A growing body of evidence suggests that biotech-stacked corn hybrids containing Bt rootworm resistance have a higher yield potential than their non-rootworm counterparts. This is thought to be due to their more extensive root systems, and the corresponding positive impacts on root functions like nutrient uptake. The extent of this improvement, however, is not known, nor is it clear if all nutrient elements are affected to the same degree.
It is also unclear if triple-stack hybrids by virtue of their higher yields and/or higher nutrient concentration in the grain remove more nutrients, and if so, which ones are most impacted and the magnitude of this effect. This information is critical to devise nutrient management plans for optimal performance of triple-stack hybrids.
It has been 45 years since Hanway's classic work outlining the patterns of N, P, and K accumulation by corn plants that became the cornerstone for modern corn nutrition (Hanway, 1962 a,b). Karlen et al. (1987; 1988) updated this work for both macro and micro nutrients in the 1980's, well before the advent of biotech-stacked traits. In addition, maize breeding has markedly increased grain yield since 1985 at a rate of 1.6 bu/ac per year (Cassman et al., 2003). This improvement, and the rapid and widespread use of biotech-stacked hybrids containing the rootworm trait, necessitates a new and through examination of mineral nutrient use by modern hybrids. We believe these hybrids will exhibit greater potential accumulation of macro and micronutrients, and have higher peaks of nutrient uptake than older genetics.
The experiment was conducted under field conditions at the Crop Sciences Research and Education Center in Champaign. Two pairs of corn rootworm resistant hybrids (DKC61-69 VT3 and DKC63-42 VT3) and their non-resistant isolines (DKC61-72 RR2 and DKC63-46 RR2/YGCB) were planted on May 5th 2008. One pair (DKC61) was 111 days relative maturity (RM) and the other pair (DKC63) was 113 days RM. Five fixed ammonium sulfate (AS) (21-0- 0-24) rates (0 to 1143 lb/ac) were broadcast and incorporated at V3 to vary nitrogen and sulfur availability. Treatments were arranged as a split-plot in a randomized complete block with four replications. Hybrid (Rootworm resistance x Pair) was the main plot and fertilizer rate the subplot. Soil insecticide was applied at planting to corn RW non-resistant hybrids. The trial was planted with a cone-planter and the stand thinned to a uniform population of 31,000 plants/ac.
At physiological maturity four plants per plot were sampled. Plants were dried, weighed, ground and analyzed for nutrient concentration (N, P, K, S, Mg, Zn, B, Fe, Mn, and Cu). Stover nutrient content was calculated as the product of stover nutrient concentration and biomass. At harvest maturity, the crop was harvested with a plot combine. Grain samples were collected from each plot and analyzed for nutrient concentration. Grain nutrient removal was calculated based on yield and nutrient concentration. Grain yield was adjusted to 15.5% moisture, whereas nutrient concentration and removal are expressed on a dry basis (i.e. 0% moisture). Total nutrient content was calculated as the sum of stover nutrient content and grain nutrient removal (ie. content).
Grain yield, stover and grain nutrient concentration, and grain nutrient removal and total nutrient content (uptake) were analyzed using the Mixed procedure in SAS. Hybrid Pair, rootworm resistance, and fertilizer rate as well their interactions were included in the model as fixed effects. This report focuses on the effect of rootworm resistance and hybrid pair.
Grain Yield
Grain yield averaged 184 bu/ac for rootworm resistant corn hybrids, which was significantly
higher (p<0.01) than average yield for non-resistant genotypes (158 bu/ac), representing a 15.8%
yield improvement. The longer season genotypes yielded significantly (p<0.05) more than the
short season hybrids (177 vs 165 bu/ac).
