Braunschweig Bundesforschungsanstalt für Landwirtschaft (FAL) Erscheinungsjahr 1998

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1 Aus dem Institut für Pflanzenernährung und Bodenkunde Haneklaus S Bloem E Schnug E Sulphur balance of a sugar beet rotation Manuskript, zu finden in Braunschweig Bundesforschungsanstalt für Landwirtschaft (FAL) Erscheinungsjahr 1998 Also available at:

2 Sulphur balance in a sugar beet rotation S. Haneklaus, E. Bloem and E. Schnug Summary Sulphur deficiency in Brassica and cereal crops is widespread in northern European agriculture and sulphur fertilisation to these crops has become obligatory. As soil analysis provides no reliable information on the sulphur supply of crops and plant analysis is not operationable at farm level, sulphur balances are often used to calculate the sulphur demand of agricultural crops. However in these balances the sulphur input by capillary ascension and shallow ground water is generally neglected and may therefore lead to an under- or overestimation of the sulphur supply. Both factors are major sources of plant-available sulphate in the soil and prognosis of fertiliser requirement can be assessed efficiently by taking the soil s physical and hydrological parameters, together with climatic conditions, into account. In general sugar beet crop rotations show a positive sulphur balance in comparison with other rotations such as potatoes or oilseed rape due to the low sulphur demand of sugar beet, the fact that sugar beet is preferably cultivated on high clay content soils and last but not least that they fully benefit from capillary ascending groundwater during the main growth period. Key words: Sulphur deficiency, sulphur balance, soil water regime, soil texture Introduction Sugar beet is known to have a high demand for macro and micro-elements such as magnesium, potassium and manganese (Finck, 1979). Only little is known about the sulphur (S) demand and S nutritional status of sugar beet, though it is meanwhile the most widespread nutrient disorder in oilseed rape and cereals in northern European agriculture (Schnug & Haneklaus, 1998). Atmospheric S depositions were an important S source for plants, but have decreased continuously during the past 15 years due to the desulphurisation of industrial atmospheric emissions to the level prevailing at the beginning of industrialisation - about 10 kg S ha -1. Another S source of similar size is the mineralisation of organic matter. This, however, means that both sources will not satisfy the S demand of a high yielding cereal or oilseed rape crop. Nevertheless the S supply of fields may vary highly from severe deficiency to sufficient supply depending on soil type, groundwater level, climatic conditions and rooting depth of the crop. Thus the main influencing factors are interactions between soil water regime and physical soil properties. For the prognosis of plant available S, traditional soil tests proved to be impracticable due to the high spatial and temporal variability of mobile S in soils (Bloem, 1998; Haneklaus, Fleckenstein & Schnug, 1995; Schnug & Haneklaus, 1998). It is the aim of this contribution to establish an S balance for a sugar beet rotation, to highlight and quantify the S input by physical and hydrological soil parameters depending on climatic conditions, and to evaluate their significance for the S supply of crops in a sugar beet rotation.

3 Material and Methods The investigations were carried out in Kassow (site I: N, E), Nienwohlde (site II: N, E) and Neuenkirchen (site III: N, E) from The soil type on site I and II was a brown earth with clay contents in the top soil ranging from 2 to 5% and 3 to 13%, respectively. On site III the soil type was para brown earth with clay contents varying between 14 and 20% clay. Organic matter contents varied between 0.9 and 2% on site I, 1.7 and 7.1% on site II and 2.2 and 3.1% on site III. The crop rotation on the experimental sites in Neuenkirchen was sugar beet - winter wheat - winter wheat, in Nienwohlde sugar beet - winter wheat - winter barley/potato, while in Kassow it was oilseed rape - winter wheat - winter barley. Soil samples were taken at 0.3 m intervals to a depth of 1.5 m. The plant available SO 4 -S content in the soil was determined by ion chromatography using KCl as extractant (Bloem, 1998). Younger, fully differentiated leaves of sugar beet were taken at the beginning of row closing in early July, those of cereals and oilseed rape at stem elongation and at harvest (Schnug & Haneklaus, 1998); the total S content in the plant material was determined by X-ray spectroscopy (Schnug & Haneklaus, 1992). Results In the experiments, in addition to yield, S removal by grain/seeds, beet roots and tubers, and the S uptake of straw and leaf material was determined (Table 1). The S removal of sugar beet roots was lowest compared to other crops with values ranging only from 3 to 5 kg ha -1 S (Table 1). The sugar beet root contains only a little S in the form of proteins or sulphate so that S removal is low with an average of 0.08 kg S per t of beet roots. The S offtake of sugar beet leaves and roots varied between 13 and 18.5 kg ha -1 S (Table 1). Though the S uptake of leaves was higher than that of the roots, the total S demand of a high yielding sugar beet crop can still be up to 30 kg ha -1 S. For the following crop - mostly winter wheat this means that comparatively high amounts of easily decomposable S in the form of leaf material is available, but soil sulphate is very mobile and easily leached by precipitation during winter (Eriksen, Murphy & Schnug, 1998). Table 1. Yield, S uptake and S removal of agricultural crops on three sites in northern Germany ( ) Crop Site Year Yield (t ha -1 ) S removal (grain/seed/ tuber/root) (kg ha -1 ) S uptake (straw/leaves) (kg ha -1 ) Winter barley II & III Winter wheat II & III 1994 & Sugar beet II & III 1995 & Potato II 1995 & Oilseed rape I

