What are the reasons for soybean plants flowering but not setting pods?

Liu Dezheng, a farmer from Xihe in Xinpu Town, Xiaonan District, and some farmers from Xiaogang Town and other places ask: Why did soybeans (yellow beans) flower but not set pods this year, or produce empty pods and shriveled seeds?

According to our field surveys, in fact, the vast majority of soybeans this year did set pods; the cases of flowering without pod set or empty pods and shriveled seeds occurred only in scattered areas and among a minority of farmers. Through field investigation and analysis, the main reasons are as follows.

First, from the perspective of varieties. This year, early and medium-maturing varieties generally flowered and set pods well, while among late-maturing varieties, some soybeans sown relatively late showed flowering without pods or empty pods and shriveled seeds. This is because during the flowering and pod-setting period of soybeans, there happened to be sustained high temperature and drought from late July to early and mid-August, with temperatures reaching as high as 38-40°C. The suitable flowering temperature for soybeans is 22-30°C, and the suitable relative humidity is 70-90%. Beyond this range, soybeans will not flower or will flower less, or will flower without setting fruit. At the same time, soybeans are short-day crops; if their short-day requirement is not met, flower bud differentiation will also stop.

Second, soybeans are a crop that should not be grown continuously on the same land. Some farmers planted soybeans this year on fields where soybeans were grown last year. Due to soil nutrient deficiency, especially boron deficiency, empty pods and shriveled seeds often occur.

Third, the proportions of major elements are imbalanced. In surveys of soybean fields where nitrogen fertilizer was applied excessively and potassium and phosphorus fertilizers were not applied, empty pods and shriveled seeds were more common. Due to fertilizer deficiency, combined with drought, flower primordia can transform into leaf buds.

Fourth, weed infestation, soil compaction, and poor drainage also trigger empty pods and shriveled seeds. On some farms, after soybeans were sown, no weeding was done even once, and the weeds grew taller than the soybeans. In some fields or sections, dodder caused severe damage; one dodder plant entwined about 100 soybean plants, and the affected soybeans basically yielded no harvest. In some poorly drained fields, the soil was compacted, and the number of pods set was also greatly reduced.

For this reason, we should sum up experience and lessons, and do a good job of prevention early next year. First, choose soybean varieties suitable for local growth and development. When purchasing seeds, identify the soybean brand clearly, check whether they have the "three certificates," and ask for and keep the seed purchase invoice. Second, pay attention to crop rotation and changing stubble to avoid continuous cropping. Third, attach importance to applying sufficient basal fertilizer according to a balanced formula, especially preventing excessive nitrogen application, and be sure to apply phosphorus and potassium fertilizers together. Fourth, carefully prepare the soil and sow, apply chemical herbicides well, and prevent and control diseases and pests. Fifth, improve drainage and irrigation facilities so that soybean fields can both drain and be irrigated, ensuring that during the flowering and pod-setting period soybeans have "dry flowers and wet pods."