Abstract

It has been a standard agricultural practice to fertilize Brassica crops with sulfur to enhance yield. However, current atmospheric deposition of sulfur does not meet pack choi (Brassica rapa Var. chinensis (L.)) requirement which is excellent sources of beta carotene and glucosinolates that are associated with reduced incidence of cancers and cardiovascular diseases. In such soils the release of sulfur from organic matter could be vital for the supply of sulfur. Thus, pot experiments in a green house was conducted at the experimental station Dürnast TU Weihenstephan to investigate the effect biogas residues as source of sulfur as measured by plant sulfur (S) uptake. The experiment comprised 20 different fertilization variants viz., 16 biogas residues and 3 mineral sulfur fertilizer variants that is, S- 30, S-60, and S- 90 mg/pot, and a control (S-0), replicated trice. Pots were arranged in completely randomized design. Plant parameters were measured at harvest. Sulfur was not a limiting factor for dry matter yield in pak choi. Fertilization variants showed significant effect on St, S uptake and plant SO₄^2- -S. The different S-fertilization resulted in total plant  sulfur content of 0.11 to 0.39% (616-S, S-60); S uptake of 26 to 94 mg pot^-1 (621-S, 626-L); plant SO₄^2- -S content of  9.0 to 119.5 mg S/100 g (623-S, S-60). There was a highly significant positive correlation of soil SO₄^2- -S with plant S_t content (r= 0.941^**) and plant SO₄^2- -S content (0.918^**). In addition there was highly significant positive correlation between plant parameters that is, plant S_t content and plant SO₄^2- -S content (0.958^**). It is concluded that sulfur limitation from less atmospheric deposition could in the short term be replaced by some biogas residues to maintain yield and quality of pak choi.

Key words: Biogas residues, sulfur, pak choi, Brassica rapa Var. chinensis (L.).