Since phosphorus is relatively immobile in the soil solution, close root proximity to fertilizer is important. Corn often responds to starter fertilizer because applying a concentrated zone close to the roots maximizes phosphorus availability when root proliferation is sparse. Southern producers often apply starter fertilizer with equipment used to apply cotton fungicides in-furrow with favorable results. Cornbelt growers commonly use coulter rigs that band starter fertilizer to the side and below the seed. These systems maximize placement efficiency, improve seedling safety, and permit higher fertilizer rates.
Corn requires as much potassium as it does nitrogen to produce good yields.
Potassium is needed to build strong stalks, fight diseases, and translocate water within the plant. Potassium deficiency often occurs following crop residue removal or uneven residue distribution of the previous crop, and the deficiency is accentuated by dry weather. Potassium is essential to good stalk health and often leads to stalk lodging at harvest that is associated with increased susceptibility to stalk rots and poor drought tolerance. High potassium levels have also aided stress tolerance due to compacted soils. Fall application of potassium fertilizer is recommended because, like phosphorus, potassium is relatively immobile in most soils.