THE EFFECT OF GREEN FERTILIZERS IN THE FORM OF FORECROPS ON THE CONTENT OF SELECTED ELEMENTS OF NUTRITIONAL VALUE IN LEEK (ALLIUM AMPELOPRASUM SPP. PORRUM) CV.'BLIZZARD'

Robert Rosa, Romualda Jabłońska-Ceglarek
Department of Vegetable Crops, Podlasie University in Siedlce, Poland

ABSTRACT

The experiment was conducted in the years 2003-2005. The purpose of the undertaken studies was, among others, to determine the consecutive effect of forecrop green fertilizers on the content of dry weight, total sugars and reduction sugars, L-ascorbic acid and protein in the utilized parts of leek, 'Blizzard' cv. Leek was cultivated in the second year after applying organic fertilization. Sugar maize grown directly after ploughing in organic fertilizers was the forecrop for leek. Plants for green manure (oats, field pea, common vetch and mixtures of those plants) were sown at the beginning of April and ploughed over in the first days of June of 2002-2004. The consecutive effect of green fertilizers was compared with the effect of manure in the dose of 25 t ha^-1, which was ploughed over in the same date as green fertilizers. The studies found out significant differences in the content of dry weight, total sugars and reductions sugars as well as protein in leek depending on the year of cultivation. The greatest amount of sugars and protein was found in leek in 2003, and the greatest amount of dry weight – in the years 2003 and 2005. Green fertilizers had a similar or more positive consecutive effect on the content of the studied elements of nutritional value in leek. Green fertilizer of oats ploughed under sugar maize caused a significant increase of the content of dry weight in leek as compared to fertilization with manure and green fertilizer of common vetch. Ploughing in the green fertilizer in the form of a mixture of oats with common vetch, on the other hand, had a more positive consecutive effect than the catch crop of oats on the accumulation of reduction sugars by leek. More reduction sugars were also found in the leek cultivated in the combinations with catch crops ploughed over as a whole than only with aftercrop residue. The cultivation of leek in the second year after ploughing over the biomass of a mixture of oats with field pea and vetch had the most positive effect on the accumulation of L-ascorbic acid and protein.

Key words: green fertilizers, manure, leek, dry weight, L-ascorbic acid, sugars, protein.

INTRODUCTION

The health, dietetic and nutritional value of vegetables is determined, among other factors, by the content of vitamins, acids, mineral salts and protein. The content of these elements is largely dependent on the cultivar, and the size and quality of the yield [13]. A significant effect on the chemical content of vegetables is also exerted by fertilization. High doses of mineral fertilizers used in horticulture may cause a worse quality of the yields. Increased nitrogen fertilization causes a decreased content of the dry weight, sugars, vitamin C and other anti-oxidants in vegetables [1,16,18]. Intensive mineral fertilization also affects accelerated decomposition of the organic matter. This has a negative effect on the fertility and productivity of soils [10]. In order to balance the quantity of organic matter in the soil, it is necessary to apply systematic organic fertilization. Worldwide tendencies to produce healthy food and to protect the environment gave rise to a renewed interest in green fertilizers. The cultivation of intercrop green fertilizers is the most effective way of limiting washing away nutritional elements, especially nitrogen, within the soil profile [3,11,14,15].

Scientific papers on the effect of organic fertilization in the form of green fertilizers on the nutritional content of vegetables are scarce. Earlier studies by Jabłońska-Ceglarek et al. [7,8,9] point out that vegetables cultivated after green fertilizers are characterized by a similar or a higher content of the dry weight, sugars and vitamin C as compared to those grown after manure.

The purpose of the present paper was to find the consecutive effect of green fertilizers sown and ploughed over in spring on the content of dry weight, total sugars, reduction sugars, L-ascorbic acid and protein in the utilized parts of leek cv. 'Blizzard'.