4 Important factors influencing the S nutritional status of crops are soil hydrology, soil texture and climatic conditions, but conventional S balances do not include the S input by capillary rise or groundwater. In the following section the relevance of these parameters is highlighted. Generally the S supply increases with ascending groundwater level (Fig. 1). Sulphate S which is geogenously abundant in groundwater varied between 5 and 80 mg l -1 S, but also values of >100 mg l -1 S were determined (Isermann, 1993). With increasing clay content the water storage capacity of the soil increases and in particular the deeper soil layers contain S- rich capillary ascending groundwater (Eriksen, Murphy & Schnug, 1998). This also means that the risk of leaching is reduced with increasing clay content of the soil. Fig. 1. Relationship between groundwater level and sulphate S content in the soil on site II and III. The closest relationship between clay/water content of the soil and total S concentration in younger leaves of oilseed rape was determined for soil layers at a depth of 0.6 to 1.5 m (Fig. 2). The clay/water content in this depth explains 50 and 64% respectively of the variation of the total S content in plants at stem elongation. The results reveal that soil texture and soil water regime of the deeper soil layers highly influence plant-available S and thus the S status of the crop. Most soils represent open systems where sulphate S losses due to leaching and enrichment through capillary rise cause an important variation in the S supply. The evaluation of these quantities depends greatly on climatic conditions. So the amount of precipitation during winter (October till March) is directly linked to the amount of leaching of sulphate. The impact of precipitation during winter on the sulphate S content in different soils is demonstrated in Figure 3. The soil on site II and III reached their field capacity at 330 and 560 mm, respectively. The rate of leaching of the water saturated soil was estimated to be 180 mm on the heavier soil (site III) and 300 mm on the lighter soil (site II) per 60 mm of rainfall (cp.

5 Chao, Haward & Fang, 1962; Kumar, Karwasra, Singh & Dhankar, 1994). The higher the amount of precipitation, the lower will be the available S content in the soil in spring time. Fig. 2. Relationship between water and clay content (mean values for the m soil layer) and total S content in younger leaves of oilseed rape on site I. Fig. 3. Relationship between amount of precipitation during winter (October - March) and sulphate S in soils in spring time on site II and III.

6 The main growth period of sugar beet is in summer while that of cereals is in spring time. In the investigated area the period from July to September is characterised by capillaryascending S-rich (>5-10 mg/l S) groundwater, which will already cover the S demand of most crops, if roots are connected to these soil layers. Therefore the S balance of a sugar beet is regularly positive. Only on light soils which are not influenced by groundwater can S deficiency in sugar beets be expected, but sugar beet is preferably grown on heavier soils. This also explains why sugar beet and sugar beet rotations are less prone to S deficiency. In Fig. 4 the completed S balance is shown which considers soil physical and hydrological parameters for the S supply of sugar beet. Fig. 4. Quantification of input and output parameters of a S balance for sugar beet on site III The S balance of sugar beet will only be negative if there is no S input by groundwater or capillary ascending water and leaching is high (Figure 1). In all other cases the balance will be positive. The S balance of sugar beet on site III was +127 kg S ha -1 when plants had access to capillary-ascending groundwater, but only +10 kg S ha -1 if the soil had a low groundwater table. For the same fields the S balance of cereals was +20 kg S ha -1 and -33 kg S ha -1, respectively.

