Crop Water Use and Growth Stages
Quick Facts...
- Water stress during critical growth periods reduces yield and quality of Crops.
- Crop water use at critical growth stages can be used in irrigation scheduling to avoid stressing Crops.
- Crop water use is weather dependent as well as soil, water and plant dependent.
- Periodically check soil water at different depths within the root zone and at different growth stages to avoid stressing the crop during critical growth stages.
Corn at full cover has a maximum water use rate,
Effect of Soil Water on ET
Crop water use also is influenced by the actual soil water content. As soil dries, it becomes more difficult for a plant to extract water from the soil.After rain or irrigation, actual ET is higher than when the soil or crop surface is dry. When the soil or crop surface is wet, the evaporation portion of ET increases significantly, resulting in a higher actual ET, especially early in the growing season.
Each soil type can hold different amounts of water while acting as a water reservoir for plants.
Managing Irrigation According to Growth Stages
Crops are different in their response to water stress at a given growth stage. Crops summarized according to their sensitivity to water stress at various growth stages (Tables 1 and 2) reveal the importance of these stages in making the irrigation decision.Crops that are in the sensitive stage of growth should be irrigated at a lower soil water depletion level than those that can withstand water stress. If a crop is last in the irrigation rotation and is at a sensitive stage of growth, the recommended strategy may be to apply partial or lighter irrigations in order to reach the end of the field before the sensitive crop is subjected to water stress.
Such a strategy can be used with sprinkler systems, but this may lead to unfavorable soil moisture conditions at the lower soil depths. When soil is repeatedly watered to only shallow depths, the lower soil depths tend to develop a soil moisture deficit that exceeds the allowable soil moisture depletion level at that particular growth stage. Therefore, quick soil moisture assessment at various soil depths to determine the actual water use is essential in irrigation scheduling as related to growth stages.
Crop appearance is considered one of many field indicators that can be used in irrigation scheduling. A crop suffering from water stress tends to have a darker color and exhibits curling or wilting. This is a physiological defense mechanism of the crop that is evident on hot, windy afternoons when the crop cannot transpire fast enough, even if the water is readily available in the soil. If the crop does not recover from these symptoms overnight, the crop is suffering from water stress. Any changes in crop appearance due to water stress may mean a reduction in yield. However, using this indicator alone for irrigation scheduling is not recommended if a maximum yield is desired.
The main advantage of this indicator is to provide direct and visual feedback from the crop.
Different Crops have different water requirements and respond differently to water stress. Crop sensitivity to water stress varies from one growth stage to another.
This information can be used in an irrigation scheduling scheme by using the appropriate MAD for each growth stage to trigger irrigation.
| Table 1: Critical growth stages for major crops1. | |||
| Crop | Critical period | Symptoms of water stress | Other considerations |
|---|---|---|---|
| Alfalfa | Early spring and immediately after cuttings | Darkening color, then wilting | Adequate water is needed between cuttings |
| Corn | Tasseling, silk stage until grain is fully formed | Curling of leaves by mid-morning, darkening color | Needs adequate water from germination to dent stage for maximum production |
| Sorghum | Boot, bloom and dough stages | Curling of leaves by mid-morning, darkening color | Yields are reduced if water is short at bloom during seed development |
| Sugar beets | Post-thinning | Leaves wilting during heat of the day | Excessive full irrigation lowers sugar content |
| Beans | Bloom and fruit set | Wilting | Yields are reduced if water short at bloom or fruit set stages |
| Small grain | Boot and bloom stages | Dull green color, then firing of lower leaves | Last irrigation at milk stage |
| Potatoes | Tuber formation to harvest | Wilting during heat of the day | Water stress during critical period may cause cracking of tubers |
| Onions | Bulb formation | Wilting | Keep soil wet during bulb formation and dry near harvest |
| Tomatoes | After fruit set | Wilting | Wilt and leaf rolling can be caused by disease |
| Cool season grass | Early spring, early fall | Dull green color, then wilting | Critical period for seed production is boot to head formation |
| Fruit trees | Any point during growing season | Dulling of leaf color and drooping of growing points | Stone fruits are sensitive to water stress during last two weeks prior to harvest |
| 1Taken from Colorado Irrigation Guide, Natural Resources Conservation Service. | |||
| Table 2: Management allowable depletion (MAD) at the root zone of selected Crops at different growth stages. | |||
| Crop | Growth stages | MAD(%) in root zone | Effect of water stress |
|---|---|---|---|
| Alfalfa | Emergence-lst cut lst cut-2nd cut 2nd cut-3rd cut 3rd cut-4th cut | 65 50 40 60-70 | Yield reduction |
| Pinto beans | Emergence-aux. budding Flower-bud filling Bud filling-maturity | 60-70 55 60-70 | Yield reduction |
| Potatoes | Early vegetative period Tuber bulking period Ripening period | 40-60 30-40 65 | Many jumbo and lower yield |
| Corn | Emergence-12 leaf 12 leaf-dough Dough-maturity | 60-70 50 60-70 | Yield reduction of 11.5 bu/A-in water deficit |
| Small grains | Emergence-first node First node-flowering Milk ripe-maturity | 65-70 40-60 50-70 | Yield reduction of 6-8 bu/A-in of water deficit |
| Soybeans | Before flowing First flower-first pod First pod-maturity | 65-70 60-65 60-70 | Yield reduction |
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.