METHODS

The experiment was conducted in the years 2003-2005 at the Agricultural Experimental Station in Zawady near Siedlce, belonging to the University of Podlasie. The field experiment was carried out on the soil belonging to the brown ones, of the grey brown podzolic type formed of dusty sands lying on loose sands. The mean content of humus was on the level of 1.5%, and the humus level reached to the depth of 30-40 cm. The soil reaction was acidic – pH in H₂O 5.6. Considering the agricultural value the soil belongs to class IVa of the good rye complex. According to the international system of classification FAO, the soil was classified within group Luvisols (LV) [17]. The experiment was established in a split-block scheme in four repetitions. It studied the consecutive effect of forecrop green fertilizers on changes of the dry weight, total sugars, reduction sugars, L-ascorbic acid and protein in leek cv. 'Blizzard'.

Plants for green fertilizer were cultivated in the years 2002-2004. The seeds of oats (Avena sativa) (the sowing norm 240 kg ha^-1), field pea (Pisu, arvense) (160 kg ha^-1), common vetch (Vicia sativa) (140 kg ha^-1) and the mixtures of oats with field pea (100 kg ha^-1 + 130 kg ha^-1), oats with common vetch (80 kg ha^-1 + 100 kg ha^-1), field pea with common vetch (70 kg ha^-1 + 50 kg ha^-1), oats with field pea and common vetch (100 kg ha^-1 + 70 kg ha^-1 + 50 kg ha^-1) were sown in the first 10 days of April. Plants for green fertilizer were ploughed over as a whole or after cutting the aboveground part, as aftercrop residues at the turn of May and June.

Before sowing the plants for green fertilizer, mineral fertilization was applied in the quantity of 30 kg N ha^-1 for field pea and common vetch in pure sowing, 90 kg N ha^-1 for oats in pure sowing, 30 kg N ha^-1 for a mixture of field pea with common vetch, 60 kg N ha^-1 for mixtures of oats with field pea and oats with common vetch, 40 kg N ha^-1 for a mixture of oats with field pea and common vetch. Phosphorus and potassium fertilization for all combinations was 80 kg P₂O₅ ha^-1 and 160 kg K₂O ha^-1.

Maize was cultivated directly after ploughing over the green fertilizers. Leek was cultivated in the second year after organic fertilization. A combination without organic fertilization and a combination with ploughed over manure in the dose of 25 t ha^-1 were the control objects. Ploughing over the manure took place simultaneously with the plants which constituted the green fertilizer.

The seedlings of leek were produced in a non-heated glasshouse. The seeds were sown into boxes in the middle of March, the seedlings were planted in a permanent stand in the first half of June at the spacing of 40×20 cm. Three weeks before planting the seedlings, mineral fertilization was applied in all combinations of organic fertilization in the quantity of 140 kg N, 140 kg P₂O₅, 215 kg K₂O per 1 ha. The agricultural treatments were in accordance with the generally accepted principles of agricultural measures for leek. Leek harvest was performed manually at the turn of October and November. Then, representative samples of the utilized parts (bulbs) were taken with the aim of making chemical analyses for the content of the dry weight (a dry-weight method), total sugars and reduction sugars (Luff-Schoorls' method).

L-ascorbic acid (Pijanowski's method) and protein (Kjeldahl's method). The conversion rate of 6.25 was used to convert the content of nitrogen to protein. The obtained results were statistically analyzed using variance analysis. The significance of differences of the mean values was established by means of Tukey's test at the level of significance p = 0.05.

Fig. 1 presents characteristics of the weather conditions in the years 2003-2005, including the mean air temperatures and the sum of atmospheric falls in the period of leek vegetation.

RESULTS AND DISCUSSION

The fertilizing value of manure and catch crops, including the quantity of the dry weight and macro-elements ploughed with it, is presented in Table 1. 6.4 t ha^-1 of dry weight was introduced with manure in the dose of 25 ha^-1. Among the green fertilizers, the greatest amount of dry weight was provided to the soil by the whole plants of oats as well as mixtures with it. Totally, the greatest amount of mineral elements was ploughed in with the total biomass of the mixtures of vetch with oats and vetch with oats and field pea (respectively, 246.1 kg NPKCaMg and 244.2 kg NPKCaMg per 1 ha). Among the aftercrop residues of forecrops, the greatest amount of mineral elements was contained in a mixture of vetch with oats and field pea as well as a mixture of oats with field pea (respectively, 60.7 kg NPKCaMg and 56.1 kg NPKCaMg per 1 ha was ploughed with them). 360 kg NPKCaMg was introduced with manure per 1 ha of the soil.

