September 17, 2013
Source: Agricen
By Fred E. Below, PhD, Professor of Plant Physiology, Department of Crop Sciences, University of Illinois at Urbana-Champaign
Agronomic advancements have brought corn yields to new heights, but producers have had little guidance on how to meet the nutrient requirements of modern, high-yield corn hybrids in a way that maximizes their yields. As a result, the high yields we see today have been accompanied in many places across the US by a significant drop in soil nutrient levels, particularly phosphorous (P), potassium (K), sulfur (S) and zinc (Zn). This combination—higher yielding hybrids and decreasing soil fertility levels—suggests that producers have not sufficiently matched their maintenance fertilizer applications with nutrient uptake and removal by the corn.
By better understanding nutrient uptake and partitioning, growers can optimize their fertilization practices to meet their crop needs and attain maximum yield potential. Since a good portion of producers will soon be heading to the field to make a dry fertilizer application, we’ll focus here primarily on P and K.
For modern corn hybrids in high-yielding systems, mineral nutrients with high requirements for production (nitrogen [N], P, K) or with a high harvest index (HI, the percentage of total plant uptake that is removed with the grain) (i.e., N, P, S, Zn) are important for obtaining high corn yield (Table 1).1 Typical fertilization for corn in the US is 180 lbs nitrogen (N), 90 lbs P2O5 and 160 lbs K20 per acre, with no S or micronutrients.
Producers must consider the impact of increased grain and stover nutrient removal on the next crop and employ appropriate fertilizer strategies to ensure that adequate nutrients are available to the crop. Phosphorous is probably one of the most overlooked nutrients, and most farmers are not putting out enough. In relation to total uptake, nearly 80% of P is removed in corn grain compared to K and B, which are retained to a greater percentage in stover.
Production practices that utilize aboveground stover (i.e., cellulosic ethanol, silage production) may remove an additional 20.8 lbs N, 4.0 lbs P2O5, 23.3 lbs K2O, along with micronutrients, per ton of dry matter. While farmers in Illinois, for example, fertilize 93 lbs P2O5 per acre, on average, for corn production2, the large majority (~80%) of soybean fields receive no applied P, and, as a result, would have only the remaining 13 lbs/acre P2O5 available for soybean production in a corn–soybean rotation3, where P and K fertilizer are commonly applied for both crops in the corn production year. This value would be inadequate to meet soybean P needs for total uptake (48 lbs/acre P2O5) or nutrient removal (30 lbs/acre P2O5) based on a conservative yield estimate of 46 bushels/acre in Illinois.4 It’s clear that typical fertilization practices may need to be adjusted to meet corn nutrient needs.
Mineral nutrients are not all acquired at the same time or used in the same way by corn plants, and some require season-long uptake by the corn roots to achieve a high yield. During the V10 to V14 growth stages, we know that 230 bushel corn requires 7.8 lbs N, 2.1 lbs P2O5 and 5.4 lbs K2O per day, needs that change at other times. To optimize their programs, producers need fertilizer sources that supply nutrients at the rate and time that match the plants’ nutritional needs.
Potassium accumulates more than three-fourths of total uptake by VT/R1 (Figure 1)1, while over 50% of total P uptake occurs during grain fill (after VT/R1) (Figure 2)1, in addition to remobilization of 57% and 77% of the maximum measured leaf and stalk P contents, respectively. This suggests that a season-long supply of P is critical for corn nutrition, while availability of K at levels that can meet the maximum rates of uptake during early season vegetative growth would be expected to meet corn nutritional needs, since the majority of K uptake occurs during vegetative growth. Thus, practices that are effective for one nutrient may not improve uptake of the other.
Nutrient management is complex, but improved fertilizer use can be achieved by understanding patterns of nutrient uptake, partitioning, and utilization. Producers should pay special attention to P requirements as productivity increases, as current data suggest a looming soil fertility crisis if adequate adjustments are not made in P usage rates. Agronomic advancements have brought corn yields to new heights, but an understanding of how to maintain soil nutrient levels can go along way in helping to sustain the high yields.
References:
- Bender RR, Haegele JW, Ruffo ML, Below FE. 2013. Nutrient uptake, partitioning, and remobilization in modern, transgenic insect-protected maize hybrids. Agron. J. 105:161–170.
- National Agriculture Statistics Service (NASS), United States Department of Agriculture. Fertilizer and Chemical Usage. 2011. Illinois Farm Report. 32:8.
- NASS. Fertilizer, Chemical Usage, and Biotechnology Varieties. 2010. Bulletin As11091, Illinois Agricultural Statistics.
- Usherwood, N.R. 1998. Nutrient management for top-profit soybeans. News and views. Bulletin RN 98105. Potash and Phosphate Inst., Int. Plant Nutrition Inst., Norcross, GA.
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