Browsing by Author "Mnthambala, Frank"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Effect of various organic fertilisers on phosphorus mineralisation, use efficiency and maize yield
    (MDPI, 2022-09-28) Mnthambala, Frank; Tilley, Elizabeth; Tyrrel, Sean; Sakrabani, Ruben
    When soils are phosphorus (P) deficient, external sources in the form of fertilisers have to be applied to increase crop yields. The world depends on mined sources for P fertilisers, and recent reports indicate that an increase in the human population has led to rising demand for P fertilisers, making its future supply uncertain. A low supply of chemical P fertilisers may lead to food insecurity. Although the efficacy of organic sources of P is unclear, organic waste materials containing P can potentially replace inorganic P sources. Previously, organic fertilisers have been used to supply N and even P, but the application rates were mostly N based, resulting in inconsistent and comparable results. This research was conducted to understand P mineralisation and the availability of the P-based organic fertilisers. The results showed that available P in the soil at 3 weeks accounted for 50%, 6 weeks accounted for 49%, and 9 weeks counted for 46% of the maize yield. The organic P sources maintained soil available P above the threshold available P value in Malawi. The P sources did not affect the maize P use efficiency (PUE). The results indicate that organic P sources could be used as an alternative fertiliser for maize production in Malawi.
  • Thumbnail Image
    ItemOpen Access
    Evaluating phosphorus dynamics from renewable sources to meet crop demand and minimise environmental pollution in Malawi.
    (Cranfield University, 2021-10) Mnthambala, Frank; Sakrabani, Ruben; Tilley, Elizabeth; Tyrrel, Sean
    Like nitrogen (N), phosphorus (P) is an essential plant nutrient. When soils are deficient in P, external P in the form of fertilisers must be applied to increase crop yields. Population growth and changes in dietary needs have resulted in increased demand for P fertiliser for food and feed production, exerting pressure on P reserves. The future availability of P fertilisers is uncertain as reports indicate that the high-grade P reserves will be depleted in the next 100 years. On the other hand, human activities like conventional tillage, continuous cropping, and burning crop residues have led to nutrient leaching, increased soil acidity, increased erosion, reduced organic matter and reduced water holding capacity, all of which have contributed to overall reduced soil productivity. Most Malawian soils have low P, and farmers apply P fertilisers to harvest enough food. The scarcity of P will lead to an increase in fertiliser prices which will in turn, affect food security in Malawi. However, research has shown that organic materials like faecal sludge, organic waste and livestock manure could be used as alternative sources of P in agriculture. In some highly industrialized countries, P flow charts were developed to identify and quantify the organic P sources for recycling and management. However, until now, there has been no complete P flow analysis in any African country. Furthermore, organic fertilisers that have been tested have only been applied to crops based on N, not P, which may not affect soil health the same way. In addition, it is unclear if P mineralising from the organic fertilisers can maintain the available P concentration in the soil and result in the same crop yield as inorganic fertilisers Against this background, this project aimed at conducting a P flow analysis (PFA) using STAN Software to characterise and quantify P sources, flows, and sinks to determine options for waste minimisation, recovery, and inorganic fertiliser use reduction in Malawi. After the organic sources were identified, field experiments were implemented to evaluate the effects of organic P sources derived from organic market waste and faecal sludge on soil health in Malawi. Furthermore, the field experiments were used to study P mineralisation and availability from the P-based organic fertilisers during the plant growth period. The PFA results highlighted that there are 35000 Mg of recyclable organic P available annually, which is over two times Malawi’s annual P fertiliser demand (14000 Mg). The total amount of P applied to the soil for crop production per year is 21000 Mg of which 5300 is applied through animal manure, 1700 Mg through the decomposing mulch and faecal sludge, and the rest through inorganic fertilisers. Although 21000 Mg was applied, 25000 Mg left the soil through crop removal (23000 Mg) and soil erosion (2000 Mg), which resulted in a negative