7 Discussion For the diagnosis of the S supply different methods of soil extraction are described and summarised by Anderson, Lefroy, Chinoim & Blair (1992) and discussed by Schnug & Haneklaus (1998). Extended investigations have shown that no relationship exists between sulphate S in the top soil and S supply of the crop (Haneklaus, Fleckenstein & Schnug, 1995). Also the determination of the S min. content yielded no satisfactory results due to the high spatial and temporal variability of sulphate in the soil (Bloem, 1998). Plant analysis is an excellent diagnostic tool, but is, not operationable at a farm level due to high costs and expenditure of time (Schnug & Haneklaus, 1998). Therefore S balances are often used to predict the S requirement of agricultural crops. In the past, mineralisation of organic matter was supposed to have the strongest impact on the S supply, but Eriksen (1994) showed that this S source has been overestimated with a mean supply of 3 to 7 µg g soil -1 yr -1 S. Conventional S balances do not consider the S input through capillary rise or shallow ground water which proved to be essential for a reliable evaluation of the S supply (Bloem, Haneklaus & Schnug, 1997; Bloem, 1998). The results of the experiments described above also prove why sugar beet crop rotations have a better S supply, because in Germany firstly sugar beets are favourably grown on heavier, more clay soils which are less prone to S deficiency, secondly sugar beets fully benefit from capillary-ascending S-rich groundwater during their main growth period, and thirdly sugar beets have a low S demand and S removal is only minor. Acknowledgements The authors wish to thank Dr. Kerr Walker (SAC, Aberdeen) cordially for the improvement of the English language of this paper. This project was funded by the German Research Foundation, DFG (SFB 179). References 1. Anderson G, Lefroy R, Chinoim N and Blair G Soil sulphur testing. Sulphur in Agriculture 16: Bloem E, Haneklaus S and Schnug E Influence of the soil water regime expressed by differences in terrain on the sulphur nutritional status and yield of oilseed rape. In: 9th International Colloqium for the Optimization of Plant Nutrition, Prague, Bloem E Schwefel-Bilanz von Agraroekosystemen unter besonderer Beruecksichtigung hydrologischer und bodenphysikalischer Standorteigenschaften. PhD thesis, TU-Braunschweig, Germany, 156pp. 4. Chao T T, Haward M E and Fang F C Movement of S-35 tagged sulphate through soil columns. Soil Science Society Proceedings 26: Eriksen J Soil organic matter as a source of plant-available sulphur. Norwegian Journal Agricultural Science Supplement 15: Eriksen J, Murphy M and Schnug E The soil sulphur cycle. In: Sulphur in Agroecosystems (ed E. Schnug), Kluwer Academic Publishers, Dordrecht, Boston, London,

8 7. Finck A Duenger und Duengung. Verlag Chemie, Weinheim, New York, 442pp. 8. Haneklaus S, Fleckenstein J and Schnug E Comparative studies of plant and soil analysis for the sulphur status of oilseed rape and winter wheat. Zeitschrift Pflanzenernaehrung & Bodenkunde 158: Isermann K Loeslicher N, Sulfat-S und (DO)C im (un-)gesaettigten Untergrund von Poren-grundwasserleitern bei unterschiedlicher Landbewirtschaftung/Duengung. Mitteilungen Deutsche Bodenkundliche. Gesellschaft 71: Kumar V, Karwasra S P S, Singh M and Dhankar J S An evaluation of the sulphur status and crop responses in the major soils of Harynan, India. Sulphur in Agriculture 18: Schnug E and Haneklaus S Sulfur and Light Element Determination in Plant Material by X-ray Fluorescence Spectroscopy. Phyton 32: Schnug E and Haneklaus S Diagnosis of sulphur nutrition. In: Sulphur in Agroecosystems (ed E. Schnug), Kluwer Academic Publishers, Dordrecht, Boston, London, Schnug E, Haneklaus S and Bloem E Significance of soil water dynamics for the sulphur balance of oilseed rape. Proceedings of the 9th Int. Rapeseed Congress "Rapeseed today and tomorrow", Cambridge, UK, 1: