Characterization of soil phosphate status, sorption and saturation in paddy wetlands in usangu basin-Tanzania. (September 2021)

• Record Type: Journal Article
• Authors: Mng'ong'o, Marco; Munishi, Linus K.; Blake, William; Ndakidemi, Patrick A.; Comber, Sean; Hutchinson, Thomas H.
• Is Part Of: Chemosphere. Volume 278(2021)
• Publication Date: 2021-09
• Subjects: Agro-environmental -- Eutrophication -- Mehlich 3 -- Phosphate loss -- Sorption capacity -- Phosphate saturation degree; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2021.130466
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Phosphorus (P) is a vital plant macronutrient required for plant growth which usually available in limited amount. P availability for plant uptake in highly weathered soil is controlled by soil erosion and high fixation. The availability of P applied from fertilizers depend on the soil pH, soil sorption capacity (PSC) and P saturation status (PSD), which determines P storage, losses, fixation, and additional P to be added with minimal loss to the environment. PSC and PSD are agro-environmental indicators used to estimate P availability and P loss to the environment. However, PSC and PSD of agricultural soils had been never studied in Tanzanian soils. This study was conducted to assess and estimate P availability, PSC and PSD and the risks of P losses in tropical soils from Usangu basin popular for paddy farming. In total, 198 soil samples from 10 paddy irrigation schemes were collected (November–December 2019) and analyzed for inherent P (PM3 ), metal oxides of Aluminium (Al M3 ), iron (Fe M3 ), and calcium (Ca M3 ) as main PSC and PSD determinant. The determined concentrations were in range of; P M3 014.9–974.69 mg/kg, Al M3 234.56–3789.36 mg/kg, Fe M3 456.78–2980.23 mg/kg, and Ca M3 234.67–973.34 mg/kg. Estimated PSCM3 ranged 5.62–34.85 mmol/kg with a mean value of 14.14 mmol/kg corresponding to high status, ensuring high P holding capacity for plant uptake. However, some soils had very low PSCM3 creating a risk of P loss to environment. Among soils, the estimated PSD M3 ranged from 0.01 to 17.57% and was below (<24%), indicating low P loss risks to surface and groundwater, however, some soils were observed to have PSDM3 above 15% which correspond to a critical degree of phosphate saturation of 25% in a watershed using oxalate extraction method. Therefore some sites were associated with high P loss to the environment, immediate and precautionary actions for sustainable P management to increase productivity, environmental safety and sustainability are needed to be in place. Highlights: Phosphorus (P) is a vital plant macronutrient but in excess amount have detrimental effect to environment. Sorption capacity (PSC) and saturation degree (PSD) determines P availability for agricultural uptakes and environment. P loss to the water sources observed in Usangu basin leading low productivity and eutrophication. Immediate precautionary actions for sustainable P management are vital to increase productivity and environmental safety.