Grain Nutrient Concentration)
There were significant differences between corn rootworm resistant and non-resistant hybrids for
N, P, K, Mg, Zn and Cu (Table 1). Corn rootworm resistant hybrids had 7% higher grain Zn
concentration, 5% higher grain P concentration and 2% higher grain K concentration than the
non-rootworm resistant counterparts. Conversely, grain Cu concentration was 15% lower and
Mg and N were 2% lower for the corn rootworm resistant hybrids. Grain N, P, Mg, B, Mn and Fe
concentration were higher for the shorter season genotypes, but grain S and Zn were higher for
the longer season hybrids.
Stover Nutrient Concentration
Hybrid maturity affected stover concentration of more nutrients than rootworm resistance, where
only S stover nutrient concentration was affected by rootworm resistance (Table 2). The nonresistant
genotypes had 13% higher S concentration than the rootworm resistant hybrids.
Calcium and Mg concentration were 11% and 15% higher for the DKC63 pair than the DKC61
pair, but Zn and Fe were 15% lower.
Grain Nutrient Removal
Corn rootworm resistance significantly increased grain removal of all nutrients except Cu, which
was not affected (Table 3). Zinc and P were the nutrients that presented the largest increase (24%
and 22%, respectively) whereas N and B were the least affected (13%). Short season hybrids
showed significantly higher grain Zn, S, and K removal than long season genotypes, but the
opposite was observed for N and B. The other nutrients were not affected.
Total Nutrient Uptake
Corn rootworm resistance significantly increased total nutrient uptake of all nutrients except for
Mn and Cu, which were not affected (Table 4). Iron, P, Zn, and B were the nutrients that showed
the largest difference (23% for Fe, 18% for P and 14% for Zn and B, respectively). Nitrogen, Mg
and S were higher for the DKC63 pair than the DKC61 pair, but the magnitude of this difference
was smaller than the difference due to rootworm resistance.
Zinc and P were the two nutrients that showed the largest difference due to rootworm resistance. This evidence suggests that protecting the root system has a more pronounced effect on nutrients absorbed by root interception and that are immobile in the soil than those absorbed by mass flow and that are mobile in the soil, like N or S, for example. Similar results were observed for total nutrient uptake, mainly as a consequence of the large harvest index for these nutrients.
The large increase of Zn and P removal (a combination of higher yield and nutrient concentration) strongly indicate that soil test levels of these nutrients may rapidly decrease as corn rootworm resistant hybrids are planted every year and become more popular, if fertilizer P and Zn recommended rates are not adjusted. The larger grain P and Zn concentration for corn rootworm resistant hybrids must be accounted for in nutrient management plans in order to sustain corn productivity of Illinois´s soils. In addition, farmers and fertilizer dealers need to pay special attention to corn P and Zn nutrition to guarantee that these nutrients do not limit the yield potential of corn rootworm resistant hybrids.
These results are the first reported evidence of changes in grain nutrient concentration and uptake due to corn rootworm resistance and must be considered as preliminary evidence because they are based on a single year of study, at one location and two pairs of hybrids. Current research funded by FREC is underway to more thoroughly study the effect of corn rootworm resistance over a larger set of environments and hybrids.
Cassman, K.G., A. Dobermann, D. T.Walters, and H. Yang. 2003. Meeting cereal demand while
protecting natural resources and improving environmental quality. Annu. Rev. Environ.
Res. 28:315-358.
Hanway, J. J. 1962. Corn growth and composition in relation to soil fertility: II. Uptake of N, P,
and K and their distribution in different plant parts during the growing season. Agron. J.
54: 222-229.
Hanway, J.J. 1962. Corn growth and composition in relation to soil fertility: III. Percentages of
N, P and K in different plant parts in relation to stage of growth. Agron. J. 54:217-222.
Karlen, D.L., E. J. Sadler, and C. R. Camp. 1987. Dry matter, nitrogen, phosphorus, and
potassium accumulation rates by corn on Norfolk loamy sand. Agron J. 79:649-656.
Karlen, D.L., R. L. Flannery, and E. J. Sadler. 1988. Aerial accumulation and partitioning of
nutrients by corn. Agron. J. 80:232-242.