In Southern Highland Zone (SHT) -Tanzania there different fertilizer brands used in paddy farming, the commonly used fertilizer in paddy farming are Nitrogenous fertilizer and Phosphatic fertilizer, these fertilizers are used for basal dressing during transplanting or sowing seeds and for top dressing during growing plants. The common used fertilizer included UREA, Calcium Ammonium Nitrate (CAN), Di Ammonium phosphate (DAP), Triple Super Phosphate (TSP) and other brands containing Nitrogen and Phosphate (Ngailo et al., 2016). In paddy farms fertilizer are applied by commonly broadcasting method where farmers just broadcast the fertilizer in the field. And after few days they flood the field with water (Amuri et al., n.d.). This fertilizer application practice and flooding practice has adverse effect since the applied fertilizer is likely to be lost by leaching and runoff resulting in poor plant response to the added fertilizer hence low yield return. Despite getting low yield due to poor fertilizer application practices, the leaching and lost fertilizer in water increase the plant nutrients to surface and ground water (Eutrophication) which increase the growth of algae blooms and other vegetation in water bodies such as dams, rivers and lakes resulting in decrease the amount of dissolved oxygen in water and decrease in water levels affecting the marine life, hydroelectric power (HEP) plants and other water users such as Human and animals (Sharpley & Mcdowell, 2016). In Tanzania currently, there is report in increased growth of algae blooms and other vegetation in lakes, rivers and dams receiving water from commercial paddy farms this signifies the increased concentration of P levels in water, hence affecting the marine life and the amount of water for HEP.
The best fertilizer application practices and fertilizer types used need to be reviewed to develop the mitigation measures and guiding policy for fertilizer users to reduce the risk associated with poor fertilizer use in paddy farms, the problem is very serious since many paddy farms are located in lowland where the water table is usually very shallow, exacerbating the processing of eutrophication, fertilizer which are less soluble and with granules which release the required nutrient slowly will be important to ensure fertilizer does not just be lost to water, also the fertilizer application practices which reduce the leaching of fertilizer are important such as banding application ensure the fertilizer is closer to the plant and can be absorbed immediately, also the practice of flooding the farms soon after fertilizer application has to be reviewed to ensure friendly use of fertilizer to the environment and other ecosystem
It would be best to consult with soil scientists with experience in the fertilization of wetlands and how the hydric soil conditions can tie up phosphorus, making it unavailable. USFS soils researcher William McKee (now retired) did several studies in applying fertilizers to coastal forest soils with high water tables. Your subject sounds like one worthy of study, especially if combining the types and properties of paddy soils, high water tables, available and leaching of nutrients, and water quality effects from flooding and runoff. Paddy farming may have different issues to consider as compared to forest. McKee and others found that phosphorus was deficient for pine tree growth in soils with high water tables, and triple super phosphate added had benefit. Spodisols did not respond well to any combination of nitrogen and phosphorus fertilizers. Also noted was the rise in water table when trees were removed, making regeneration difficult in some cases. As the new forest stand used water (transpiration) and lowered the water table, the phosphorus became available and growth markedly increased in response. Due to the cost of fertilizers, it would be best to have soil scientist involvement to help determine nutrient deficiency, conditions of optimum timing for fertilization, fertilization rate, consideration of flooding practices, etc.
Your ideas suggest you are well on your way toward viable study and including the desire to help identify best management practices and advice for responsible paddy farming to help minimize adverse effects. If there are significant issues with fertilizer leaching identified In some areas, you might want to check for example effects of nitrate increases in vicinity groundwater, which can limit some potable water use if excessive. As indicated, runoff or other discharges of fertilizer can have severe effects to aquatic ecosystems.
William F. Hansen yes that's is my target to identify best management practices and advice for responsible paddy farming to help minimize adverse effects, since there is huge increase in fertilizer use in paddy farming which associated with flooding practice of irrigation posing a huge risk to water resource in the vicinity.
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