After a dryer than normal month of December, the rainfall in Mato Grosso during the month of January has been excessive, which has not been good news for the farmers trying to harvest their early maturing soybeans. Heavy rains fell across the state over the weekend and more are forecasted for this week as a frontal system stalls out over central Brazil. The soybean crop in the state is about 5% harvested at this point compared to 7% last year and 8% average.
The nearly constant wet weather has resulted in deteriorating seed quality and lower yields in the fields that have been waiting the longest to be harvested. When the harvest started several weeks ago, the most common yield being reported was 50 sacks per hectare (3,000 kg/ha or 43.5 bu/ac). Since then, yield reports have declined and now you hear reports of 45, 42, 39, 35 sacks per hectare (39, 36, 34, 30 bu/ac). The lower yields are due to light, shriveled, and moldy seeds.
Once the soybean pods are dry enough to harvest, each time the pod goes through a wet and dry cycle, there is an increased chance of fungi attacking the seed, which results in light weight, shriveled, white and moldy seeds.Under the worst case scenario when it stays constantly wet for a number of days and the temperatures are in the 90s, the soybean seeds can start to sprout in the pods. If that happens, the field might be abandoned and not even harvested. That is an extreme case of course and there have been a few reports of that already happening in Mato Grosso.
This is exactly why farmers in Mato Grosso generally do not plant all their acreage to early maturing soybeans. These early soybeans need to be harvested in January, which is the peak of the rainy season. Most farmers will plant a combination of early, medium, and late maturing soybeans in order to spread out their risk and reduce the chance of dry weather during the critical pod filling period or delayed harvest due to wet weather.