EFFECTS OF PSEUDOGLEY CHEMICAL AMELIORATION ON THE CHANGES IN SOIL AND PLANT PHOSPHORUS AND POTASSIUM

Pseudogley is a soil type that is under natural conditions characterized by unfavourable properties, the most pronounced being insufficient amounts of basic plant nutrients. Using different amelioration measures, numerous researchers have tried to overcome the problems resulting from soil acidity (increased aluminium and manganese contents, deficiency of alkaline cations in the adsorption complex and reduced available phosphorus content). Calcification was the most common measure almost always producing the best results of all the measures. In order to determine the effect of some neutralization acidity materials derived from natural sources (bentonite, zeolite, lifos, CaO and MgO) on the change in the available phosphorus and potassium contents, a trial was set up on extremely acid soil to determine the manner of change in the nutrients concentrations in maize leaf and grain. The results obtained show that all ameliorative measures used affected the soil phosphorus and potassium contents increase, depending on the reduction of acidity and the mobile aluminium content, resulting also in a better uptake of the nutrients from the soil.


I n t r o d u c t i o n
The existence of poor physical, chemical and biological properties of the pseudogley soil type is a complex problem occurring in plant production organization on the soil.Of the chemical ones, the most commonly investigated seem to be pronounced soil acidity, increased aluminium and manganese contents, alkaline cation deficiency in the adsorption complex and reduced available phosporus content (O k i l j e v i ć , 1982; D u g a l i ć , 1997; R a d a n o v i ć and Predić, 1997).
According to the investigations of O k i l j e v i ć (1982) great soluble aluminium amounts caused not only the readily available phosphorus reduction in the soil, but also the slow rate of movement of the uptaken phosphorus from the root to the aboveground plant part, due to which phosphorus content in the root and the content in the stalk and leaves were respectively alike and twice lower than that in healthy plants.
Using different amelioration measures, numerous researchers have tried to overcome the problems resulting from soil acidity.Calcification was the most common measure almost always producing the best results of all.Using calcification, J o v a n o v i ć et al. (1995) achieved an increase in the available phosphorus and potassium contents from 3.0 up to 4.6 mg/100 g soil and from 11.4 to 13. 2 mg/100 g soil, respectively.The use of chemical ameliorations by B r k o v i ć and P e t r o v i ć (1995) resulted in phosphorus and potassium increase from 6.9 to 10.5 mg/100 g soil and from 5.0 to 7.1 mg/100 g soil, respectively.The investigations of D u g a l i ć (1997) conducted on the Kraljevo pseudogley also confirm the positive calcification effect, considering the increase of readily available phosphorus (by 8.4 mg/100 g soil compared to the control) and potassium (by 6.8 mg/100 g soil compared to the control).
The available phosphorus and potassium contents in the soil investigated exceeded average values, being previously determined in some natural pseudogleys (A n i c e v a et al., 1981).
In order to determine the effect of some ameliorative measures on the change in the available phosphorus and potassium contents, a trial was set up on extremely acid soil, for the observation of the change of the concentration of the nutrients in the leaf and grain of maize, considering the potential difficulties in plant mineral nutrition on acid soils.

Material and Method
The trial was set up on the pseudogley type of soil of extremely acid reaction (pH/KCl about 3.55) with high mobile aluminium content (>37 mg/100 g soil).
The available phosphorus and potassium contents, depending on the site, ranged from 13.2 -15.0 mg/100 g soil and from 23.8-30.1 mg/100g soil, respectively (tab.1).Three years' investigations were conducted with the change of the trial location on an annual basis.The surface area of the basal plot was 14 m 2 , and the variants studied were carried out in three replications, using the random block design method.The trial was set up in the 11 variants, being as follows: 1 Every year, prior to conducting the experiment, soil samples were taken from the plowed up layer of the soil for chemical analyses.
The acidity neutralization materials mentioned were applied to the soil surface and then introduced by disking with the NPK fertilizer (15:15:15, 600 kg/ha).The same NPK fertilizer rate was added to the control variant.250 kg/ha KAN (ammonium nitrates) were added by top dressing.
Maize planting (hybrid NSSC 201) was performed towards the end of April during the maize growing seasons in 1996, 1997 and 1998.
During the growing seasons of 1997 and 1998, at the tasseling stage, maize leaves were sampled for laboratory investigations.Samples of maize grains at the technological maturity stage were collected for examining the phosphorus and potassium concentrations.
Following the maize harvesting, soil was sampled from each variant and replication for the analysis of the available phosphorus and potassium contents.
The soil content of available phosphorus and potassium was determined by AL-method after Egner-Riehm, phosphorus concentration in the leaf and grain of maize was established by the molybdate-vanadate method and potassium -by flame photometry.
Statistical significance between the obtained data was determined by the LSD-test and the analysis of interaction effects is presented graphically.

