Decomposition and nutrient release patterns of municipal solid waste composting in two agro-ecological regions in Uganda
Soil fertility degradation is a major constraint to smallholder agricultural production and food security in Uganda and throughout sub-Saharan Africa, where the majority of the population depends on subsistence agriculture for their livelihoods.
This study evaluated the decomposition and nutrient release patterns of municipal solid waste composting (MSWC) in a 36-week garbage bag experiment under field conditions in two agro-ecological zones (AEZs) in Uganda.
However, since most of the nutrients are released almost immediately in both AEZs, planting should be started during the high rainfall months when soil moisture is higher to synchronize nutrient release from MSWCs with crop demand and maximize nutrient uptake by crops while minimizing loss to the soil.
The MSWCs used in this experiment were sampled from a CDM composting plant in Mbarara. Samples in triplicate are randomly collected from different parts and depths of the compost pile, which are thoroughly mixed to form composite samples (about 20 kg), etc.
The three samples (approximately 1 kg of composite sample) were individually packed in sealed labeled polyethylene bags, transported in the refrigerator to the MetLab East Africa Ltd laboratory in Kampala, and stored at 4 °C until further analysis.
Finenet garbage bag technology is used to study the decomposition and nutrient release patterns of MSWCs over time under field conditions. The technique remains the most widely used method for studying the decomposition process of green manure and plant residues in terrestrial ecosystems.
This technique assumes that all the mass loss of the garbage bag has been mineralized. In this technique, fresh waste is packed into fine mesh bags, buried in the soil, and collected periodically to measure the remaining mass. Mesh sizes are often chosen to optimize access to litter by all organisms while minimizing excessive particle loss.
When assessing the amount of nutrients and heavy metals released by MSWCs and the remaining nutrients and heavy metals, N (25.9%), P (23%), K (10.1%), Ca (26.7%), Cu (0.001%), Fe (33.0%), Mg (27.7%), Mn (21.5%), Zn (53%) remained after 36 weeks of the garbage bag study and were therefore available for subsequent crops.
In another specimen, N (26%), P (18.4%), K (6.0%), Ca (23.3%), Cu (0%), Fe (22.1%), Mg (10.1%), Mn (17.2%), and Zn (18.1%) remained in the field after the experiment and could be used for subsequent crops. The order of release of macronutrients was K (89.9%)> P (77%)> N (74.1%) and K (94%) in SGF > P (81.6%), > N (74%).
The correlation between climatic factors (mean monthly rainfall and mean monthly temperature) and nutrient release in the two experimental regions showed that the mean monthly rainfall had a significant and positive effect on the release of N, P, K, CA, Cu, Fe, Mg, and Mn. Conversely, Zn is not affected by average monthly rainfall.
The average monthly temperature has a significant and positive effect on the release of K, Cu, Mg, and Mn in the former, but does not affect Zn, Fe, Ca, N, and P.
In the latter, the average monthly rainfall has a significant and positive effect on the release of N, P, Ca, Mg, Cu, Fe and Mn, while it has a significant and negative effect on the release of K. Zinc is not affected by average monthly rainfall.
The average monthly temperature has a significant and positive effect on the release of N, P, Ca, Cu, Mn and Mg. However, the average monthly temperature has a significant negative effect on potassium release. The average temperature does not affect Zn and Fe release in the latter study area.
After 36 weeks of decomposition, 20% and 32% of the original mass were retained in the two experimental sites, respectively, confirming the long-term residual effect of MSWCs in soil.
The results showed sustained nutrient release from all first experimental areas throughout the study period, coinciding with two planting seasons in Uganda, suggesting that MSWCs can be used by smallholder farmers as soil amendments to address soil fertility decline, nutrient availability, and crop productivity.
As decomposition and nutrient release dynamics show different trends between different regions, farmers should adopt different fertilization plans that aim to synchronize nutrient release with the time when the crop has the greatest nutrient requirements.
Therefore, MSWCs should be applied at least one week after planting, Cu and Zn are released almost immediately, and by the end of the study period, almost nothing is left.
As plant nutrient requirements and uptake will vary during the planting season, MSWC application needs to be carefully timed during active crop growth to maximize the agronomic benefits of crop nutrient uptake while minimizing the environmental impact of nutrient loss due to leaching and runoff release.
bibliography
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