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Plant performance and appearance in deficient and toxic levels of nutrients are well characterized. However, less is known about the potential subtleties of plant growth, form, development, nutrient uptake, and biotic stress tolerance in the broad tolerable range. Begonia [Beg (Begonia × tuberhybrida Voss)] and new guinea impatiens [NGI (Impatiens hawkeri Bull.)] were grown over a wide range of N (from 1.78 to 57.1 mm NH4:NO3 ratio at a 1:1 ratio supplied as nutrient solution) in a peat:perlite soilless substrate in greenhouse conditions. Plant growth, development, chlorophyll content, leaf angle, nutrient uptake, tissue caloric value, and susceptibility to Botrytis cinerea Pers.:Fr. disease were evaluated in two experiments. Elevated N supply resulted in decreased plant height (16% in Beg and 7% to 16% in NGI), flower count (3% to 48% in Beg and 7% to 49% in NGI), bud numbers (23% to 80% in Beg), canopy area (11% to 33% in NGI), and mass (21% to 33% in Beg and 18% to 58% in NGI). Chlorophyll content saturated at an N supply of 28.6 mm. N uptake efficiency, shoot N use efficiency, and shoot N utilization efficiency decreased with increasing N supply. Elevated levels of N supply from 7.15 to 57.1 mm also increased the susceptibility of Beg to B. cinerea disease by 10% to 80% in stems and 3% to 14% in leaves. The increase in susceptibility also corresponded with increased tissue energy content (kJ·g−1) and altered leaf orientation. This study indicates many plant changes occur between nutrient extremes that can have a significant impact on growth, development, and the ability to withstand disease.

A sequential egg mass sampling plan was developed for prediction of stalk tunneling damage by 2nd-generation European corn borer, Ostrinia nubilalis (Hubner), in field corn in eastern North Carolina. The plan was based on a critical density constructed from a linear relationship between egg mass numbers and subsequent stalk tunnel numbers ; the sampling unit consisted of 5 leaves on 10 consecutive plants. Decision lines were constructed using the mean crowding-mean method developed by Iwao (1975). The plan was evaluated through computer simulations and comparison with field data. Average sample number and operating characteristic curves for a range of thresholds are estimated. The expected costs and feasibility of scouting for European corn borer under various economic conditions are examined.

The effectiveness of using moving mean covariance analysis (MMCA) rather than randomized complete- block design (RCBD) in experimental error control was compared in a large-scale mungbean (Vigna radiata (L.) Wilczek) yield trial. The MMCA was superior to the RCBD, since it significantly reduced the experimental error and the coefficient of variation (cv). Inclusion of five neighboring plots in the moving mean computation provided better error control. However, the estimation of optimum number of neighboring plots to be used and moving mean calculations were tedious. The feasibility of using border-row measurements such as mean plant height at 50% flowering or mean seed yield/m of row as a covariate in an analysis of covariance (BRMCA) was examined in a separate mungbean yield trial in which border rows were planted with a check cultivar. Both border-row measure- ments were equally effective in reducing the experimental error. However, plant height measurements were simpler than measuring seed yield. Because border-row measurements could be readily used as covariate in analysis of covariance without a need for moving mean computation from the response variable, BRMCA could be advantageous for error control in row crops yield evaluation. Non-uniform fertility gradients caused by nonsystematic spa- tial soil variation in the experimental sites are impediments to the reliable estimation of treatment and/or cultivar effects (Baker and McKenzie, 1967; LeClerg, 1966; Mak et al., 1978). Ex- perimental errors are usually escalated under these circum- stances and high cv values are usually associated with the results. Various experimental designs were considered for controlling local trend effects in experimental sites. The conventional way is to use RCBD or Latin square design for error control. The RCBD is effective in experimental sites with a uniform fertility trend. Latin square requires an equal number of treatments, rows, and columns, which can restrict the choice of sites. Lat- tice designs are effective for trials consisting of many treat- ments; however, the analysis is relatively complicated and is restricted to certain fixed numbers of treatment. Check plot designs in which a systematic arrangement of check plots is superimposed on a RCBD have been proposed as an alternative method of error control in experiments with many treatments (Baker and McKenzie, 1967; LeClerg, 1966). The performance of a cultivar is expressed as the differences be- tween it and the adjacent check plot or as a percentage of the check plots if a high correlation between check plot and test plot exists. If the check plot misrepresents the soil variation, improper adjustment might result (Mak et al., 1978; Townley - Smith and Hurd, 1973; Rosielle, 1980). The use of check plots was substantially less efficient than using lattice designs or ap- propriate incomplete designs (Besag and Kempton, 1986). Fur- thermore, the check plot design requires additional experimental units (Mak et al., 1978). To prevent such an error in check plot design, MMCA has been recommended (Mak et al., 1978; TownIey-Smith and Hurd, 1973; RosielIe, 1980). The mean of the neighboring plots, ex- cluding the test plot in question, is assumed to be a measure of the fertilityof the test plot and is used as a covariate to adjust

