Production of tillers and their subsequent survival are important events in growth and development of barley ( Hordeum vulgare L.) that affect the number of spikes produced per unit land area. Studies were conducted at St. Paul and Crookston, MN to evaluate tiller production, tiller mortality, and yield of 10 barley genotypes with different tillering capacities. In addition, these studies evaluated the influence of row spacing and seeding rate on tillering. The genotypes differed significantly in shoot and spike number. Shoot number for the highest tillering genotype was 42 to 71% greater than for the lowest, depending on the study, but the genotypes ranked consistently over years and locations. The high tillering genotypes tended to form tillers more frequently at the coleoptile node, in the axil of the third leaf, and from the primary tiller in the axil of the first leaf on the main shoot. In general, absolute shoot mortality (difference between maximum shoot number and spike number) was higher in the high tillering genotypes. Genotype M72‐269 was an exception to this generalization in having high shoot number and low shoot mortality. Row spacings of 7.5 and 15 cm had more shoots per unit area than the 30 cm spacing. However, narrower rows also had higher shoot mortality which led to similar spike numbers for the three row spacings. Higher seeding rates of 101 and 134 kg ha ‐1 increased shoot number and spike number compared to the 67 kg ha ‐1 rate. Changes in row spacing and seeding rate did not differentially affect shoot production or absolute shoot mortality among the genotypes. Grain yields of both low and high tillering genotypes were as high or higher than those of intermediate tillering cultivars. The extremely high and low tillering genotypes were not consistent in their yield performance at Crookston, suggesting a possible association between tillering capacity and yield stability. Small stem diameter and a tendency to lodge were characteristic of the high tillering genotypes. Identification of apparent genetic diversity for tiller mortality provides material for further study of the relationship between tiller mortality and yield.
Plant growth regulators (PGRs) alter tiller growth in cereals. This response may be dependent on daylength (DL). Standard height (HE) and dwarf oat cultivars were grown at 14‐ and 18‐h DLs. Foliage was sprayed with chlormequat chloride (CCC) and ethephon at early growth stages to evaluate PGR effects on the growth of the main shoot and tillers. Two successive experiments with 10 replicates were arranged in two growth chambers (14‐h and 18‐h DL) at the University of Minnesota. Preanthesis main shoot and tiller HEs and dry weights (DWs) were measured. In Exp. 1, the numbers of leaves and green leaves were counted. Relative growth rate (RGR), relative elongation rate (RER), and shoot DW:HE ratio were measured. Plant growth regulators retarded growth of the main shoot in conventional oat cultivars without stimulating growth of T1 and T2 tillers. Response of the dwarf cultivar to PGRs was modest. Only ethephon enhanced T1 tiller growth at 18‐h DL. However, PGR‐treated plants had up to five more green leaves per plant at preanthesis due to stimulated leaf emergence on T3 and T4 tillers especially at the 18‐h DL. In Exp. 1, PGR treatments reduced the DW to HE ratio, that is, shortened rather than strengthened the stem. In Exp. 2, measurements were made more frequently and ethephon first increased this ratio followed by a decrease. Thus, even though long‐day conditions somewhat enhanced DW accumulation and stem elongation, few marked differences in oat response to PGR treatments were noted when comparing short‐ and long‐day conditions.
Decision case education is becoming increasingly important in agriculture. However, use of decision cases within extension education has lagged behind that in resident education. One serious constraint to the use of cases in extension education is the lack of a sufficient number of cases suited to the particular needs and demands of extension. The Perkins Farm case was developed specifically for extension audiences. The case concerns the Perkins' farm management decision whether to purchase a larger row-crop planter and associated equipment to improve efficiency and save time in the field. Complications in the decision include uncertainties about the Perkins' future in farming and the implications of the larger equipment for their son, should he assume operation of the farm in the future. The case is formatted in two easily assimilated segments to make it possible for learners to discuss the case even with little opportunity to prepare prior to the session. The case also includes a two-part video that enhances the capability of learners to identify with the decision makers and their situation. The Perkins Farm case was developed to increase understanding of farming and sustainable agriculture issues with particular emphasis on profitability, quality of life, and the environment. The case also helps learners to become better informed about sustainable agriculture techniques and approaches, and improves their decision-making skills. A lesson plan for using the case with extension audiences is described.
Kernels formed at specific florets in central spikelets of the spring wheat ( Triticum aestivum L.) cultivars ‘Era’ and ‘Kitt’ were compared in 1975 for N percentage, N content (mg), and dry weight (mg) per kernel. There was a lower N percentage in the third and fourth kernels of Era (numbered from the base of the spikelet) than in the first two. The third and fourth kernels of Kitt did not show this lower N percentage, however. In both genotypes the fourth kernel was noticeably smaller and contained much less N than any of the first three. When a fifth kernel was present, as with the genotype designated ‘8037’, that kernel, in turn, was substantially smaller and contained less N than the fourth. In 1976 kernel number per spike was systematically reduced in two ways for the genotypes Era and 8037, resulting in increased assimilate supply to the remaining kernels. Nitrogen percentage, N content, and dry weight of the remaining kernels from altered spikes were substantially greater than in corresponding kernels of intact spikes. The fourth and fifth kernels from the base of a spikelet in the altered spikes, however, were still much smaller and contained less N than the first three. Examination of the vascular connections in the rachilla for Era and 8037 revealed that the fourth and fifth kernels in a spikelet were served by much smaller diameter vascular bundles than the first three. In addition, all bundles that served the fourth and fifth kernels were ultimately connected to bundles that also served one or more of the first three. In contrast, some of the bundles that served each of the first three were independently linked to the rachis. Our results suggest that kernels formed in the fourth and more distal florets of central spikelets may be limited in their capacity to accumulate assimilate compared with the first three. This maybe a result of their position relative to the rachis and, possibly, dif. ferences in their growth potential.
