Field measurement of temperature and leaf growth on maize/bean inter-crop

[摘要] English: Notwithstanding the emphasis of research on the intensification of sole-crop systems, thepractice of inter-cropping remains widespread. Evidence is accumulating that indicates thatunder many situations it may represent a more efficient use of natural resources. Much ofthe basic information on the response of leaf growth to a single environmental factor wasobtained during the 1960s when controlled environment facilities became available, yet itproved difficult to extrapolate results obtained in a controlled environment to the fieldsituation. From this background emerged the notion that temperature constitutes one ofthe main environmental factors influencing leaf growth at the field level for bothmonocotyledonous and dicotyledonous crops.Sole- and inter-crop maize (Zea mays L.) and dry beans (Phaseolus vulgaris L.) weregrown in order to examine the mechanisms by which temperature influences leaf growthduring the early growth stage using of three consecutive planting dates in summer. Fordaily measurements of leaf growth 15 individual plant samples were measured from eachreplicated plot. Temperature variations were observed during the three planting dates,namely in November, January and March, from the automatic weather station at theexperimental site. Generally the temperature increased gradually from the first planting inNovember until late January during the second planting and thereafter decreased from thebeginning of February to reach the lowest temperature in May. Due to the difference intemperature at the consecutive planting dates the seedling emergence in the third plantingshowed took longer.From daily leaf length measurements of sole and inter-crop maize the leaf length proved tobe almost linear with time (days after planting). During the first planting, the leaf growthwas more rapid and the largest leaf size was recorded. In the case of the third planting ittook a longer time to reach the same length due to low temperatures, while in the secondplanting heat stress caused the maize crop to grow at a slower rate and reach a smallersize compared to the other planting dates. For sole and inter-crop beans during the firstplanting, the leaf growth displayed some form of sigmoid curve, whereas In the secondplanting due to the high temperatures the growth appeared to have two sigmoidal cyclesduring the growing period.For simplicity in the analysis, the mean leaf growth rate, and the slope (rate) of a linearregression was applied for each leaf length. In maize, both approaches showed an increasein its rate with increasing leaf number with the exception of leaf 11 in first planting,whereas in the third planting the leaf growth was lower and fewer leaves resulted. Inbeans, these two approaches showed some differences during the growth period for allplanting dates but they followed the same general trend of growth rate. Comparing the twoapproaches, the slope of the linear regression could render a more representative rateprovided the leaf growth was linear with time .On the other hand, the behaviour of leaf growth as a function of temperature was recordedby searching for the most appropriate thermal responses by curve fitting, using theRichards function model. This gave the highest correlation of maize leaf growth withthermal time. Generally, in all planting dates and cropping systems there was a significantcorrelation between the leaf growth variables and thermal time after emergence whenusing 10°C and 30°C as Tbase and extreme temperatures respectively. In contrast, for thebean crop the estimates displayed a weak correlation and it became important to considerother environmental factors along with the temperature variations.The study also assessed the field measurements of hourly leaf extension rate versus leaftemperature for sole- and inter-cropped maize plants. On each cropping system 6auxanometers were installed to measure hourly leaf extension rate along with leaftemperatures for three days during warm and cool periods. It was shown that the leafextension rate (LER) is one of the first components of plant growth to be affected by shortperiod changes in temperature. Its importance led to the measurement of hourly growthrate in conjunction with leaf temperature. In this study the LER of maize as an average forthree hours was used during both warm and cool periods. The measured rate was higherduring the warm period, yet declined sharply above 29.5°C. Nonetheless, most of the dataconcentrated on temperatures up to 24°C with very few measurements In the range of 29-29.5°C of temperatures. These values were used as common values for both fitting lines.The combination of data from both periods produced two linear regression equation. LERreached a maximum (3.2 mm h-1) at 27.8°C and was expected to be zero at the lowertemperature of 6.2°C and the higher temperature of 35.3°C.These measurements of leaf growth and temperature show how temperature variationsduring the early growth stage of sole- and inter-crop maize/bean influence the leaves'subsequent expansion to final size. It was also observed that temperature greatlyinfluences the rate of leaf expansion in chronological time, particularly for leaves in thefield. It is difficult to resolve leaf growth data without recourse to thermal time analysis.From the study it was seemed, that accurate estimation of Tbase and Tmax as well as themethod of calculating the thermal time play a great role in assessment of possible variationof leaf growth in different planting dates.

[发布机构] University of the Free State