Nutrition of Horticultural Crops Measurements for Irrigation. Lincoln Zotarelli Horticultural Sciences Department University of Florida Spring 2015

Transcription

1 Nutrition of Horticultural Crops Measurements for Irrigation Lincoln Zotarelli Horticultural Sciences Department University of Florida Spring 2015

2 Principles of plant nutrition Principle 1. Plants take up 13 essential elements from the soil in the form of charged particles Principle 2. The most important element in plant nutrition is the one that is limiting growth Principle 3. No correlation exists between PRESENCE in the soil and AVAILABILITY for uptake Principle 4. Relative amounts of nutrients are as important as absolute quantities Principle 5. Water plays a central role in fertilizer issues, as a solvent and as a nutrient carrier within and below the root zone

3 Irrigation It should be considered: Soil properties Atmospheric conditions Crop needs Characteristics of the irrigation system

4 Effect of soil texture and soil tension on soil water availability Kramer and Boyer (1995)

5 Florida s sandy soils Low water holding capacity: Little water is stored in the root zone.

6 Soil moisture estimation by feel ftp://ftp-fc.sc.egov.usda.gov/mt/www/technical/soilmoist.pdf

7 Effect of soil texture and soil tension on soil water availability

8 Actual soil moisture on sandy soils Saturation Field Capacity Wilting Point VWC > 30% VWC > 0.3 in 3 /in 3-1 cbar MPa VWC approx. 12% VWC > 0.12 in 3 /in 3-10 cbar MPa VWC approx. 6% VWC > 0.06 in 3 /in cbar -1.5 MPa

9 Soil water tension measuring tools Tensiometers. Changes in moisture in a porous cup in equilibrium with the soil can be expressed in changes in air pressure inside the cup.

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11 Time Domain Reflectometry (TDR) The soil dielectric constant is proportional to soil moisture Practical example: Strawberry More water is applied than what plants use because of leaching, evaporation, inefficient application, and an inadequate ability to assess water requirements on a daily basis. Methodology: Every other week (5 inches deep)

12 soil volumetric water content in the soil profile /05 07/12 07/19 07/26 08/02 08/09 08/16 08/23 08/30 09/06 09/13 09/20 09/27 Soil volumetric water content (m 3 m -3 ) cm 15 cm 30 cm 45 cm 60 cm precipitation (mm) Rainfall (mm)

13 Strawberry early and total yield Season. Irrigation Programs Volume Frequency Early Yield Total Yield gal/100 ft/week (cycles/day) (ton/acre) (ton/acre) Significance (P<0.05) NS NS efficient water use will help strawberry growers to maximize crop production and water savings.

14 It is difficult to visualize water movement in the soil

15 8 x 300L/100m/hr Water front: 60 cm Lakeland fine sand: -<10% WHC -<1% OM

16 T0-1h T0-2h T0-4h T0-8h

17 Irrigation It should be considered: Soil properties Evapotranspiration and crop needs Characteristics of the irrigation system

18 Evapotranspiration Water transpired by plants and the evaporation from soil surface combined. Occur simultaneously and there is no easy way of distinguishing between the two processes. Normally expressed in millimetres (mm) per unit time. ET rates which range from < 0.10 during the winter to over 0.18 inches/day during the summer.

19 8 Florida Rainfall & ET (in.) Jan Jun May Apr Mar Feb Jul Dec Nov Oct Sep Aug Monthly Potential ET Monthly Rainfall

20 Crop evapotranspiration under standard conditions (ETc) The evaporating demand from crops that are grown in large fields Under optimum soil and water Excellent management and environmental conditions And achieve full production under the given climatic conditions.

21 US Weather Bureau Pan Evaporation Method The evaporation rate from pans filled with water is easily obtained. In the absence of rain, the amount of water evaporated during a period (mm/day) corresponds with the decrease in water depth in that period. Pans provide a measurement of the integrated effect of radiation, wind, temperature and humidity on the evaporation from an open water surface.