Foliar accumulation of mercury has been demonstrated to occur as plants leaf out, yet the primary source of this mercury is not known. Using closed-system growth chambers, uptake of mercury by quaking aspen (Populus tremuloides) foliage was measured over time as a function of soil mercury concentrations (0.01, 6.2, and 25.6 microg/g) and atmospheric mercury exposure concentrations (1.4, 14.9, and 68.5 ng/m3). Foliar mercury concentrations increased as a function of time for all exposures. Twice during the experiment, leaf washes were analyzed for mercury to assess surface deposition, and little mercury was removed (0.02-0.04 ng/m2), suggesting that direct deposition to the leaf surface was not significant during this experiment. At the end of the four-month experiment, whole-plant mercury concentrations were determined. It was found that whereas mercury in the atmosphere primarily influenced foliar uptake, root concentrations were related to the soil mercury concentration. The implication of this study is that litterfall may serve as a pathway for new, atmospherically derived mercury to be deposited to forest soils. This has significant implications for watershed management of ecosystems where mercury is of concern.

Angle of repose slopes associated with mine waste dumps are difficult to revegetate due to steep slope angle, poor soil proper ties, and potential for extensive soil erosion. We examined the extent that seed movement, seedling establishment, soil characteristics, nutrient availability, and water availability were responsible for limiting plant establishment or survival on steep (average slope ~80%), south-facing angle of repose slopes at a gold mine north of Elko, Nev. Four treatments were established: 1) unaltered mine waste soil; 2) mine waste soil with fertilizer; 3) mine waste soil draped with at least 0.3 m of a fine-textured cov ersoil; and 4) treatments 2 and 3 combined. All treatments had study plots that received either broadcast seeds or containerized transplants. Seedlings from broadcast seeds only emerged on plots that were coversoiled, but transplants survived in all treat ments. Thus, coversoiling was necessary at this site for seedling germination and establishment, but survival of transplants in unaltered mine waste soil indicated that nutrient availability, soil-root contact, and water availability were sufficient for plant survival. In addition, long distance transport of seeds down sta ble, angle of repose slopes was not detected during the first grow ing season after seeding, indicating that the lack of seedlings on angle of repose slopes was not due to movement of seeds down slope. However, coversoiling resulted in unstable slope surfaces; both erosion and soil mass wastage were observed on coversoiled treatments. Thus, although coversoiling increased establishment and survival of plants on angle of repose slopes, slope stabiliza tion is necessary to ensure the success of revegetation efforts and to prevent the coversoil from eroding and moving downslope.

Using the 9th and 10th International Mungbean Nursery (IMN) data, quadratic response surface models were developed to predict days to flowering (DF) of mungbean [Vigna radiata (L.) Wilczek] genotypes grown at 11-hr and 30 min and 13-hr and 30-min preflowering mean photoperiod (P) and 22 to 30C mean diurnal temperature (T) regimes. Both linear and quadratic effects were significant on DF and on the rate of progress towards flowering (1/DF); however, only the linear effect was significant in days to maturity (DM). The effect of T was more pronounced than that of P on DF of reduced-photoperiod-sensitive (RPS) genotypes. The earliest DF (flowering tendency) was estimated at 34 days after planting at the optimum mean diurnal temperature (T0) of 28C and the optimum mean photoperiod (P0) of 12 hr. At the suboptimal temperature (T < T0), the estimates of the base temperature Tb and the thermal time θr were 10C and 555 degree-days, respectively. Thus, flowering dates of these RPS mungbean lines can be predicted, which in turn will assist in the selection of proper planting dates.

Reciprocal and self-grafts were made using four cowpea [Vigna unguiculata (L.) Walp.] genotypes, ‘H-Brown Crowder’, ‘H-Calico Crowder’, ‘L-Bush Purple Hull’, and ‘L–TX460’, previously identified for their high (H) or low (L) N2 fixation efficiency. Grafts were made on day 12, and N2 fixation variables were evaluated 38 days after planting. Highest nitrogenase activity was obtained in the self grafts of high N2 fixing lines, whereas nitrogenase activity of low N2-fixing genotypes was generally increased by grafting onto high N2-fixing stocks. Nodule number was influenced only by rootstock. Whether rootstock or scion is the limiting factor in N2 fixation efficiency may be cultivar-specific.