Preparing your land for high quality yields

Land preparation is an important component of farming. In Kenya, we have different methods of land preparation that include burning, digging and chemical application. The choice of the method will depend on the financial capacity of the farmer and the target crop.

Though burning is highly discouraged, farmers are still practising it since it gets rid of weeds, snakes and rodents such as rats. Burning, however, reduces the nutrient value of the soil as well as the organic matter on the surface since the weeds are converted to ash.

Land preparation is done in two steps, that is, primary and secondary cultivations. Both operations should be done during the dry season. Primary cultivation entails deep penetration of the soil up to a depth of 15cm to 75cm by use of heavy machinery.

These machines that include ploughs, listers, bedders and rotary tillers leave a rough surface. For the small farmer, a fork-jembe is normally used. The aim of this operation is to prepare the land for secondary cultivation.

Secondary cultivation is done to pulverise, level and firm the top layer 5cm to 15cm of the soil. The main machines used during this operation are disk harrows, cultivators and rotary tillers. However, for small-scale farmers, jembes and rakes work.

The main objectives of this operation is to prepare the seedbed, manage crop residue, incorporate fertilisers and agro-chemicals, control weeds, de-compact soil layers, increase water infiltration and level the soil surface.

The downside of tillage is that the soil is more exposed to sunlight, in turn this increases water loss. In addition, tillage may cause soil erosion and thus loss of fertility and decrease the capability of soil to hold water. Non-intensive tillage, which include zero-tillage method and use of agro-chemicals such as Round up (Glyphosates), conserve soil moisture, encourages ecological biodiversity and weeds acts as soil cover.

Secondary cultivation may include preparation of ridges and furrows for crops such as potatoes. Crops such as wheat, barley and other small seeded plant require a fine tilth. On the other hand, large seeded crops require a medium tilth. 

TYPES OF TILLAGE

Reduced tillage

Reduced tillage leaves between 15 and 30 per cent residue cover on the soil, that is, 560 to 1,100kg/ha of small grain residue during the critical erosion period. It involves the use of a chisel plow, field cultivators, or other implements.

Intensive tillage (conventional agriculture)

Intensive tillage leaves less than 15 per cent crop residue cover or less than 560kg/ha of small grain residue. Intensive tillage often involves multiple operations with implements such as a mould board, disk and/or chisel plow. Then a finisher with a harrow, rolling basket and cutter can be used to prepare the seed bed. There are many variations.

Conservation tillage

Conservation tillage leaves at least 30 per cent of crop residue on the soil surface, or at least 1,100 kg/ha of small grain residue during the critical soil erosion period. This slows water movement, which in turn conserves the soil.

With the changing climate, conservation tillage is the most suitable since it helps to preserve the soil moisture for longer periods. This means that the moisture will be available during the flowering stage, where crops requires plenty of water.

Muriuki Ruth Wangari, Department of Crops, Horticulture and Soils, Egerton University.