Fieldclimate User Manual

1 von 8 13.11.2009 12:42 Fieldclimate User Manual Inhaltsverzeichnis: Getting Started With FieldClimate.Com Irrigation Management Evapotranspiration ETzero Penman Monteith ET pan Soil Moisture Measurement Tensiometer Watermark Sensor Enviroscan Echo Probe Soil Water Balance Irimet Lite 1 Getting Started With FieldClimate.Com Fieldclimate User Manual 2 Irigation Managment The steady growing demand of food is leading to an increase in irrigated landscape and with this to a dramatic increase in agricultural water use. Rational irrigation management based on soil water measurement or evapotranspiration data can increase the effect of the water used and with this reduce the amount of water needed for agriculture. FieldClimate.com is offering a wide range of tools to improve our knowledge and management praxis in irrigation. Table of Content: Evapotranspiration ETzero Penman Monteith ET pan Soil Moisture Measurement Tensiometer Watermark Sensor Enviroscan Echo Probe Soil Water Balance Irimet Lite 2.1 Evapotranspiration The term Evapotranspiration describes the water loss of the land surface do to the evaporation of the soil surface and the transpiration of the plants growing on this surface. Unfortunately evapotranspiration can not be measured in an agricultural environment. The only systems allowing us to measure evapotranspiration is a weighing lysimeter, what is a very good tool to evaluate the calculations of evapotranspiration and to develop crop factors for different crops. In our agricultural environments we have to assess the evapotranspiration by a calculation basing on wind speed, global radiation, temperature, relative humidity, longitude latitude and altitude. Actually we will find the biggest acceptance and the best possibilities to compare our data with others by using the Penman Monteith calculation like it is published in the "Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56". Another Method to assess the evapotranspiration rates is the use of evapotranspiration pans. Table of Content: ETzero Penman Monteith ET pan 2.1.1 ETzero Penman Monteith

2 von 8 13.11.2009 12:42 A consultation of experts and researchers was organized by FAO in May 1990, in collaboration with the International Commission for Irrigation and Drainage and with the World Meteorological Organization, to review the FAO methodologies on crop water requirements and to advise on the revision and update of procedures.the panel of experts recommended the adoption of the Penman-Monteith? combination method as a new standard for reference evapotranspiration and advised on procedures for calculation of the various parameters. By defining the reference crop as a hypothetical crop with an assumed height of 0.12 m having a surface resistance of 70 s m-1 and an albedo of 0.23, closely resembling the evaporation of an extension surface of green grass of uniform height, actively growing and adequately watered, the FAO Penman-Monteith? method was developed. The method overcomes shortcomings of the previous FAO Penman method and provides values more consistent with actual crop water use data worldwide.from the original Penman-Monteith? equation and the equations of the aerodynamic and surface resistance, the FAO Penman-Monteith? method to estimate ETo can be derived (Box 6): The reference evapotranspiration, ETo, provides a standard to which: evapotranspiration at different periods of the year or in other regions can be compared; evapotranspiration of other crops can be related. The equation uses standard climatological records of solar radiation (sunshine), air temperature, humidity and wind speed. To ensure the integrity of computations, the weather measurements should be made at 2m (or converted to that height) above an extensive surface of green grass, shading the ground and not short of water. No weather-based evapotranspiration equation can be expected to predict evapotranspiration perfectly under every climatic situation due to simplification in formulation and errors in data measurement. It is probable that precision instruments under excellent environmental and biological management conditions will show the FAO Penman-Monteith? equation to deviate at times from true measurements of grass ET o. However, the Expert Consultation agreed to use the hypothetical reference definition of the FAO Penman-Monteith? equation as the definition for grass ET o when deriving and expressing crop coefficients. 2.1.2 ET pan Evaporation pans are giving the evaporation of an open water surface. The water evaporated can be converted into evapotranspiration. The following FAO document IRRIGATION WATER MANAGEMENT Training manual no. 3 Part I Principles of irrigation water needs Part II Determination of irrigation water needs a manual prepared jointly by C. Browser International Institute for Land Reclamation and Improvement and M. Heibloem FAO Land and Water Development Division gives the following conversion table in annex 1. PAN COEFFICIENTS FOR CLASS A PAN PAN COEFFICIENT (K pan) FOR CLASS A PAN FOR DIFFERENT GROUND COVER AND LEVELS OF MEAN RELATIVE HUMIDITY AND 24 HOUR WIND

3 von 8 13.11.2009 12:42 Class A pan Case A: Pan placed in short green cropped area Case B 1 : Pan placed in fallow area RH mean % low < 40 medium 40-70 high > 70 low < 40 medium 40-70 high > 70 Wind km/day Windward side distance of green crop m Windward side distance of dry fallow m Light 1.55.65.75 1.7.8.85 < 175 10.65.75.85 10.6.7.8 100.7.8.85 100.55.65.75 1000.75.85.85 1000.5.6.7 Moderate 1.5.6.65 1.65.75.8 175-425 10.6.7.75 10.55.65.7 100.65.75.8 100.5.6.65 1000.7.8.8 1000.45.55.6 Strong 1.45.5.6 1.6.65.7 425-700 10.55.6.65 10.5.55.65 100.6.65.7 100.45.5.6 1000.65.7.75 1000.4.45.55 Very strong 1.4.45.5 1.5.6.65 > 700 10.45.55.6 10.45.5.55 100.5.6.65 100.4.45.5 1000.55.6.65 1000.35.4.45 2.2 Soil Moisture Measurement

