A STUDY ON THE EFFECTS OF FOLIAR FEEDING UNDER DIFFERENT SOIL FERTILIZATION CONDITIONS ON THE YIELD STRUCTURE AND QUALITY OF COMMON OAT ( Avena sativa L . ) Stanis ł

The present study was conducted based on a field experiment established on very acidic medium soil (silt loam). The experimental design included 4 soil fertilization treatments: O, NPK, NPK + MgSO4. 7H2O, NPK + CaO + MgO, and 3 foliar feeding treatments: O(H2O), Insol PK + 5% urea solution, Ekosol U. The test plant was the oat cultivar ‘Kwant’. The aim of this study was to characterize in detail the response of oats to foliar feeding under the conditions of different soil fertilization with calcium and magnesium compounds. The experimental factors applied increased the yield parameters and differentiated the nutrient content in oat grain and straw. Soil fertilization had a greater effect on the quality parameters of primary yield than the foliar fertilizers used in the study. The best production and quality effects in growing oats were obtained after the application of MgSO4 and magnesium lime. Foliar feeding also affected beneficially the quantitative and qualitative characteristics of the yield. Among the fertilizers used, Insol PK showed a better effect than Ekosol U, in particular on the yield structure and the amino acid composition of proteins.


INTRODUCTION
The oats acreage in Poland has decreased from year to year and in 2012 it was at a level of 543,000 ha with an average yield of 2.6 t ha - 1 .In spite of an increasing trend in oat yields in this area, there is still a large growth potential in relation to other Europe's oat producers.Oats is cultivated mainly for fodder purposes.Up to 20% of the world production is used in food industry uses.In our country, for consumption only 3% of the oats harvest is used, but this cereal crop is becoming more widely used in the production of healthy food, because it is a valuable source of dietary fiber.One of the most important criteria of the value of cereal grains is their protein content, since it determines their nutritive, feeding and technological values [1].
In addition to the growing qualities, fertilization, the basic aim of which is to meet the nutritional requirements of the crop plant, is an essential element of agricultural technology that determines the quantity and quality of final yield.Apart from basic nutrients (NPK), other elements showing yield-increasing effects, which include Mg, S and micronutrients, are also used more and more frequently in fertilization under intensive plant production conditions [1,2,3,4].Plants take up nutrients mainly from the soil through the root system, but foliar application of nutrients has been gaining an increasing importance in recent years.For this purpose, an aqueous solution of urea or liquid, suspension or crystalline compound fertilizers are used to prepare solutions.These solutions are able to penetrate across the cuticle layer through the ectodesmata which are mainly located near the xylem and phloem bundles.
A major advantage of foliar feeding of plants is the speed of action and a high level of use of nutrients supplied [5,6,7].Foliar applied nutrients are better used by plants compared to conventional soil application [8,9,10].Foliar fertilizers can be used in combination with other agrochemicals [11], if only there are no manufacturer's contraindications and economic reasons and higher effectiveness of agents applied speak for that [12,13].Foliar feeding of plants belongs to the most effective and at the same time most environmentally beneficial fertilization techniques [14,15,16].

