productivity over long periods of time, these efforts did not attempt to identify the environmental variables thatThe effectiveness of a cultivar evaluation system largely depends were most important in influencing GEI and thus the on the genetic correlation between genotype performance in multigenetic correlations for genotype performance among environment trials (MET) and in the target population of environments (TPE). Previous classifications of maize (Zea mays L.) environ-testing sites, a key factor in determining the efficiency ments on the basis of climate and soil did not quantify their impact and efficacy of a cultivar evaluation system. Consequently, on the genetic correlations among environments. Consequently, plant plant breeders have more extensively used classificabreeders have favored classifications based on the similarity of cultivar tions of environments based on similarity of cultivar discrimination in trials. However, these efforts frequently fail to prodiscrimination using crop performance data collected vide adequate assessments of the TPE, since they require long-term from their cultivar evaluation or ad hoc trials, rather performance data, which are not normally collected due to high cost. than basing the classification on environmental data. To describe the TPE, we performed crop simulations for each U.S. Cooper et al. (1993) compared the relative merit of Corn Belt Township for the period 1952 through 2002, using standard four strategies for classifying wheat (Triticum aestivum CERES-Maize model inputs. To classify METs, input data were col-L.) environments and favored classifications based on lected at or near the trial sites. Grain yield and biotic stress data for model confirmation were collected from 18 hybrids grown in repli-

A single transgene ARGOS1 positively impacts yield of field-grown hybrid maize. Two predominant alleles from elite hybrid breeding germplasm differed in transgene efficacy, but both alleles combined in a transgenic stack outperformed each alone, consistent with a single-locus heterotic effect

Nitrate leaching from maize (Zea mays L.) fields fertilized in excess of plant requirements continue to threaten water quality even though many agronomists have recommended reducing N fertilization rates to contain this environmental risk. Inbred maize has lower N uptake than conventional hybrid maize; therefore, inbred maize production exposes soils to even greater ground water pollution risks by nitrates. A 3‐yr field experiment was conducted on sandy loam soils in southwestern Michigan to investigate the combined effects of N fertilization rates and rye (Secale cereale L.) cover crops on NO3 leaching in inbred maize fields. Inbred maize was fertilized at 0, 101, and 202 kg N ha−1. Annual NO3 leaching losses were 7 kg N ha−1 higher in fields fertilized at 101 kg N ha−1 than in nonfertilized controls. Annual NO3 leaching losses to ground water between May 1995 and April 1998 from lysimeters fertilized at 202 kg N ha−1 averaged 88 kg NO3‐N ha−1. Rye interseeded with inbred maize fertilized at 202 kg N ha−1 sequestered from 46 to 56 kg ha−1 of excess fertilizer N. Rye scavenged little residual fertilizer N in plots fertilized at 101 kg N ha−1. Well established rye cover crops in 1996 reduced NO3 leaching by as much as 65 kg N ha−1 when the previous crop was fertilized with 202 kg N ha−1. Therefore, rye cover crops sequestered substantial amounts of soil NO3 in heavily fertilized inbred maize fields.

Detasseling is the operation that consists of removing the tassels of the female plants prior to silk emergence CERES-Maize, which was designed for simulation of hybrid maize and pollen shed to prevent self-pollination. During this (Zea mays L.), cannot be applied directly to seed-producing inbred maize because of specific field operations and physiological traits of operation, several leaves are generally removed from inbred maize plants. We developed CERES-IM, a modified version the plants. Though male-sterile inbreds have also been of CERES-Maize 3.0 that accommodates these inbred-specific operaused to avoid detasseling of seed-bearing female plants, tions and traits, using a set of phenological measurements conducted most maize inbreds planted in the USA are not malein Nebraska (NE), and further tested this model with a set of field sterile and require mechanical detasseling (Wych, 1988; data from Michigan (MI). Detasseling (i.e., removal of the tassels J. Wei, personal communication, 1999). Detasseling is from the female plants) was conducted prior to silking. Male rows an important field operation that modifies the plant were removed approximately 10 d following 75% silking. The thermal canopy. The number of leaves removed by detasseling time from emergence to the end of the juvenile phase (P1) and the depends on plant morphology, the time of detasseling potential number of kernels per plant (G2) were assessed from field relative to the time of tassel emergence, pollen shed data, and were the only two coefficients allowed to vary according to the inbred line. Rate of leaf appearance of the inbreds was accurately D.P. Rasse and J.T. Ritchie, Crop and Soil Sciences Dep., Plant and gions during the wintertime. Inbred maize, used for the Soils Building, Michigan State Univ., East Lansing, MI 48824-1325;production of hybrid-maize seeds, represents a specific W.W.

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