With tight planting windows, it can be a challenge to get seeds in the ground at the optimal time. That was the case for the hemp research plots at the Purdue Agronomy Center for Research and Education (ACRE). This year a heavy rainstorm followed by a drop in temperature delayed germination and emergence. Once the soil dried out, a crust formed, creating a hard barrier. Establishment in some of the research plots was poor, while others fared well (Fig 1.). Some cultivars had much larger seeds, a contributing factor in seedling vigor. The fiber plots, which have a higher seeding rate, also had better establishment.
Fig 1. The hemp plot in the bottom right has struggled to establish compared to the plot in the center of the photo.
Hemp plants, like soybeans, struggle to get through crusty soil. Fine-textured soils with low organic matter and little surface residue are more prone to crusting. Plants that do make it through the crust can be damaged. The hypocotyl, the section of the plant below the cotyledon and above the roots, can be twisted or bent or break off completely as the plants push emerge through the crust (Fig 2).
Fig 2 Many of the hemp seedlings had curled and dried leaves. Digging revealed damaged hypocotyls (blue arrows).
There are strategies that can reduce hemp seedling loss due to crusting. Planting at a depth between ¼-½ inch will help with quick establishment. Planting when soils are warmer will speed up germination, aim for soil temperatures above 55°F. Hemp can be planted earlier, but cooler soils can slow germination and emergence. Planting hemp after a rain event, not right before can also reduce the risk of crusting injury. If a crust does form soon after planting, seedlings will find cracks in the soil to emerge from, but stand will be reduced (Fig 3). The use of a rotary hoe can break up a crust after planting.
Fig. 3 A hemp seedling has found a crack to emerge through.
