Two major aspects of plant nutrition are important to understand when developing fertilizer recommendations :
1. Total Nutrient Uptake or the amount of a given nutrient that needs to be acquired during the growing season.
2. Nutrient Removed with Grain or the amount of a given nutrient contained in the grain.
Table 1 shows the total uptake and removal with grain of major nutrients in research conducted with modern corn products under high yield conditions at the University of Illinois.1 It also shows how much of the nutrient was taken up by the time corn reached reproductive growth (R1).
The portion of each nutrient that is not removed with the grain remains in leaf, stalk, and reproductive tissues and constitutes the stover that is returned to the field. Corn grown for silage production using aboveground stover can remove additional nutrients that need to be accounted for in fertility programs. A large percentage of the total uptake of nitrogen (N), phosphorus (P), and sulfur (S) is stored in corn grain; whereas, potassium (K) is mostly stored in the stover.
Table 1. Total nutrient uptake and removal in corn.1
Harvest Index (%)is a percentage of total plant uptake removed with the grain.
The highest rate of N uptake occurred from V10 through V14 vegetative growth stages of corn (Figure 2). Of critical importance is supplying N to meet the peak needs of corn at this time. The majority of N was taken up during vegetative growth with two-thirds of the uptake completed by R1 or the beginning of reproductive growth. Uptake of N did not cease at R1, with as much as 50 lb N/acre accumulated and partitioned directly into the developing seeds during grain fill. About 60% of the total accumulated N was removed with the grain.
More than 50% of total P uptake occurred after tasseling and silking. Nearly 80% of P was removed with the grain, more than any other nutrient. Much like N, two-thirds of the total uptake of K was completed by VT/R1. However, only 33% of the total accumulated K was removed with the grain. K was retained to a greater percentage in stover. Much like P, more than 50% of total S uptake occurred after tasseling and silking. The percentage of total accumulated S removed with the grain was similar to N.
The research indicated that a season-long supply of P and S is critical for corn nutrition, while the majority of N and K uptake occurred during vegetative growth. As a percentage of total uptake, P was removed more than any other nutrient, suggesting that soils could be rapidly depleted without proper management. At-planting applications such as starter fertilizer applied with the planter can be used to supply N, P, K, S, and needed micronutrients. An application schedule that applies a small amount of N early in the season (preplant or starter) followed by later in-season applications of higher amounts is ideal. This schedule can take care of the small, but important, early season-N needs and maximizes uptake by applying N during the rapid growth and N requirement period. Side-dressing N around the V4 to V8 growth stages of corn can be used to supply N closer to when the plant needs the nutrient. With irrigated corn that can be fertigated (adding nutrients in irrigation water), N and other nutrient fertilization can be timed more efficiently to match the needs of the plant.
Nutrient management in corn is a complex process. However, improving our understanding of nutrient uptake timing and rates, partitioning, and remobilization by corn can help optimize fertilizer rates and application timings.
1Bender, R., Haegele, J., Ruffo, M., and Below, F. 2013. Modern corn hybrid’s nutrient uptake patterns. Better Crops volume 97. number 1.