Actual and potential evapotranspiration of a grass stand according to small smart field lysimeters

Mukhitdin Gulamov

Diplomová práce

Abstract:

Lysimeters are basic instruments for evapotranspiration measurement. This master thesis characterizes the actual evapotranspiration of non-irrigated and unfertilized grass in a warm region of the Czech Republic on a Chernozem loamy soil. A weighing lysimeter SFL-300 (diameter 0.3 m, depth 0.3 m) was used for this purpose. The suction at its bottom was maintained at the same level as in the native soil nearby. 585 rainless days with regular records were selected for the analysis of daily sums. On most days, the lysimeter-measured actual evapotranspiration ETa was smaller than the Penman-Monteith FAO 56 reference crop evapotranspiration ET0. The FA0 56 procedure was found to be a reasonable estimator of the non-stressed evapotranspiration in a moderately stressed environment. The ETa/ET0 ratio and the canopy surface resistance rs depend on the soil water content and suction measured at 5 cm. This dependence breaks down into a horizontal non-stressed part and declining (for ETa/ET0) or inclining (for rs) water-stressed part. The ratio ETa/ET0 is about 85 % and rs is about 250 s m-1 when the grass is not under water stress. The annual curve of the non-stressed crop coefficient has a sine shape. An energy balance criterion suggests that advection of heat is important in winter but not so much in summer. The paper provides parameters of evapotranspiration for a canopy that can be found on many standard weather stations and demonstrates that high-quality research of evapotranspiration of low, dense and shallow-rooting crops is possible with small lysimeters of this type.Virtually all results were obtained with the newer and more perfect of the two lysimeters available, while the older lysimeter and its problems were discussed only shortly. The older lysimeter can be operated in parallel with the new one, mainly to serve as a check for soil water suction and percolation measurementsA brief overview of some lysimeter research results obtained in Uzbekistan is also provided. The main topic of this research is the effect of shallow groundwater on total water consumption of irrigated and non-irrigated cotton crop. The very shallow fresh groundwater may replace surface irrigation, but there is always a risk of soil salinization and oxygen stress. The lysimeters for this type of research would have to be much deeper (more than 2 m) and its diameter would have to be larger, of the order of 1 m or more, to adequately represent the cotton canopy.

Keywords

reference crop, evapotranspiration, weather station, FAO 56 Penman-Monteith equation

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 24. 4. 2017

Obhajoba závěrečné práce

• Vedoucí: prof. Ing. Svatopluk Matula, CSc.
• Oponent: František Křovák, CSc.

Česká zemědělská univerzita v Praze

Fakulta agrobiologie, potravinových a přírodních zdrojů

Magisterský studijní program / obor:
Natural Resources and Environment / Natural Resources and Environment