Modern hybrid corn makes better use of nitrogen, study shows
WEST LAFAYETTE, Ind. - Today's hybrid corn varieties more efficiently use nitrogen to create more grain, according to 72 years of public-sector research data reviewed by Purdue University researchers.
Tony Vyn, a professor of agronomy, and doctoral student Ignacio Ciampitti looked at nitrogen use studies for corn from two periods – 1940-1990 and 1991-2011. They wanted to see whether increased yields were due to better nitrogen efficiency or whether new plants were simply given additional nitrogen to produce more grain.
"Corn production often faces the criticism from society that yields are only going up because of an increased dependency on nitrogen," said Vyn, whose findings were published in the early online version of the journal Field Crops Research. "Although modern hybrids take up more total nitrogen per acre during the growing season than they did before, the amount of grain produced per pound of nitrogen accumulated in corn plants is substantially greater than it was for corn hybrids of earlier decades. So, in that sense, the efficiency of nitrogen utilization has gradually improved."
Vyn and Ciampitti's analysis covered about 100 worldwide studies. Of those, 870 data points were taken from the earlier period through 1990, and 2,074 points were taken from studies after 1990, when transgenic hybrids started hitting the market. All studies involved analyses of total nitrogen uptake and grain yield by corn plants at maturity, usually in response to multiple nitrogen application rates.
Grain yields in these research studies averaged about 143 bushels of corn per acre over the last 21 years compared with an average of 115 bushels in the previous 50 years. Those studies showed that in the earlier period, one pound of nitrogen taken up by corn plants from soil and fertilizer sources produced about 49 pounds of grain. In the more recent period, that same amount of nitrogen accumulated in the above-groundplant parts produced about 56 pounds of grain.
About 90 percent of the corn data points examined in Vyn's study evaluated nitrogen rates between zero and 250 pounds per acre. Over both periods, the average rate of nitrogen fertilizer distributed in experimental fields was nearly the same – 124 pounds per acre in the earlier period vs. 123 pounds in the later period.
Vyn said genetic improvements have led to corn plants that require less space around them, allowing growers to squeeze more plants into an acre. Research fields from the modern era averaged about 28,900 plants per acre – about the average final plant populations in Indiana cornfields in 2011 - compared with 22,800 plants per acre from 1940-1990.
"The maximum individual plant nitrogen uptake stayed exactly the same despite the average gain of 6,000 more plants per acre," Vyn said. "The modern plants are just more efficient at taking nitrogen up and utilizing it than they were before."
Vyn and Ciampitti are working toward methods to increase grain yields further by investigating the contribution of nitrogen to plant biomass and yield formation processes in high-yielding hybrids under a wide range of nitrogen inputs and production stress factors. Knowing that modern hybrids are sustaining a reasonable quantity of nitrogen uptake even under progressively higher plant densities is a good start, Ciampitti said.
"We are getting clues on how plants have already improved nitrogen use efficiency, and we will use that to push for further increases," Ciampitti said. "We finally feel like we're shedding some light on what traits plant breeders should select for to increase nitrogen efficiency even more."
Vyn and Ciampitti plan to further investigate how water use efficiency and nitrogen use efficiency are tied together, as well as how plants can achieve more tolerance to environmental stresses.
Dow AgroSciences, PotashCorp and the U.S. Department of Agriculture National Institute of Food and Agriculture funded their work.
Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu
Sources: Tony Vyn, 765-496-3757, tvyn@purdue.edu
Ignacio Ciampitti, 765-418-8867, iciampit@purdue.edu
Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
Agriculture News Page
ABSTRACT
Physiological Perspectives of Changes Over Time in Maize Yield Dependency on Nitrogen Uptake and Associated Nitrogen Efficiencies: A Review
Ignacio A. Ciampitti, Tony J. Vyn
Over the past three decades, the study of various mechanisms involved in maize grain yield (GY) formation and its relationship with nitrogen (N) uptake dynamics has been increasingly acknowledged in the scientific literature. However, few studies have combined investigations of GY response to N fertilizer with detailed physiologically based analyses of plant N dynamics such as N uptake quantities, timing, and (or) partitioning – and the complex interactions of those with specific genotypes (G), management practices (M), and (or) production environments (E). Limited reporting of both N and yield dynamics at plant-component, individual-plant, and community levels has contributed to a considerable knowledge gap as to whether the physiological mechanisms that govern maize plant N dynamics and their relationship with GY formation have changed with time. We, therefore, undertook a comprehensive review to discern trends in physiological aspects of maize response to changing plant densities and fertilizer N rates (M components) under the umbrella of evolving G x E interactions. We reviewed 100 published and unpublished papers based on field experiments which consistently reported total plant N uptake at maturity and maize GY (frequently among other physiological variables). Our analyses were limited nearly exclusively to experiments involving hybrid (as distinct from inbred) response to M input levels where plant density data was available. Dissection of the complex interactions among years, plant densities and N rates began with division of treatment mean data (close to ∼3000 individual points) into two time periods defined by year(s) of the original research: (i) studies from 1940 to 1990 – "Old Era" and, (ii) studies from 1991 to 2011 – "New Era." For the Old Era, maize GY averaged 7.2 Mg ha−1 at a mean plant density of 5.6 pl m−2 with a total plant N uptake of 152 kg N ha−1, a grain harvest index (HI) of 48% and N harvest index (NHI) of 63%. For the New Era, maize GY averaged 9.0 Mg ha−1 at a mean plant density of 7.1 pl m−2, total plant N uptake of 170 kg N ha−1, a grain HI of 50% and a NHI of 64%. The most striking findings in terms of overall GY and plant N uptake were: (1) on a per-unit-area basis, both potential GY and NIE (GY/N uptake) increased from Old to New Era at comparable N uptake levels, and (2) on a per-plant basis, total plant N uptake at maturity had not changed between eras despite increased plant density in the New Era genotypes. Other important findings in terms of plant growth and component partitioning responses to N were (i) a consistently strong dependency between dry matter and N allocation to the ear organ in both eras; (ii) higher total plant biomass (BM) accumulation and N uptake, on an absolute basis, during the post-silking period with New Era genotypes accompanied by relatively smaller changes in HI and NHI; (iii) a strong correlation between plant N uptake at silking time and per-plant GY and its components in both eras; (iv) New Era (56.0 kg GY grain kg−1 N) was primarily associated with reduced grain %N, and to a minor degree with NHI gains; and (v) New Era genotypes showed higher tolerance to N deficiency stress (higher GY when no N fertilizer was applied), and larger GY response per unit of N applied, relative to Old Era hybrids. This improved understanding of the physiological factors underlying progress in maize yield response to N over time, within the context of changing G x E x M factors, serves to help guide maize programs focused on achieving further improvements in N use efficiency.