Pessl Instruments Tiki 4 von 8 Thanks to our electronic weather stations we can measure soil moisture continuously in site. With this we can see how the plant takes out the water and when it needs irrigation. For imetos we can offer sensors following the two major principles: The tensiometric principlee measuring soil water suction The volumetric principle measuring soil water content in volume parts. All soil water fixed in small pores and capillaries is hold force of gravity. The holding force is a function of the pore size and the surface tension of the water. The water suction can be measured by devises like tensiometers or gypsum blocks (watermark sensors). If the water contend of a soil is over field capacitance a portion of the water is inside of big pores and this water is moved by gravity. Water suction measuring devices can not be used to measure in this area. In an ideal soil all pores and capillaries can to be assumed to be connected. With this the whole soil will show the same water suction if we can wait long enough. In reality we will find some horizontal and vertical distribution of soil water suction too do to the fact that rain or irrigation is reaching the top soil layer first and plant roots are extracting water in restricted areas of the soil. The volumetric water contend of the soil is containing all water independent if it is filling big pores and it is moving trough the soil by gravity or if it is fixed inside the soil minerals. Therefore the data about volumetric soil water contend can tell us nothing about the plant availability of the water. To learn about the water needs of an specific crop on a specific site we will have to apply some external data or we will have to analyse longer time series of data. Table of Content: Tensiometer Watermark Sensor Enviroscan Echo Probe 2.2.1 Tensiometer The water inside a tensiometer has to be part of the soil water body to be able to measure soil water suction. This is provided by the porous ceramic tip at the bottom of the tensiometer. The water containing neck of the tensiometer can be of variable length. The length of the neck is depending of the depth in which we like toe measure water suction. If the soil water suction is higher than -100 mbar (-10 cbar) this suction is expressing on the tensiometer and it can be measured by a manometer or by an electronic 13.11.2009 12:42

5 von 8 13.11.2009 12:42 pressure sensor at the top of the tensiometer. Tensiometers can not give results if the soil water contend is higher than field capacitance. The maximum soil water suction which can be measured by a tensiometer is limited by its pressure sensor or manometer and by the ceramic tip. The electronic pressure sensor provided by Pessl Instruments can measure suction up to -800 mbar. The ceramic tip of our sensors will brake trough at approximately -2000 mbar. The break trough means that the tensiometer will lose all its water because some of the pores of the ceramic tip are wider than the pores holding water at -2000 mbar suction and this wider pores are becoming air filled and the air will enter the tensiometer neck and the water will run out of the tensiometer. 2.2.2 Watermark Sensor The Watermark sensor (granular matrix sensor) is an indirect, calibrated method of measuring soil water. It is an electrical resistance type sensor, read by data logging equipment or a Soil Moisture Meter (pictured below, centre) which converts the electrical resistance reading to a calibrated reading of Centibars (or kpa) of soil water tension. Introduced in 1979, patented in 1985, and manufactured by the Irrometer Company since 1989, this irrigation sensor has been a major break-through in soil moisture measurement technology. It has been the subject of scientific investigation by plant and soil science since the mid-1980's, and has demonstrated itself to be an affordable and practical substitute for tensiometric measurement in most agricultural and landscape irrigation environments. The Watermark sensor is an ideal solution for both agricultural and landscape applications.it can be used very well with our imetos data loggers.

6 von 8 13.11.2009 12:42 Watermark Sensor Operating range of the watermark sensor The watermark sensor fits perfect to all crops which need a moderate water supply. If you grow apple, cherries, strawberries, tomato or potatoes this sensor will be perfect and cost effective tool to improve your irrigation. It does not fit if you are planning to do some deficit irrigation in warm climate vine production or when your want to optimise the irrigation of corn by using the optimum amount of water. In this cases we support to use a capacitive sensor. Watermark sensors in non irrigated grape vine hourly resolution

7 von 8 13.11.2009 12:42 Watermark Sensor in Cherries with Drip Irrigation During Picking(lower three sensors in drip line other three sensors under non irrigated cover crop) Daily Resolution Watermark Sensors in Apples in the wet season 2008 in South Badenia 2.2.3 Enviroscan Sentek's flagship product, EnviroSCAN has become the most widely used continuously logging, irrigation management tool in the world. EnviroSCAN is a complete and stand alone soil water monitoring solution. The data obtained by the EnviroSCAN sensors is collected by a central logger and then downloaded by the user through a variety of manual and telemetry methods. The acclaimed IrriMAX 7.1 software program converts this information into a user friendly graphical format to provide users with a better understanding of profile soil water dynamics. Equipment Setup and Aims: Access tubes (56.5 mm in diameter) for Sentek soil moisture sensors are installed into the soil, and the sensor is then placed into the tube. Sentek sensors use electronic capacitance to detect changes in the dielectric properties of soil as it varies in water content. An electromagnetic field produced by the sensor extends beyond the access tube, and the amount of water in the sphere of influence of the sensor affects the frequency at which the electromagnetic field oscillates. In this way, the amount of water in the soil around the access tube can be detected. The signals from the sensor are translated into Volumetric Water Content (VWC), which can be plotted against a time scale to show trends in changing soil water conditions during the growing season. The amount of water, in mm, can also be calculated from VWC to compare the results with rainfall quantities. There are two main benefits of the enviroscan or enviroscan like technology. Volumetric soil moisture measurement can give us information over the whole range of possible soil moisture content. The possibility to measure in different depths at the same time allows us to see where the plant can find more water and it shows where the plant takes the water. Looking into a corn field with 2m of soil depths would show us if the corn is able to use the water inside the whole soil profile and this information will lead us to irrigate as effective as possible.

8 von 8 13.11.2009 12:42 Comparing Watermark and Capacitive Soil Moisture Measurement 2.2.4 Echo Probe Inhaltsverzeichnis: 2.3 Soil Water Balance Inhaltsverzeichnis: Irimet Lite 2.3.1 Irimet Lite Inhaltsverzeichnis: Show php error messages