Simulating Inbred-Maize Yields with CERES-IM

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 and silk emergence, and the settings of the mechanical simulated using a measured phyllochron interval of 54 degree-days detasseling machines (Wilhelm et al., 1995b). Removal (8Cd). Simulation of detasseling and male-row removal improved grain of the tassel alone was reported to augment maize grain yield simulation for inbreds. For a set of 35 inbred-site-year simulayields by increasing the amount of light available to the tions, the model simulated grain yield with satisfactory accuracy top leaves (Duncan et al., 1967; Hunter et al., 1969). (RMSE 5 429 kg ha21). Average grain yields were 4556 and 4721 kg Leaf removal associated with detasseling induces a linha21 for the measured and simulated values, respectively. CERESear decline in grain and stover yields proportional to IM simulations suggest that the effect of male-row removal on grain the number of leaves removed (Wilhelm et al., 1995b). yield is extremely sensitive to the precise date at which this operation Stover biomass was reduced by 4 to 18% when one to is conducted. This would explain the inconsistent effect of male-row three leaves were removed with the tassel (Wilhelm et removal on female grain yields reported in the literature. al., 1995b). Inbred maize plants differ from grain-producing hybrids in size and potential grain yield. The canopy of T vast majority of maize marketed in the USA inbred-maize fields varies greatly depending on the inand Canada comes from single-cross hybrids probred, but is generally much reduced compared with that duced from crosses between two inbred lines (Wych, of hybrid maize (Orr et al., 1997). Grain yields are lower 1988). The pollen-supplying inbred line is referred to for inbreds than for hybrids (Peterson and Corak, 1993). as male, while the seed-bearing line is referred to as In the Platte River Valley of Nebraska, grain yields of female. Uniform distribution of pollen to the female inbred maize averaged only 3.5 Mg ha21 (Wilhelm et plants requires that alternate male and female rows are al., 1995b). Published data suggest that total numbers planted in a pattern that optimizes marketable kernel of kernels per plant are substantially lower for inbreds yields (Culy et al., 1991). The row pattern is designed than for hybrid maize plants (Wilhelm et al., 1995b). to provide sufficient pollination of all female rows while The seed industry has a great interest in predicting minimizing the surface allocated to nonproductive male grain yield responses to environmental conditions. Irrirows (Culy et al., 1991). Male plants are mechanically gation scheduling and N fertilization can be better mandestroyed following complete pollen shedding. This opaged through a decision support system. Grain yield eration is conducted to prevent ears from the self-polliand growth duration of inbred maize can be estimated nated male plants from being harvested together with with an accurate crop model to determine optimum the female ears. Male-row removal is supposed to inareas for seed production in regions of the world where crease seed yields by leaving more nutrients and water there is no history of growing inbred maize but where available to the remaining female plants. Nevertheless, potential markets exist for hybrid maize seeds. Prethis effect has not been clearly demonstrated (Wych, dicting maize seed production in North America a cou1988). ple of months prior to harvest can help companies better plan for the seed production campaign in tropical reD.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. Wilhelm, USDA-ARS, 117 Keim Hall, Univ. of Nebraska, Lincoln, NE 68583-0934; J. Wei, Pioneer Hi-Bred International Inc., 7100 NW 62nd Ave., P.O. Box 1150, Johnston, IA 50131-1150; and Abbreviations: CRM, coefficient of residual mass; G2, maximum posE.C. Martin, Dep. of Agricultural and Biosystems Engineering, Marisible number of kernels per plant; G3, kernel filling rate; GPP, grain copa Agricultural Center, University of Arizona, 37860 W. Smithper plant; LAI, leaf area index; MI, Michigan; NE, Nebraska; P1, Enke Road, Maricopa, AZ 85239. Received 4 Jan. 1999. *Correspondthermal time from emergence to end of juvenile phase; P2, photoperiing author ([email protected]). odism coefficient; P5, thermal time from silking to physiological maturity; PHINT, phyllochron interval; RMSE, root mean square error. Published in Agron. J. 92:672–678 (2000).