engleski

Environmental constraints for satisfied hybrid seed-corn yields in Croatia and their ovecoming

Seed hybrid maize has been traditionally grown in Croatia for about 40 years. It is mainly situated in the eastern part of country, in Slavonia and Baranya provinces, where well drained brown soil prevail, the mean annual precipitation is between 600 and 700 mm, 330 of which in the maize growing season. Also, June, July and August rainfall and mean air-temperatures are 95, 73 and 64 mm, as well 19.5, 20.8 and 20.2oC, respectively. In the favorable years, 8,000 to 10,000 ha have been planted under maize seed crop, with total seed yield from 15,000 to 20,000 t. Both domestic and foreign hybrid maize seed crop are grown. Part produced seed exported to European countries. In general, on average hybrid maize seed yields in Croatia are satisfied. For example, average seed yield of the most growing “Bc” domestic hybrids (Bc Institute for Plant Breeding, Zagreb) is 1.95 t/ha for the last 16 years. However, annual variations are high and ranged from only 1.13 t/ha in 1990 to 2.70 t/ha in 1984. Yield variability in hybrid maize seed production is much greater than in grain production. It is occurred even in the best maize production area in Baranya province. Our experience with OsSK407 hybrid, which was grown in this province at “Belje” holding showed that mean 4-year yield was 9.72 t/ha in grain production and 2.28 t/ha in seed production. Grain yields varied between 8.96 and 10.10 t/ha or only from -4 to +8%. On the other hand, in seed production these yields varied from 1.36 to 3.39 t/ha or from -40 to +50% in relation to the 4-year mean. As maize in Croatia is grown under natural conditions of water supply, water and heat stress in the critical stages are main responsible factors of the low seed yields in some years. Analyzing maize seed production at PIK “Djakovo” holding during 10-year period, close connection between July rainfall and seed yields was found. For example, in the three favorable years, mean seed yield was 2.15 t/ha, while in the worst three less favorable years only 1.10 t/ha. July rainfall as 3-year means were 61 and 36 mm while rainfall quantities in the maize growing season (May-September) were 306 and 251 mm, for more and less favourable years, respectively. Our own results and limited production experiences show that yield in seed production can be considerably increased, up to 70-100%, and yield variability decreased by the application of irrigation. In general, high-fertile soils have been selected for seed-corn growing. However, lawful obligation of space isolation and occurrence of less favourable soils in some areas are main reasons for choice of problem soils (inadequating of pH, ion unbalance etc.) for seed-corn growing. Based on growth retardation and seed-corn chlorosis at early growth stage (the signs of either Zn, P or K deficiency), 16 field experiments of fertilizer incorporation in soil immediately before sowing ( a = ordinary fertilization, b = a + 60kg ZnSO4.7H2O/ha, c = a + 650 kg NPK 8:26:26/ha ) were conducted. Significantly increase of seed yield were found in eight experiments following Zn (mean 10%) and in seven experiments by increased NPK (mean 12%) application. Irrigation of seed-corn crops, and in connection with that greater use of intercroping procedure, adequate fertilization based on soil test performance and choice of adequate parents which are more tolerant to possible soil stress, are main directions for seed-corn growing improvement in Croatia.

Seed-corn; Yield; Environment; Croatia

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