Applying fertiliser to soya crops is not common practice here, but farmers like myself who are committed to sustainable production believe it is important to focus on long-term production systems and invest more in fertiliser and technology.
In our region, a soya bean crop after maize is where you get most yield. On average 4.6t/ha against 4.2t/ha for a second soya bean crop, or 3.8t/ha after a double crop (wheat then soya) in the same season.
Analysis of our yields show longer-term benefits of balancing nitrogen, phosphorus and sulphur. The impact is not noticeable in the early years, but there is an benefit from the fifth or sixth year onwards.
Beyond the direct effects, crops with a balanced N, P and S nutrition have a better water use efficiency and it also encourages microbial activity in the soil. Thus, soya bean crops begin to benefit the environment and yields stabilise too.
In this context, the question is what is the potential yield of soybean?
We carried out trials in soya crops given a fertiliser mixture at planting (/ha) of 18kg N, 24kg of P, 15 kg of S, and 1.5 kg of zinc. We also reapplied N, P and S as a foliar feed at the beginning of the critical period (growth stage R3).
In addition, the crop was inoculated with rhizobium bacteria for N fixation, treated for any diseases, and rainfall was optimal during the entire growing period.
With this fertiliser technology, the average yield achieved was 6.6t/ha, 2t/ha greater than with the traditional fertiliser application – with peaks of up to 8t/ha. But the key finding was that the investment was only $90/ha (£56).
For N, soya fixes it from the air and the quality of the inoculation treatment is important. However, for P, the focus is on its availability in the soil and at higher doses, higher yields are achieved. Sulphur is deficient across a wide area and so its application is necessary.
But I believe it is the mix of the ingredients that is leading to the yield benefits. Undoubtedly there is still a long way to go to further improve yields in soya beans.
Federico Rolle farms 2,250ha of rented arable land in the Pampa area of Argentina. He grows soya beans, sorghum, maize and wheat using no-till techniques and GM crops. He has a part-time role helping Brown & Co in the region