Broadly speaking, the practical methods of soil and water conservation fall into two important classes, viz. Agronomic measures and mechanicla measures.

Agronomic practices for soil and water conservation help to intercept rain drops and reduce the splash effect, help to obtain a better intake of water rate by the soil by improving the content of organic matter and soil structure, help to retard and reduce the overland run-off through the use of contour cultivation, mulches, dense-growing crops, strip-cropping and mixed cropping.

Contour-farming.   During intense rain storms, the soil cannot absorb all the rain as it falls. The excess water flows down the slope under the influence of gravity. If farming is done up and down the slope, the flow of water is accelerated, because each furrow serves as a rill. The major part of the rain is drained away without infiltrating into the soil. The top fertile soil, along with plant nutrients and seeds, is washed off. All this results in a scanty and uneven growth of a crop.

A simple practice of farming across the slope, keeping the same level, as far as possible (which is technically called contour-farming) has many beneficial effects. The ridges and the rows of the plants placed across the slope form a continual series of miniature barriers to the water moving over the soil surface. The barriers are small individually, but as they are large in number, their total effect is great in reducing run-off, soil erosion and loss of plant nutrients.

It has been experimentally proved that contour-farming reduces run-off and prevents soil erosion as compared with the up-and-down cultivation in the major groups of soils in India, viz. Alluvial soils, black soils and deep lateritic soils.

Apart from conserving the water and soil, contour-farming conserves soil fertility and increases crop yields.

Contour-farming on alluvial soil, 2.2 per cent slope at Kanpur has conserved 11.3 kg of N, 11.7 kg of P₂O₅, 44.4 kg of K₂O, 398.1 kg of CaO, 118.1.kg of MgO in one season alone. These nutrients converted into fertilizers amount to 56.5 kg of sulphate of ammonia, 70 kg of single super-phosphate and 74 kg of muriate of potash per hectare in one season.

Contour-farming has also given 490 kg of johar grain and 273 kg of johar stalks more than the up-and-down cultivation at Kanpur. Thus every mm of rain-water conserved by contour-farming gave 22.5 kg of johar grain and 12.5 kg of johar straw more than the up-and-down cultivation.

It has been proved that much less power is required to be exerted by man, animals and machines, if the cultivation is done in the contour instead of up-and-down the slope. There is less wear and tear of the implements and the same job is done in less time when contour-farming is practiced.

How to practice contour-farming .   On long slopes, bunding is usually done to reduce the length of the slope. These bunds will serve as a good guide for contour-farming. All the cultural operations have to be done parallel to these bunds.

On gentle slopes (between 0.5 to 2.0 per cent) bunding may not be essential. Contour (the line passing through the points having the same level) guidelines can be marked with the help of a hand level. On uniform slopes, these lines are to be marked about 50 m apart. Farming is done parallel to these lines.

The establishing of contour-farming on undulating land (having many depressions and ridges) is somewhat tedious. The water from each furrow collects in the depressions and results in breaches. The depressions are required to be filled up by levelling or may be left under grass.

Mulching   Surface mulches are used to prevent soil from blowing and being washed away, to reduce evaporation, to increase infiltration, to keep down weeds, to improve soil structure and eventually to increase crop yields. Inter-culture kills weeds and produces a five or seven cm thick soil mulch which helps to reduce evaporation from the top soil. It also breaks the surface crust which forms after each downpour. Studies on mulching carried out in India under rain-fed agriculture have concentrated on the measurement of crop responses rather than on the manner in which crop responses are influenced.

At Dehra Dun, mulching with maize residues did not significantly influence the yield of the succeeding yield crop.

At Kota, mulching, in general, gave a higher yield of wheat grain and stalk than no mulching.

At Bellary, mulching with different materials (e.g. paddy husk, Encap Esso mulch, grass mulch, johar stubble) did not give encouraging results in increasing the yields of cotton and johar crops. Mulching with straw og Encap Esso mulch increased the infiltration rate, improved soil moisture and increased the yields of wheat, barley, gram and linseed, succeeding the maize crop on eroded soils at Ranchi.

Growing of crops which provide the maximum cover, reduce run-off and soil loss.   Cultivated legumes, in general, furnish a better cover and hence better protection to cultivated land against erosion than ordinary cultivated crops. The crops and the cropping systems will naturally vary from region to region, depending on the soil and climatic conditions.

At Dehra Dun, cowpeas provided the maximum canopy with or without the application of phosphate fertilizer. This was followed by mung, urad and dhaincha.

At Vasad, cowpeas provided the best vegetative cover for the soils. Sunnhemp was the next best; mung and groundnut were effective to some extent.

At Kota, velvet bean formed the canopy effective to the maximum extent. Cowpea was the next best.

At Kanpur, mung served as the most effective canopy, followed by urad and guar. The application of phosphorus increased the canopy.

At Rehmankhera, cowpea formed the best canopy, followed by Styzolobium mung, groundnut, urad, moth, and soybean. Sunnhemp, mung and Styzolobium helped to conserve soil moisture well, leading to a higher yield in the case of the succeeding barley crop. All the legumes were equally effective in reducing the loss of soil and nutrients.

Thus among the legumes, cowpea and mung proved to be important crops for providing a good cover for the land during the rainy season.