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Scheduling irrigations for lettuce using climate data

Scheduling irrigations for lettuce using climate data. Ted Sammis. The Water Budget Method. The lelttuce root zone is a reservoir Water is added by irrigation or rainfall. Water is removed by evapotranspiration.

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Scheduling irrigations for lettuce using climate data

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  1. Scheduling irrigations for lettuce using climate data Ted Sammis

  2. The Water Budget Method • The lelttuce root zone is a reservoir • Water is added by irrigation or rainfall. • Water is removed by evapotranspiration. • Added water can be lost by deep percolation if the amount exceeds the field capacity of the soil.

  3. Management Allowed Depletion • Management Allowed Depletion Is the percent of water that can be removed before soil moisture stress limits growth. • (For lettuce MAD is % 30.)

  4. Evapotranspiration • Evapotranspiration is determined from climate data to calculate potential Evapotranspiration (water used by grass) and a scaling coefficient or crop coefficient for lettuce • The crop coefficient depends development of the crop or the land area covered by the crop. The crop coefficient changes throughout the growing season increasing to a maximum at maximum leaf cover.

  5. Calculation of Evapotranspiration • Potential Et= 0.3 inches / day • Et= K*PET • K= 0.8 • Et= 0.8* 0.3 = .24 inch/day

  6. Calculated when to irrigate • Readily available water (RAW) = available water (AW) * management allowed depletion (MAD) • Example: • Aw = 2 inches/ft * 1.5ft root zone • Mad = 30% • RAW= 2 inches/ft*1ft*0.3 = 0.9 inches

  7. Irrigation Interval • Irrigation interval = RAW / Et / day • Irrigation interval = 0.9 inches / 0.24 inches /day = 4 days • Irrigation interval changes with changes in the Et or soil type. • Et changes with cover of lettuce and weather.

  8. Source of Potential Evapotranspiration • New Mexico Climate Center Homepage • http://weather.nmsu.edu

  9. Temperature sensor and radiation shield

  10. The Water Balance Spread Sheet • Inputs • Climate data, paste into spread sheet • Soil water holding capacity inch/ft • Irrigation amount applied at each irrigation. • Output – Date to irrigate on

  11. Conclusion • The water balance-check book method can be used to schedule irrigations for lettuce. • The water use of lettuce can be calculated from climate data, and this is all that is needed to apply the correct amount of water at the correct time • The check book method can also determine the decrease in yield and amount of water stress when time between irrigation is to long.

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