These two important nutrients can mutually enhance each other's effects when used together. The focus of the investigated crops was on the four major grain legumes used in arable farming: broad beans, peas, lupins, and soybeans. The cultivation of grain legumes plays a crucial role in organic farming for the production of high-quality animal feed and thus also guarantees a valuable source of protein for animal nutrition. In crop rotation – especially on farms dedicated solely to arable farming – they make a significant and important contribution to soil improvement, humus formation, nutrient supply, and weed control.
Results
A balanced supply of phosphorus and sulfur to plants ensures good nitrogen fixation and utilization, as well as rapid and uniform growth. Legumes are an important component of crop rotation, especially on farms without livestock, because their ability to fix nitrogen in symbiosis with rhizobia bacteria compensates for nitrogen deficiency and makes it available to subsequent crops. However, they require longer crop rotation intervals than, for example, cereals. Furthermore, grain legumes play a crucial role as high-quality sources of protein and fat in feed, particularly for monogastric animals, thus contributing to a closed-loop system.
The widespread cultivation of grain legumes can gradually lead to complete self-sufficiency in protein production in Austria, thus achieving a high degree of independence from imports. The initial results from the first year of the trial showed a general reaction of the applied fertilization to the grain legumes broad bean, lupin, pea, and soybean, specifically regarding the influence of sulfur fertilization as well as combined phosphorus and sulfur fertilization. With the exception of lupin, all variants fertilized with phosphorus and sulfur showed the highest yields. However, these differences were not statistically significant. In contrast, another trial using faster-acting sulfate fertilizers showed no effect, or even a negative effect, on yield in the short term.
The experimental hypothesis of increased effectiveness of phosphorus and sulfur when applied together initially seemed to point in the right direction. Soaud et al. (2011) observed improved and longer-lasting phosphorus availability when elemental sulfur was used in conjunction with phosphorus. However, this hypothesis could not be confirmed; perhaps the duration of the effect was too short, in addition to unfavorable weather conditions. In the second year of the experiment, the order in which the fertilizers were applied changed, in addition to an increased yield.
Both the leading values for phosphorus fertilization in general, and specifically for soybeans, demonstrate the best uptake by this grain legume. This is particularly evident in the high fixation by rhizobia bacteria in combination with the fertilization. However, it must be noted that the overall effect of the fertilization was largely insignificant.
