Khardi j Mukuyu
Consider it an old irrigators’ tale, if you want, but the idea that irrigation must continue up to and beyond crop maturity to assure full yield could result in the single largest waste of water during the season. Such undiscriminating irrigation fills the soil capacity. Yet, the crop may only need half of that moisture to reach maturity.
During the season, the best recommendation is to keep the available soil water level above the 50% depletion level, explain Tony Ingram, Chuck Burr, and William Kranz of the University of Nebraska.
“To do this, we recommend irrigating as the soil water level approaches 35% depletion,” Ingram says. “This allows a few days for the irrigation to be completed before the crop experiences any stress. As you near the end of the season, you can push the threshold to 60% depletion.”
adjust watering rates to soil type
The capacity of a soil varies with its texture, and that needs to be considered when determining how much soil water is available, the advisers explain.
“For example, a loamy sand will hold about 1.1 inches of water per foot or 4.4 inches in the top 4 feet. A silt loam soil can hold 2.2 inches per foot or 8.8 inches in the top 4 feet,” Burr points out.
“If the silt loam is at field capacity and you draw down the available soil water to 40% (60% depletion), you would have about 5.3 inches of useable water in the top 4 feet of soil.”
Corn at the beginning dent stage needs 5 inches of water to reach maturity. With silt loam, the example field would have enough water to reach maturity and have an estimated 0.3 inch to spare if the corn is beginning to dent now (5.3-5.0 =0.3 inch).
The loamy sand, at field capacity, would have 2.6 inches available above the 40% (60% depletion) level. This field would need an additional 2.4 inches of water to reach maturity.
“The time needed for corn to mature is dependent on growing-degree days,” Kranz says. “If corn needs 5 inches of water to reach maturity and you receive some hot, windy days in late August, the corn will still use 5 inches. It will just finish up a few days quicker.”
bean needs differ
Soybean maturity is dependent on day length. Since beans may use more or less water than the averages listed in the table and because it may be difficult to determine the actual growth stage, it’s important to monitor soil water until maturity.
“This is where tools like an ETgauge and soil water sensors come into play,” Ingram says. “An ETgauge will give you potential crop water use, and sensors give an idea of how much water is stored in the soil profile. Then, you can determine how much water is needed to finish out the year.
African Agriculture
The vast majority of the continent’s populations living in the rural areas also lives in extreme poverty.
The enhancement of sustainable agricultural and rural development is therefore fundamental to the attainment of the Millennium Development Goals (MDGs) in Africa, particularly the eradication of hunger and poverty.
Africa is endowed with a wide diversity of agro-ecological zones. These zones range from the heavy rain-forest vegetation with bi-annual rainfall to relatively sparse, dry and arid vegetation with low uni-modal rainfall. This diversity is a tremendous asset, but it also poses a substantial challenge for African agricultural development.
On the one hand, it creates a vast potential with respect to the mix of agricultural commodities and products which can be produced and marketed in domestic and external markets.
On the other hand, the diversity implies that there are no universal solutions to agricultural development problems across the continent.
Consequently, programming and implementing interventions in the sector must be tailored to the particular conditions of the different agro-ecological zones and to prevailing socio-economic conditions of rural households within individual countries.
On the one hand, it creates a vast potential with respect to the mix of agricultural commodities and products which can be produced and marketed in domestic and external markets.
On the other hand, the diversity implies that there are no universal solutions to agricultural development problems across the continent.
Consequently, programming and implementing interventions in the sector must be tailored to the particular conditions of the different agro-ecological zones and to prevailing socio-economic conditions of rural households within individual countries.
Over the last three decades, increases in agricultural output in Africa have come largely through extending rain-fed crop cultivation, particularly food crops, on to more and more marginal soils and/or by reducing traditional fallow periods in cropping cycles.
Under conditions of rapid human population growth, rural households have been forced to adopt agricultural practices that guarantee their survival.
Unfortunately, raising the productivity of crop enterprises through intensification per unit of land cultivated -- i.e., through increasing crop yields per hectare - has not been adequately promoted as an important household food security strategy.
Apart from commercial agriculture which covers a relatively small share of crop production, the use of agricultural inputs - that is, improved seeds, inorganic fertilizers, insecticides and pesticides -- has been much lower in Africa than in other parts of the developing world. Inorganic fertilizer use is often less than ten kilograms of nutrients per hectare.
Use of agro-chemicals and/or integrated pest management techniques to deal with plant diseases and pests is still largely confined to export crops.
Under conditions of rapid human population growth, rural households have been forced to adopt agricultural practices that guarantee their survival.
Unfortunately, raising the productivity of crop enterprises through intensification per unit of land cultivated -- i.e., through increasing crop yields per hectare - has not been adequately promoted as an important household food security strategy.
Apart from commercial agriculture which covers a relatively small share of crop production, the use of agricultural inputs - that is, improved seeds, inorganic fertilizers, insecticides and pesticides -- has been much lower in Africa than in other parts of the developing world. Inorganic fertilizer use is often less than ten kilograms of nutrients per hectare.
Use of agro-chemicals and/or integrated pest management techniques to deal with plant diseases and pests is still largely confined to export crops.
Continuous expansion of crop cultivation has been done at the expense of the natural resources. One consequence has been the accelerated destruction of forest resources by land clearing and over-exploitation for fuel-wood and other household uses.
Another, more subtle effect, has been the deterioration of livestock farming as larger and larger areas formerly allocated for dry season grazing are put under the hoe and plough.
Over-exploitation of fisheries resources has been a serious problem where common resources are exploited for private gain.
Lack of adequate regulatory provisions and, where present, their ineffective enforcement have resulted in catch declines and have severely challenged prospects for adequate stock replenishment in the future.
Another, more subtle effect, has been the deterioration of livestock farming as larger and larger areas formerly allocated for dry season grazing are put under the hoe and plough.
Over-exploitation of fisheries resources has been a serious problem where common resources are exploited for private gain.
Lack of adequate regulatory provisions and, where present, their ineffective enforcement have resulted in catch declines and have severely challenged prospects for adequate stock replenishment in the future.
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