22 Class A pan Is circular, cm in diameter and 25 cm deep. Made of galvanized iron (22 gauge) or Monel metal (0.8 mm). Is mounted on a wooden open frame platform which is 15 cm above ground level.

23 Class A pan Pans should be protected by fences to keep animals from drinking. It must be located in the center of a 20 x 20 m 2 actively growing grassy area.

24 Ep from Class A evaporation pan

25 How reference ET is calculated ET o = reference evapotranspiration rate (mm d- 1 ), T = mean air temperature ( o C), u 2 = wind speed (m s- 1 ) at 2 m above the ground. e s o = mean saturated vapor pressure (kpa) computed as the mean e o at the daily minimum and maximum air temperature ( o C), e a = mean daily ambient vapor pressure (kpa) and Δ= slope of the saturated vapor pressure curve [ δe o / δt, where e o = saturated vapor pressure (kpa) and R n = net radiation flux (MJ m -2 d -1 ), G = sensible heat flux into the soil (MJ m -2 d -1 ), γ = psychrometric constant(kpa o C -1 ), and E a = vapor transport of flux (mm d- 1 ).

26 inch/h Evapotranspiration during the day Evapotranspiration (inches) inch/h ET0 (mm h-1) ET0 cum(mm h-1) inch/day inch/day :00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 Time (h) MJ m-2 h-1 Temperature (C) :00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time (h) m/s Solar Radiation RS (MJ m-2 h-1) Temperature ( C) Min Temp ( C) Max Temp ( C) 10 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time (h) Wind speed Aver Wind Speed (m s-1) 1 0 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time (h)

27 FAWN weather stations

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29 Crop coefficient: Kc Crop water use (ETc) is related to ETo by a crop coefficient (Kc) which is the ratio of ETc to the reference value Eto Crop water requirement = Reference evapotranspiration x Crop coefficient

30 Crop Evapotranspiration ET provides reference measure of water use based on plant water demand Scalable for specific crop, growth stage, climate, and season of year ET c = ET o * K c

31 Vegetable Production Handbook for Florida: Chapter 3: Principles and Practices of Irrigation Management for Vegetables. Table 7 pg 25

32 Crop water requirements and irrigation system water requirements Crop water requirements: water needs for evapotranspiration (ET) and plant growth, and depend on crop development and climatic factors. Irrigation requirements: determined by crop water requirements, but also by the characteristics of the irrigation system, management practices and the soil characteristics.

33 Sample calculation: Overhead irrigation We grow potato with a center-pivot Our pan indicated= 24-hr ETo of 0.32 inch The Kc of potato = 0.70 We can calculate ETc as: ETc = Kc x Ep ETc = 0.70 x 0.32 = inch We will apply x 27,150 = 6082 gallons/acre

34 We grow peppers on 6-ft centers Our pan indicates 0.20 in 24-hr Ep We need to convert vertical amounts of water into gallons/100ft. How? Sample calculation: Drip-irrigated crops

35 Example: PEPPER LBF for 6-foot centers: 43,560 ft 2 /6 = 7,260 LBF /acre Lateral water movement from the drip line is about 8 inches on each side The total wetted width in the bed is then 16 inches or 1.33 feet The wetted area of the field: 1.33 ft every 6 ft or 22% of the field The total irrigated area is then only (7,260 ft)*(1.33 ft)= 9,583 sq ft 1 acre inch = 27,150 gallons of water So, 0.1 inch of water applied over the entire field corresponds to 2,715 gallons We only wet 22% of the field Hence, 0.1 inch applied via drip corresponds to 597 gallons

36 Sample calculation: Drip-irrigated crops We need to convert vertical amounts of water into gallons/100ft. How? ETc= Kc x ETo x Fraction of wetted acre-inch ETc = 1.25 x 0.20 x 27,150 x 0.22 = 1,493 gallons/acre = 1,493/72.60 = 21 gal/100ft If overhead: ETc = 1.25 x 0.20 x 27,150 = 6,687 gallons/acre

37 References Food and Agriculture Org. (FAO) Pub.56 VPH Chapter 8, pp BMP manual, BMPs 36 to 48, pp. 136 FAWN