Tuesday, 11 July 2006

Long-term Investigations of Water Regime Parameters of an Agriculturally Used Field by Lysimeters.

Reinhard M. Günther, Thuringian State Institute of Agriculture, Naumburger Str. 98, JENA, 07743, Germany

Basis for the presented results is the lysimeter plant Buttelstedt of the Thuringian State Institute of Agriculture (GUENTHER 1987, ROTH et.al. 2005). It consists of two lysimeter cellars, each with two large monolythic, weighing type lysimeters, with a surface of 2m² and a depth of 2,5m. The lysimeter location, at latitude 51° 03' N, longitude 11° 19' E, elevation 228 m, is characterized by a profound Tschernosem, a mean annual temperature of 8,2°C , a mean yearly precipitation of 552 mm and an annual irradiation of 3400 MJ/m². In order to avoid the so-called "oasis effects" ( HAGRAEVES 1977; KLAGHOFER 1991; PYCHA 1977), for the plants growing in the lysimeters the same micro-climatic conditions were provided as for the cultivated plants on the field. One of the two lysimeter cellars represents the well irrigated (I), the other one the nonirrigated and/or reduced irrigated part (II) of the field. The results to the water regime and water consumption investigations in the period of 1983 to 2001 can be summarized as follows: The average amount of precipitation determined with the lysimeters is approximately 10% higher than the rain quantity measured in the standard rain-gauge 1,0 m above the topographic surface (GUENTHER 1986). More than 90% of the precipitation and irrigated water vanished by evapotranspiration (ET). This is a substantially higher value than indicated in the literature (i.g. BAUMANN 1961). In years with low precipitation like 1985 or 1988 to 1991 the evapotranspiration clearly exceeds the precipitation. The reason is the high water store ability of the profound loess. Particularly all crops rooting depht can temporarily cover their water requirement even in years or growth periods of low precipitation from the soil water content, which is formed in periods with high precipitation. In many years however the winter precipitation is not sufficient for a complete soil water recharge. High evapotranspiration rates and high soil moisture losses with contemporary low precipitation, causes low seepage water quantities. On the average the infiltration on the lysimeters better supplied with water was 8.4% and on the less supplied it was only 6.3 % of the total applied water (precipitation + irrigated water). From 1983 to 1993 the seepage water quantities on the nonirrigated lysimeters amounted to only 1 to 2% of the annual precipitation, on average. With beginning of the vegetable cultivation period in 1995 the seeping losses increased clearly by the more intensive irrigation and by the smaller yearly water consumption of the vegetable crops. For well irrigated conditions (lysimeter I) the measured losses was 15%, with reduced irrigated conditions (lysimeter II) 14%. The seeping water rates are primarily affected by the water consumption of the individual crops, in addition, by the distribution of the annual precipitation. The total water consumption of the examined agricultural and vegetable crops under potential evapotranspiration conditions extended from 219 mm with shrub beans (phaseolus vulgaris) up to 692 mm with Welsches Weidelgras (italian reygras) whereby there existed a close relationship with the length of the growth period. The differences in the mean daily water consumption in the main growth period are relatively small with a variation from 3,7mm to 4.2 mm between the individual kinds of fruit. On the average 4mm can be assumed. An irrigation according to the demand supplied a better water use efficiency(WUE) in all cases.

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