Methods Of Controlling Runoff
A. Mechanical Methods:
1. Contour bunding
2. Graded bunding
3. Biological Bunding or live Bunds or vegetative bunding; or Vegetative barriers
4. Water shed management- inter bund management
5. Broad bed furrow
6. Vertical mulching
B. Agronomical practices:-
1. Strip cropping
3. Contour cultivation
4. Planting of grasses for stabilizing bunds.
6. Sequence cropping
7. Relay cropping
Vertical mulching: –
This is the practice followed in dryfarming areas for moisture conservation. The in filtration rate to black soils of dry lands is very low. In the event of high intensity rainfall much more water is lost as runoff instead of infiltrating into the soil profile. This process still accelerated under sloppy lands. Under these conditions the technique of vertical mulch has been found useful in Dryland farming.
This technique consists of digging suitable trenches across the shope and thus making more surface area available for absorption. The open trenches are filled with organic farm wastes like straw stubbles the stalks etc. which is called as filter. The filter should be resistant to decomposition and provide service for 3 – 4 years. The upper portion of filter should be 15 – 20 cm above the soil surface.
The trenun should be of 20 cm width in between two crop rows. The trench depth of 60 to 90 cm is optimum. The interval between trenches should be 4 m. the runoff water is trapped by the filter and allowed to percolate in the trenches the stored water in trenches recharge the soil profile by lateral movement of water. The findings on vertical mulching at Solapur & Mohole indicated 35 to 40% increase in grain yield of Rabi sorghum.
Vegetative or Biological bunding:-
The bushes like Subabul shevri of the grasses like vitiveria i.e. khus grass are planted in between the bunds in the fields across the slope or along the average contours. The system is called as vegetative bunding or biological bunding. The grasses or the bushes are cut close to the ground periodically leaving 20 to 30 cm top portion above the ground. This above ground portion helps to arrest the surface flow of excess water. The water halts temporarily along the vegetative bunds and helps in silting of soil particles. During this time water gets some time to infiltrate into the soil. Then partially clear excess water goes up to the field bunds with non erosive velocity which is further drained into field drains. The interval between two vegetative bunds will depend on the slope of the field. However 10 – 12 m interval between two bunds is convenient for carrying out field operations.
The bushes like Subabul or shevri can also be planted at 15 – 20 m intervals across the wind direction in the fields which acts as wind breaks and useful for checking soil erosion and moisture conservation.
Effective rainfall: –
From crop production point of view it is the portion of rainfall which contributes to the crop water needs is the effective rainfall. In other wounds the and of in tall watch becomes the part of consumptive use of water of a crop. An activicual farmer considers that the effective rainfall whiches that total rainfall which is useful in raising crops planted on his soil. Water which moves out of his field by surface runoff is the portion of total rainfall which is ineffective. Also the water that moves below root zone as deep percolation is ineffective. Any rainfall received after the soil has attained the field capacity up to rot zone depth is ineffective.