Influence of Sulfur Fertilization on Yield and Quality of
Oilseed Rape and Mustard
Haneklaus1, S., Paulsen1, H.M., Gupta2, A.K., Bloem1, E. and Schnug1, E.
1Institute of Plant Nutrition and Soil Science, Federal Agricultural Research Centre Braunschweig-Voelkenrode, Bundesallee 50, D-38116 Braunschweig, Germany, e-mail: email@example.com; 2Rajasthan Agricultural University-Campus: Jobner-303329, India
Brassica crops show a high demand for sulfur and an insufficient sulfur supply will not only reduce crop productivity but also affect crop quality either positively as in case of mustard where glucosinolates enhance organoleptic features or negatively as in case of extracted oilseed rape meal where glucosinolates have an anti-nutritive effect. From an ecological point of view, a sufficient sulfur supply is essential to prevent undesired nitrogen losses to the environment due to reduced nitrogen utilization. Brassica species are grown worldwide for their edible oil which may also be used as a renewable source of energy. Production of oilseed rape aims to produce seeds which are rich in oil and low in glucosinolates while an important criteria in mustard production is a high glucosinolate content. It was the aim of this contribution to quantify the influence of sulfur fertilization on yield and quality parameters of oilseed rape and mustard.
KeywordS: Glucosinolates, oil content, S-utilization
Sulfur (S) deficiency in Brassica crops is increasing worldwide due to the use of high-grade, S-free fertilizers, the breeding of high yielding crop varieties, the declining use of elemental S for plant protection purposes and last but not least the efficient reduction of atmospheric S depositions in industrial countries (Schnug and Haneklaus, 1994 and 1998; Tandon, 1995). The symptomatology of severe S-deficiency symptoms in Brassica crops is described comprehensively by Schnug and Haneklaus (1994 and 1998). Brassica crops such as oilseed rape and mustard show a high S demand because of the high protein content in their seeds and also the characteristic presence of S-containing glucosinolates. The extracted rapeseed meal is widely used as a feed for farm animals and poultry but the presence of glucosinolates can have a goitrogenic effect, consequently a reduced glucosinolate content is regularly required during oilseed rape production. In comparison a high glucosinolate content of mustard seeds is beneficial in terms of crop quality due to enhanced organoleptic features.
It was the aim of the investigations presented in this contribution to highlight the influence of S fertilization on yield and quality parameters of oilseed rape and mustard.
Materials and Methods
Field trials were conducted under humid conditions on four locations in northern Germany (Luebbersdorf: 54°24.5´N, 09°50.8´E, Warxbuettel: 52°25.4´N, 10°28.9´E, Dreetz: 53° 48.1’ N, 11° 57.2’ E and Kirchheim: 50° 21.2’ N, 9° 34.4’ E) where oilseed rape was grown and under semi-arid conditions on one site in India (Jobner, Rajasthan 26°06´N, 75°28´E) with mustard. Details concerning the experimental design of both experiments are given by Paulsen (1999) and Gupta et al. (1997). S was applied in three levels to oilseed rape (control, 40 (level 1)and 80 (level 2) kg ha-1 S) and mustard (control, 37.5, 75 (level 1), 112.5, 150 and 187.5 (level 2) kg ha-1 S). S was applied as natural gypsum in India and as FGD-gypsum from flue gas desulfurization in Germany (Haneklaus et al., 1999a).
Plant analysis: Vegetative plant material (younger, fully differentiated leaves of the upper third of the plant of oilseed rape) was collected at the beginning of stem extension. The plant material was dried in a ventilated oven at 85° C until constant weight was achieved. The plant samples were finely ground to a particle size < 0.12 mm. S was determined by X-RF spectroscopy according to Schnug and Haneklaus (1992). The glucosinolate content in air-dried oilseed rape and mustard seeds was determined indirectly by X-RF according to ISO/CD 9167.2. The oil content was determined by NMR (Nuclear Magnetic Resonance).
