The growth of timothy (Phleum pratense L.), bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), and Kentucky bluegrass (Poa pratensis, L.) was studied under controlled temperatures varying by 3.3 C intervals from 18.3 to 34.8 C during the day and from 1.8 to 18.3 C during the night. A day temperature between 18.3 and 21.6 C was optimum for top growth with timothy, orchardgrass, and bluegrass. With bromegrass, the optimum day temperature was between 18.3 and 24.9 C. As the day temperature was increased from these optimum ranges to 34.8 C, all of the species decreased in yield, but the decrease in bromegrass yields was less than in any of the other species. In some cases, night temperature also affected yields; but the optimum night temperature depended upon the species and the day temperature. The dry weight of etiolated growth indicated that the level of food reserves varied greatly. The species ranked orchardgrass > bromegrass > bluegrass > timothy for level of reserves. The most important factor affecting the level of reserves in a particular species was night temperature. In general, the food reserves decreased as the night temperature was increased from 1.8 to 18.3 C.

No abstract

A procedure for adventitious shoot regeneration from leaf explants of quince (Cydonia oblonga Mill.) using thidiazuron (TDZ) was developed. Excised leaves of cultures grown on Murashige and Skoog (MS) medium containing 5 p~M benzyladenine (BA) and 0.9% Gibco Phytagar were used. Several experiments were conducted to determine optimum concentrations of thidiazuron, a-naphthaleneacetic acid (NAA) and sucrose. When the medium contained 1.5 txM TDZ and 2.5 ~M NAA, 85% of the discs regenerated shoots with an average of eight shoots per leaf disc. An incubation period of three weeks in the dark was necessary for optimum shoot regeneration. Leaves excised from four to six-week-old cultures gave a higher percent shoot regeneration than leaves from cultures older than six weeks. Regeneration percentages were significantly reduced when sucrose concentration in the medium was less than 3%. A significantly higher percentage of shoots regenerated when leaf discs were placed on the regeneration medium abaxial side down as compared to the adaxial side.Regenerated shoots were cultured on MS medium containing 5 txM BA and rooted on half-strength MS medium containing 10 txM NAA. Rooted plantlets were acclimatized to greenhouse conditions for evaluation of any somaclonal variation. The importance of these findings are discussed in relation to in vitro improvement of plants.

Estimates of hay yields are frequently desirable for purposes of measuring fertilizer response, studying effects of management and cultural practices, and determining animal units that can be maintained on forage produced from a given area. Estimates of forage yield can be obtained by cutting and weighing, but the random collection of forage samples for estimating yields is not a viable alternative in some cases. A convenient, quick, and accurate method of determining forage yields in situ would benefit research workers and those involved in commercial and extension agriculture operations. The purpose of this investigation was to determine the suitability of using a disk meter to estimate dry matter yield of mixed swards. A 0.5m2 disk meter was constructed from hardboard paneling, steel pipe, and a flange. Paired disk meter readings and dry matter yields from clipping were taken from 708 swards used for hay production in 1978. Swards consisting of cool season grasses, legumes, and weeds were characterized into 14 categories according to species composition and growth stage. Regression equations were determined for each category from paired disk readings and dry matter yields from clippings. The slopes of the regression lines for the different categories were not significantly different. The coefficient of determination (r2) was 0.82 when using a single regression line for all categories. The points of intercept of the regression lines on the vertical axis for the different categories were different with a definite trend for regression lines for first cutting swards to intercept higher than regression lines for aftermath. The formula which best described the relationship between disk reading and yield was: yield estimate = intercept for category + 183 (disk reading) − 1.73 (disk reading)2. In order to test the disk meter and formula method, yields on 40 swards were determined independently using two methods. The correlation coefficient between sward yields estimated using the disk meter and formula and sward yields estimated using weighed clippings was +92.

Nearly optimal solutions in linear programming provide useful information to decision makers. Modeling to generate alternatives may be used to generate a set of nearly optimal solutions from which a decision maker may select the desired solution by considering criteria not quantified in the model. The mathematical problem is to find vertices of a convex polytope. A pivoting method of vertex enumeration is used to generate all extreme-point nearly optimal solutions of an example problem involving selection of a marketing strategy for beef calves. Compared to the optimal solution, nearly optimal solutions have more diversity or use less cash or hired labor.Key words: farm management, linear programming, modeling to generate alternatives, nearly optimal solutions. During the last three decades, linear programming (LP) has been used extensively in agricultural economics research and extension. But extensive use does not alter the fact that the LP model is a simplification of reality. The well-known assumptions of additivity, linearity, divisibility, finiteness, and single-value expectations (Heady and Candler) are used to reduce complex real-world situations to mathematical formulations which can be optimized using the simplex method. Typically, LP solvers report only one optimal solution, and the number of decision variables included in a solution cannot exceed the number of mathematical constraints.Because of these limitations, considerable interest has been expressed in the informational value of multiple optimal or nearly optimal LP solutions (NOS). Appreciation is expressed to Larry Padgett. Muhammad Bari. and Jong-i Perng for computer assistance: to Margaret Burton for computer and editorial assistance: and to Anwarul Hoque. Robert Jack. Dennis Smith. Bryan Schurle. Cleve Willis. and an anonymous Journal reviewer for helpful comments on earlier manuscripts. ematics of finding extreme point NOS of an LP model. The usefulness of information provided by NOS is illustrated using a model designed to evaluate management strategies for small, family farms. Single Objectives, Multiple Objectives, and Modeling to Generate AlternativesThe rationale for generating NOS is seen by focusing on the objective function in modeling decision problems. The objective function formalizes the criterion for ranking alternative decisions. For multiple criteria, one can formulate multiple objectives and perform multiobjective programming using methods such as goal programming and generating techniques (see Willis and Perlack 198ra, b).In some situations, the relevant criteria are difficult to quantify. While multiobjective programming may seem appropriate, the practical difficulties of quantifying criteria such as risk aversion, environmental impacts, and the like may limit the usefulness of model results. To cope with such problems, researchers in water resources planning have developed a set of techniques known as "modeling to generate alternatives" (MGA) (e.g., Brill; Chang, Brill, and Hopkins; Hopkins, Brill, and Wong). Other resear...