Results and Discussion
All ameliorative measures used affected the improvement of available phosphorus soil supply (tab.2).
The use of bentonite in both variants and of lime, pure or in combination with MgO, caused the increase of available phosphorus in the range of 3.7 to 5.8 mg/100 g soil, as compared to the control.The increase in available phosphorus after the use of lime materials was due to the release of phosphorus from slowly soluble soil compounds (Al, Mn and Fe -phosphates) in the newly developed soil acidity conditions.The proof thereof are negative coefficients of correlation between the parametres investigated (r= -0.601 (Al), r = -0.439(Fe), r = -0.460(Mn)).Similar increases in available phosphorus in the pseudogley following calcification were obtained by J o v a n d i ć et al. (1973) The use of zeolite and lifos, which did not significantly alter soil acidity, resulted in the smaller increase of available phosphorus ranging from 0.8 to 2.5 mg/100 g soil.
Direct dependence of the content of available phosphorus in the soil on the state of soil acidity was proved by high correlation degree (r = 0.531 (pH/H 2 O), r=0.628 (pH/KCl)), graph 1.In the pseudogley studied, prior to the setting up of the experiment, the potassium content varied from 23.8 to 30.1 mg/100 g soil, depending on the trial locality (B o s k o v i ć -R a k o c e v i ć Ljiljana, 2001).However, regardless of the good soil supply with available potassium, all ameliorative measures used exerted a positive effect on the increase of the content of available potassium in the soil (tab.3).
In most cases, the decrease in the soil acidity caused an increase in the potassium content.However, in the variant with zeolite, where the decrease of substitutional acidity was minimal (0.08 pH units), the potassium content increase was maximal (about 9 mg/100 g soil) due to the application of higher rates of potassium to the soil from zeolite consisting of considerable amounts of potassium (0.56 %, unpublished data ITNMS).In order to explain the phenomenon, the antagonistic effect of Ca and K-ions must be taken into account.Namely, the use of zeolite caused the lowest increase of the available calcium content in the soil as compared to other ameliorative measures, whereas in the same variant potassium increase was highest.On the other hand, the initial soil heterogeneity in the content of available potassium leads to a conclusion that the ameliorative measures used could not have a significant effect on the increase of potassium content in the newly created soil conditions but it was rather the result of natural heterogeneity of the terrain.Different opinions could be found in literature.Some authors (J o v a n d i ć , 1973; P r e d i ć et al., 1997, M a r k o v i ć , 2000) maintain that calcification has a positive effect on the increase of the content of available potassium in the soil, others (R a d a n o v i ć , 1996; B r o ć i ć , 1997) either attribute the changes to natural heterogeneity of the terrain or have not obtained any significant increases in the potassium content in their investigations.Average values of phosphorus concentration (tab.4) in the leaf of maize varied from 0.242 % (higher lifos rate) to 0.317 % (higher lime rate).
The changes in phosphorus concentrations in the leaf of maize show the expected increasing trend, depending on the ameliorative measure used and the changes they caused in the soil.It was only in the variant with the higher lifos rate used that the phosphorus concentration in the leaf of maize was lower than in the control variant, which had been expected, since this measure had insignificantly reduced soil acidity and the content of mobile aluminium, whereas the established content of available phosphorus in the soil was lowest of all variants since aluminium prevents phosphorus uptake by Al-phosphate deposition in the soil.All the rest ameliorative measures had a positive effect on the increase of phosphorus concentration in the leaf of maize, because they reduced the content of aluminium in the soil to a greater or smaller degree, and thus problems made by aluminium during the phosphorus uptake had been differently solved, which was also determined by R a d a n o v i ć and P r e d i ć (1997).Phosphorus concentration in the grain of maize does not depend on the ameliorative measures used and it ranges from 0.218 -0.326 %, being within the average values (J e v t i ć , 1986).
The analysis of the content of available potassium in the soil has shown high supply of the investigated pseudogley with this nutrient, and thus the values of potassium concentration in the leaf and grain of maize are above the average ones and have not significantly changed under the effect of ameliorative measures used (tab.5).
Of special importance are high potassium concentrations in both leaf and grain of maize in 1997, being the result of higher content of available potassium in the soil and favourable climatic conditions, due to which potassium uptake in this year was better than in 1998.
The determined changes in the potassium concentration in the leaf of maize can be explained in two ways.Considering the high content of available potassium in the soil, no reaction to the effect of ameliorative measures was likely and differences in the concentration of potassium in the leaf of maize were the result of the effect of initial differences in the available potassium caused by the heterogeneity of the terrain.Furthermore, if we assume that the uptake of potassium, as well as of majority of cations, was made difficult due to toxic effect of aluminium in the soil, then the increase in potassium concentration in the leaf of maize, determined in all the variants where acidity and mobile aluminium were reduced, could be explained by positive effect of these measures.In their investigations, R a d a n o v i ć and P r e d i ć (1997) came to a similar conclusion, whereas L u t z et al. (1972a) identified minimal or no effect of calcification on the availability and uptake of potassium by maize plant and the increase of potassium uptake with the soil pH increase being, however, the result of the increase in the maize biomass yield at higher pH values.The values of potassium concentration in the grain of maize are far above the average ones and do not show any dependence on the ameliorative measures used.

C o n c l u s i o n
Based upon the paper goal and three-year studies, the following conclusions could be drawn : All ameliorative measures affected the improvement of soil supply with available phosphorus.Average increase ranged from 0.8-5.8mg/100 g soil, depending on the reduction of acidity and the content of mobile aluminium in the soil.
Notwithstanding good soil supply with available potassium, all ameliorative measures used had a positive effect on the increase of the content of available potassium in the soil.

2 O
Readily available phosphorus (mg/100 g) Graph 1. -The pH value effect on the content of available phosphorus in the soil R E F E R E N C E S PROMENE SADRŽAJA PRISTUPAČNOG FOSFORA I KALIJUMA I NJIHOVIH KONCENTRACIJA U LISTU I ZRNU KUKURUZA GAJENOG NA KISELOM ZEMLJIŠTU Ljiljana Bošković-Rakočević, 1 M. Ubavić, 2 M. Jakovljević 3 i Jelena Milivojević 4 , D u g a l i ć (1995,1997) and M a r k o v i ć (2000).
The content of readily available potassium in the soil (mg/100 g soil) T a b. 3. - T a b. 4. -Phosphorus concentration in the leaf and grain of maize (%) T a b. 5. -Potassium concentration in the leaf and grain of maize (%)