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North-West University (2020)

Effect of composted Phalaborwa ground phosphate rock on performance of grain sorghum grown on variable soil conditions

Letsoalo, Maimela Solomon

Titre : Effect of composted Phalaborwa ground phosphate rock on performance of grain sorghum grown on variable soil conditions

Auteur : Letsoalo, Maimela Solomon

Université de soutenance : North-West University

Grade : Master of Science in Crop Sciences 2020

Résumé partiel
Grain sorghum (Sorghum bicolor [L.] Moench), is a cereal crop that is indigenous to Africa. The desire to reduce the negative impact of industrial wastes on the environment through the use of inorganic fertilisers and promote harmony between nature and the earth inhabitants calls for identification of viable and cheaper alternative non-hazardous fertiliser source for maintaining soil fertility and increasing crop yields on farmlands. This can also help farmers to manage on-farm wastes as wealth resources. It also minimizes the waste removal costs and serves as way of increasing income. This study assessed soil phosphorus (P) and other soil nutrients availability when using cheaper and locally available P-rich organic-based fertiliser sources for increased grain sorghum yields. Compost preparations, greenhouse and field trials were conducted at the North-West University experimental farm in Mahikeng. The P-enriched compost produced contained adequate levels of nutrients including P, which was 68.37 g/kg but with high level of Cd that was above the threshold level of 39 mg/kg it may pose serious threats for agricultural soils. The most common threats caused by Cd are stunting and chlorosis in plants. Evaluation of growth, yield, nutrient and nutritional contents of grain sorghum were carried out under greenhouse and field conditions following application of variable rates of the P-enrich composts. Two greenhouse trials consisted of factorial arrangements. The first greenhouse trial consisted of two soil textural classes (loam and a sandy loam) and seven compost rates (i.e. unamended control, 5, 10, 20, 40, 80, 160 t/ha) and inorganic NPK rate as a positive control while the second trial consisted of two soil types (Hutton and Coega) and seven compost tea rates. The compost tea rates included unamended control, 250 ml fortnightly, 250 ml weekly, 250 ml bi-weekly, 500 ml fortnightly, 500 ml weekly and 500 ml bi-weekly. In addition, a laboratory incubation study on phosphorus release from the P-enriched co-composted manures was conducted to quantify and compare P availability from co-composted GPR in two soils with variable textural characteristics. Results from the first greenhouse trial revealed that all measured sorghum growth parameters performed better under loam soil than the sandy loam. Higher compost application rates promoted early flowering first observed in the 80 t/ha rate at 49 days. However, biomass accumulation in the inorganic NPK fertilizer rate was higher (53.63 g) than any of the P-rich compost rates.

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