Jane R. Fellows

Investigating trends in vegetable crop response to increasing temperature associated with climate change

Abstract A thermogradient tunnel, 8.6 m wide and 31.9 m long, generating temperatures ranging from ambient at one end to ambient plus approximately 4 °C at the other, was used to assess the potential impact of increased temperatures associated with global warming on the growth of Iceberg lettuce (Lactuca sativa L.), leek (Allium ampeloprasum L.) and Roscoff cauliflower (Brassica oleracea var. botrytis L.) crops. Optimum mean temperatures for head weight in Iceberg lettuce and trimmed weight in leeks were identified as 12 °C and 15.7 °C, respectively, corresponding to temperature rises of 2 °C and 2.4 °C above the average ambient temperature during the experiments. Increased temperatures gave consistently earlier maturity of lettuce, delayed cauliflower curd initiation by up to 49 days and increased the final number of leaves in cauliflower by 36. The implications of these effects are discussed in relation to global warming.

The effect of the time of seedling emergence of crisp lettuce on the time of maturity and head weight at maturity

SummaryThe effect of the time of seedling emergence on the time of maturity and the head weight at maturity of the American crisp lettuce cvs Salinas and Pennlake was examined using crops sown in April, May and July. Within a crop, later emerging seedlings of both cultivars produced plants which matured later. There was a trend towards later emerging seedlings producing lighter heads though the opposite was true for Salinas sown in May. These results suggest that, within a crop, variation in the time of maturity and in head weight at maturity can be reduced by improving the uniformity of seedling emergence.

Studies on some sources of variation in carrot root weight

Five investigations were carried out to determine the magnitude of root-size variation within crops of cv. Chantenay Supreme grown under competitive and non-competitive conditions, and to study possible sources of inter-plant variation. In the first experiment root-size variation from crops grown at a high population density (245 plants/m 2 ) and at a low density (25 plants/m 2 ) were compared over a 21-week period from sowing. The c.v.s of root weight were always higher from the high density than from the low density over the harvesting period from 11 to 21 weeks after sowing, and ranged from 74 to 94% and from 50 to 63%, respectively. A second study showed that even with a very low population density (3 plants/m 2 ) the c.v. of root weight at harvest was 58%. The third study showed that 40% of the root weight variation was accounted for by the time of seedling emergence. The results of a pot experiment indicated that when the size of seed, sowing depth, rooting medium and time of seedling emergence were made as uniform as possible, a very uniform population of roots was produced with a c.v. of root weight of 32%. In the final field experiment when time of seedling emergence, seed size and spatial distribution of the plants were the experimental variables, the results confirmed the importance of variability in time of seedling emergence and seedling size in creating variation at an early stage of growth. The results of these studies indicate that competition per se was not a prime source of variation in root size but magnified any initial variation within the crop at the time of seedling establishment. The importance of this early establishment phase in determining the spread of root-size distribution within a crop is discussed together with the factors which influence the time of seedling emergence and seedling size.

The influence of solar radiation and temperature on the head weight of crisp lettuce

SummaryFive experiments in 1986,1987 and 1988 using cv. Saladin examined the influence of shading, which halved the amount of solar radiation the crop received, on the growth of lettuce heads and head weight at maturity. There were significant positive correlations between head weight and mean solar radiation in the seven-day periods beginning five days before hearting and continuing until 11 days after hearting. There were also significant negative correlations between head weight and mean temperature in the seven-day periods beginning at least 13 days before hearting and continuing until ten days after hearting. This suggests that head weights at maturity are increased by high solar radiation in a specific period beginning just before hearting and by low temperature in a longer period up to and around hearting, though it is accepted that other, as yet unexplained, factors also affect head weight. The Relative Growth Rate (RGR) of plants was positively correlated with solar radiation at hearting and post...

The influence of field environmental conditions on calabrese growth and development

SummaryExperiments studying calabrese growth and development were conducted in four years (1986-1989), using five cultivars and a range of transplanting dates each year. Crop growth was monitored by weekly sampling and dissection and the data are used to provide information to improve crop planning and prediction. The relationship between the time from transplanting to maturity and the date of transplanting was best described by fitting parallel quadratic curves for each cultivar. These accounted for 76% of the variance in the time from transplanting to maturity and could be used to plan continuity schedules. However, the magnitude of the variation about the fitted lines due to the crops’ responses to weather suggested that in practice continuity would be difficult to achieve. A logistic relationship for all cultivars between the logarithm of head diameter and accumulated effective day-degrees from head initiation accounted for 96% of the variation in head diameter and in individual cultivars up to 97% of...

A model of cauliflower curd growth to predict when curds reach a specified size.