MATERIALS AND METHODS
This study was carried out based on a threeyear field experiment on medium soil with a pH of 4.2 in 1 mole KCl.dm -3 and with the granulometric composition of silt loam in Rudnik (50 o 53' 23.9912 " N 22 o 57'59.8938"E).This soil was characterized by a low content of available phosphorus and potassium as well as a very low content of sulfur and magnesium.
In 48 m 2 plots in which the oat cultivar 'Kwant' was grown, mineral fertilization was used at a rate of 90 kg N × ha -1 , 38 kg × P ha -1 , 108 kg K × ha -1 in the form of Polifoska 6-20-30 and ammonium nitrate as well as every year before sowing magnesium was applied at a rate of 19 kg Mg × ha -1 .Magnesium oxide lime was used in the first year of the experiment immediately after harvest of the previous crop according to single hydrolytic acidity.Foliar feeding was used 3 times during the growth period of oats at the stages of tillering, stem elongation and panicle emergence.In the treatments where plants were fed with Insol PK with the addition of urea, the rate of soil-applied nitrogen was reduced by 20.7 kg N × ha -1 , since such an amount of this nutrient was supplied to the foliage using the spray liquid in the form of 5% urea solution.
After the plants were harvested, grain and straw yield were determined.Qualitative evaluation includes the following basic yield components: grain weight per panicle, number of panicles × m -2 , 1000 grain weight, number of grains per panicle.These traits were determined based on samples collected from 1 m 2 in 3 replicates and subsequently the material obtained was used to prepare samples for laboratory analysis.
After mineralization in concentrated sulfuric acid with the addition of hydrogen peroxide, the following were determined in oat grain and straw: total N by the Kjeldahl method, K, Ca and Mg by AAS on a Hitachi Z-8200 polarized Zeeman atomic absorption spectrophotometer, P colorimetrically by the vanadium-molybdate method using a Cecil 2011 colorimeter.Total sulfur was determined according to B u t t e r s -C h e n e r y [17].The removal of macronutrients was calculated as the sum of a given nutrient in primary yield and straw based on the nutrient content in these organs.The qualitative evaluation of the yield showed the K : (Ca + Mg) mole ratios and N : S mass ratios, total protein content (N x 6.25), protein yield, and the amino acid composition of proteins.The grain amino acid content was determined by column chromatography using an Aminochrom II amino acid analyzer after hydrolysis in 6M HCl at 110 o C for 20 h according to the D a v i e s and T h o m a s method [18].Sulfur amino acids were determined according to Schramm and Moor method [19].
The total sum of amino acids, the sum of endogenous and exogenous amino acids as well as the limiting amino acid score for lysine, isoleucine and tryptophan were calculated.The limiting amino acid score (Chemical Score -CS) expresses the ratio of the exogenous limiting amino acid content in the tested protein to the content of this amino acid in the egg reference protein (WE).
The obtained results were evaluated by twoway analysis of variance and presented as means for the 3-year study period (1999)(2000)(2001).Means were analyzed by Tukey's multiple comparisons at a significance level of 0.05.

Yield potential
The experimental factors used differentiated the grain and straw yield as well as the basic yield components (Table 1).The foliar fertilizers increased the yield and basic yield components compared to the control treatment and only the variation in 1000 grain weight was below the level of significance.Out of the two fertilizers used in the study, Insol PK showed a better effect on the grain yield than Ekosol U, mostly by increasing the number of panicles × m -2 , number of kernels per panicle, and number of spikelets per panicle.The particular soil fertilization treatments also differentiated the yield and yield components.The grain and straw yield, 1000 grain weight and number of panicles had the highest values after the application of NPK with CaO + MgO in fertilization, whereas magnesium sulfate MgSO 4 had a beneficial effect on the number of spikelets and number of grains per panicle.The interaction of soil fertilization and foliar feeding had a significant impact on the straw yield and number of grains per panicle.

The mineral composition of oat
The fertilization treatments used significantly affected the macronutrient content in oat grain (Table 2).Ekosol U caused an increase in phosphorus content, while Insol PK increased the calcium content.Both Insol PK and Ekosol U decreased the sulfur content in oat grain.The nitrogen content was significantly higher in the analyzed samples collected from the plots in all soil fertilization treatments in relation to the control.
Fertilization with the addition of CaO + MgO to the fertilizer dose significantly increased the calcium content compared to the other soil fertilization treatments.The lowest magnesium content in grain was found in the basic fertilization treatment (NPK), whereas the highest content of S and K as well as the lowest P content were obtained in the treatment with MgSO 4 .
Deacidification of soil also significantly increased the sulfur content compared to the control and basic fertilization treatments.The highest N content in grain, P and Mg content in grain and straw as well as Ca content in grain were obtained in this fertilization treatment.The interaction of soil fertilization and foliar feeding had a significant effect only on the sulfur content in oat grain.
The foliar fertilizers used caused a significant increase in the contents of macronutrients determined in straw (Table 3).Compared to the control treatment, only the potassium content was significantly lower than in the treatment with Ekosol U.
The nitrogen and potassium content in straw was higher in all soil fertilization treatments.A significantly higher content of phosphorus was found after the application of NPK + CaO + MgO, while a higher magnesium content was found in the treatments where this component was added to the fertilizer dose.All soil fertilization treatments increased the sulfur content in straw, which reached the highest content in the treatment with NPK + MgSO 4 .The interaction of the treatments used in the study significantly affected the contents of all macronutrients analyzed in straw.Feeding plants with Insol PK resulted in the highest removal of all macronutrients relative to the lowest values of this indicator in the control treatment (Table 4).The lowest values of nutrient removal, significantly differing from the other soil fertilization treatments, were found in the control treatment without fertilization.The highest macronutrient contents were generally observed in samples from the treatment with NPK + CaO + MgO, and only the amounts of potassium and sulfur were highest after the application of NPK + MgSO 4 .The interaction of foliar feeding and soil fertilization had a significant effect on the removal of all nutrients analyzed in the study.