The present experiment found out considerable differences in the content of green weight, total sugars and reduction sugars in 'Blizzard' cv. leek in particular years of the studies (Table 2). The greatest significant content of dry weight (17.51% and 17.88%) was characteristic of the leek cultivated in the years 2003 and 2005 while it was considerably smaller (16.06%) in 2004. The greatest amount of reduction sugars (4.03% fresh weight) was found in the bulbs of leek cultivated in 2003, significantly the smallest amount was found (2.92% fresh weight) in 2004. The greatest amount of total sugars (7.44% fresh weight) was also found in the leek cultivated in 2003, significantly less in the years 2004 and 2005 (respectively, 7.07% fresh weight and 6.99% fresh weight).

The mean content of dry weight in 'Blizzard' leek was at the level of 17.05%. That content was modified by the kind of organic fertilization applied under sugar maize. The greatest amount of dry weight was found in the leek from the combination where green fertilizer of field pea (17.87%) was ploughed in, significantly less was found in the combination with ploughed manure (16.63%) and green fertilizer in the form of common vetch (16.82%). The content of dry weight in the leek cultivated in the second year after ploughing the other green fertilizers did not differ in a significant way.

The amount of reduction sugars in leek depended on the form of ploughing the green fertilizers and on the kind of the applied organic fertilization. Leek cultivated in the second year after ploughing the whole catch crop plants was characterized by a significantly higher content of reduction sugars as compared to the leek cultivated after ploughing only the after crop residues. The difference was 0.18% of fresh weight. While studying the consecutive effect of the kind of organic fertilization it was found out that the greatest amount of reduction sugars (3.67% fresh weight) was contained in the leek from the combination with ploughed in green fertilizer in the form of a mixture of oats with common vetch. A significantly smaller content (3.21% fresh weight) was found for leek cultivated in the second year after ploughing in the catch crop of oats. The content of reduction sugars in leek cultivated in the second year after ploughing in green fertilizers did not differ in a significant way.

The content of total sugars in the leek gathered from particular combinations of organic fertilization ranged from 6.91 to 7.48% of fresh weight. The statistical analysis of the obtained results found out no significant consecutive effect of the studied factors on this content.

In earlier studies, Jabłońska-Ceglarek and Rosa [6] observed no significant differences in the content of dry weight in red beet cultivated in the third year after forecrop green fertilizers and manure. The best effect on the accumulation of total sugars and reduction sugars was exerted by ploughing a mixture of oats with field pea and vetch. Beet cultivated after this fertilizer had a significantly higher content of reduction sugars that that cultivated after manure. The authors also found out that red beet cultivated after ploughing as a green fertilizer of the whole biomass of catch crops was characterized by a significantly smaller content of dry weight and a significantly higher content of total sugars that beet cultivated after green fertilizer from the aftercrop residues of catch crops. The positive effect of green fertilizers on the content of dry weight and sugars, which was similar to the effect of manure, was also proved in the studies by Franczuk et al. [4].

In the present studies the mean content of L-ascorbic acid in the utilized part of leek cv. 'Blizzard' was 16.38% of fresh weight (Table 3). Leek cultivated in the second year after ploughing in a catch crop of a mixture of oats with field pea and common vetch had a significantly higher content of L-ascorbic acid that the leek cultivated in the control combination without any organic fertilization, and after ploughing in manure and green fertilizers in the form of oats, common vetch and a mixture of oats with common vetch. The consecutive effect of green fertilizers depended on the form they were ploughed in. The most L-ascorbic acid (17.46 mg% of fresh weight) was found in the leek cultivated in the second year after ploughing in the whole plants of a mixture of oats, field pea and common vetch. A significantly smaller content of it was observed in the leek cultivated after green fertilizers in the form of whole plants of a mixture of oats with common vetch (15.56 mg% of fresh weight), a mixture of field pea with common vetch and common vetch in pure sowing (16.07 mg% of fresh weight each), after manure (16.17 mg% of fresh weight) and in the control object without any organic fertilization (16.20 mg% of fresh weight). Leek cultivated after green fertilizers ploughed in under sugar maize in the form of aftercrop residues of field pea and the mixtures of oats with field pea, oats with common vetch, field pea with common vetch, oats with field pea and common vetch was characterized by a significantly higher content of L-ascorbic acid as compared to the leek cultivated in the second year after ploughing in the aftercrop residues of oats. The difference in the content of this element of the nutritional value ranged from 1.59 to 1.22 mg% of fresh weight.

