THE EFFECT OF SOIL-MANAGEMENT ON WASHING- OFF NITRATES AND RISK ELEMENTS

The trial has been conducted at the roofless lysimetric station of the Research Institute for Soil and Water Conservation at Borkovice, Tabo r district, from April 1, 1995 to December 31, 1996; 36 scalable lysim eters of 0.63 m in diameter and 0.60 m height of soil column (volume 0 .187 m(3)) were used. Out of them in 1988 12 were filled with sandy so il, 12 with loamy soil and 12 with swamp peat. Physical and chemical p roperties of these soils can be seen in Tab. I. In the year of filling all lysimeters were sown with grass mixture of the same species compo sition (meadow fescue, timothy, meadow-grass). Each soil had these var iants of management: 1. year-around black fallow, 2. green fallow, 3. uncut, 4. one cut, the mass stays in lysimeter, 5. one cut, the mass i s removed from lysimeters, 6. two cuts fertilized in the spring. The c ontent of risk elements in fertilizers is in Tab. II. This contributio n gives only results obtained in variants 1, 5 and 6, investigated in 1995 and 1996. On May 2, 1995,:he following substances were applied in the form of solution: 1 g of cadmium as CdCl2 . H2O, 10 g of lead as Pb(CH3COO)(2) . 3H(2)O and 10 g of nickel as NiCl2 . 6H(2)O. Sum of pr ecipitation was 653.7 mm for 1995 and 661.8 mm for 1996. The soil wate r content was kept by irrigation at 80% of utilizable water capacity. Amount of irrigation water in variants of soil utilization investigate d during two years is evident from Tab. III. In each lysimeter during weighing, carried out fortnightly, amount of infiltration water was me asured and its sample was taken for chemical analysis. The content of nitrates in infiltration water was in 1995 and 1996 highest of all-aro und black fallow as on sandy soil, as on loamy and swamp soil (Tab. IV ). In this way of soil utilization it was greater by two or three orde rs compared with variants with permanent grassland (it ranged in tees to hundreds of mg.l(-1)) and generally exceeded their limit value in d rinking water (50 mg.l(-1)). The dose of 50 kg N.ha(-1) in the form of ammonium nitrate in 1995 and 1996 was not a cause of statistically si gnificant increase of the content of nitrates in infiltration water. H igh content of nitrates in infiltration water from black fallow can be explained by the fact that in the soil without vegetal cover were bet ter conditions for mineralization of organic matter and nitrification. In this way of soil utilization no nitrogen was drawn by the harvest of the grassland. In sandy and loamy soil was, except it, greater unde rground discharge (Tab. III). Yearly cycle of the content of nitrates in infiltration water, described in natural field conditions, was not found in lysimeters. Ablation of nitrates from black fallow on all soi ls was in both years statistically significantly greater than from soi ls with permanent grassland (Tab. V). The most of nitrates were washed out from swamp soil (Fig. 1), containing high amount of organic matte r (C-ox = 33.9%). In 1995 and 1996 from black fallow on this soil more nitrates by about 65% in total were washed out compared with the blac k fallow on sandy and loamy soils. Ablations of nitrates from soil wou ld be probably greater without application of risk elements. High dose of risk elements and chlorine supplied together with them with greate st probability had especially in the first year of tile trial negative impact on nitrification processes in soil. This can be considered one of the reasons of lower ablation on nitrates from soil, particularly on sandy and loamy soils, in 1995 than in 1996. In calculation per I k g of dry soil in lysimeter the dose of cadmium in sandy soil was 3.5 m g, in loamy soil 3.9 mg and in swamp soil 22.2 mg. The dose of nickel and lead was ten times greater compared with cadmium. The top layer of soil profile, in which nitrification runs with greatest intensity, wa s more loaded with risk elements particularly in the first months afte r their application. Natural content of cadmium, nickel and lead in in filtration water from lysimeters at Borkovice are their contents measu red in April 1995 (Tab. VI), that is before application of these eleme nts in the form of their chemical compounds. They were greatest on ave rage in infiltration water from swamp soil. The content of cadmium and nickel in infiltration water from each way of utilization of each soi l was greater roughly by one order on average in 1995 compared with 19 96 (Tab. IV). Similarly the same was the situation with the amount of these risk elements washed out from soils (Figs 2 and 3). The content of leed in infiltration water in 1995 and 1996, along with its amount washed out from soil (Fig. 4), did not usually significantly differ. D ifferences in cadmium and nickel ablation in 1995 and 1996 were highly statistically significant, differences in ablation of lead were stati stically insignificant (Tab. IV). On all soils ablations of all risk e lements were greatest in variants with greatest underground discharge. On sandy and loamy soils the same situation was with all-around black Fallow, on swamp soil, typical by extra high content of organic matte r and low pH, in two-cut variant. Differences between ablation of risk elements from various ways of utilization were not mostly statistical ly significant. Results of experiments showed that greatest danger of contamination of underground waters with nitrates, cadmium, nickel and leed is represented by all-around black fallow. This way of soil util ization should be maximally reduced particularly in protective zones o f water resources of underground waters destined for supply of drinkin g water.