Increasing demand to use corn plant biomass for producing energy and other products has spurred interest in harvesting corn stover and specific plant components in addition to grain. The technology and infrastructure needed for effective use of total corn plant biomass in energy production is currently being investigated and its implementation at a large scale in the near future is a real possibility. Harvesting more biomass means increased carbon (C) and other nutrient removal from fields. What is the nutrient removal when different corn plant components are harvested?

Corn plant nutrient content

Most producers in Iowa are familiar with harvesting corn for grain and less familiar with other plant biomass removal. Those harvesting corn silage are aware of the increase in phosphorus (P) and especially potassium (K) removal, and fertilization guidelines consider this increase. For example, with corn silage based on a bushel grain equivalent, the pounds of P as P₂O₅ goes from 0.375 to 0.55 and the pounds of K as K₂O goes from 0.30 to 1.25, respectively, for corn grain and corn silage (Table 1, taken from Iowa State University Extension publication PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa).

For corn stover (nutrient concentration at plant maturity) the pounds per ton are 5.9 lb P2O and 25.0 lb K₂O (Table 1). This data indicate there is considerable K in the non-grain part of the corn plant. These nutrient concentrations are expressed on a dry matter basis, so adjustment downward is needed to account for stover moisture content. Examples of P and K removal in corn grain and stover for contrasting yield levels are shown in Table 2. Calculating the P and K removal in harvested stover is somewhat complicated as nutrients can be leached (especially K) from leaves and corn stalks with rainfall after grain harvest. The effect of rainfall on K is much more important than for P because all plant K is in a soluble inorganic form while most P is in organic forms of low solubility. Therefore, the concentration of nutrients at plant maturity will typically be higher than found for baled stover because it often rains after grain harvest. Also, the frequency and amount of rainfall will affect the concentration remaining. Costs for replacing removed nutrients will vary depending upon prevailing prices. At an example price of $0.38 per lb P₂O₅ and $0.24 per lb K₂O, the cost with complete stover removal at plant maturity with a 240 bu/acre crop (Table 2) is $11.78 for P and $31.92 for K.

Table 1. Nutrient removal in crop harvest.

*Dry matter at maturity.

Source: Iowa State University Extension publication PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa.

Table 2. Example estimated P and K removal in corn stover.

P and K removal estimated from values in Iowa State University Extension publication PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa.

Corn grain at 15.5 percent moisture.

Corn stover (including cob) dry matter basis.

Corn biomass also contains other plant nutrients. Examples for nitrogen (N), P, K, calcium (Ca), magnesium (Mg), and sulfur (S) are shown in Tables 3 and 4 for two sources of data. Table 3 gives the composition for corn stover without ears. Table 4 gives the composition for corn cobs. There is variation in concentration values due to differing data sources, hybrids, fertilization levels, etc. While there may typically be adequate supply of nutrients like Ca, Mg, and S from Iowa soils (not usually fertilized with these nutrients), greater removal with stover harvest can lead to increased deficiency and removal of large amounts of "basic cations" (K, Ca, and Mg) and can result in accelerated decrease in soil pH. Liming or manuring soils will aid in replacement of these nutrients.

Table 3. Elemental composition of corn stover.

Ears removed.

Sources: United States-Canadian Tables of Feed Consumption (NRC); Feeds and Feeding, abridged (Morrison).

Sources: United States-Canadian Tables of Feed Consumption (NRC); Feeds and Feeding, abridged (Morrison).

Dry matter and nutrient composition in corn plant components

Silage harvest results in almost complete removal of aboveground plant biomass. Baling corn stover typically does not remove as much plant biomass and amounts removed vary greatly across fields and years due to many factors. Also, there may be interest in specific plant component removal, such as targeting corn cobs. Table 5 lists the various corn plant components, the associated dry matter, and the nutrient composition from Iowa research in the 1970s. Research results from recent N rate trials at six locations in Iowa in 2006 indicated a corn grain harvest index of 52 percent (percent of the total aboveground biomass as grain on a dry matter basis at maturity), a shelling percentage of 88 percent (percent of grain and cob as grain), and a grain N concentration at 1.31 percent N or 0.62 lb N/bu (at an adequate and not excessive N rate). These values are approximately similar to those in Table 5, although grain N currently is slightly lower than it used to be as it has declined over time. The estimates of grain harvest index and shelling percentage can be used to calculate non-grain biomass and cob biomass from grain yield. For example, at a grain yield of 200 bu/acre (at 15.5 percent moisture standard, the per bu grain dry matter is 47.32 lb) the grain dry matter is 9,460 lb/acre, the cob dry matter is 1,135 lb/acre, and the non-grain biomass is 8,730 lb/acre.

Table 5. Dry matter and nutrient composition by corn plant part at maturity.

Corn yield at 161 bu/acre.

Source: Iowa State University research, J. J. Hanway.

Summary

Harvesting corn plant components in addition to grain does result in greater removal of plant nutrients. Effects of increased P and K removal on nutrient needs of corn are immediate and should be accounted for in fertilization plans. Effects on needs of other nutrients such as N and S, liming requirements to maintain desirable soil pH levels, soil organic C, and several physical, chemical, and biological soil properties are less apparent in the short term but have consequence in the long term. Therefore, consideration of the impact on nutrient cycling (including C), nutrient removal, and soil resources should be a part of the decision process regarding harvesting corn biomass.

Data sources

Morrison, F. B. 1961. Feeds and Feeding, abridged, ninth edition. The Morrison Publishing Company, Clinton, IA.

National Research Council. 1982. United States-Canadian Tables of Feed Composition. Nutritional Data for United States and Canadian Feed, third revision. National Academy Press, Washington, D.C.

John Sawyer is an associate professor of agronomy and Antonio Mallarino is a professor of agronomy, both with research and extension responsibilities in soil fertility and nutrient management.