The effect of rainfall on crop fertilization factors, such as macronutrients and yield, were studied during a long-term field experiment on a calcareous sandy soil with low humus content in North Hungary at the OrbottyAn Experimental Station of Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences from 1961 to 2004. At the time of the set-up of the experiment, in 1959, the soil's ploughed layer had the following characteristics: pH(H2O): 7.5-7.8, pH((KCI)): 6.9-7.1, humus content: 0.6-1.0%, clay content: 5%, CaCO3 content: 3-7%, AL soluble P2O5 and K2O content: 40-60 and 50-100 mg-kg(-1). The experiment included ten treatments in five replications, giving a total of 50 plots (35 M-2 each) arranged in a Latin square design. From the 1st to the 25th year the fertilization rates were 0, 50 and 100 N kg center dot la(-1) year(-1); 0 and 54 kg P2O5 ha(-1) center dot year(-1); 0 and 80 kg K2O ha(-1) - year(-1) and their combinations. From the 26(th) year on these rates were 0 and 120 kg N ha(-1) center dot year(-1); 0, 60 and 120 kg P205 ha(-1) center dot year(-1) and 0, 60 and 120 kg K2O ha(-1) center dot year (-1) and their combinations. The major findings can be surnmarised as follows. At average rainfall years on the control plots without any mineral fertilization the rye yield in monoculture stabilised at a level of around 0.8 t - ha(-1) (Table 3). The yield doubled (1.8-1.9 t center dot ha(-1)) in the N, NP and NK treatments while the full NPK doses gave the maximum yield of 2.1 t center dot hal (-1)significantly (mean: 1.7 t - ha(-1)). Without mineral fertilization on the control plots in droughty and dry years yields of 0.7 t center dot ha (-1)and 0.8 t - ha(-1)ere h(a)rvested. This was a 13% yield reduction in droughty years ascompared with an average year. Yield depressions of 33, 16, 21 and 20% were caused bydrought (dry and droughty years) in the N, NP, NK and NPK treatments. In wet year the yield was 0.9 t - ha-' in the control plots, representing a yield grown of 12.5% compared with average years (0.8 t - Ila). In the case of N, NP, NK nutrition the increase ill the harvested main yield was 43. 1 % while NPK treatments led to yield increment of 36.9% only. In the very wet years the rye yield declined even more than in case of drought. The unfertilised plots yielded25% less than in the average years. In the case of unfavourable nutrition (N, NP, NK) the decrease in the main grain yield was 32.8% and in the case of NKP plots the negative effects was 26.2%. Rye in monoculture has approx. 29.4% less tolerance of very wet years than to dry. This yield depression is in line of Mdrton et al. (2007) statement whereas the over-wet conditions could be resulted oxygen deficiency in the crop's root zone. Depending on the nutrient supplies, significant quadratic correlations were observed between the rainfall quantity and the yield (Control: R=0.7489***, N: R=0.8974***, NP: R=0.8020***, NK: R=0.7370***, NPK: R=0.9047***, mean R2=0.8180; 66.9%) during the vegetation period. The increase in grain yield per mm rainfall ranged from 3.0 to 6. 4 kg ha(-1) in the case of optimum rainfall supplies, while the quantity of rainfall during the vegetation period required for the production of I kg air-dry yield ranged from 1529 t 3360 litres in the case of maximum yield. Based on the meteorological database for the 44 years of the long-term experiment (1961-2004) the frequency of years in which the rainfall was optimum for various levels of nutrient supply was as follows: control: 2%, N: 7%, NP: 7%, NK: 9%, NPK: 7%, giving an average of 6% over the treatments. This suggests that the occurrence of optimum rainfall supplies and the possibility of achieving optimum yields in the rye production will decline in the future, Under two different arable site plant ecological conditions (rainfall quantity, NPK fertilization) the yield average of rye in monoculture on calcareous sandy soil (OrbottyAn) was 86% less than that achieved in a biculture (rye and potato) on acidic sandy soil (Nyirlugos).
