Conservation agriculture: Prevention is better than cure
Last week, we learnt that many crop farmers do not practice environmental friendly methods of growing crops. This week, we shall look at practices that crop farmers could implement that will help to conserve the environment and, in particular, the soil. In other words, we will be focusing on conservation agriculture. Let us begin by looking at soil crusting, or capping. In small plots, hoeing the surface of the soil will break up the crust and therefore make it easier for water and air to enter the soil. If the crust is very hard, a pick may be used. Digging deep into the soil may also break up hard pans in plots, and in large fields, a chisel plough, or ripper, may be used. These implements have heavy long tines that can rip hard pans apart [ a garden rake has tines that are much shorter]. But prevention is better than cure! To prevent crusting in the first place, the soil surface may be mulched, or covered, with materials such as dry leaves or grass. This will reduce splashing and runoff and so will result in more water infiltrating the soil.
Where the soil crumbs have been broken down into dust, the soil structure may be improved by the addition of organic matter, such as kraal manure. This will help bind the soil particles together to produce crumbs. And farmers should not cultivate the soil if it is too wet or dry. Digging a hole in the soil with a spade can tell the farmer much about the moisture content of his soil. Alternatively, probes may be inserted into the soil; these instruments will provide the farmer with a more accurate analysis of the soil moisture content.
In recent years, conservation agriculture has stressed the need for farmers to adopt minimum tillage and no- tillage. Minimum tillage simply means reducing the number of times a farmer cultivates, or tills, the soil. It may be achieved by combining farming operations. For example, the Department of Agricultural Research at Sebele has developed a number of farming implements that are simple to use and are affordable to most farmers. One such implement is the animal- drawn Sebele plough planter. This is a small mould- board plough that has seed containers, or hoppers, attached to it so that it can plough and plant seeds at the same time. A larger plant planter is tractor- drawn and so farmers here can cut costs of fuel and tractor hire significantly, as compared to using two separate implements, one for ploughing, and the other for planting.
Farmers can also practice rotational tillage. Here the soil is tilled every two years, or less often. Strip tillage is another minimum tillage method. Here narrow strips, some ten centimetres or so wide, are tilled where seeds are to be planted thus leaving the soil in between the rows untilled. No till, or zero tillage, means just that – no cultivation at any stage of land preparation or plant growth. Here crop residues of the previous crop remain in the field after harvesting. For example, maize stalks may be cut and then laid on the ground. This will reduce the velocity of rainwater before it comes into contact with the soil surface thus preventing soil splashing, surface runoff, and the breaking up of soil crumbs. Therefore, more water will enter the soil and be absorbed by the plant roots. Crop residues also shade the soil and so limit evaporation thus conserving water in the soil. At planting time, seed drills position seeds in the soil at the correct spacing and then bury them. Such seed drills may need to be a little heavier in order to penetrate through the crop residues. However, tractors can be smaller than those used for ploughing and this should help minimize the formation of hard pans in the soil. Scientists these days are of the opinion that minimum tillage and no tillage are more suitable for semi- arid areas, such as Botswana, where the environment is very fragile and can easily be disturbed by human activities like farming. Frequent cultivation of the land, on the other hand, is now considered more suitable for farming in cooler, more temperate parts of the world.
Cover crops are those plants that are planted to cover the soil rather than for the purpose of being harvested. Suitable crops include legumes, such as vetch and clover, and those that have a creeping habit of growth and so can quickly cover the soil. If cover crops are grown together with a main crop, such as maize, they may later be ploughed into the soil once the main crop has established itself. This will reduce competition between the crops for water and space. When ploughed back into the soil, legumes crops may help increase soil fertility by releasing nitrogen into the soil.
To prevent destroying soil structure, farmers can also apply organic, rather than inorganic, fertilisers to their soil. Such fertilisers include kraal manure, compost and organic fertiliser that can be bought in bags. Such fertilisers help to improve soil structure by binding soil particles together to produce crumbs.
Last week, we saw that fertilisers containing plant nutrients can be washed into river water and so increase nutrient levels in the water – a process known as eutrophication. Farmers can reduce this problem in several ways. Firstly, trees, shrubs and grasses may be planted along the edges of fields to help trap runoff water and so enable plant nutrients to infiltrate the soil. Secondly, ground cover crops may be planted year round. And finally, farmers should never apply more than the recommended amount of fertiliser to their soils [ many farmers believe that by adding more and more fertilizer their crop yields will always increase, but this is not always true!].
If farmers grow crops on sloping land, they should practice contour ploughing. Now a contour line on a map is simply a line that joins places that have the same altitude, or height above sea level. Therefore, if we were to walk along a contour line drawn on the ground then we would be walking on flat land at the same altitude. Similarly, contour ploughing means ploughing across the slope, at a direction at right angles to the direction in which the land is sloping. So, if we were to walk across the slope along a furrow, we would always be at the same altitude. During heavy rains, rainwater will now not be able to rush down the slope and erode the soil. Instead, rainwater will now be trapped in the furrows and infiltrate the soil.
Strip cropping is similar to contour ploughing. Here fields are arranged in narrow strips across the slope. Some of these strips may be planted with crops like maize and sorghum which are usually planted far apart thus leaving a lot of soil bare. However, other strips may be planted with crops such as beans, peas, groundnuts or grasses. These crops are planted closer together and so provide much greater soil cover thus helping to reduce runoff by trapping rainwater which, in turn, will sink into the soil.
On very steep land, contour ploughing may not be enough to prevent runoff and soil erosion. On such land in Lesotho farmers may construct terraces. Here steps, like in a staircase, are cut into steep slopes and these steps have wide, flat areas for planting crops. The front of each terrace may have a vertical stone wall, or an earth wall planted with grass.
In conclusion, both livestock and crop farmers must do all that they can to conserve their soil. After all, it takes just a few years, or less, to erode all the soil on a farm, but it has taken thousands of years to produce that soil! And most of the methods that we have discussed can be implemented at little extra cost to the farmer.