Nutrient supply of crops is determinant from the aspect of yield levels and quality as well as yield stability (Fageria, 1992; Kádár, 1992; Sárdi, 1995; Kamprath, 2000; Sumner, 2000).
Changes in the parameters characterizing the nutrient status of plants in the early vegetative period shows that yield losses and decreases in yield quality cannot be avoided because of the inadequate nutrient supply.
For characterizing the nutrient status of crops, nutrient concentrations of plants and ratios are suitable. Nutritional status of plants can be adequate and optimum if the amounts of all the nutrient elements in the plant meet the specific requirements of the species and varieties.
Accordingly, the ratios of these elements are optimum for the plant. Adequate supply of nutrient elements related to crop requirements is determinant for ensuring high yield levels (Frageria et al., 1995). The maximum efficiency of fertilization can only be obtained when concentrations of essential nutrients in plants are near the critical nutrient supply category, thus potentially maximum yields can be reached without getting excessive amounts of nutrients into the soil (Fageria, 1992). Consequenly, obtaining exact information on the nutritional status of crops is an essential criteria for optimizing nutrient management practice.
Nutrient concentrations and ratios needed for the high yield levels and good quality were determined for describing the nutritional status were established by several authors (Reuter and Robinson 1988, 1997; Kádár 1992; Jones 1998; etc.). However, the database is still insufficient, reliable nutrient category intervals for several plant species, nutrient elements, growth stages and plant parts are incomplete and missing. Concentration ranges of nutrient supply categories published by different authors show a big variability, and sometimes they are inconsequential.
Because of their outstanding nutritive value – particularly as they have high protein content –, leguminous crops play a significant role both in animal feeding and human nutrition. By improving soil fertility and mobilization of soil nutrients, their production has several favourable influences on the following crops. In the last decades, peas and soybeans have been the two leguminous crops grown in the largest area in Hungary (http://portal.ksh.hu, http://www.akii.hu).
One of the main objectives of our research was to demonstrate responses of pea and soybean varieties to the increasing levels of nutrient supply with different nutrient ratios from the results of pot experiments and field trials.
Literature data available in Hungarian and international publications on the nutritional status of peas and soybeans were widely reviewed especially the numerical values characterizing nutrient supply. Our experimental results were compared to the collected database.
The other subject of this research was to extend the existing Hungarian database regarding the nutrient supply intervals and nutrient ratios suitable for characterizing their nutritional status.
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In the period of 2004-2006, pot and field experiments were carried out with peas (Pisum sativum L.) and soybeans [Glycine max (L.) Merrill]. Both the pot and the field experiments were carried out parallel and repeated in the second year with both crops under the same conditions.
The’Power’ pea and ’Boróka’ soybean varieties of the Bóly Agricultural Production and Commercial Share Company were applied in the experiments. Under greenhouse conditions plants were grown in pots using a lessivated brown forest soil (FAO taxonomy: Luvic phaeosem). Under field conditions, experiments were carried out in a chernozem brown forest soil (FAO taxonomy: Haplic Chernozem). The same treatments i.e. nutrient amounts were applied for peas and soybeans. Besides of the unfertilized control, 10 different treatment combinations were applied with increasing NPK fertilizer rates. The single rate nutrient amounts (N1, P1, K1) were calculated based on the amounts of available soil nutrients and the expected yields, as suggested in the literature.
Harvest and sampling dates were determined in order to evaluate the main parameters characterizing nutritional status of plants during the important periods of vegetation. Peas were harvested at the stage of 4 nodes, at the start of flowering and at full ripening; while soybeans at the start of flowering, at the start of pod filling and at full ripening.
For evaluating the results of experiments, average plant height, fresh weight, dry matter (DM) production, several yield parameters (number and average weight of pods, number and average weight of seeds, in field conditions also raw yield), N, P and K concentration, and nutrient ratios (N/P, N/K, K/P) were determined.
Plant height, fresh weight, dry matter production, number of pods and seeds, average weight of pods and seeds and raw yield were determined by simple measurements. Total nitrogen content of plants was analyzed with the Kjeldahl method. Phosphorus concentration was determined by using a spectrophotometer at 430 nm wavelength and potassium content by flame photometry at 766 nm. Nutrient ratios were calculated from the concentrations.
Experimental results were evaluated with analysis of variance at the P= 0.05 level (ANOVA test).
Hungarian and international literature of peas and soybeans since 2001 was thoroughly studied. One of the main tasks of this present study was to get reliable information on the optimum nutrient supply of these two crops, so intervals of nutrient supply categories and the adequate nutrient ratios were collected and evaluated.
While evaluating the experimental results, differences i.e. surpluses in production were compared to the unfertilized control. Because of the increasing costs of agricultural production and also from the aspect of environmental considerations, an other comparison was also important: experimental results were compared to the N1P1K1 treatment as well, as
„adequate” level, according to the previous „standard” fertilizer recommendation system MÉM NAK (Antal et al., 1979) in Hungary.
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Results of the experiments called the attention to the favourable results of low rates of fertilizer treatments for both environmental and economic considerations. The productivity and the NPK nutrient content obtained with the N1P0.5K1 and N0.5P1K0.5 combinations of peas was not significantly different from those of the N1P1K1 treatment. In the field experiments carried out with soybeans, productivity of the N0.5P0.5K0.5 and N1P0.5K1 treatments were similar when compared to the results of N1P1K1 treatment. These results showed the necessity of further studies whether lower fertilizer rates for pea and soybean production practice may be reasonable.
N, P and K concentrations and N/P, N/K and K/P ratios measured in the experiments were compared to and evaluated together with data available in Hungarian and international literature.
It was found that the database describing the level of N, P and K nutrient supply is still not complete. Comparing the nutrient concentration intervals and ratios of the experiments with literature data was not enough to obtain reliable information on the physiological status of plants. Relatively more sources could be found regarding the „adequate” nutrient supply category. The published data are often inconsistent, intervals are overlapping, are sometimes seemingly too close or even too wide.
Based on the comparison of nutrient concentrations and ratios of the experiments with literature data it could be stated that data interpretation was rather difficult. In several cases there could not be found any treatment where the concentration values would not be classified as „adequate” based on at least one of the sources. The same values may show nutrient deficiency or even nutrient excess compared to the results given by other authors. Literature data regarding the nutrient ratios were also rather variable. Based on these, it was difficult to evaluate experimental results in an objective way.
Results of pot and field experiments discussed in the PhD dissertation and thesis provided new and complementary results for the evaluation of nutrient supply level of peas and soybeans. These results give an extension of the Hungarian database and contribute to the evaluation of further experiments in order to obtain more information on the nutrient supply of these two crops.
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