Abstract:The effect of municipal wastewater irrigation on the yield and quality of vegetables and crops was studied by means of pot and lysimetric experiments. The pots were seeded with lettuce salad, radishes, and carrots in all experimental years; the lysimeters were planted with early potatoes in 2005 and 2007, and with sugar beet in 2006. Secondary-treated wastewater (in 2005) or only primary-treated wastewater (in 2006 and 2007) were used in the experiments. The control treatment involved the irrigation with water from a local well (in 2005) or public water supply (in 2006 and 2007). Contrarily to the secondary-treated wastewater, the primary-treated wastewater increased the yield of all vegetables and crops, the increase having been statistically significant in most cases. The irrigation with secondary-treated wastewater increased only the sodium content in radishes and carrots. However, the irrigation with primary-treated wastewater led to a statistically significant increase in the sodium content in the consumable parts of all vegetables, sugar beet bulbs, and potato tubers in both years, and in 2007, in the nitrate contents in lettuce salad and radishes as well. A high bacterial contamination of vegetables and crops irrigated with this wastewater was found out, but there was no evidence for the contamination with pathogens. Also, no risk was shown of contamination of the crops with intestinal nematodes.

Water movement and uptake by roots in a drip-irrigated potato field was studied by combining field experiments, outputs of numerical simulations and summary results of an EU project (www.fertorganic.org). Detailed measurements of soil suction and weather conditions in the Bohemo-Moravian highland made it possible to derive improved estimates of some parameters for the dual permeability model S1D DUAL. A reasonably good agreement between the measured and the estimated soil hydraulic properties was obtained. The measured root zone depths were near to those obtained by inverse simulation with S1D DUAL and to a boundary curve approximation. The measured and S1D DUAL-simulated soil water pressure heads were comparable with those achieved by simulations with the Daisy model. During dry spells, the measured pressure heads tended to be higher than the simulated ones. In general, the former oscillated between the simulated values for soil matrix and those for the preferential flow (PF) domain. Irrigation facilitated deep seepage after rain events. We conclude that several parallel soil moisture sensors are needed for adequate irrigation control. The sensors cannot detect the time when the irrigation should be stopped.

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For the research of irrigation optimization and nitrate leaching it is important to know the shortterm soil moisture variation during percolation episodes as well as its seasonal pattern. Dielectric soil moisture sensors Virrib (AMET -Consortium) and ThetaProbe ML2x (Delta-T) were used for this purpose over several years for measuring soil moisture content at hourly intervals in Valečov (49°38'40" N, 14°30'25" E, 461 m a.s.l.), Czech Republic, in a deep loamy Stagnosol soil underlain by weathered paragneiss. One-point field calibration was made each spring at the time of sensor installation over three (for Virribs) or two (for ThetaProbes) consecutive years by taking sensor readings and soil samples (at least one 100 cm 3 core sample near to each sensor) in parallel. A supplementary check was then made in the laboratory by taking readings of individual sensors, inserted into pre-made loamy-sand mixtures with various moisture contents. During both the field calibration and the laboratory check, the readings were taken manually, using either the AMET hand-held meter or the EMS ModuLog datalogger. The results suggest that the average slope of the secondary Virrib calibration curve (defined as the plot of y = sensor readings in terms of moisture content vs. x = soil moisture content determined gravimetrically) is near to unity, but the offsets are quite large and vary from probe to probe. The axial zone of influence of the Virrib sensors is up to about 30 cm, as it follows from both laboratory and field observations. The results of the laboratory check of Virribs were biased, because the volume of the soil was not large enough and the soil had different dry bulk densities at different moisture contents. The field secondary calibration curve of ThetaProbes appears to be roughly linear, in contrast to the laboratory calibration curve, because of absence of very low moisture contents in the field. If the same calibration line is applied to several different depths, then its slope is statistically significantly lower then unity, due to the dependence of ThetaProbe readings on the soil bulk density. The overall accuracy of the sensors and its components due to different factors is estimated from the statistics of repeated measurements.

Abstract:The paper deals with optimisation of threshold suction pressure of soil water on light soils for early potatoes, early cabbage, late cauliflower and celery on the basis of results of small-plot field experiments with differentiated irrigation regime. Experiments were conducted in [2003][2004][2005]. Threshold suction pressures of soil water were identical for all crops: 15 kPa in treatment I, 30 kPa in treatment II, 60 kPa in treatment III, and 120 kPa in treatment IV. Precipitation, air temperature and relative humidity, global solar radiation, wind speed and direction were measured by an automated meteorological station. Reference and actual evapotranspiration was determined for the experimental crops according to FAO Paper No. 56 and by means of a biological curve (BC) in [2003][2004][2005]. To compare these two methods of calculation of actual evapotranspiration the soil moisture balance was found out. Based on the influence on marketable yield and proportion of the crop quality grades it is possible to determine the optimum threshold suction pressure on light loamy-sand soils in early potatoes, late cauliflower and cabbage 30 kPa and in celery 15 kPa. 80% of available soil water capacity (ASWC) corresponds to the threshold suction pressure 30 kPa, and as much as 96% of ASWC corresponds to 15 kPa. The seasonal irrigation depths determined on the basis of soil moisture balance, in which the crop evapotranspiration (ET c ) is calculated either according to FAO 56 or by the BC, are substantially different from the really achieved irrigation depths in the treatments where optimal suction pressure is maintained. For potatoes, the really achieved values of seasonal irrigation depths are nearer to the depths calculated by the BC, while for the other vegetables (cauliflower, cabbage and celery) they are more similar to the depths calculated by FAO 56 methodology. The theoretical irrigation depths calculated by the BC method sometimes differ substantially from those based on FAO 56. These differences are at maximum for cauliflower and celery and at minimum for cabbage and decrease with the decreasing irrigation depths.