Yield quality parameters
In the present study, foliar feeding practices were of little importance for differentiating the protein content in oat grain compared to the soil fertilization treatments used and this trait had the highest value in the treatment with NPK + CaO + MgO (Table 5).Among the foliar fertilizers used, Insol PK increased the protein yield by 16.5 %, while Ekosol U by 12.8%.Such a high increase in protein yield results from the beneficial effects of the foliar fertilizers used not only on the oat grain yield, but also on the grain protein content.Soil fertilization also had a greater influence on the protein yield than the foliar fertilizers, since all its treatments increased the protein yield compared to the con-trol, with the highest value in the treatment with NPK + CaO +MgO (Table 5).The value of the K : (Ca+Mg) ratio in straw was in the optimal range (1.6-2.1 : 1) in all soil fertilization and foliar feeding treatments; this range was minimally exceeded in the treatment with water spraying.The value of the K : (Ca+Mg) ratio in grain, much lower from the minimum value (1.6), does not result from a disturbance in the balance between these nutrients but from a naturally low content of potassium in the generative organs which contain reserve substances.The use of foliar fertilizers caused the N : S ratio in grain to widen, whereas among the soil fertilization treatments only NPK + MgSO 4 distinctly decreased the N : S ratio (Table 5).
Insol PK increased the content of endogenous and exogenous amino acids and beneficially affected the value of the quality parameter calculated for tryptophan (Table 6).After the application of Ekosol U, the endogenous amino acid content was at the level found in the control treatment and the proportion of exogenous amino acids (E/T) increased, but Ekosol U decreased the value of this quality parameter for lysine.A higher value of valine and histidine compared to the reference was found under the influence of Insol PK application.Relative to the control treatment, soil fertilization caused a decrease in the proportion of exogenous amino acids in protein.The application of NPK + MgSO 4 and NPK + CaO +MgO in soil fertilization contributed to obtaining the highest contents of endogenous and exogenous amino acids after the application of NPK + CaO +MgO fertilization (Table 7).When NPK + CaO + MgO fertilization was used, a higher content of va-line compared to the reference and the highest value of the quality parameter for lysine were obtained.A decrease in isoleucine was found in the treatments NPK + MgSO 4 and NPK + CaO +MgO, whereas the highest content of this component was obtained in the basic soil fertilization treatment (NPK).In the treatment NPK + MgSO 4 , the highest content of sulfur amino acids was found.

Yield potential
Numerous studies show the beneficial effect of foliar application of nutrients on the yield of crop plants and their quality parameters [1,2,20].The foliar fertilizers used in the present research increased the grain and straw yield, which is confirmed by other studies [20,21].The variation in the oat grain yield components was more dependent on soil fertilization used than on foliar feeding of plants.The oat belongs to plants that tolerate a high degree of soil acidification, but it responds favorably to liming of very acidic soils [22].Furthermore, it should be noted that magnesium lime was used in this study, which increased the beneficial effect of soil deacidification, since oats have higher requirements for this nutrient than other cereals [22,23].

