Effects of irrigation and fertilization on yields of main crops

The problems were studied in a stationary experiment started in 1973 on carbonate chernozem in south western Slovakia. The paper assesses yields of main crops over the 26 year period (1973 to 1998), namely of corn maize grown 5 x, silage maize grown 4 x, winter wheat grown 6 x, spring barley grown 4 x, sugar beet grown 2 x (4 years). Even though the experiment included a number of fertilization variants, the paper evaluates just five of them, namely O, PK, NPK, N1PK, N1P1K1. The index 1 corresponds approximately to 1.5 dose of a given nutrient. Results reveal varying responsiveness of stated crops to irrigation and fertilization. Maize yields are higher with irrigation rather than fertilization applied, specifically in case of corn maize taken as 5 year average by as much as 54.7%. Years characterized by large precipitation deficit in July and August, as was the case in 1990 and 1973, had very high efficiency of irrigation, namely as much as 456.8% and 72.5%, respectively. Favourable distribution of precipitation meant low irrigation generated increases in yields. Maize responded to fertilization by 1.3 % to 15.3 % yield increase, whereas non-irrigated maize virtually did not respond to the former (see Figure 1). A similar high responsiveness to irrigation was found in case of silage maize. Fertilization proved more efficient than in corn maize, with yield increases for non-irrigated and irrigated variants ranging from 6.5% to 11.6% and 7.4% to 15.8%, respectively. Yields of cereals and the responsiveness of the former to irrigation varies according to the distribution of precipitation in May, June and July. Provided precipitation deficiency occurs at least in two of the above stated months, then winter wheat responds positively to irrigation. To illustrate this, in 1993, when April and May were considered as dry, irrigation generated yield increases represented as much as 26%. Fertilization is more efficient with irrigated wheat, ranging in efficiency from 4.6% to 18.2%, where higher nitrogen doses contribute to lower yields as a consequence of lodging. Spring barley grown 4 x did not provide any valid evidence as to beneficial effects of irrigation. Increased yields were registered only in 1977 when May and June were dry. A similar high increase in barley yields, by as much as 1 t/ha, was found in the same location in 1998 (BIZIK et al., 1998), characterized by high temperatures and low precipitation volume over these months. On average, barley responded to fertilization in a larger measure. Increased nitrogen doses caused lodging. Results obtained in sugar beet growing confirm high responsiveness to irrigation and furthermore reveal that there was a sufficient supply of nitrogen from soil and manure and that application of nitrogen from fertilizers to increased refined sugar production proved inefficient. These facts point out to the need to use available data on various nitrogen forms contained in soil when applying nitrogen as a fertilizer to sugar beet. Alfalfa is a crop in which it is necessary to offset the shortage of water resources by means of irrigation, the more so if June, July and August are dry. Non-irrigated alfalfa responded to fertilization in a greater measure