Problems of sulphur in plant nutrition and sulphur containing fertilizers in Poland

Problematika výživy a hnojení sírou v Polsku

Filipek-Mazur Barbara, Mazur Kazimierz, Labudda J.

Souhrn

Zemědělské půdy v Polsku obsahují od 70 do 1070 mg celkové síry . kg-1 v závislosti na půdním druhu a obsahu organické hmoty. Během posledních deseti let se v Polsku emise SO2 snížily o 48 % a v průměru představují 40 kg S . ha-1 za rok. Na plodinách náročných na síru se začaly objevovat příznaky deficitu tohoto prvku. Z používaných průmyslových hnojiv třicet obsahuje S a těmito hnojivy je každoročně do půdy dodáno maximálně 60 kg S . ha-1.

Sulphur is an element, which belongs to food macroelements. The sources of sulphur in agrosystems may be divided into two groups: natural and anthropogenic. Among natural sources are products of weathering of primeval minerals in the matrix (pyrite and marcasite) and volcano eruptions. In sulphides and sulphates the element contents may reach 25%. Sulphur contents in the sedimentary rock in Poland is estimated 0.4% S and is higher than an average in the Earths crust (0.02-022 % S). Because 90% of soils in Poland developed from sedimentary rocks (in 90%), sulphur is one of their 6 main nutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulphur). The greatest amounts of sulphur are found in the native sulphur deposits where they range from 20 to 30% S, sometimes even reaches 90%. The anthropogenic sources include atmospheric sulphur from various industrial emissions, mineral extraction and processing, burning liquid and solid fuels, transport or chemicalization of agriculture), which later returns to the soils and waters with precipitation and as sulphur from mineral and organic fertilizers. The most important sulphur compounds emitted into the atmosphere are sulphur dioxide and sulphur hydrogen.

Economic crisis in the nineties and pro-ecological activities led to decreased emissions of sulphur dioxide into the atmosphere in 1988-2000. According to the data of Central Statistical Office in 1988-1998 SO2 emission into the atmosphere decreased by 48%. The greatest share in SO2 emission into the atmosphere has power industry (55%), municipal sector (19%), motoring and unorganised sources (17%) and industrial technologies (9%) [Rocznik Stat. 1998,1999,2000; Zanieczyszczenie powietrza w Polsce 1994-1998].

In 1997-1998 average annual concentrations of sulphur dioxide ranged from 2 to 54 ě · m-3. In 58% of measuring points the values were lower by half that the permissible values. Currently (2000) emission of sulphur compounds into the atmosphere remains on c.a. 40 kg S · ha · year-1 level and reveals a decreasing tendency. Despite limiting the emission of sulphur compounds in the regions where previously the greatest emissions were noted (Katowice and Kraków vicinity) it still remains a factor, which to a greatest degree contributes to soil acidification. Rapid decline in soil pH also happens in the direct vicinity of opencast sulphur mines (Tarnobrzeg region). In these areas oxidation of elementary sulphur is the reason of their chemical degradation. Just soil degradation due to their acidification and accompanying excessive uptake of some toxic elements (Cd, Pb, Zn or Al) leading to worse yield quality, are the disadvantageous effects of elevated soil sulphur contents as sulphates.

Sulphur contents in the soils of Poland

Three forms of sulphur: total sulphur, organic sulphur and sulphate sulphur [Motowicka-Terelak et al. 1988] are considered in the evaluation of this element contents, plant supply and threat of its excess to ecosystems.

Total sulphur contents is mainly affected by the matrix, the amount of organic matter and SO2 emission. In the soils of Poland the contents ranges from <20 mg to over 200 mg S 100 g-1 in mineral soils, and in organic soils it did not exceed 500 mg S·100g -1. Soils from the agricultural regions are characterised by a narrower range of total sulphur (7-107 mg S 100 g-1) and vary depending on the soil textural groups (tab.1).

