Seed Physiology, Production & Technology

Detasseling is used in hybrid corn (Zea mays L.) seed production to ensure harvested seeds have the desired genetic complement. Both mechanical and hand detasseling result in loss of some leaf tissue and plant N. The objective of this study was to determine if seed yield and quality and N content of grain and stover were affected by leaf removal during detasseling. The treatments evaluated were removal of tassel only, tassel plus one leaf, tassel plus two leaves, tassel plus three leaves, tassel plus four leaves, and no tissue removed (control). The leaf area index (LAI) declined linearly, about 0.16 LA1 units per leafremoved. Grain and stover yield also declined linearly with number of leaves removed with the tassel (r" 0.W and 0.92, respectively). Each leaf removed reduced grain yield about 0.36 Mg ha-'. Yield reduction was caused by decreased kernel size. Grain and stover N concentration and amount of N in stover did not vary among detasseled treatments. However, total N in the grain declined linearly as number of leaves removed increased (r2 = 0.97). Warm and cold germination and warm germination after accelerated aging were not affected by leaf removal during detasselig. Results reported here suggest that when leaves are removed from the plant at detasseling, the loss of photosynthetic capacity, the ability to intercept light, and plant N all contribute to grain yield reduction. T HE PRODUCTION OF HYBRU) CORN seed requires that only pollen from the male parent be available for pollination in the seed production field. Detasseling (both mechanical and hand) is used to prevent pollen shed from the female parent. The number of leaves removed with the tassel depends on plant morphology, the time of detasseling relative to time of tassel emergence, pollen shed and silk emergence, and settings on mechanical detasseling machines. As many as f&r leaves may be removed from the female parent to ensure complete tassel Removal of the tassel may increase yield because of improved light interception by underlying photosynthetically active tissue (Duncan et al., 1967; Hunter et al., 1969) and more favorable translocation of photosynthate to the grain (Mostert and Marais, 1982), but results are variable depending on interplant competition, water availability, and soil fertility (Grogan, 1956; Hunter et al., 1973). Inbred lines produce far less grain than hybrids. Under irrigation in the central Platte River Valley of Nebraska, a prime U.S. hybrid seed production area, yields vary greatly among inbreds, but average about 3.5 Mg ha-'. Although production is low, the value per unit of yield is 6 to 10 times greater than that of feed grain. Because of the high seed value, producers are encouraged by contracting companies and economic logic to maximize yields. Producers try to keep soil water (in irrigated areas) and fertilizer N non-limiting. A survey by Schepers et al. (1991a,b) indicated the average seed producer in the Central Platte Natural Resource District applied 130 kg N ha-'. This rate of N application was twice the calculated amount of N removal by the crop (assuming 18 kg N removed kg-' corn removed) and fertilizer recommendations for feed grain production based on soil tests. Environmental awareness by producers, seed companies, and the general public has increased the need for data to use in recommending fertilizer N application rates for hybrid seed production. The objective of this study was to determine the effect of leaf removal during detasseling on seed yield, kernel quality, and N use. MATERIALS AND METHODS removal and genetic of seed produced. These This experiment was conducted during 1991 and 1992 in leaves represent a significant source of photosynthate the central Platte River valley near Shelton, NE, (40" N, 99" and N for the developing kernels. Their loss may impact W) on a Hord silt loam (fine-silty, mixed, mesic Cumulic yield and quality of the hybrid seed produced and the Haplustolls) at the site of the Nebraska Management Systems N used by the crop. Evaluation Area (MSEA) project. Before planting, stover from Several studies have been conducted to evaluate the the previous crop (corn feed grain) was chopped and the soil tilled twice with a tandem disk. The inbred line, N192, was inRuence of On grain yield. Dungan and planted at 8.2 kernel m-?. on 7 May 1991 and 6.5 kernel m-?. Woodworth Kiesselbach and Hunter on 30 April 1992 in 0.91-m rows Plant were thinned al. (1969; 1973) reported reductions in grain yield and to 8.0 plants m ~ in 1991 and 6.0 plants m ~ in 1992, prior kernel mass when leaves were removed with tassels. to the four-leaf stage. weeds were controlled with a combination of herbicides, mechanical cultivation, and hand hoeing. W. W. Wilhelm, USDA-ARS, 117 Keim Hall, UNV. of Nebraska, Lincoln, Anhydrous ammonia was applied at 80 kg N ha-' at the five-leaf NE 68583-0934; B. E. Johnson, 326 Keim Hall, Dep. of Agronomy, stage. The experimental area was irrigated as needed using Univ. of Nebraska, Lincoln, NE 68583-0915; and J. S. Schepers, USDAmanagement practices typic, for the area with a linear drive ARS, 113 Keim Hall, UNv. of Nebraska, Lincoln, NE 68583-0934. This paper is a joint contribution of the USDA-ARS and the Agric. Res. Div. of the UNv. of Nebraska. Published as Journal Series no, 10449. Received Abbreviations: C, control-no tissues removed; LAI, leaf area index; T 30 June 1993. *Corresponding author (wilhelmQunl.edu). only, tassel only removed; T+ 1, tassel plus one leaf removed; T+2, tassel plus two leaves removed; T+3, tassel plus three leaves removed; Published in Crop Sci. 35:209-212 (1995). T+4, tassel plus four leaves removed.