A simple model is described which predicts when curds of any specified size will be produced. The model uses a quadratic relationship between the logarithm of curd diameter and accumulated day-degrees >0°C from curd initiation. Work in controlled environment cabinets showed a linear relationship between early curd growth rate and temperature between 8°C and at least 18°C, and that the base temperature for curd growth was 0°C. Data from samples taken after curd initiation are used to predict the number of day- degrees required for the crop to reach a specified size. This requirement is then converted into a predicted date by using long-term average weather data. This prediction can be updated progressively to take account of observed weather data where these deviate from average weather. Differences between the fitted relationships for different sites, years, transplantings and cultivars are discussed and data are presented showing the results of validation of the model.

LEAF PRODUCTION AND CURD INITIATION OF WINTER CAULIFLOWER IN RESPONSE TO TEMPERATURE

SummaryIn experiments in 1994 and 1995 a range of transplanting dates and thermal crop covering treatments were used to produce different environmental conditions for the growth of two Roscoff cauliflower selections ‘December/January’ and ‘March’. In 1994 non-covered plants of ‘March’ initiated on average 19 d later and with 19 leaves more than ‘December/January’. In the two seasons, covering the crops gave delays in curd initiation of up to 93 d, depending on planting date, and increased the number of leaves produced by up to 50 compared with non-covered crops. Leaf production was best described by an accumulated effective day-degree scale using day-degrees <17°C for ‘December/ January’ and day-degrees <16°C for ‘March’. This shows that both light and temperature are concerned with controlling leaf production. During the juvenile phase of growth, apex diameters expanded linearly with temperature up to a diameter of about 0.2 mm. After this there was a different response to temperature suggesting that a p...

The influence of water stress during crop growth on the postharvest quality of broccoli

Two glasshouse experiments studied the effect of moisture stress on head and postharvest characters of broccoli. The work demonstrated that moisture stress occurring during head growth affected the postharvest shelf life of broccoli heads. The stage of head development at which moisture stress was applied determined which postharvest character was influenced. This suggests that the genes controlling these characters can be switched on at different times. Moisture stress imposed close to head maturity appeared to have a positive benefit in terms of both head colour and stem turgor.

Climate change: a response surface study of the effects of CO 2 and temperature on the growth of beetroot, carrots and onions

Ten daylit, controlled-environment cabinets were used to investigate the possible impacts of global rises in atmospheric CO 2 concentration and temperature on beetroot (Beta vulgaris L.), carrot (Daucus carota L.) and bulb onion (Allium cepa L.) plants. Their responses to CO 2 concentrations of 350, 450, 550, 650 and 750 vpm and temperatures of 12, 13.5, 15, 16.5 and 18 °C were examined by using a fractional factorial design for the two treatment factors. Use of the daylit cabinets allowed the plants to be grown in natural light, common atmospheric humidities (vpd 0.7 kPa) and nonlimiting supplies of water and mineral nutrients. Polynomial models were used to summarize the whole plant dry weight and fresh weight yield responses and to indicate the potential impact of climate change. Additionally, the models were used to generate predictions of the percentage change in whole plant dry weight and plant fresh weight yield for the years 2025 and 2050 relative to 1992. Baseline values of 350 vpm for CO 2 and a mean temperature of 13.5°C for 1992 together with forecast CO 2 values of 407 and 442vpm and temperature increases of 0.7 and 1.1 C for 2025 and 2050 respectively were used. For 2025, fresh weight yield changes of +19%, +9% and +13% were obtained for beetroot, carrot and onion crops respectively, while for 2050 the respective changes were +32%, +13% and +21%. Measurements of the ratio of the maximum diameter of the bulb to the minimum diameter of the neck for onions showed that there was little or no influence of CO 2 , whereas the effect of temperature was substantial. Bulbing was accelerated by high temperature and was greatly delayed at low temperature. At temperatures <15°C, the delays to bulbing resulted in the development of undesirable, thick-necked onions which tended to remain green with erect leaves. These results suggest, therefore, that a warmer climate will be advantageous for the commercial production of bulb onions in Britain.

The effect of some environmental factors on potato tuber numbers

SummaryFive experiments studied the effects of shading, temperature and stolon growth medium on stolon and tuber formation. The lowest numbers of stolons and tubers were produced at the higher and lower nodes. Numbers of primary stolons and tubers were relatively stable across nodes and treatments and variation in total numbers was largely due to changes in numbers of lateral and branch stolons. In the field, 70% shading reduced numbers of stolons and tubers by reducing lateral and branch stolons, while in hydroponics, 45% shading and temperatures at initiation had no effect on tuber numbers. In both environments later planting tended to reduce numbers of stolons and tubers. There were large effects of the physical environment, with compost producing three times as many tubers as dry vermiculite. The potential number of tubers may be determined by the number of stolons and the environmental conditions affecting stolon formation and development.