Zimbabwean farmers are enjoying an abundance of rainfall this season, thanks to the La Nina effect, the cool phase of the El Nino-Southern Oscillation (ENSO) climate change phenomenon.
However, excessive rainfall could have negative consequences, as it destabilises soil-plant nutrition dynamics, reducing nutrient availability and accessibility, ultimately reducing crop yields and threatening food security.
Agronomist Hamond Motsi warns that soil erosion is one of the most noticeable indications of excessive rains, as topsoil, which contains critical properties such as plant nutrients, organic matter, and microbes, is washed away, and nutrients are leached downwards to depths where they become inaccessible for root uptake.
This can cause high acidity in the soil, which is a sign of a drop in pH levels, elevating aluminum toxicity, reducing nutrient availability, and affecting plant growth. Furthermore, too much rain can cause soil saturation, which can create floods and waterlogging conditions, restricting root nutrient uptake and causing anaerobic conditions that regulate aeration in the rhizosphere, explains Motsi.
Eutrophication is also a concern, caused by nutrients lost from agricultural fields being discharged into water bodies such as lakes, ponds, and rivers, where they cause algal bloom, river bank blocking, aquatic life fatalities, and overall water quality decline.
Motsi stresses that farmers must undertake prescribed measures to counteract these concerns. Firstly, replenishing soil organic matter in soil is generally effective in strengthening soil aggregates, reducing soil physical disturbances, and enhancing gradual soil infiltration, which reduces waterlogging and holds nutrients tightly in its organic complex, thus inhibiting losses through leaching.
Organic matter can shelter and offer energy to soil microorganisms, reducing their mortality. Soil organic matter may also reduce and mitigate soil acidity due to its richness in cations.
This can be managed directly by adding animal manure or crop residues, or indirectly through other conservation practices, including crop rotations, cover cropping, multi-cropping, reduced tillage, and contour management, which can be influential in diverting running water into appropriate waterways.
Farmers should also ensure proper timing of fertiliser application and spraying of chemicals to avoid losses, while frequent farm renovations on infrastructure such as roads and buildings are necessary to strengthen their resilience to damage.
Early warning communication is crucial for alerting farmers of approaching dangers, and platforms such as broadcasting television and radio stations, newspapers, magazines, and social media can be resourceful for maximising weather information dissemination to farmers.
In addition, Motsi suggests that insurance uptake should be recognised, especially in cases of severe damage, which is irreversible. Disasters of this magnitude are usually common in tobacco production, where hailstorms can destroy the whole leaf, which is the plant’s organ of economic significance. However, insurance uptake has been very low among farmers, especially from the smallholder class.
While rainfall is a fundamental factor in agriculture, it is highly heterogeneous and unpredictable. Motsi concludes by advising farmers to remain vigilant, frequently listening to news broadcasts or looking for weather information, and being prepared for excessive rainfall’s potential negative consequences.