P balance of 1 kg P per hectare. Almost 5000 Mg of P in crop products goes to waste materials during postharvest handling processes, and 1100 Mg is exported in agricultural products. At the consumption level, 100 Mg of P is in food waste and 10000 Mg of P is consumed by the people. Out of the P consumed by people, 91% ended up in pit latrines, and the remaining 9% went to open defecation, WWTPs, and septic tanks. There is also 13000 Mg of P in manure and 4000 Mg in organic waste dumped in unofficial dumpsites, and 500 Mg P in landfills. Although there is organic P in faecal sludge, manure, and organic waste, only 16% of the organic P is recycled for agriculture. Inorganic P fertiliser represents 66% of the P fertiliser used for crop production. Manure is the most recycled organic P source (38% recycled), followed by organic solid waste (6%) and crop residues (5%). Annually, 9000 Mg of P is transferred to faecal matter, but none is recycled. In crop trials, the application of the organic P based fertilisers increased soil organic matter by 60% in two seasons at one field site (Bvumbwe) and 82% at the second (Makoka). Soil pH, which affects plant nutrient availability and microbial activities in the soil, increased from 4.75 to 5.82 in two seasons. There were almost six times more earthworms in the soil at Bvumbwe and four times more earthworms at Makoka compared to inorganically fertilised soil. Bulk density decreased only at Bvumbwe, and maize yield was not affected by P sources. The results on P mineralisation showed that available P in the soil from three weeks after planting to nine weeks increase the maize yield. Modelled results indicated that available P in the soil at three weeks accounted for 50%, at six weeks accounted 49%, and nine weeks after counted for 46% of the maize grain yield. At Makoka, at three and six weeks after planting in both seasons, available soil P was the same regardless of P source, but at nine weeks, the NPK treatment had lower available P. At Bvumbwe, in the first season, available P was the same at 3 and 9 weeks after planting but lower in NPK, NPK+MW and NPK+FSMW at six weeks. There was the same available P concentration in all treatments in the second season. In general, the organic P sources maintained available soil P at 25 mg/kg on average, above the threshold available P value for Malawi (18 mg/kg). At both sites, during the first season, PUE was the same. Only NPK and MW at 15 application rates had higher PUE in the second season. A comparison of PUE between the two sites showed that Bvumbe had a higher PUE than Makoka in both seasons. These findings indicate that Malawi can reduce its dependence on imported inorganic P by using organic sources that will supply P for crop growth and production just as well as the NPK fertiliser while improving soil health and reducing P losses to the environment
  • No Thumbnail Available
    ItemOpen Access
    Phosphorus flow analysis data.xlsx
    (Cranfield University, 2021-06-16 09:03) Mnthambala, Frank
    The P flow model for Malawi was produced using these data. The data was from the year 2016.
  • Thumbnail Image
    ItemOpen Access
    Phosphorus flow analysis for Malawi: identifying potential sources of renewable phosphorus recovery
    (Elsevier, 2021-06-21) Mnthambala, Frank; Tilley, Elizabeth; Tyrrel, Sean F.; Sakrabani, Ruben
    Population growth and dietary needs changes have exerted pressure on phosphorus (P) reserves, and the future availability of P fertilisers is uncertain. Most Malawian soils have low P and farmers apply P fertilisers to harvest enough food. Scarcity of chemical P fertilisers and rising prices will affect Malawi's food security. To avert the impact of P future uncertainty a P flow analysis (PFA) was conducted to characterise and quantify sources, flows, and sinks of P to determine options for waste minimisation, recovery, and chemical fertiliser use reduction for Malawi. The PFA results highlighted that; there are 35000 Mg of recyclable organic P annually, which is over two times Malawi's annual P fertiliser demand (14000 Mg). Currently, only 16% of the organic P is recycled to agriculture. Chemical P fertiliser represents 66 % of the P fertiliser used for crop production. Manure is the most recycled organic P source (38 % recycled), followed by organic solid waste (6%), and crop residues (5%). Annually, 9000 Mg of P is transferred to faecal matter, but none is recycled. Overall, Malawian soils have a negative P balance of -4000 Mg. Malawi can reduce its dependence on imported chemical P if recycling of organic P source is adopted. However, regulations should be put in place to control the quality of organic fertilisers