Fertilization for Establishing Stands

Since switchgrass is slow to establish and often does not compete well with weeds during the establishment phase. Most annual weeds are responsive to fertilizer applications, and particularly to nitrogen (N), whereas switchgrass displays little response to N during establishment (Sanderson and Reed 2000). Thus, the general recommendation is to defer N fertilizer applications until switchgrass is considered established—typically this means waiting until the second growing season (Jung et al. 1988; Brejda 2000; Sanderson and Reed 2000).

Soil phosphorus (P) and potassium (K) levels (> 20 soil P and > 200 soil K by the Mehlich 3 index) should be sufficient for establishment. Although general recommendations for P and K are to have these nutrients at moderate levels at planting, there is little data to suggest that adding K fertility can boost seedling growth at establishment. Soil P has been implicated in increased plant size and first-season yield, but this response may be short-lived (McKenna and Wolf 1990).

Switchgrass is moderately tolerant of soil acidity, but liming is generally recommended prior to planting if soil pH is below 5.0 to ensure other plant nutrients like P and K are more available. The literature equivocates, however. Several studies report no benefits from liming (Harper and Spooner 1983; Bona and Belesky 1992; Hopkins and Taliaferro 1997), although McKenna and Wolf (1990) found that limestone (2016 kg ECCE ha1) increased first-harvest yield in one year but not the second.

Responses to lime are more likely to be observed when it is applied in combination with nutrients such as N or P. For example, yields were maximized when a combination of limestone and P were applied (McKenna and Wolf 1990). Similarly, on highly acidic (pH 4.3-4.9) soil in Pennsylvania, USA, switchgrass grown on untreated plots yielded about 50% of that receiving limestone and fertilizer (Jung et al. 1988). In a greenhouse pot experiment with five acidic soils (pH 4.5-5.2), yield did not increase when soil pH was brought to 6.5 with limestone, however, a yield response was reported when N and P or N, P, and K were co-applied with limestone (Taylor and Allinson 1982).