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Experts pitch for 10 strategies to help farmers in arid areas cope

By Catherine Ngamau and Clifford Obiero
Cover crops help to maintain soil moisture.

As climate change continues to bite, more farmers are realising they need to adopt certain measures if they are to continue enjoying yields from their farms. Farmers in semi-arid and arid areas are particularly vulnerable in these harsh times.

Today, we will give them coping strategies to use minimal water, maintain soil moisture and fertility and increase yields. Arid and Semi-Arid regions are dominated by alkaline (pH 7 and above) and salt-affected soils.

In regions where precipitation is less than potential evapotranspiration, the cations released by mineral weathering accumulate because there is not enough rain to leach them away. Minimal leaching in dry environments means minimal soil acidification.

Problems of alkaline soils include

Nutrient deficiencies: Availability of most nutrient elements is markedly influenced by soil pH. Micronutrients (Zn, Cu, Fe, B and Mn) are readily available in acid soils but much less soluble at pH levels above 7.

Therefore, in alkaline soils plant growth is usually limited by deficiencies of micro nutrients especially Fe. Foliar feed application of micro nutrients is thus recommended.

The macronutrient P is also deficient in alkaline soils because it is tied up in insoluble Ca and Mg phosphate minerals. Combining ammonium-forming N fertiliser with P fertiliser often enhances the uptake of P because of the acidifying effect of ammonium uptake by roots.

Molybdenum toxicity: Mo availability is high under alkaline conditions, so high that in some areas its toxicity is a problem to plants and grazing animals.

Salt-affected soils

Salt-affected soils adversely affect plants because of the total concentration of salts (salinity) in the soil solution and specific ions, especially sodium (sodicity).

Reclamation of Saline Soils

Reclamation of saline soils is largely dependent on the provision of effective drainage and the availability of good-quality irrigation water so that salts can be leached from the soil. In areas where irrigation water is not available, the leaching of salts is not practical. In such areas, deep-rooted vegetation may be used to lower the water table and reduce the upward movement of salts. If the natural soil drainage is inadequate to accommodate the leaching water, an artificial drainage network must be installed.

Reclamation of Saline-Sodic and Sodic Soils

For saline-sodic and sodic soils, attention must first be given to reducing the level of exchangeable Na+ ions and then to the problem of excess soluble salts.

Removing Na+ ions from the exchange complex is most effectively accomplished by replacing them with either Ca2+ or H+ ion. Providing Ca2+ in the form of gypsum (CaSO4·2H2O) is the most practical way to bring about this exchange.

The resulting soluble salt Na2SO4 can be easily leached from the soil.

 Limited Soil water supply

Many of these soils are fertile and if irrigated, can be among the most productive soils in the world.

Water conservation strategies

Kenya’s agriculture is mainly rain-fed. With rainfall in Kenya exhibiting a complex spatial and temporal variability a situation which has been made worse by climate variability and climate change leaving the farmers at the mercy of an unpredictable rainfall regime. This situation is worse in arid and semi-arid parts of our country which make up to about 85 per cent of our land mass.

The following strategies can be employed by farmers in the dryland areas:

1)   Drip Irrigation

Drip irrigation systems deliver water directly to a plant’s roots, reducing the evaporation that happens with spray watering systems. Properly installed drip irrigation can save up to 80 per cent more water than conventional irrigation, and can even contribute to increased crop yields.

2)  Rainwater and storm water harvesting

Rainwater harvesting using rock, large trees and roof catchments. Storm water harvesting from paved surfaces and during excess rainfall periods like El Niño can be harvested and stored in; hand dugs wells, used for artificial groundwater recharge, polythene lined earth dams and subsurface dams. 

3)   Irrigation Scheduling

Smart water management is not just about how water is delivered but also when, how often, and how much. To avoid under- or overwatering their crops, farmers should carefully monitor the weather forecast, as well as soil and plant moisture, and adapt their irrigation schedule to the current conditions. This involves knowing the crop water requirements and monitoring the soil moisture conditions by physical inspection or use of tensiometers.

4)  Drought-Tolerant Crops

This is the selection and planting of crop cultivars that are native to arid regions and are naturally drought-tolerant.

5)   Dry Farming

This is relying on soil moisture to produce crops during the dry season. This involves special tilling practices like zero tillage and careful attention to microclimates (the climate of a very small or restricted area, especially when this differs from the climate of the surrounding area).

Dry farming enhances flavours, but produces lower yields than irrigated crops.

6)   Rotational Grazing

Rotational grazing is a process in which livestock are moved between fields to help promote pasture regrowth. Good grazing management increases the fields’ water absorption and decreases water runoff, making pastures more drought-resistant. Increased soil organic matter and better forage cover are also water-saving benefits of rotational grazing.

7)  Compost and Mulch

Compost, or decomposed organic matter used as fertiliser, has been found to improve soil structure, increasing its water-holding capacity.

Mulch is a material spread on top of the soil to conserve moisture. Mulch made from organic materials such as straw or wood chips will break down into compost, further increasing the soil’s ability to retain water. Farmers may also use black plastic mulch as a soil cover to suppress weeds and reduce evaporation.

8)   Cover Crops

These are crops planted to protect soil that would otherwise go bare. They reduce weeds, increase soil fertility and organic matter, and help prevent erosion and compaction. This allows water to more easily penetrate the soil and improves its water-holding capacity. Examples of these are perennial grass and clover.   

9)   Conservation Tillage

Conservation tillage uses specialised plows or other implements that partially till the soil but leave at least 30 per cent of vegetative crop residue on the surface. Like the use of cover crops, such practices help increase water absorption and reduce evaporation, erosion, and compaction.

10)  Organic farming

This is farming using organic fertilisers and pesticides as compared to conventional farming, which use inorganic fertilisers and pesticides. In addition to keeping many of the more toxic pesticides out of our waterways, organic methods help retain soil moisture.

Healthy soil that is rich in organic matter and microbial life serves as a sponge that delivers moisture to plants. Field trials have shown that organic fields can recharge groundwater supplies up to 20 per cent.

 [Dr Catherine Ngamau and Dr Clifford Obiero are lectures in the College of Agriculture and Natural Resources Jomo Kenyatta University of Agriculture and Technology]

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