I. Total sulphur contents in soil textural groups (mg S 100 g-1)*

*Motowicka-Terelak et al. 1998

The contents of sulphur in the soils of Poland changes with the depth of soil profile

II. Total sulphur contents in humus horizons of various soil textural groups

(mg S·100 g-1)

1.

Sulphur contents in the top soil horizons of mineral soils increase with raising share of floatable fraction. The highest concentrations were found in mineral-organic and organic soils (tab. II).

Among mineral deposits rendzinas are soils the most abundant in sulphur. This is due to high contents of organic matter in these soils and their reaction favouring precipitation of sulphate ions from emissions [Motowicka-Terelak 1993].

In the soils of Poland organic sulphur is a dominant form of this element (tab. 3). The share of organic S in humus horizons of mineral soils ranges from 50 to 80% and in organic soils reaches even 97% [Lityński, Jurkowska 1982].

III. Contents of organic sulphur (mg S 100 g-1) in some soil types

and textural groups*

*Motowicka-Terelak et al. 1988

Quantities in which sulphate sulphur occurs in Polish soils ranges from trace amounts to several mg S ·100 g-1 (tab. IV). Only in some organic deposits it approximates many mg S ·100 g-1. Studies conducted at the Institute of Soil Science and Plant Cultivation and Fertilisation reveal that in some heavily polluted regions of Poland the contents reach 50 mg S·100 g-1 [IUNG Report 1997].

IV. Average S-SO4 contents (mg S 100 g-1) in soil texture groups*

* Motowicka-Terelak et al. 1988

Limit numbers for sulphate sulphur and total sulphur are used for the assessment of soil abundance in sulphur and to estimate the degree of soil contamination with this element (tab. V). Because of plant requirements 10 mg kg -1 has been accepted as the critical S-SO4 soil level. In 1997 low contents of sulphur was found in 75% of arable soils in Poland.

V. Limit contents of sulphur (mg S ·100 g-1) in the topsoil

1/ 10-20% of organic matter; 2/ > 20% of organic matter

Class I - natural contents; Class II - elevated contents;

Class III - slightly polluted; Class IV - strongly polluted

VI. Percentage share of soils polluted with sulphur in Poland

The highest share of the soils most polluted with sulphur is noted in the southern and western provinces of Poland (tab. VI).

Total abundance of arable soil layer in sulphur noted in Poland ranges between 300 and 4500 kg·ha-1. Application of fertilizers containing this element may enrich the soil up to 60 kg S·ha -1·year-1. Additionally soils are enriched in sulphur from precipitation. So, despite relatively low abundance of Polish soils in sulphur and sulphate liability to washing out, up till the nineties the soil balance of this element was positive +13 kg S·ha-1 yearly. Currently there are regions where soil sulphur contents are too low, particularly when crops requiring higher soil concentrations of this component are cultivated.

Sulphur in plants

Sulphur contents in plants depend on the species and even on the variety. It may range from 0.06 to 1.2%, but most often it does not exceed 0.5% in dry mass. Plants were divided into three groups according to their demand for sulphur:

· plants with very big demand for sulphur including the cruciferous (rape. cabbage. mustard. radish and turnip) and liliaceous (garlic and onion). They take up 40 and more (up to 80) kg of sulphur per 1 hectare. Their sulphur content exceeds 3.0 g S·kg-1 dry mass.

· plants with great demand for sulphur including the papilionaceous (alfalfa and clover), maize and beetroots, which take up between 20 and 40 kg S·ha-1.

· plants with small demand for sulphur including grasses and potatoes, which absorb between 12 and 25 kg S·ha-1.

In plants sulphur is an element of proteins, coenzyme A, sulpholipides. Ferredoxin, vitamins (B1. H), volatile compounds (sulphoxides) and mustard oils (glucosinolates).

Sulphur determines the proper development of plants, improves yield quality including taste values and also increases plant disease and pest resistance and resistance to lodging. Sulphur deficiency limits the quantity and quality of protein. At sulphur deficiency plants produce protein containing less exogenic amino acids. Sulphur decreases the plant contents of sugars and fat and limits excessive accumulation of nitrates in plants. In case of oily plants this element deficiency leads to decreased fat concentrations [Boreczek 2000].

