effective method for alleviating P deficiencies, their high cost and inaccessibility limit their use to the majority of Zambia farmers, particularly the smallholder farms [3]. Application of farm yard manures and crop residues does add some limited quantities at farm level [4] [5] due to their low P content.…”

Managing Phosphate Rock to Improve Nutrient Uptake, Phosphorus Use Efficiency, and Carrot Yields

“…This points to the need to find better ways to manage PR to enhance P availability to plants and increase agricultural productivity. Several studies have identified different possible ways to increase P availability from PR: grinding it and combining with compost (Nishanth and Biswas 2008) or manure (Zafar et al 2017), solubilizing it in milk sludge also known as buttermilk (Cicek et al 2020), or making use of phosphate solubilizing microorganisms (bacteria and fungi) (Abbasi et al 2015;Panhwar et al 2013). Low molecular weight organic acids (such as oxalic, malic, citric, lactic, malonic, tartaric, and succinic) have also been used to solubilize P from PR (Jamal et al 2018;Klaic et al 2017;Wahba et al 2018).…”

“…However, the P recovery efficiencies from the first two approaches are only between 18 and 29% (Zafar et al 2017). Farmers in SSA lack the knowledge and skills to use P-solubilizing bacteria (PSB) and fungi and lack access to PSB inoculants (Mukhongo et al 2016) and there is inadequate information on how to use milk sludge or organic acids to dissolve PR (Cicek et al 2020;Zapata and Zaharah 2002). Information on the use of natural acids from organic materials, suitable ratio of PR to organic material concentrations, and the optimum time for PR dissolution are limited (if available at all).…”