13 pp. / A nitrogen fertilizer study was conducted in order to determine the effect of N rates on forage sorghum yield and quality and to develop tissue testing guidelines for fertilizer application to forage sorghum. The study was conducted at the University of Arizona Maricopa Agricultural center on sandy clay loam soil irrigated using the flood method. Forage sorghum was fertilized with six N rates varying from 0 to 250 lb N/acre in 50 lb N/acre increments. The whole plant, lower stem, and most recently expanded leaf were sampled five times during the growing season and analyzed for N content in order to establish tissue N guidelines for fertilizer application. The plant part that was most sensitive to N fertilizer application and plant N status was lower stem. Leaf and plant N levels were not affected by fertilizer application. The stem nitrate and stem N tests were able to identify N deficient plants very early in the season, long before plant growth was affected by the N deficiency, unlike leaf and plant N. Forage yield at final harvest fitted to a quadratic function was maximized at the 250 lb N/acre N rate. However, the yield increase with any amount of fertilizer did not pay for the cost of the fertilizer and the most economical N rate for yield was no N fertilizer applied at all. In terms of milk per acre, the maximum was achieved at 150 lb N/acre, and the economic optimum in terms of milk was slightly less than this amount of fertilizer.

In ruminants the aerobic host animal is dependent on the anaerobic fermentation within the rumen to supply protein and energy. This anaerobic fermentation results in a rather constant ratio between protein and energy. In young growing animals and lactating animals the demand for protein is greater than the demand for energy. Plasma amino acid data indicate that protein could be limiting in these two situations. In the first phase of the study, plasma free amino acids, milk volume and milk components were determined at two week intervals throughout the lactations of two mature Ayrshire cows. The large amounts of protein that were secreted daily during the first third of lactation placed heavy demands on the animals for protein supplies. These demands were reflected in changes in plasma free amino acids during the lactation cycle. Lysine, leucine, isoleucine and methionine exhibited the greatest variation in response to the demands of lactation. A series of abomasal infusions of the above amino acids and others was undertaken to determine the importance of amino acids for the synthesis of milk protein. The infusions were grouped into three lots; those containing methionine, those containing isoleucine and those containing lysine. Effects observed during infusions containing methionine suggested that methionine itself had little effect on- protein production. Methionine did not alter the effects of other amino acids on milk protein synthesis. The responses noted when methionine was accompanied by branched chain amino acids or by lysine were typical of responses of branched chain amino acids or lysine alone. Infusions containing isoleucine and other branched chain amino acids caused an increase in milk protein concentration, a decrease in milk production and no increase in total protein production. Plasma amino acid data revealed that infusion of branched chain amino acids resulted in decreases in concentrations of the other plasma amino acids. The decrease in plasma amino acid concentration, the lack of response in milk protein production and the known effects of branched chain amino acids on insulin secretion suggest that insulin might be affecting the intake of amino acids by muscle tissue. When lysine-containing infusions were examined milk production was found to increase. Milk protein concentration remained constant resulting in an increase in total milk protein production. The most dramatic increase in milk and protein production occurred when lysine was infused alone. Infusions containing lysine did not result in decreases in plasma free amino acids. There was a general trend for all the essential amino acids to increase or remain at the same level during the infusion. Lysine appears to be the limiting amino acid for milk protein synthesis. It is possible that the increased supply of lysine from the abomasal infusion affected the amino acid metabolism in muscle in such a way as to free amino acids for milk protein synthesis and energy metabolism. / Land and Food Systems, Faculty of / Graduate

