Characterization of soil phosphate status, sorption and saturation in paddy wetlands in usangu basin-Tanzania

Marco Mng'ong'o; Linus K Munishi; William Blake; Patrick A Ndakidemi; Sean Comber; Thomas H Hutchinson

doi:10.1016/j.chemosphere.2021.130466

Characterization of soil phosphate status, sorption and saturation in paddy wetlands in usangu basin-Tanzania

Chemosphere. 2021 Sep:278:130466. doi: 10.1016/j.chemosphere.2021.130466. Epub 2021 Apr 2.

Authors

Marco Mng'ong'o¹, Linus K Munishi², William Blake³, Patrick A Ndakidemi², Sean Comber³, Thomas H Hutchinson³

Affiliations

¹ School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O.Box 447, Arusha, Tanzania; School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK. Electronic address: mngongom@nm-aist.ac.tz.
² School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O.Box 447, Arusha, Tanzania.
³ School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK.

PMID: 33839385
DOI: 10.1016/j.chemosphere.2021.130466

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 (P_M3), 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 PSC_M3 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 PSC_M3 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 PSD_M3 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.

Keywords: Agro-environmental; Eutrophication; Mehlich 3; Phosphate loss; Phosphate saturation degree; Sorption capacity.

MeSH terms

Phosphates
Phosphorus
Soil Pollutants* / analysis
Soil*
Tanzania
Wetlands

Substances

Phosphates
Soil
Soil Pollutants
Phosphorus