Importance of vegetation in rainfed dryland agriculture

G.N.S. REDDY

Rainfed dry land agriculture continues to be a gamble, but it need not be.  It is generally perceived that rainfall pattern alone determines the success or failure of crops.  This perception is only partly correct.  What happens to the rainwater received is as important as the quantum of rainfall itself.  Equally important is the pattern of utilization of other natural resources such as sunshine, soil, soil microbes, type of crops, local vegetation, livestock, birds etc. We all understand that rainfall is the major source of water.  In a typical dry land situation without adequate vegetative cover, 90% of the precipitation will be runoff and only 10% will be retained in-situ.  The proportion of the rainwater retained in-situ increases with increased vegetative cover.

How does vegetative cover help?

• Vegetative cover to the soil in form of trees, shrubs, creepers, grasses etc., helps to intercept the raindrops and retain maximum water in the canopy and the excess rainwater slowly runs down the leaves, branches and the main trunk thereby avoiding splash erosion. This also helps in increasing the percolation.
• The grass cover on land also directly checks the velocity of flow of water on ground. Slow passes of water results in increased percolation.
• Increased vegetative cover also adds a lot of organic matter to the soil thereby changing the structure of the soil particles. This enhances the water holding capacity of the soils which in turn have a bearing on          the survivability of crops during dry spells.
• Vegetative cover provides home for variety of insects and birds. some of these fauna are directly beneficial to the farmers while others act as predators on the attacking insects. Apart from their direct role in crop production these insects and birds help to add a good proportion of micronutrients to the soil through their droppings, plumage of birds and due to decomposition of dead birds and insects themselves.

How to increase vegetative cover in cultivated lands

Farmers’ fields are normally divided into several sub plots using bunds.  A hectare of land can have 800 to 1200 running meters of bunds including the boundaries.  All these bunds can be covered with perennial fodders like Stylo hamata and other local grass which help to stabilise bunds.

Trees with long rotation period can be planted on the boundary -bunds with a plant – to plant distance of 2m.  Internal bunds can be planted with trees of short rotation period and with those which can produce maximum leaf biomass.

Trees that can be constructed for bunds are, Glyricidia sepium, Leucena leucocephala, Cassia seamea, sesbania sesban (Chogache), Erythrina lndica (Halvana), Moringa pterigosperma (Nugge), Pongamia pinnata (Pongan). Trees that can be promoted on the internal bunds are

Casuarina equisetifolia ( Sarve), Eucalyptus spp (Nilgiti), Tectona grandis (Teak), Thespasia populnea (Huvarsi), Abbigia lebbek (Bage), Leucena leucocephala (Subabul), Anona squamosa (Seetaphal)

In addition to the above , horticultural species should be planted in the field. some of the horticultural species that can be considered are: Mango -30 to 50 plants per hectare, Tamarind (grafted) -10 to 20 per hectare, Papaya -20 to 30 per hectare and Pomegranate – 10 to 15 per hectare.

Why should we plant so many trees in an agricultural field? Will it not affect the agricultural crops?

1. Let us not forget that as it is dry land, agriculture is a gamble.
2. Farmers completely lack security in the present system.
3. Trees provide security. Trees are not as vulnerable to the vagaries.
4. Trees should also be seen as means of accumulating Wealth for poor farmers insulating them against the local money lenders. Trees are liquid assets that can be disposed off in the local market.
5. Livestock is an important component in the farming system. Trees provide valuable fodder for livestock, especially the small ruminants such as sheep and goats which are normally kept by small and marginal farmers.
6. Trees do affect the field crops to some extent. But this loss will be more than compensated by the profits from the trees.
7. In a year of very bad rainfall with complete failure of field crops, the returns from the tree crops will be able to sustain the farmers preventing them from hunger and from failing into debt traps.
8. The design of the trees planting programme should be to harvest sun energy throughout the year even when there are no crops.
9. The increased vegetative cover also acts as wind break and helps to retain maximum moisture in soil.
10. The trees planted on the internal bunds and on the boundaries should be properly managed for getting maximum benefit.
11. The biodiversity on the farm helps to contain pests and diseases.

What are the management practices for trees in an agroforestry plot?

1. The trees in internal bunds should be pruned periodically at a height of about 5 ft and all the leaf biomass should be incorporated into the soil. This increases the soil organic content and also promotes soil humus content and soil microflora and fauna. The twigs obtained during pruning can be used as stackes for certain crops or can be used as fuel wood.
2. At a distance of half a metre from the tree line a trench of about 112 feet depth should be dug to cut surface roots of trees from spreading into the field.
3. Trees on the boundary should be allowed to grow straight by pruning the side branches only.

G.N.S. Reddy, BAIF Institute for Rural Development, #3, Sharada Nagara, TIPTUR – 672202 Karnataka.  INDIA.

This is part of the paper presented in the IFOAM-Asia Conference organized by University of Agricultural Sciences, Bangalore, India. More details can be found in the “Food Security in Harmony with Nature” Proceedings of IFOAM- Asia Conference, Ed. Dr. K. Shivashankar, pp186-189.