Plants take up sulphur as SO42- by their roots systems and as SO2 through their leaf stomatal apparatus. In agricultural regions of Poland situated far from major industrial centres and cities sulphur deficiency in soil is observed regularly. A plant test is among others used to estimate plant sulphur supply. The critical value of S in whole rape young plants is 0.4%, in wheat 0.22% and in soybeans - 0.16%. Limit values of plant sulphur were given in table 7.

VII. Threshold values of total S in plants (% in dry mass)

1.

Average amounts of sulphur in the main crops were presented in table VIII and demand for this element in table IX.

VIII. Amounts of sulphur in basic crop yields

(kg S per 1 t of main + side yield)

IX. Sulphur demand at determined yield level

Because of generally low natural contents of sulphur in the soils of Poland a high efficiency of sulphur fertilisation has been observed, particularly in case of plants with very big demand for this element. Rape absorbs over 50 kg S · ha-1 and it is most exposed to this element deficiency. In the absence of sulphur in the subsoil even young plants have bright yellow leaf ridges, which then become veined, stiff and assume spoon shaped habit. The lower the sulphur value from the limit value, the more apparent symptoms of deficiency. However, sulphur dose in rape should not exceed 50 kg S·ha-1, as higher doses may cause an excessive increase in glucosinolane contents in seeds, thus worsening the seed quality.

High efficiency as a result of sulphur fertilisation is achieved also on grasslands situated on organic soils. The share of the papilionaceous increases together with the activity of Rhizobium bacteria. With sulphur treatment it should be remembered that too high doses of this element unfavourably affect both plants and soil. For a majority of plants N:S ratio should be 10:1 and for the plants with big demand for sulphur between 7:1 and 5:1.

Sulphur in fertilizers

Polifoska B (which meets rape requirements for boron and sulphur). Polimag 300 and 405. Polimag 311 and Polimag S are recommended for rape cultivation. Polimags introduce magnesium and sulphur, while Polimag S supplies also microelements. Multicomponent fertilizer application as undersowing is recommended. In this way nutrient uptake and plant frost resistance increase, as well as efficiency of spring nitrogen treatment [Grześkowiak 2001].

Among the fertilizers used in Poland about 30 contain sulphur. Among unicomponent fertilizers the biggest concentrations of sulphur are found in: ammonium sulphate (24%). kieserite (MgSO4·H2O) - 22% and potassium sulphate (18%). Ordinary superphosphate contains 12%S and MgSO4·7 H2O - 13% S [Filipek 2001].

Sulphur is a part of wide range of combined fertlilizers.

An efficient way to fast increasing sulphur contents in plants is foliar fertilisation. One of the best fertilizers used in this way is magnesium sulphate with 13% S. A solution containing 10 kg of magnesium sulphate (MgSO4·7H2O) and 53 kg of urea in 100 dm3 is used in a dose of 250 dm3·ha-1.

Organic fertilizers provide another source of sulphur for plants. Farmyard manure contains about 0.08% S thus coupled with a dose of 20 t per hectare. 16 kg of sulphur is supplied to the soil. However, these fertilizers have a slowed down activity. Sulphur must be transferred into sulphate form (mineralisation) absorbed by plants.

Conclusion

As one of the essential nutrients sulphur limits the amount and quality of crop yield. During 10 years SO2 emission decreased in Poland by 48% and currently (2000) approximates 40 kg S·ha-1·year-1. A majority of soils in Poland (57%) has low natural sulphur contents and decreasing emission of this element from the air leads to its deficiency in plant supply. particularly in those with big demands for S (rape. legumes an other). Thus fertilisation with this element is necessary. The assortment of fertilizers used in Poland includes over 30 fertilizers containing sulphur, which would supply up to 60 kg S ha-1 yearly.

References mentioned in the paper are available from authors.