Healthy Soils

Soil structure and fertility are essential to healthy crop establishment and development. Not only does soil act as a growing medium and supports plant roots, it regulates water and air supply, provides nutrients and is home to a multitude of interdependent organisms which can improve soil health and aid plant growth.

As well as its mineral components (a combination of silt, sand and clay), soil is typically composed of organic matter, air and water which fill the small pores between the mineral particles and are vitally important for a healthy plant development.

Plant roots and soil organisms need oxygen to respire, and good aeration is thus an essential ingredient of healthy soil. Limited oxygen availability restricts the respiratory process and creates anaerobic conditions which hamper root development and encourage the growth of anaerobic bacteria responsible for denitrification.

Plants absorb water though their root system and fully rely on it for growth and access to nutrients such as nitrates, phosphorus, potassium, and soluble sulphate. Excess water, however, can damage plant roots and good soil structure is key to ensuring unrestricted water supply and circulation.

Healthy soil requires a sufficient proportion of both water and air: low moisture content makes nutrient uptake difficult resulting in plant stress, whereas poor aeration leads to the development of anaerobic conditions, restricting the reproduction of beneficial soil organisms.

Regularly assessing soil condition should therefore be a vital part of any farming programme. Identified issues such as compaction or erosion should be addressed. Implementing a farming regime that supports the soil’s natural structure, such as the Mzuri system, will help to restore its condition and in time will result in healthier, better yielding crops. The Mzuri system promotes the retention of straw and previous crop residue on the surface which will help conserve moisture and reduce erosion, as well as provide organic matter to be recycled into nutrients thus aiding plant development.

Constituting the smallest fraction of soil yet playing the leading part is organic matter. As well as dead components such as straw stubble and previous crop roots, it consists of a combination of living organisms – including worms, mites, beetles and micro-organisms – which are essential when it comes to efficient food production. Not only do they help the decomposition of organic particles and turn them into nutrients, they keep soil in good shape, protect roots from soilborne diseases and regulate greenhouse gasses.

Often referred to as ‘the soil food web’, myriads of organisms in this closely knit community co-exist and rely on each other for food and energy:

• Bacteria decompose organic matter, mineralising the nutrients they contain and converting them into a form that can be instantly absorbed by plants. As well as enriching soil fertility, these useful members of soil biological community release hormones that stimulate plant growth and produce antibiotics to fight root diseases.
• Fungi also feed on surface litter and release enzymes which break them down into simpler forms. They also help to bind soil particles thus improving soil composition.
• Microbes including nitrogen-fixing bacteria and mycorrhizal fungi live in the rhizosphere – a zone of soil around that root of the plant – where they form mutually beneficial relationships. The roots release carbon which is used as food by the microbes and the plant is supplied with essential nutrients in return. Nitrogen-fixing bacteria deliver nitrate which can be readily absorbed by the roots whereas mycorrhizal fungi offer minerals such as phosphorus to the host plant. The symbiotic relationship makes the plants less prone to disease and drought stress and stimulates fine root growth, subsequently increasing nutrient uptake.
• Protozoa, a group of water-residing beneficial organisms which feed on bacteria and fungi, facilitate the ease of nutrient uptake to the plant thanks to their ability to convert nutrients into mineral forms that can be instantly utilised by plants.

Some conventional farming techniques, including ploughing, cause the reduction in beneficial microbes which in turn restricts plant access to natural nutrients and makes them more prone to soilborne diseases. Minimising soil disturbance, on the other hand, preserves its structure and protects the habitats of the valuable organisms living within. The benefits include higher levels of organic matter, better nutrient availability and a healthier crop with a better root system and increased disease resistance.