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.
School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O.Box 447, Arusha, Tanzania.
Chemosphere. 2021 Sep;278:130466. doi: 10.1016/j.chemosphere.2021.130466. Epub 2021 Apr 2.
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), metal oxides of Aluminium (Al ), iron (Fe ), and calcium (Ca ) as main PSC and PSD determinant. The determined concentrations were in range of; P 014.9-974.69 mg/kg, Al 234.56-3789.36 mg/kg, Fe 456.78-2980.23 mg/kg, and Ca 234.67-973.34 mg/kg. Estimated PSC 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 creating a risk of P loss to environment. Among soils, the estimated PSD 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 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.
磷（P）是植物生长所需的重要大量营养素，通常含量有限。在高度风化的土壤中，植物对磷的吸收可用性受到土壤侵蚀和高固定性的控制。肥料中提供的磷的可用性取决于土壤 pH 值、土壤吸附能力（PSC）和磷饱和度状态（PSD），这决定了磷的储存、损失、固定以及添加到环境中的额外磷，损失最小。PSC 和 PSD 是用于估计环境中磷的可用性和磷损失的农业环境指标。然而，坦桑尼亚土壤中从未研究过农业土壤的 PSC 和 PSD。本研究旨在评估和估计热带土壤中磷的可用性、PSC 和 PSD 以及乌桑古流域（以水稻种植而闻名）农田土壤中磷损失的风险。共采集了 198 个来自 10 个水稻灌溉计划的土壤样本（2019 年 11 月至 12 月），并对其固有磷（P）、铝（Al）、铁（Fe）和钙（Ca）等主要 PSC 和 PSD 决定因素的金属氧化物进行了分析。测定的浓度范围为：P 014.9-974.69 mg/kg、Al 234.56-3789.36 mg/kg、Fe 456.78-2980.23 mg/kg 和 Ca 234.67-973.34 mg/kg。估计的 PSC 范围为 5.62-34.85 mmol/kg，平均值为 14.14 mmol/kg，对应于高状态，确保了植物吸收的高磷保持能力。然而，一些土壤的 PSC 非常低，存在磷向环境流失的风险。在所研究的土壤中，估计的 PSD 范围为 0.01-17.57%，低于（<24%），表明对地表水和地下水的磷流失风险较低，然而，一些土壤的 PSD 观察到超过 15%，这对应于流域中使用草酸盐提取法的 25%磷酸盐饱和度的临界程度。因此，一些地区与向环境中大量流失磷有关，需要采取立即和预防措施，以实现可持续的磷管理，提高生产力、环境安全和可持续性。
