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Grace Njeru

BY GRACE NJERU

Thursday 14th October 2021, 17:03 London

Better soil management urgent

In order to boost sustainability, the way we treat our soils is fundamental, write Grace Njeru and Simon Odhiambo of Kenyan avocado exporter Kakuzi

Better soil management urgent

Simon Odhiambo, Kakuzi's executive head of corporate affairs

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Soil is fundamental to crop production and without it no food could be produced on a large scale. Understanding the basics of how nutrients are added to and released from soil organic matter is therefore helpful in choosing crop sequences and amendments to optimise organic crop fertility.

Additionally, by understanding how the soil processes that support plant growth and regulate environmental quality are affected by soil management practices, a farmer is able to design a crop and soil management system that improves and maintains soil health over time.

To start with, one of the farming practices that ensures sustainable agriculture is the long-term improvement of soil properties. At Kakuzi, we undertake activities that prevent soil erosion and thus reduce the loss of nutrients and the negative impact on water bodies. We also actively monitor soil properties and characteristics, climatic conditions, topography, and agricultural practices affecting the crop through soil tests. In addition, we have a soil or crop fertilisation programme based on the characteristics and results of the soil tests.

Cover drive

To effectively manage soil fertility, farmers should be keen to incorporate cover crops that add organic matter to the soil for improved soil structure and fertility. Cover crops help retain nitrates and other nutrients that are susceptible to leaching losses by keeping the ground covered when no plants are growing and therefore reducing the risk of erosion. Usually, the biomass produced by cover crops is returned to the soil, further enhancing organic matter levels.

Indeed, fibrous-rooted cover crops are useful in promoting aggregation and stabilising the soil. Species of cover crops that host mycorrhizal fungi do help in sustaining and increasing the population of these beneficial fungi. This is achieved by using green manure or growing legumes to fix nitrogen from the air through biological nitrogen fixation. At Kakuzi, we also promote the use of fallow areas with natural or planted vegetation such as beans and oats, to recover natural fertility and interrupt pest life cycles.

Embracing organic inputs

Minimising the use of herbicides is also a desired practice for sustainable agriculture. Farmers should embrace other types of organic amendments such as compost and manures. For instance, livestock provides renewable energy for agriculture, saving a considerable amount of fossil energy. As such, integrating crop-livestock systems can have subtle effects on soil quality over time. Manure produced from livestock offers a flow of nutrients that is fairly rapidly available to plants during the growing season. 

Animal manure is recognised as an excellent source of plant nutrients including nitrogen, phosphorus and potassium. Moreover, manure returns organic matter and other nutrients such as calcium, magnesium and sulphur to the soil, building soil fertility and quality. This, of course, is dependent on the type of manure and bedding content.

Mixing it up

From our field experience, crop rotation is another essential agricultural practice in pest management and for enhanced soil health. Long-lasting food crops such as hay and other pasture help build soil organic matter and improve the soil’s physical structure. Instructively, each type of crop provides a different environment and encourages various microorganisms to thrive. Notably, trees and some soil-improving legumes that have deep roots can pump up nutrients from the subsoil that would otherwise never reach crops. With crop rotation, therefore, biodiversity is increased and the build-up of pathogens and pests reduced.

Lastly, trees and forests play pivotal roles in soil protection, food security and a healthy environment. The Kakuzi forest cover has greatly helped to maintain the environmental conditions needed for our agricultural enterprise. Agroforestry ensures a productive food system and a healthy environment in the face of change, hence the need to ensure our planet is stable by managing our forests to control soil erosion and conserve soil. Less soil exposure to sunlight can conserve soil biodiversity and preserve soil moisture, which is also another way to prevent drought stress.

Tree roots also provide the ground with the necessary mechanical and structural support to prevent landslides. They further help in mitigating climate change by absorbing carbon dioxide emissions by storing it in the form of carbon and releasing oxygen into the atmosphere. Sadly, continued deforestation is exposing our land and soil to direct attack from the wind, soil erosion and land degradation, undermining the resource base for agriculture, as well as contributing negatively to climate change.

In essence, better soil management practices ensure recycling of nutrients, biological control of plant pests and water and air supply regulation for higher yields, while using fewer external inputs.

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