ALBERT

Description: SummaryThe increase in dry weight of field lettuce from sowings made between March and August in 1973 and 1974 started exponentially but this did not persist throughout growth. Departures from exponential growth were most marked in the 10 days of growth prior to maturity and a logistic rather than an exponential curve gave a better overall fit to the data. The rates of increase in plant dry weight were similar from all sowings made between mid-May and early to mid-July, when air temperatures and total radiation during the growth period of these crops exceeded 11–12 °C and 250 mWh/cm2, respectively. Sowings made earlier than mid-May took longer to mature and in 1973 gave crops with lighter heads. Quadratic regressions of harvest date on sowing date gave good fits to data obtained in different years at different sites but separate equations were required for each site.

Description: SUMMARYThe relationships between the number of stems per tuber and tuber characters measured before planting were studied using a wide range of tuber weights of the varieties Désirée and Maris Piper. The effects of the storage temperature of the seed tubers and the site of growth on these relationships were then investigated over 3 years.Linear relationships between the numbers of stems per tuber and tuber weight accounted for more of the variation in numbers of stems than linear relationships established using tuber shape or sprout measurements. The linear relationships had positive slopes and intercepts, showing that small seed tubers produce more stems per unit weight than large seed tubers. There was little evidence of non-linear effects.On average over all treatments, using ten plant samples, single linear relationships between above-ground stems and tuber weight accounted for 64 % of the variation in above-ground stems with D6sire'e and 58 % with Maris Piper. When separate regression lines were fitted for each treatment the best models in each variety accounted for about 86 % of the variation in above-ground stems. The best model with Désirée had parallel lines showing that the advantage, in terms of stem production, of small seed over large seed increases in environments favouring stem development. The relationships for each treatment are used to show how the stem density established can vary when planting tubers at the recommended spacing.Seed tubers of comparable weight, planted at different sites, gave different numbers of stems suggesting that the optimum spacing may vary from one site to another.It is suggested that breeding varieties for yield stability might be aided by selectingfor low variation in the relationship between the number of stems per tuber and tuber weight.

Description: SUMMARYFor many horticultural crops the distribution of weight over size grades is of more importance than the total weight. This paper shows how simply determined features of interrelationships of the weight, size and shape of an individual in the crop can be combined to provide estimates of various aspects of the distribution of crop weight over size grades. The two relationships required are (i) the probability density function of the grading variable for the crop; (ii) a function relating the weight of an individual to the corresponding value of the grading variable.The paper shows how each of these can be determined either from published data or by simple experiment. Examples using data on onions and carrots are given to illustrate this and also to show some of the more important practical applications of the methods. For example, they allow the results of grading with one set of size grades to be extrapolated to a different set of grades without recourse to further measurement or experimentation and this is illustrated using published data on carrots. Other possible uses are also discussed and outlined.

Description: SummaryTwo experiments were carried out to study the effects of five agronomic variables on the marketable yield of transplanted leeks. In the first experiment two cultivars were used, cvs Splendid and Winterreuzen, and the treatments compared three plantraising systems, two ages of transplant when planted, and two plant population densities, two row spacings and two levels of nitrogen nutrition in the field. In this experiment some treatment interactions were confounded with each other.In the later experiment only cv. Splendid was grown. There were two plant-raising systems, two plant-raising temperatures, two plant-raising nutrition levels, two times of transplanting (63 or 84 days from sowing) and four different sowings (7 and 28 February, 20 March and 10 April 1984). The duration of the growth period in the field was standardized by harvesting each treatment combination on two occasions, 168 and 189 days after transplanting.The results from the first experiment showed that plants raised in modules at high temperature, planted early at a high plant density with higher than normal levels of nitrogen gave high marketable (〉 12·5 mm in diameter) yields of 7·31 kg/m2, greater than that from any other treatment combination. The second experiment confirmed these general trends but also showed that the date of transplanting was of critical importance with the earliest plantings in the year giving the highest yields and with later plantings resulting in progressively lower yields irrespective of the way in which the transplants were raised. Comparisons with meteorological data showed that decreasing yields were associated with decreasing values of accumulated solar radiation and accumulated day-degrees during field growth.These results are discussed in relation to other published data. They do not support some of the current recommendations for growing the crop but suggest that much more work needs to be done on production systems for this crop because of the potential for increasing marketable yields.