The effect of age, breed, days open at conception, stage of lactation and pregnancy upon daily body weight and milk weight in lactating dairy cattle were studied. The cattle used in the study were those of the University of British Columbia Research Farm at Oyster River, B.C. 76 Holstein and 60 Holstein X Ayrshire crossbred milking cows at different stages of lactation and both either open or pregnant, were used in this study. The study was carried out during the months of May and June of 1975. The procedure involved weighing the animals daily after the afternoon milking and recording the daily milk yield along with the weight of each cow. The cows were classified into three groups, namely All, Open and Pregnant, the first group being a combination of the last two. For All and Open cows, the effect of age, breed, age by breed and number of days in milk on body weight and milk weight were investigated. For the Pregnant cows, the effect of age, breed, number of days open at conception, age by breed, age by number of days open at conception, breed by number of days open at conception and number of days pregnant on body weight and milk weight were investigated. Using the number of days open at conception as a dependent variable, the effect of age, breed and age by breed were investigated. The results showed that among All, Open and Pregnant cow groups, the older cows were significantly (P <0.05) heavier and were producing significantly (P <0.05) more milk than the younger cows. Age accounted for 0.9%, 1.5% and 0.8% of the body weight variation and for 0.1%, 0.5% and 1.3% of the milk weight variation in All, Open and Pregnant cow groups respectively. Among the All, Open and Pregnant groups, the older cows weighed more by 143.22, 133.12 and 125.07 lbs and produced 3.72, 6.98 and 12.14 lbs more milk per day respectively than the younger cows. Among All, Open and Pregnant groups, a significant breed effect (P <0.05) on body weight and milk weight was observed. In the three groups, breed accounted for 2.3%, 3.8% and 0.1% of the body weight variation and for 0.1%, 0.3% and 0.6% of the milk weight variation respectively. Among All and the Open cow groups the Hoi steins were heavier by 223.00 and 214.04 lbs and were respectively producing 5.20 and 5.26 lbs more milk daily than the crossbreds. Among the Pregnant cow group the Hoi steins were lighter by 49.33 lbs and produced 7.74 lbs less milk daily than the crossbreds. The number of days open at conception was a significant source of variation (P <0.05) affecting body weight but not milk weight in the Pregnant cow group. It accounted for 1.3% of the body weight variation. Those cows who stayed open longer than 123 days were heavier by 159.21 lbs than those who became pregnant earlier or on day 123 after calving. Age by breed for the All cow group was significant (P <0.05), accounting for 0.1% of the body weight variation. This interaction was not significant for body weight of the other two groups and for milk weight of all the three groups. Age by number of days open at conception was significant (P <0.05) for the Pregnant cow group milk weight and accounted for 1.2% of the variation. This interaction was not significant for body weight. Breed by number of days open at conception was not significant for the Pregnant cow group body weight and milk weight. Number of days in milk for All and Open cows had a significant (P <0.05) effect on both body weight and milk weight. It accounted for 10.2% and 2.9% of the variation in body weight and 35.6% and 18.4% of the variation in milk weight in All and Open cow groups respectively. In the Pregnant cow group, the number of days pregnant resulted in significant (P <0.05) effect on both body weight and milk weight. It accounted for 30.8% and 61.4% of the body weight and milk weight variation respectively. When number of days open at conception was used as a dependent variable, age, breed, and age by breed showed a significant (P <0.05) effect in the pregnant cow group. Age, breed, and age by breed accounted for 0.3%, 0.4% and 0.9% of the variation respectively. / Land and Food Systems, Faculty of / Graduate

In this dissertation we survey a variety of methods for constructing zero-coupon yield curves. We show that, when accuracy is of the utmost importance, the bootstrap described by Hagan and West (2006), Smit (2000), and Daeves and Parlar (2000) provides the ideal framework. This bootstrap requires the use of an interpolation algorithm, and a large portion of this dissertation will thus be devoted to the task of establishing an ideal method for interpolating yield curve data. Only two of the interpolation methods considered in this dissertation are seen to perform promisingly: the monotone convex method developed by Hagan and West (2006), and the monotone preserving r(t)t method developed in this dissertation. We show that the monotone preserving r(t)t method performs slightly better than the monotone convex method, in terms of the continuity of the forward curve, and in terms of the stability of the interpolation function. When economic appeal is of the utmost importance, we find parametric models to be more suitable than bootstrapping. However, we show that bootstrapping can be used to obtain a hypothetical set of zero-coupon bond prices, which can be used to calibrate parametric models. We compare the performance of the Nelson and Siegel (1987) and Svensson (1992) models, when applied to a historic set of South African swap curves, and show that the Svensson (1992) model performs better than the Nelson and Siegel (1987) model on a consistent basis. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Mathematics and Applied Mathematics / unrestricted

No description available.

An extant amount of studies has evaluated the impact of soil crop yield. However, only few studies examined the influence of soil yield variability (higher moments). This research evaluates the impact of soil on yield and examines whether corn yield variability (risk) changes with soil types. The study uses the data from the Mississippi Agricultural and Forestry Experiment Station annual corn variety trial from 2000-2018 and the PRISM climate group. The two-step Just-Pope (1978,1979) production function is employed. Pooled, random-effects, and fixed-effects models are estimated by OLS and FGLS for the mean equations. The dependent variables of the variance equations are the squared residuals estimated from the mean equations. The results from the study show that average corn yields were higher in loam soils than in clay soils. Also, loam soil was associated with a considerable magnitude of corn yield risk compared to clay soils. The study provides substantial proof of the impact of soil type in corn yield risk. As a results, the RMA of the USDA may integrate soil information in their rating technique to achieve higher accuracy of crop insurance premiums.

