Richard Taylor, Extension Agronomist; rtaylor@udel.edu
If you were one of those producers whose pasture or hay field replanting was prevented by this past spring’s cold rainy weather, now is the time to consider a method of preparing the field for late-summer/early-fall (LS/EF) reseeding. The beginning of June’s hot weather (warm soil conditions) is ideal for seeding warm-season annual, weed-suppressing grasses such as hybrid pearl millet, sudangrass, the sorghum-sudangrass hybrids, or even teff. These grasses, if seeded when soil temperatures are >75° F and adequate soil moisture is present, can germinate and establish very rapidly. They have the ability to suppress many weed species and can add organic matter to the soil via the root mass left at the end of the season or the root mass plus final top growth of the season.
Another advantage of the warm-season annual grasses comes from the need for land preparation prior to the permanent LS/EF seeding. This soil preparation provides the producer with the opportunity to check the pasture or hay field’s soil fertility status and to make early adjustments that can be rechecked prior to planting the more expensive perennial grass seed. As an agronomist, I typically recommend checking six months to a year ahead of reseeding a field so that pH adjustment (liming) and nutrient amendments (phosphorus, potassium, or manures) can be applied and will have time to correct any problems in the field. Although the timing here may be tight, it still will allow a producer to recheck the field before establishing the permanent cover.
Another obvious benefit is the increased tonnage the summer annuals offer forage producers. However, care must be taken in selecting not only the annual grass species but the animal species that the forage will feed. Summer annual grasses can have a number of limitations/problems that can be successfully managed by the knowledgeable producer.
Common to all the species (even the cool-season grasses) is the potential for nitrate accumulation and nitrate toxicity during drought or cloudy weather when nitrates are not metabolized rapidly enough by the plant into proteins and amino acids. Nitrates taken up from the soil then accumulate, especially in the lower stems, and can reach toxic levels and are not reduced during hay harvest. Cyanide toxicity issues exist for sudangrass and the sorghum-sudangrass hybrids but this can be managed with grazing or cutting height. Sorghum species and species such as foxtail millet (Setaria spp.) can be harmful to horses (cystitis problems to name one concern). Hybrid pearl millet and pearl millet do not cause these problems and are generally considered safe for horses. Most of the species also have thick stems and large leaves that make hay making a bit more challenging. With careful management, the benefits from weed suppression, forage production, soil tilth, and early soil fertility adjustment out-weigh other concerns.