SUMMARY

 

Most of arable land in Croatia has satisfied amounts of potassium (K) but nutritional disorders accompanied with K deficiency have been found on some clay soils of Posavina area. K nutrition problem was confirmed by chemical analysis and field trials. Survey of these investigation were shown in this study, We presume that similar problem exists on soils situated on the Posavina area in Republic of Srpska.

Four experimental fields were conducted in the period from 1984. to 1990. g in area of Zupawa, Slav. Brod and Nova Gradiska area. K fertilization rates (KCI form) in some cases were more than ten times higher compared to usual amounts. In the next years, subsequent effects were tested and field trials were fertilized usualy. Ear-leaf (beginning of silking) and upper three-leaf of soybean (immediately before flowering) samples were taken for chemical analysis. For testing different corn hybrids were used also four replicates and ordinary fertilization.

By K fertilization were considerable increased corn and soybean yields. For example, in the one trial was applied 2670 kg K2O/ha and yields (3-year means) were increased from 1.93 t/ha to 7.64 t/ha or four-fold (corn) and from 1.29 t/ha to 2.61 t/ha or twofold (soybean). At same time, K and Mg status in corn (0.60% K, 1.94% Mg and 1.66% Ca on the control; 1.58% K, 0.95% Mg and 1.64% Ca on the highest K tretment) and soybean leaves were improved.

Two groups of seven corn hybrids contain same inbred line as a father (Os1 -48 for the A group and Os87-24 for the B group) were grown under soil stress. The hybrids of A group characterized considerable lower percentage ol' stalk lodging, lower P contents in the lower part of stalk at maturity and higher yield (means: 4.9%, 0.13% P and 5.64 t/ha, respectively) compared to the B group (59.1%, 0.22% P and 4.16 t/ha, resspcctively), By the second trial, ten corn hybrids were grown on similar soil and ordinary fertilization and depending on the hybrid grain yields were in the range from 3.61 to 9.59 t/ha. Two hybrids ((0sSK568exp. and OsSK602) yielded over 8.0 t/ha (mean 8.80 t/ha), and il is also possible by regular choice of hybrids considerably to increase corn yields under soil stress.

 

          Key words: corn, soybean, potassium, magnesium, grain yield, fertilization