No description available.

Periodic evaluation of improvements in yield and disease resistance is necessary to assess breeding progress over time, and the elucidation of underlying traits responsible for yield gains can help direct future breeding. Objectives of this study were: 1) to determine the rate and magnitude of yield progress in eastern soft red winter (SRW) wheat (Triticum aestivum, L.) cultivars released from 1950 to 2009 relative to a historical cultivar Red May (1919) and; 2) to determine effects of leaf rust (Puccinia triticina f. sp. tritici) and powdery mildew [Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal] on grain yield components and agronomic traits. Replicated yield trials were grown at Warsaw, VA in 2010 and 2011, and at Holland and Blacksburg, VA in 2011. For objective 1, the genetic progress experiment: flag leaf angle, kernel weight, spikes m-2, lodging, flowering date and harvest index collectively explained the most yield variation in multiple environments on the basis of linear regression analysis. Rate of genetic yield improvement ranged from 0.56% yr-1 at Holland in 2011 to 1.4% yr-1 at Blacksburg in 2011. For objective 2, the disease loss experiment: yield losses ranged from 1% at Holland in 2011 to 21% at Warsaw in 2011. Losses primarily due to powdery mildew and leaf rust were as high as 14% and 33%, respectively. Powdery mildew had the largest negative correlation with harvest index and seeds spike-1, while leaf rust had the largest negative correlation with plant biomass and harvest index. / Master of Science

The effect of source-sink relationships on the performance of tomato and hot pepper was investigated in glasshouse experiments by pruning tomato trusses and hot pepper fruit from plants trained to a single stem. The objectives were to characterize the effect of time, method and intensity of pruning on the yield and quality of tomato and hot pepper. Pruning at anthesis as compared to pruning at fruit-set had little effect on yield and fruit quality of both crops. Yield per truss increased steadily with intensity of pruning in tomato, due to increase in fruit size and fruit number per truss. Thus, total yield was not affected by pruning. In hot pepper fruit size increased with intensity of pruning but total yield was significantly reduced and total plant dry mass depressed at higher source : sink ratios (two and three fruit pruned out of a total of six). Occurrence of fruit disorders such as blossom-end rot and fruit cracking increased with increasing source: sink ratio. Pruning of one truss in tomato and one fruit in hot pepper gave the best fruit quality in terms of fruit size, pericarp thickness and freedom from defects, without decreasing total and marketable yield. Removing a middle truss of tomato (third truss) gave the highest yield as compared to removing the youngest truss (sixth truss) or the oldest truss (first truss). The yield increase (relative to the control) in the remaining individual trusses tended to decrease with increasing distance of the trusses from the pruned truss. In hot pepper removal of the youngest fruit (sixth fruit) resulted in the highest yield in comparison to removal of the middle fruit (third fruit) and the oldest fruit (first fruit). The quantity of yield increase in the remaining individual fruits had no consistent trend regarding the relative distance of the fruits from the pruned fruit. Two pruning methods were tried on hot pepper and tomato to compare yield and fruit quality. The first method involved pruning of the first three consecutive trusses of tomato and the first three consecutive fruit of hot pepper out of a total of six. The second method involved pruning of three alternating tomato trusses or hot pepper fruit. Yield and yield components did not differ significantly for the two methods, but pruning alternate trusses of tomato and fruit of hot pepper reduced occurrence of fruit disorders. / Dissertation (MSc (Agric) Agronomy)--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

Economists often use complex mathematical models to forecast the future path of the economy and the likelihood of recession. But more simple indicators such as interest rates, stock price indices, and monetary aggregates also contain some relevant information about future economic activity. In this thesis we revisit the usefulness of one such indicator, the yield curve or, more specifically, the spread between the interest rates on the ten-year Treasury note and the three-month Treasury bill. By using four different models we examine whether the yield spread has still some predicitve power for future real GDP growth in selected european countries. What is more, we are comparing the predictive power of the yield spread with different variables, both in- sample and out-of-sample. We decompose the yield spread into expectations effect and term premium effect in order to investigate which factor contributes more to predicting real GDP growth. Using modified definition of recession we conclude that that yield spread still contains some useful information for predicting future economic activity, although its predictive power deteriorates.