The mineral composition
Foliar feeding influenced the macronutrient content in oat grain to a lesser extent than soil fertilization.This was related to the greater stability of the mineral composition of the generative organs, which mainly accumulate reserve materials in the form of organic compounds poor in potassium, unlike the vegetative parts, as well as to the small amount of nutrients supplied with the foliar fertilizers.The variation in the content of N, P and Ca in oat grain was not associated only with their penetration through the aerial part, but it also resulted from their higher uptake from the soil.The research using combinations of foliar fertilizers has shown their beneficial effects on increasing the rate of uptake and use of nutrients from the substrate [2,24].The activation of physiological processes such as photosynthesis, transpiration and respiration as a result of foliar supplied nutrients causes an increased demand of plant biomass for soil nutrients [25,26].A rise in the transpiration rate also increases nutrient uptake by increasing the suction force of the roots and the speed of movement of ions transported through the conductive tissues, while the respiration of plants is a source of energy necessary for transporting ions taken up by the root system [27,28,29].
Foliar feeding differentiated to a greater extent the macronutrient content in straw than in oat grainsimilar correlations have been found in other studies [24,30].
The used soil fertilization treatments differentiated the content of N, Ca, Mg and S in grain.Fertilization with the addition of MgSO 4 to the fertilizer dose increased the sulfur content in grain and straw, but decreased the P content in oat grain, which is in agreement with other results [31,32].The highest total S content in grain and straw was obtained in the treatment with MgSO 4 in the fertilizer mix, which has been shown in other studies [31,33].Sulfur deficiency in the soil results in a disturbance in basic physiological processes of the plant, primarily by reducing the photosynthesis rate, protein synthesis and nucleic acid content [34].A higher content of K, Ca and Mg in the treatment with S use in fertilization, compared to basic NPK fertilization, should be explained by the synergism of these cations in relation to SO 4  2-anions taken up by the plant [32,35,36,37].The lower N content in this fertilization treatment was associated with the antagonistic effects of SO 4  2-ions in relation to NO 3 ions [31].
The increase in the content of N, Ca, Mg and S as affected by liming results from the conversion of these nutrients into available forms, because liming of acidic soils increases the soil availability of macronutrients and improves their use by crop plants [22].K o z ł o w s k a [31] also showed an increase in Ca and Mg content in oat grain and straw after the application of CaCO 3 .Apart from N, Ca and Mg, liming also increased the content of P in straw, the availability of which is limited under acidic soil pH conditions due to its binding to Al 3+ and Fe 3+ ions in the form of sparingly soluble compounds [38].
As a result of foliar feeding with Insol PK, the highest values of nutrient removal were found for all nutrients analyzed in primary and secondary yield.Other studies also indicate higher nutrient removal as influenced by foliar feeding of plants [2,24].On the other hand, the highest removal of N, P, Ca and Mg was obtained in the liming treatment, since the availability of these nutrients increases with decreased soil acidity.

Yield quality parameters
Numerous studies have shown a beneficial effect of foliar application of micronutrients as well as of N and Mg among macronutrients on protein yield [1,2], but in the present study the increase in protein content as affected by foliar feeding was below the level of significance.The protein yield was more associated with the influence of foliar fertilizers on the grain yield than on the protein content in oat grain.
The N : S ratio in grain was in the optimal range of 10-15 :1 [39,40,41].Its higher values in the treatments poor in sulfur resulted from the lack of possibility to transfer SO 4 2-ions from the older vegetative organs of the plant to the younger developing generative organs [42].The K : (Ca+Mg) ratio was in the optimal range.Among the fertilization factors applied, foliar feeding narrowed the values of the K : (Ca+Mg) ratio in oat grain and straw, while the soil fertilization treatments used widened its value compared to the control treatment.
A valued property of oat protein is its high level of exogenous amino acids with a stable amino acid composition, regardless of its content in grain [43,44].According to the literature reports, isoleucine can be considered to be an amino acid that reduces the nutritional value of cereal protein [45,46,47], but in the present study lower values were found for lysine and tryptophan, aside from isoleucine.Despite that soil fertilization had a greater impact on the yield quality parameters than foliar fertilizers, foliar feeding should also be considered to be an agronomic practice that beneficially affects the amino acid composition of protein in oat grain.

CONCLUSIONS
1. Foliar feeding and soil fertilization increased the grain and straw yield of oat and had a beneficial effect on the yield components, but use of foliar fertilizers slightly differentiated the macronutrient content in oat grain.2. Feeding oat plants with Insol PK resulted in the highest removal of all macronutrients analyzed, but the differences were small in relation to the treatment with Ekosol U application, where as highest removal of N, P, Ca, and Mg was found under the influence of liming, while the treatment with the use of MgSO 4 had the greatest effect on the removal of K and S. 3. The foliar fertilizers showed a similar and small effect on the basic quality parameters of oat, but a by far higher yield of protein was obtained under the influence of Insol PK. 4. Soil fertilization exerted a greater effect on the quality parameters of oat than foliar feeding.The highest protein content and yield were found in the liming treatment.

Table 1
Grain and straw yield as well as the yield structure of foliar fertilized oats under different soil fertilization conditions

Table 2
Macronutrient content in oat grain after application of foliar feeding under different soil fertilization conditions

Table 3
Macronutrient content in oat straw after application of foliar feeding under different soil fertilization conditions

Table 4
Removal of macronutrient after application of foliar feeding of oats under different soil fertilization conditions

Table 5
Quality parameters of oat after application of foliar feeding under different soil fertilization conditions

Table 6
Effect of foliar feeding on the amino acid composition of oat grain protein AA -total amino acid; E/T -essential amino acid participation; CS -chemical score of restrictive amino acid; WE -whole egg protein standards

Table 7
Effect of soil fertilization on the amino acid composition of oat grain protein