The content of protein in the utilized part of leek was differentiated in particular studied years (Table 4). Its highest content (2.07% of fresh weight) was observed in 2003, while being significantly smaller (1.90% of fresh weight) in 2005. Organic fertilizers applied in the experiment had a similar consecutive effect on the amount of protein accumulated in leek. However, ploughing in manure and a green fertilizer from the mixture of oats with field pea and common vetch under sugar maize caused a significant increase of protein as compared to the control combination without any organic fertilization. Studying the total effect of the form of ploughing in the green fertilizer and the kind of organic fertilization, it was found out that after ploughing in the whole catch crop plants, the highest content of protein (2.16% of fresh weight) was found in the leek cultivated after a mixture of oats with field pea and common vetch. That quantity was greater than that which was found in the control object without any organic fertilization (1.91% of fresh weight) and after ploughing in oats (1.90% of fresh weight). Leek after ploughing in manure had a significantly more protein (2.08% of fresh weight) than leek cultivated after a green fertilizer from aftercrop residues of a mixture of field pea with common vetch (1.82% of fresh weight). Earlier studies by Jabłońska-Ceglarek and Rosa [5] observed a similar consecutive effect of forecrop green fertilizers on the content of protein in red beet to that of manure. The highest tendency to an increased content of protein in the roots of red beet was observed when beet was cultivated after a green fertilizer in the form of a mixture of oats, field pea and vetch. The authors also found out a significant increase of protein in beet cultivated after ploughing in the whole catch crop plants as compared to the beet cultivated after ploughed over aftercrop residues. Jabłońska-Ceglarek et al. [9] point to a positive effect of green fertilizers on the accumulation of protein in cabbage.

Results of studies presented here prove that despite a smaller quantity of dry weight and mineral elements introduced into the soil with green fertilizers as compared to manure, the nutritional value of leek cultivated in the second year after ploughing in the catch crop green fertilizers was similar to or higher than that which was observed in the cultivation after manure. Borna [2] claims that mineral elements contained in green fertilizers are more easily accessible to plants than the elements of manure, which can have an effect on their biological value. The studies by Kołota and Adamczewska-Sowińska [12] show that the content of mineral elements in vegetables cultivated on the ploughed over green fertilizers in the form of live bedding is similar to those cultivated after manure.

CONCLUSIONS

1. Significant differences were found in the content of dry weight, total sugars, reduction sugars and protein in leek depending on the year of cultivation. The weather conditions of 2003 had the best effect on the accumulation of sugars and protein, and those in 2003 and 2005 influenced the accumulation of dry weight in the best way.

2. The applied green fertilizers had a similar, and sometimes better consecutive effect on the content of the studied elements of the nutritional value of leek cv. 'Blizzard' as compared to manure used in the same time.

3. Ploughing in the catch crop of oats under maize had a significant effect on the increase in the content of dry weight in leek in comparison to ploughing in manure and catch crop of common vetch. On the other hand, ploughing in the green fertilizer in the form of a mixture of oats with common vetch had a better consecutive effect than the catch crop of oats on the accumulation of reduction sugars by leek.

4. Ploughing in the whole biomass of catch crops had a better consecutive effect on the content of reduction sugars in leek as compared to ploughing in the after crop residues themselves.

5. In its consecutive effect green fertilizer in the form of whole plants of the mixture of oats with field pea and common vetch caused a significant increase of the content of L-ascorbic acid in relation to the combination with ploughed over manure and green fertilizers in the form of common vetch, a mixture of field pea with vetch, a mixture of oats with vetch and in the control without any organic fertilization.

6. Leek cultivated in the second year after ploughing in a mixture of oats, field pea and common vetch was characterized by a higher content of protein than that cultivated after ploughing in oats and in the control object without any organic fertilization.

7. The content of L-ascorbic acid and protein in leek cultivated in the second year after ploughing in the aftercrop residues and manure was similar.

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Accepted for print: 23.10.2008

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