Research led by CEH could help improve the estimates of the amount of water needed for crop irrigation, helping to alleviate both water stress and food security issues in many regions by allowing more efficient irrigation across more land. The results have worldwide implication, as irrigation uses 70% of freshwater resources globally. The studies, published in the journal Irrigation and Drainage, were completed as part of the EU-funded Water4Crops project. Lead author Dr Ragab Ragab of the Centre for Ecology & Hydrology explains more:
The current methods of calculating crop irrigation water requirements use equations fed by meteorological data such as temperature, wind speed, relative humidity etc. However these equations calculate the atmospheric demand for water, not the crop demand for water. The results are values that represent the maximum evaporation, not the actual.
An accurate crop water requirement should be based on crop and soil demand, not on atmospheric demand for water.
Modern technologies such as the use of scintillometers or the eddy covariance technique measure actual evaporation that represent the real crop need for water. We installed instruments using these methods at an experimental farm near Bologna in Italy to measure actual evapotranspiration / crop water requirement during two cropping seasons (2014 and 2015).
Photos: Scintillometer (transmitter on left, receiver in middle) and Eddy covariance (right)
The results showed significant differences when compared with the present practice. On average the actual crop water requirement based on the modern technologies could save at least 50% of irrigation water for this region. Another benefit is that these technologies do not need what is called the crop coefficient (calculated from evapotranspiration data) which can be difficult to obtain for many irrigation practitioners.
Photo: Members of the project team visit the the experimental farm site near Bologna in Italy
"On average the actual crop water requirement based on the modern technologies could save at least 50% of irrigation water for this region"
We also used a new technology, the Cosmic-Ray Soil Moisture Observation System (COSMOS), to determine the crop water requirement through real-time continuous soil moisture content and deficit. This method can sense soil moisture for an area of 300-700 metres radius. In the Water4Crops project it was shown to be useful for estimation of both irrigation need and suitable time for irrigation.
We used the COSMOS probe over a mixed crops area during the same cropping seasons. The results showed that soil moisture values obtained by COSMOS were comparable with those obtained for the top 0-60cm layer by sensors, soil cores, profile probes and with values simulated by the SALTMED model. This indicates that the COSMOS probe’s effective depth is within the top 0-60cm.
Photo: Partial Root Drying subsurface drip irrigated potato where only the vertical half of the root zone gets irrigated in alternation with the next drip line. This strategy saves over 40% of water used for sprinkler irrigation and 25% of normal drip irrigation. COSMOS can help to accurately provide when and how much water to apply.
Knowing that almost 80% of the crop root systems is accommodated within the top 0-60cm, the COSMOS measurement could be useful for monitoring the soil water status and deficit in the root zone in irrigated agriculture.
The COSMOS technology is one step in the right direction as it provides continuous, integrated, area-based values and solves the problem of spatial variability often found in point measurements. This method could also be used to determine the soil moisture deficit, hence determine when and how much to irrigate. It could be made operational for irrigation managers to determine when and how much to irrigate to avoid harmful water stress.
The results of our studies have worldwide implications as globally 70% of freshwater used for agriculture. Doubling food production by 2050, when we will need to feed 9 billion people, requires efficient water use to achieve this aim from the same amount of water. Accurate estimate of crop irrigation requirement based on actual evapotranspiration is the way forward.
Full paper references
Ragab, R, Evans, J G, Battilani, A, and Solimando, D. (2017) Towards Accurate Estimation of Crop Water Requirement without the Crop Coefficient Kc: New Approach Using Modern Technologies. Irrig. and Drain., 66: 469–477. doi: 10.1002/ird.2153.
Ragab, R, Evans, J G, Battilani, A, and Solimando, D. (2017) The Cosmic-ray Soil Moisture Observation System (Cosmos) for Estimating the Crop Water Requirement: New Approach. Irrig. and Drain., 66: 456–468. doi: 10.1002/ird.2152.