New Irrigation Scheduling Software combining ETo and soil water dynamics to improve the measurements of daily crop water use, Kc factors and the onset of crop water stress of a flood irrigated alfalfa crop Buss, P.; Stevens, S. and Dalton, M. Sentek Pty Ltd, Adelaide, Australia
Questions Can the combination of near continuous soil water data and daily ETo assist with the detection of the onset of crop water stress? Can this combination approach assist with refining crop coefficients which are used for field scale irrigation management?
Water Budget Method ETc - Effective Rainfall = Net Irrigation Requirement Daily Cumulative Net Irrigation Requirement http://www.cimis.water.ca.gov/cimis/infoirrschedule.jsp
Measurement of ETc and ETo Reference evapotranspiration (ETo) represents the rate of evapotranspiration of green grass under ideal conditions, 8 15 cm tall, with extensive vegetative cover completely shading the ground. evapotranspirometer http://www.adagio-eu.org/documents/meeting_jois/08_r_nolz_water_balance_lysimter.pdf
Standard to calculate ETo An FAO review in 1990 recommended the adoption of FAO 56 Penman Monteith equation as a new standard to calculate ETo. http://www.bom.gov.au/watl/eto/reference-evapotranspiration-report.pdf
Calculating Crop Evapotranspiration (ETc) ETo x Kc = ETc In order to relate ETo to crop water requirements (ETc), the specific crop coefficient (kc) must be determined. Reference evapotranspiration is a measure of evaporative demand, while the crop coefficient accounts for crop characteristics and management practices (e.g., frequency of soil wetness) Lazzara, Rana - www.meliaproject.eu/members/p35isa/cropcoeff.pdf
Kc Seasonal Development The crop coefficient (Kc) depends on the crop leaf area and its roughness, the stage of growth, the growing season and the prevailing weather conditions http://www.fao.org/docrep/x0490e/x0490e0a.htm
Accuracy of Kc values No limitations are placed on crop growth or Evapotranspiration from soil water and salinity stress, crop density, pests and diseases, weed infestation or low fertility. http://www.fao.org/docrep/x0490e/x0490e0b.htm Crop coefficient values reported in the literature can vary even significantly from the actual ones if growing conditions differ from those where the said coefficients were experimentally obtained (Tarantino and Onofrii, 1991) The use of Kc developed in other regions with respect to those where it is calibrated will not meet accurate crop water requirement and result in either increased production costs due to over-irrigation or reduced profits due to deficit irrigation. Lazzara, Rana - www.meliaproject.eu/members/p35isa/cropcoeff.pdf
Factors affecting Kc 1. Developing crop leaf area 2. Crop variety 3. Crop height 4. Length of crop growth stage 5. Planting density 6. Crop disease 7. Weed infestation 8. Crop pests 9. Stomata closure through excessive heat 10.Climate conditions (humid arid) 11.Soil characteristics determining evaporation 12.Soil water stress 13.Soil salinity 14.Soil fertility 15.Irrigation method 16.Irrigation frequency 17.Agronomic techniques 18.waterlogging The crop coefficient (Kc) values of the major Crops grown under Mediterranean climate Paola Lazzara, Gianfranco Rana CRA- Research Unit for Agricultural in Dry Environments, via C. Ulpiani, 5, 70125 Bari, Italy www.meliaproject.eu/members/p35isa/cropcoeff.pdf
Soil Water Dynamics as the Mirror of Crop Water Use? anttisbiology.blogspot.com
Relationship between ETo and Daily Soil Water Change Irrigation Daily crop water use matching ET ETo Daily Steps of Soil Water Extraction by the crop
Similar ET Different Crop Water Use Crop under no water stress Crop under water stress
Comparison between Lysimeter and Soil Water Content data http://www.adagio-eu.org/documents/meeting_jois/08_r_nolz_water_balance_lysimter.pdf
Trial Location Wandella, Victoria, Australia
Parameter Crop: Alfalfa Production: Hay Variety: Pioneer L56 Soil: Clay Loam Irrigation: Flood Water delivery: pre-ordering of irrigation water 4 7 days ahead!! http://www.seq.irrigationfutures.org.au/imagesdb/news/cropcoefficients.pdf
Standard Default Calibration Equation SF 0.608695652 14.73 Vol % USDA_ARS Beltsville Research Center
Rain
Rain ETo by FAO56 PM
ETc by FAO56 ETo by FAO56 PM Rain
ETc by FAO56 ETo by FAO56 PM Rain
ETc by FAO56 ETo by FAO56 PM Rain
ETo by FAO56 PM Total Daily Negative Change of Soil Water
ETo by FAO56 PM Total Hourly Negative Change of Soil Water
ETo by FAO56 PM Total Hourly Negative Change of Soil Water
ETo by FAO56 PM Total Hourly Negative Change of Soil Water
ETC FAO56 ETo by FAO56 PM
Volumetric Day Time Negative Change VDTNC = Corrected Daily Crop Water Use DayTimeNegChange ((DayTimeHours / NightTimeHours) * NightTimeNegChange)
Definitions Algorithms Daily calculated Value Average Total
Daily Soil Water Change ETc by FAO56 ETo by FAO56 PM
Bureau of Meteorology, FAO Algorithms
Definition of the Evapotranspiration ETo Stress Index (ETSI) Daily Soil Water Change : ETSI = Inverse of the Kc Factor Day 1 : = 10 5 2 Day 2 : 8 4 = 2 Day 3 10 : 32 3.33 5 =
ETSI ETSI Daily Soil Water Change ETo by FAO56 PM
ETo by FAO56 PM Rain
ETSI Daily Soil Water Change ETo by FAO56 PM
Rain ETo by FAO56 PM
ETo by FAO56 PM Rain
Summary Closing the Gap ETSI, the ratio of daily ETo and daily soil water change (corrected VDTNC) can serve as an important indicator of the onset of crop water stress. Daily calibrated soil water change and its relation to ETo are providing new insights into real crop water use under numerous and ever changing influencing factors. Relating climatic and soil water change data will assist in the development of more accurate Kc factors incorporating: variety and environment specific crop physiology development regional changing climatic conditions abiotic and biotic crop stress conditions soil and agronomic management conditions
It is time to close the gap......in combining the weather and soil measurement based approaches to calculate variables of the The Soil-Water-Plant- Atmosphere-Continuum (Hillel, D. 1998)