What type Irrigation do you use? What do you know of irrigation schedule?
The choice of irrigation method has to consider the site conditions, the irrigation water quality, crops grown, labour availability and cost. The choice of irrigation system will depend upon the importance of each parameter. In horticultural irrigation with wastewater there are also the concerns specific to wastewater, such as the opportunity for foliar injury, pathogens that may affect plants, and pathogens that may affect humans. These latter factors may be of greatest importance.
The crop characteristic is very important in terms of establishment and tolerance of waterlogged or saline conditions. Establishment is of critical concern to annual crops. Many horticultural crops are small-seeded, such as onions and tomatoes, and are difficult to establish under many environmental conditions. In other circumstances, establishment is a less critical concern, for instance where transplants are used or the crop is perennial, such as fruit crops. Other considerations are the crop tolerance to water stress or waterlogging. For example, lettuce crops are extremely sensitive to water stress, and many horticultural crops, for example tomatoes, are susceptible to root phytophthora, and hence waterlogging should be avoided.
The method of irrigation also often affects crop quality in terms of marketability. Tomatoes are prone to low solids content when grown with drip irrigation compared with furrow irrigation. Onion crops are at risk of downy mildew, which can be exacerbated with sprinkler irrigation, as the foliage is frequently wetted.
There can be no definitive answer as to which type of irrigation system is most suitable for vegetable irrigation as there are so many variables. It is possible to broadly rank the three main irrigation systems against the key criteria related to irrigation for vegetables. The main areas of assessment for irrigation systems are against water quality parameters, likelihood of minimising environmental problems, and appropriateness for efficient and economic crop production.
For good crop production there needs to be an appropriate match between the soil physical properties controlling water movement and retention and the irrigation system. This affects the amount of water that can be stored in the soil after an irrigation, the depth of wetting, wetting pattern and aeration status.
Control of leaf and root diseases, especially fungal diseases, is affected by the irrigation system, crop and soil type. In general, sprinkler systems increase risk of leaf fungal and bacterial infections, whereas furrow irrigation increases the risks of root rots due to waterlogging. Effective weed management is important. With vegetable production, minimal competition is a high priority, and the weed control that can be achieved by different systems is important. Drip systems offer the best potential, as they wet little of the soil. Buried drip systems are even better, as they can be managed so as not to wet the soil surface. Drip in combination with plastic polythene mulch or the use of transplants can be particularly effective for controlling weeds.
It is important to note that certain pre-emergent vegetable herbicides require ‘fixing’ into the soil with 10-15 mm of overhead irrigation to be most effective. This could preclude the use of drip if alternative herbicides cannot be used.
There are a few irrigation methods in Agriculture but only Sprinkler and Drip irrigation will be discussed as we all know that they are the most common ones.
Sprinkler irrigation
Sprinkler irrigation is commonly used in horticultural irrigation. There is a large range of equipment which allows the application rate to be matched to the soil infiltration rate. This is advantageous in that irrigation of sandy soils can occur where furrow irrigation would be unsuitable. Sprinkler irrigation is also suitable for irrigating undulating or steep terrain, although surface run-off can then become a problem. Sprinkler irrigation has the advantage of providing good germination and crop establishment, since small amounts of water can be applied frequently and uniformly, and with many systems the labour requirement for this is low. Sprinkler irrigation also has other agronomic advantages such as control of wind erosion and incorporation or activation of herbicides.
Drip irrigation
Drip irrigation is likely to be the most suitable form of irrigation for use with effluent water for two important reasons: it limits contact of the effluent water with plants and workers in the fields and it provides the best control over the irrigation water if well managed. Drip irrigation requires high levels of management skill and financial investment and thus is best considered when the chosen crops have already been successfully grown with furrow irrigation, and agronomy, marketing and financial skills are already well developed. Drip irrigation is particularly difficult to manage. In some cases, yields under drip-irrigated crops are the same as or even less than comparable furrow irrigated crops. This can be due to poor system design or poor system management. It will necessarily take a few seasons of experience to learn the best management for any new irrigation system.
The Advantages of drip irrigation includes:
Improved plant production, Increased irrigation efficiency, Improved chemical application, Reduced weed growth, Reduced disease, Irrigation of sloping ground and low water-holding capacity soils
Drip irrigation allows for improved irrigation efficiency by reducing evaporation from the soil surface, since only a small area of the paddock surface is wetted (or none at all if the drip is buried). It also by the elimination of irrigation run-off. Rainfall run-off should be much reduced as it can be stored in the dry soil between the drip lines. Drip irrigation allows for improved irrigation efficiency by eliminating the tendency to over-irrigate the top end of the paddock to apply sufficient water at the bottom end, as occurs with furrow.
The Disadvantages of drip irrigation include:
Restricted root zone, High maintenance requirements, Restricted tillage, Soil structural decline, High cost, Difficult crop germination and Salt accumulation near the root zone.
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