|Evett, Steven - Steve|
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2007
Publication Date: 5/17/2007
Citation: Evett, S.R., Ibragimov, N., Kamilov, B., Esanbekov, Y., Sarimsakov, M., Shadmanov, J., Mirhashimov, R., Musaev, R., Radjabor, T., Muhammadiev, B. 2007. Neutron moisture meter calibration in six soils of Uzbekistan affected by carbonate accumulation. Vadose Zone Journal. 6:406-412. Interpretive Summary: In water-short regions of the world, including the U.S. Great Plains and the central Asian Republic of Uzbekistan, producing the most crop per unit of water used in irrigated agriculture is critical. The amount of crop produced per unit of water used is called the water use efficiency (WUE). Research on irrigation methods, deficit irrigation, management practices, tillage methods, crops, and combinations of these with soil types is key to improving WUE and reducing irrigation water use, since all these factors affect crop water use and yield. Determination of crop water use is commonly accomplished by measuring water applied to the crop by irrigation and precipitation, and measurement of water removed from the soil by the crop. The latter measurement is routinely done using the neutron moisture meter (NMM), which must be calibrated for each soil and soil layer in order to be accurate. We developed methods and tools for NMM calibration and use in the Great Plains, and tested these methods for broad applicability by assisting the Uzbekistan National Cotton Growing Research Institute to calibrate and use NMMs in six soils of Uzbekistan. Successful determination of crop water use and WUE showed that our methods are broadly applicable. This result, and the similarity between crop yield and WUE in Uzbekistan and the High Plains of Texas under deficit irrigation, lend credibility to results obtained in both countries and demonstrate the improvement in WUE that moderate deficit irrigation can provide.
Technical Abstract: Improvements in water use efficiency of irrigated agriculture begin with determination of crop water use under different climates, soils, and other environmental factors and under different management practices, including conservation tillage. Crop water use may be calculated from the soil water balance if changes in soil water storage due to irrigation and precipitation and crop water uptake can be accurately determined, and if losses to deep percolation or upward fluxes from shallow water tables can be eliminated in the experimental setup. We detail accurate field calibrations of neutron moisture meters (NMM) at six locations in Uzbekistan, in soils ranging from deep, uniform silt loams of loessal origin to highly stratified alluvial soils near the Amu Darya river. In all soils, separate calibrations were found for the 10-cm depth due to closeness to the soil-air interface. Near Tashkent and at the Syrdarya Branch Station, the soil below 10 cm was divided into two layers based on the increased CaCO3 and/or CaSO4 content of the lower of the two layers. Distinctly different calibration equation slopes were found for these layers. At the Kashkadarya Branch Station, a single calibration was sufficient for the soil below 10 cm. At the Khorezm Branch Station, an abrupt change in soil texture near 70-cm depth caused separate calibration equations for the 30 to 70-cm depth range (silt loam) and the 110 to 170-cm depth range (fine sand). Calibration at the Fergana Branch Station was successful for the 10-cm and the 30 to 90-cm depth ranges. Overall, root mean squared errors (RMSE) of calibration ranged from 0.009 to 0.025 m**3 m**-3 and r**2 values ranged from 0.91 to 0.99. Two examples of water content measurement for crop water use efficiency studies are discussed.