Results and Discussion
The sites chosen for the experiments in Germany and India were S-deficient and S-fertilization improved not only the S-nutritional status significantly but also yield of both crops (Figure 1). Yield of oilseed rape increased on severe S-deficient sites on average by 88%. Yield on moderate S-deficient sites was tendentiously higher with S-fertilization but the differences were statistically not significant (Figure 1). The high yield level in the control plots can probably be attributed to an enrichment of sulfate-containing capillary water and movement due to evapotranspiration into the root space of the crop. The significance of soil physical properties, especially soil texture, for the sulphur supply of crops is discussed by Bloem (1998). On all experimental sites an application of 25 kg ha-1 S proved to be adequate for a sufficient S-supply with total-S contents above the critical nutrient threshold of 6.5 mg g-1 S (Schnug and Haneklaus, 1998; Paulsen, 1998). Mustard showed a linear yield response up to application rates of 187 kg ha-1 S with a mean increase of 0.22 dt ha-1 per 10 kg S (Figure 1).
Figure 1. Influence of S-fertilization on yield and total S-contents in straw and seeds of oilseed rape and mustard.
S-fertilization needs to be higher than S-uptake of the crop because the S-utilization is only low under conditions of moderate S-deficiency (Figure 2). The S-utilization of applied S was closely related to the S-status of the oilseed rape crop (Figure 2). Under conditions of severe S-deficiency the mean S-utilization was as high as 90% with an application rate of 40 kg ha-1 S and 52% when 80 kg ha-1 S was applied. Under conditions of moderate S-deficiency the corresponding values were only 36 and 19% (Figure 2). A sufficient S-input is not only important with regard to the yield of the oilseed rape crop but also with regard to nitrogen utilization. Schnug (1991) showed that under conditions of S-deficiency nitrogen utilization may be as low as 25%.
Figure 2: Utilization of applied S in dependence on the natural S-status of oilseed- rape and S-fertilization.
S-fertilization not only significantly increased the S-content of straw and seeds of oilseed rape and mustard, but also their glucosinolate content (Figure 1 and 3). The glucosinolate content of double-low oilseed rape increased under conditions of severe S-deficiency on average by 2.1 µmol g-1 per 10 kg applied S. Earlier experiments carried out by Schnug (1988) confirm these results. On sites with moderate S-deficiency the glucosinolate content increased on average by 0.8 µmol g-1 per 10 kg applied S. The application of 40 and 80 kg ha-1 S yielded no statistically significant (t-test) differences in the glucosinolate content of oilseed rape seeds. A linear relationship was found between S-fertilization and glucosinolate content of mustard (Figure 3). While the glucosinolate content in the control plots was 19 µmol g-1, values of 32 µmol g-1 were determined at the highest level of S-fertilization. The synthesis of glucosinolates in seeds was proportional to the S-supply of mustard (Figure 3) and low single low oilseed rape varieties (Schnug, 1988) while double low oilseed rape cultivars store S as intermediary products in pod walls, thus inhibiting transport of intact glucosinolates into seeds (Schnug, 1997).
Figure 3. Influence of S-fertilization on the glucosinolate content in mustard seeds.
The oil content of oilseed rape seeds was not influenced by S-fertilization and varied between 42.2 and 44.8% on the different sites (Paulsen, 1998). Differences in the oil content relied on varietal differences. Schnug and Haneklaus (1994) showed that only under conditions of very severe S-deficiency the oilseed rape crop produces dwarf seeds with a reduced oil and protein content as well as reduced thousand grain weight.
S-deficiency in oilseed rape causes tremendous losses of yield and S-fertilization is required in order to achieve a high yielding crop. S-fertilization of 40 kg ha-1 S proved to be sufficient to fully satisfy the S-demand of oilseed rape. For an environmentally sustainable production of Brassica crops a sufficient S-supply is necessary in order to minimize undesired nitrogen losses (Schnug, 1991; Haneklaus et al., 1999b). S-fertilization of 40 kg ha-1 S increased the glucosinolate content of double low oilseed rape varieties by 3 to 8 µmol g-1 dependent of the S status of the crop. In India more than six million hectares of agricultural farmland is grown with oilseed rape and mustard but the average yield level is very low with 0.9 t ha-1. The results of the experiments reveal that S-fertilization increased yield of mustard by about 30%. S-fertilization caused a linear increase in the glucosinolate content of mustard which is an important quality criteria. Beside the S-nutritional component of gypsum fertilization, it has a meliorative effect on saline soils (Gupta et al., 1997).
The authors gratefully thank Dr. R. Walker (SAC, Aberdeen) for the linguistic revision of this paper.
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