Field studies with the spring wheat ( Triticum aestivum L.) cultivars ‘Era’ and ‘OlaF’ were conducted to assess the effects of reductions in kernel number per spike and defoliation of individual culms on kernel growth characteristics. The importance of stage of kernel growth at which treatments were applied was also examined by treating both at anthesis and anthesis + 14 days, the later date being after the beginning of the kernels linear dry matter accumulation period. The effects of the treatments on final weight per kernel depended on the time of treatment and on the relative weights of kernels from the untreated (control) culms. Reduction in kernel number per spike increased final kernel weight, particularly when control weights were low, whereas defoliation always reduced final weight. Treatment at anthesis usually had a larger effect. Growth rates of kernels during the linear dry matter accumulation period were enhanced by kernel removal and depressed by defoliation. Within each genotype, growth rates were highly correlated with final kernel weight. This association, however, differed between years because of variation in length of the grain filling period. No consistent effect of the treatments on grain filling duration was found. The response to early kernel number reduction, as well as the response in additional experiments to spikelet “trimming” suggested that upper limits, or potentials, for both final weight and growth rate were approached. These potential kernel weights and growth rates appeared to depend on genotype, kernel position in a spikelet, and possibly environment.
In 1976 we investigated whether or not nitrate reductase (NR) enzyme activity in shoots of two spring wheat ( Triticum aestivum L. em Thell) cultivars limits N assimilation during the grain filling (post anthesis) period. Twice weekly after anthesis NR activities in the flag leaf blade, flag leaf sheath, and first leaf blade below the flag leaf were estimated on field‐grown plants with an in vivo assay. Activity declined during the period in apparent association with senescence of the tissues. In contrast, when NR estimates were made by a modified assay in which no exogenous nitrate was supplied, activity was consistently low. This suggests that relatively little nitrate was available for reduction in these tissues although NR enzyme appeared to be there. The cultivars accumulated approximately 90% of their total reduced N before anthesis, as estimated by sequential sampling of shoots from the same plot area from which the NR samples were taken. Nitrogen accumulation after anthesis was predicted from the enzyme activities measured by both assay methods. Nitrogen accumulation predicted from the NR activities measured when nitrate was included was substantially greater than the accumulation actually observed. Our results suggest that the minimal accumulation of reduced N after anthesis by the cultivars in this study should not be attributed to the level of NR enzyme. It may be more a function of a limitation in a process responsible for supplying nitrate to the enzyme .
Teaching experience has traditionally been a feature of graduate education in departments of agronomy in U.S. universities. However, a 1982 survey confirmed that an unequal proportion of graduate students actually teach as part of their graduate studies, depending on the department. In this paper, a wider participation by graduate students in a well-structured, positive teaching experience is advocated. Personal benefits from the teaching experience include learning to relate to and motivate others, improving communication skills, gaining confidence, and developing a better understanding of the subject matter. These benefits would be important regardless of whether a student's future career orientation is toward research, administration, or teaching. Results of a 1983 survey of the teaching backgrounds of agronomy department heads in U.S. universities showed that teaching as a graduate student also influences future administrative attitudes toward teaching. High priority should be placed now on providing the best teaching experience possible to a larger porportion of our graduate student population.
Decision cases have been used in the United States for higher education in agriculture and natural resources, as well as in extension education. Few cases have been developed for secondary education audiences and fewer yet for both secondary and higher education applications. This case was developed for use in both secondary- and university-level classes to address the important topic of municipal solid waste (MSW) disposal. The case describes a dilemma faced by a county in northern Virginia that needed to decide whether to proceed with its suit against a farm that it had deemed to be “an unlicensed landfill.” The case examines the farmer's philosophy about his operation and provides background information about his method for producing compost from vegetative solid wastes solicited from areas beyond the farm's boundaries. The case reviews information about MSW and its disposal on both national and state levels. As the result of deliberating this case, students will gain knowledge about composting, landfills, and the regulations that govern them, as well as a better understanding of the decision making process around issues concerning environmental safety and conflicts involving agriculture and broader societal interests. The case was tested in a secondary environmental science class, as well as a university-level general education course. In an evaluative written questionnaire distributed to the students following their completion of the case, 70% reported being “engaged” by the case learning activities whereas 99% reported that they had encountered “new viewpoints” through the case. Similarly, 92% of university students evaluated the case as “good” to “excellent” and noted that the case was “thought-provoking” and stimulated them to think about waste disposal and how it might be improved.
