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Frequency

Frequency. Pivots. Adapted to High Frequency Once a day or less. Reasons for long intervals. High frequency increases evaporation losses For certain soils longer intervals allow more surface drying and cracking – increases infiltration. The maximum interval.

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Frequency

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  1. Frequency

  2. Pivots • Adapted to High Frequency • Once a day or less

  3. Reasons for long intervals • High frequency increases evaporation losses • For certain soils longer intervals allow more surface drying and cracking – increases infiltration

  4. The maximum interval • Is when one of two conditions are met • Plant begins to suffer stress between irrigations • Applications become too large to infiltrate in one pass and runoff occurs

  5. Reasons for not using long intervals • Increases potential for runoff • Beneficial to use the root zone as a potential “rainfall reservoir” • “Safety buffer” in case of breakdown

  6. Rule of thumbs • 2.5 days for sandier soils • 3.5 to 4.5 days for medium textured soils

  7. Always use fraction of a day • .4 to .6 fraction of a day • Minimizes daytime/nighttime impacts • Improves overall uniformity of infiltration and ETc

  8. Example of multiple passes

  9. Partial circles • If a part-circle machine is operated “dry” on the reverse leg, then the fraction of operating time, t, should be adjusted as: Speedwet = the speed of the end of the lateral during application of water, ft/minute Speeddry = the speed of the end of the lateral during the dry return, ft/minute

  10. Deficit Irrigation • an overall strategy in effectively stretching a limited water supply, or, (2) for reducing the costs of irrigation where an adequate water supply exists. • So soil moisture deficit is allowed to occur and the crop undergoes some degree of stress during the season.

  11. The primary objective is to increase the Water Use Efficiency (WUE) by scheduling the timing of irrigations during growth stages having the greatest impact on yield. • The WUE is the yield obtained per unit of water consumed (more crop per drop) • Hopefully , the reduction in irrigation costs from the deficit irrigation are greater than the reductions in revenue associated with any reduction in yield.

  12. Applied water Losses Transpiration

  13. Strategies • Soil Surface Modification • Residue Management

  14. Soil Surface Modification

  15. Field Residue

  16. Plant Population/Row Configuration Modification

  17. Crop Rotation/Management Modification

  18. Water Supply Management • restricted Supply- Reduced Irrigation System Capacity

  19. Peak crop water use management with root zone soil moisture maintenance. Insufficient Supply- Reduced Water Allocation

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