Tests with soya

Inoculation

Last year, the focus of the tests was on inoculation to achieve an optimum formation of rhizobia. It is an essential measure to make sure that soya can tap its full economic yield potential. As the Bradyrhizobium varieties that establish a symbiosis only with the soybean normally do not occur naturally in our soils, a seed inoculation is important so that the nodules establish at the root and supply the plant with atmospheric nitrogen.

What do bacteria need? This was the question the main focus was on. Among others we tested different micronutrients that are produced by bacteria: molybdenum, zinc, cobalt but also sulphur and sugar. “We tested if the bacteria quantity has to be adapted for a better and safe inoculation. In addition, we sprayed cola into the seed furrow. Another test was to place the inoculum on a carrier and mix it with the beans only in the seed furrow. What we definitely noticed, is that the effect became insecure the further away from the seed the rhizobia were located. To spray the inoculum only superficially, e.g. with the pre-emergence herbicide, had the worst effect. The survival rates of bacteria for seeds that were inoculated several weeks before sowing, were insecure, too.

It is optimal if the inoculation is spread evenly and is not exposed to sunlight for a long time, if the grains are well embedded and if the bacteria immediately have humidity at their disposal. It basically is advantageous for the establishment of rhizobia if you sow immediately after the inoculation.

With regard to the tests with double and single inoculations we noticed little respectively no significant differences. If the conditions for the bacteria are not optimum, more bacteria can compensate for this on a limited scale. If the inoculation was ok and if the conditions in the soil are good, a double inoculation is not required. The same is true for the treatment with sugar. “The sugar did not improve the fixing performance”, Josef Stangl confirms. “The rooting was minimally better, but this can probably be attributed to the phosphor and the general change of the environment caused by the cola.”

Nutrients and fertiliser

With regard to the analysis of the fertiliser tests the observations were more tangible. Potassium and phosphor for example were placed at the seed with underground fertilisation, widely spread and the quantities varied, too. “We know that potassium is generally important for legumes, and for soybeans, too, we noticed a positive influence on the yield”, Josef Stangl says. The same is true for phosphor. PPF fertilisation, i.e. the placement of fertiliser separately from the seed a little bit below the seed grain, resulted in a significantly better (side) root development of the tap-root. However, this was not reflected in the yield. I.e.: the lots evidently were stronger and grew better, but there was no noticeable result with regard to the yield. The reason may be that the conditions at the time of maturation were not optimum and therefore everything finally still matured prematurely at a relatively high yield level (4.2 t/ha). In total, we sowed rather late this year respectively we lacked vegetation time. As of the second week of May conditions are rather suboptimal for 000 varieties. We are now trying to start with soybeans after the maize seed.”

Moreover, we experimented with leaf fertilisers (Yara Vita Raps Pro, Biotrac, boron/molybdenum, urea, Epsom salts, …). The fields partly developed significantly more intense colours. However, we only noticed a positive influence on the colour of the leaves but not on the yields. “Our yields were only a little bit higher. But it is an excellent possibility to soothe the herbicide stress of after-emergence variants.” After the second year with leaf fertilisation tests, we can summarise that especially stress situations in connection with herbicides or water/temperature can be soothed.

Soybeans originally come from warmer regions and thus prefer soils that warm up easily. In total, the tap-roots of the soybean like rather loose soils but can better cope with compact soils than for example maize. On light sites, the grain embedding often is better. Crusts are rarer. “If you have soils that are prone to crusts and if on silt and clay soils there is the risk of silting, I would try single grain sowing – regardless of the yield advantages and disadvantages.” However, single grain sowing is not required in general. The soil surface has to be loose so that the seed grain can pull itself out completely during the epigeous germination with normal sowing depths of 3-4 cm as well as with possible 7 cm. This means: With regard to the tractor, even in case of wet soil conditions you should rely on a smaller tractor as it is lighter. All-over soil crusts that resulted from the rainfall in spring are an important issue for soya in the third year consecutively. Good emergence significantly depends on the fact that you can avoid or remove these crusts. In this respect, single grain sowing has its advantages. “One single grain has to break the soil alone. If you have several seed grains relatively close together in one furrow, they sort of form a team to break one big furrow.” For the yield itself, there are other factors that play a more important role. If there is enough water at the time of or after the bloom in July does not always only depend on the rainfall. In case of a bad soil structure the then cramped and limited roots do not reach all parts of the soils and water (and nutrients) remains unused. Weeds, too – especially orache – cannot be tolerated. The competition for water and space is too fierce. This is why the pre-emergence herbicide has to be applied optimally. Agents that might cause phytotoxical reactions (Pendimethalin or Metribuzin in sensitive varieties like e,g. ES Mentor) require a sound placement accuracy and see to it that you always have to keep an eye on the weather forecast.”

It makes sense to use a harrow to break the crusts. However, you should thoroughly deliberate about whether the destroyed herbicide film might cause problems later on. One hoeing pass shortly before the rows close (for a row width of 50 cm usually at the beginning of the bloom) often is the most secure and most efficient solution. Problem weeds that with the existing herbicide range often cannot be fought efficiently (thistle, horsetail, bindweed) are pulled out, the crust is broken and the weeds that germinate afterwards are covered by the population. As the plant loses leaf mass after the bloom, you have to keep an eye on the subsequent weed infestation on fields that tend to be weedy. 

Row widths and sowing depth

“We observed that the 00 varieties dispose of more vegetation time and thus, of more time for branching than the early mature 000 varieties. This influences the seed rate and the row spacing. The lower limit for seed rates is reached faster with 000 varieties. In practice, in Bavaria we work with row spacings of 15 to 50 cm“, Josef Stangl summarises. “For varieties with a low branching performance and for soils that are not prone to silting you should reconsider the wide row spacings as weed infestation and subsequent infestation might become an issue. Especially chamomile, burdock etc. have to be taken into account in case of gaps.”
Soya is a sensitive bean and has to be treated with care to avoid influencing the germination capacity negatively. This applies to storage, transport and, of course, to the metering in the seed drill. “For the HORSCH metering units we have appropriate rotors which cause as little mechanical stress for the seed as possible“, Josef Stangl explains. Here it pays off to take a look into the operating manual of the machine.
“As this year rain has not been foreseeable, we placed the seed at a depth of approx. 5 cm into the capillary water-bearing layer. Especially when you are sowing early, you should not place the seed too deeply as it needs heat. It is better to achieve the water contact by means of a good consolidation. If the germination horizon was wet, we placed the soya grains at a depth of 3 cm.” However, it is important to level the fields in autumn so that threshing works more smoothly. Threshing only a few centimetres higher might already result in yield losses tine of 5 to 10%. “We recommend that you make one more pass in autumn with a levelling tine tool and rely on a catch crop that can easily be removed in spring. Hardy catch crops and nitrogen collectors are not required. It is not about achieving high amounts of nitrogen in the sowing year, but on our test fields a small starter input of 30 kg ammonia nitrogen at the time of sowing had a positive effect on the yield. Even if the application depends on the regional legislation, the nitrogen balance should only be covered minerally should it be absolutely necessary.  If there is a high nutrient supply in the soil, the economically required nodule fixation will be reduced because of the higher effort for the plant. Grain maize fields are ideal for a following soya crop due to the nitrogen-consuming straw. The remaining nutrients after the soybean, however, should not be overestimated especially if the soya yields were very high. The soil structure mostly is good, the remaining nitrogen content often is disappointing as the harvested crop extracts a lot of nitrogen. After field beans or peas, there is considerably more nitrogen available.