Soybean planting dates: Is earlier a good idea?

A one-year study conducted at Manhattan in 2010 as a complement to the above experiment added more planting dates. Results in that year showed a consistent 0.22 bushel/acre/day reduction in yield as planting was delayed from late April through early July (Figure 2). In reality, the yield reduction was slightly less than that through May and slightly greater as planting was delayed into late June and July. This is a limited data set so it may not be predictive over a wide area or for many years, but it agrees with other work that has shown reductions in yield as planting is delayed in northeast and north central Kansas.

click image to zoomFigure 2. Effect of planting date on soybean yield at Manhattan in 2010. The previous major round of research studies in Kansas looking at planting dates, was in the early 2000’s, which was a period of generally very low yields. The basic conclusions varied by region of the state:

North Central/Northeast: At Topeka, with yields up to 55 bu/acre, yields increased with planting dates in late April compared to May for Group III and IV varieties. In Belleville, with yields up to 50 bu/acre, yields were generally unaffected by planting dates up to mid-May, but had a fairly sizable yield drop when planting in June. In Powhattan, with yields less than 30 bu/acre, there was no advantage to planting any earlier than early May.

* East Central: There is no evidence to support earlier planting.

* Southeast: There were no tests conducted in southeast Kansas during this round of studies.

* South Central: At Hutchinson and Wellington, yields were low but generally maximized by planting in late April.

* Western Kansas: Yields were very poor during the years of these studies. Planting dates had no effect on yields.

Conclusions and recommendations

* In northeast Kansas planting dates should be as early as practical. Late-April planting would be advisable if soil conditions allow. If you have already planted soybeans in this area of the state, research would support your decision, especially if the seed was treated with a fungicide and insecticide. Varieties with resistance to soybean cyst nematode and sudden death syndrome should be used if possible when planting early. Do not plant into soils that are too wet, however. Also, do not plant until soil temperatures are at least 55 to 60 degrees. If planted into soils cooler than that, seedlings may eventually emerge but will have poor vigor.

* In drier areas of Kansas and on shallow soils, research results would suggest that yields are most consistent when planting soybeans in late May to early June. By planting in that timeframe, soybeans will bloom and fill seed in August and early September, when nights are cooler and the worst of heat and drought stress is usually over.

* Ultimately, weather patterns dictate soybean yields, especially under dryland conditions. There is no guarantee any certain planting date will always result in the greatest soybean yields in Kansas.