125

WEATHER FLUCTUATIONS AND THE DAILY RATE OF GROWTH OF PURE STANDS OF

THREE GRASS SPECIES

By R. W. BROUGHAM* AND THE LATE A. C. GLENDAYt

(Received 29 July 1968)

ABSTRACf

Fluctuations in the growth rates of pure stands of perennial and short-rotation ryegrass and cocksfoot attributable to daily changes in weather factors were determined during five periods of the year.

The technique of measurement included replication in time as well as space.

Marked differences in seasonal growth rates obtained were attri­butable to seasonal changes in temperature, light, and rainfall.

Significant correlations were also obtained between daily fluctuations in growth rate of the species and short-term (daily) changes in weather. Time-lag correlations of as much as 4 days were also shown for some of the weather factors.

Fluctuations in growth rate attributable to components of the daily weather were generally of a greater magnitude than growth increments attributable to smoothly changing weather in each experimental period.

The results are discussed in terms of the relative importance of the various weather factors on growth in this environment and of the length of the periods of adaptation required before changes in weather factors are expressed as changes in dry matter increments in the field.

The technique of measurement is also assessed.

INTRODUCTION

The experimental data available on the comparative growth of pasture and crop species as influenced by short-term changes in climatic factors have been obtained from controlled environment studies such as those described by Mitchell (1954, 1955), Went (1958), Evans (1963), Thorne et al. (1967), and others; from measurements and calculations of photosynthetic capacities and energy balances of leaves and leaf canopies (Gaastra 1958; Lemon 1963; Muramoto et at. 1965; and others); and from field m~asurements of variations in growth com­ponents such as Net Assimilation Rate and Relative Growth Rate (Blackman et aZ. 1955; Black 1955; Watson 1958; and others. These data have then been used to estimate yield potentials and climatic optima of the different species (Mitchell 1956; De Wit 1959, 1965; Loomis and Williams 1963; Monteith 1965).

* Grasslands Division, D.S.I.R., P.B., Palmerston North. t Late of Applied Mathematics Division, D.S.I.R., P.B., Palmerston North.

N.Z. JI agric. Res. (1969),12: 125-36

126 Weather fluctuations and grass growth

As a complement to the above approaches to evaluating weather influences on plant growth a field measurement technique based on a method of constant fitting applied via a suitable mathematical model and experimental design (Glenday 1955, 1959) was used to determine the magnitude of the effects of weather changes on the rate of growth of pasture species when grown in association in the field (Brougham 1955, 1959). In these investigations positive correlations were obtained b~tween weekly fluctuations in growth rate and weather factors and between seasonal trends in growth rate and light and temperature.

The study reported in this paper was an attempt to extend the scope of this field measurement technique to evaluate the effects of short-term changes in some weather factors on the daily growth rates of pure stands of three pasture species commonly used in New Zealand.

EXPERIMENTAL

The experimental work was carried out at the Grasslands Division, Department of Scientific and Industrial Research, Palmerston North, on an area of land that had previously been in single-spaced plants for more than 5 years.

Pure stands of perennial ryegrass (Latium perenne L. var. 'Grass­lands Ruanui'), short-rotation ryegrass (Lotium perenne X L. multi­florum var. 'Grasslands Manawa'), and cocksfoot (Dactylis glomerata L. var. 'Grasslands Apanui') were established after sowings in March 1959. Because of the high degree of sward uniformity required, the seed-bed was intensively prepared and levelled to prevent surface water from accumulating, pre-emergence weed spraying was carried out, and the method of sowing was such that each plot area received four coverages of seed.

Grazings by sheep and mowing were employed during the 12-month establishment period, the objective being to obtain dense and evenly dispersed tiller populations of the different grass species in the plot areas. Over this period and throughout the experiment, nitrogen (as nitro-lime: 20%N) and phosphate (as superphosphate) were applied in excess of plant requirements so that growth of all species was not limited by lack of these ell(ments. At the beginning of the investigation all stands had reached the desired uniformity and were densely tillered.

The experimental lay-out included replication in time as well as in space (see Brougham 1955, 1959; Glenday 1955, 1959), there being 4 space replicates of each species and 3 time replicates. Each time replicate was of sufficient area to allow for 14 daily cuts of herbage from separate plot sizes of 2 ft X 20 ft, with due allowance for margins between each day plot to prevent edge effects. This lay-out was used for each of 5 experimental periods of 16 days, the first beginning on 21 April 1960 and the last ending on 18 December 1960. In the intervals between measurement periods the stands of each species were brought back to uniformly dense swards by frequent mowings. The total experimental area was IVr; acres.

R. W. BROUGHAM AND A. C. GLENDAY 127

Before measurements began in each experimental period all areas were carefully pre-trimmed to a base height of herbage of 1 in. with a Dennis motor-mower. After one week of regrowth the first time replicate of each space replicate was re-trimmed. This was designated day 0 of that experimental period. On day 1 the second time replicate was trimmed and the first plot of the first time replicate was cut. On day 2 the third time replicate was trimmed and the second plot of the first time replicate and the first plot of the second time replicate were cut. On day 3 plots were cut in each time replicate. Plots were then cut on each succeeding day until 14 plots had been cut in each time replicate. except in the early summer, when only 11 plots were cut in each replicate. All cuttings were to the base height of 1 in. and all plots were cut within an hour of sunrise, except in the winter on the days when the herbage was frosted. On these days the plots were cut approximately 2 hours after sunrise when the frost had melted. Measurements were confined· to the hour about sunrise so that the daily growth increments measured were the net gains from photo­synthesis of the previous day less respiration losses during the hours of darkness.

For each plot all the herbage cut was collected, weighed green, then sub-sampled for dry weight determinations, except in the early stages of regrowth, when all material collected was dried. The material was dried in air-draught ovens at a temperature of 180°F. Weighings of all material were to an accuracy of 0.5%.

The weather records presented, with the exception of the radiation measurements, were obtained from a meteorological station approx­imately 100 yd from the experimental site. The instruments used in this station are standard equipment for New Zealand (New Zealand Meteoro­logical Official Circ. No. 18, June 1943). The radiation measurements were obtained from an instrument designed to integrate short-wave radiation incident on a horizontal surface on a relative daily scale (Allan and McCree 1954). It was sited on the experimental area and required manual reading (at the time of cutting).

It is realised that the weather measurements against which growth has been correlated in this study are not the environmental conditions that prevailed at the synthesising sites in the leaves of the different species. However. it is considered that the correlations against standard meteorological data (those available in agriculture) are important, parti­cularly when related to data such as those obtained by Lemon (1963), Slatyer (1965), and others.

RESULTS

The dry matter (D.M.) yields (not presented) obtained for each species during each experimeptal period were separated into growth parameters for smoothly ch~.nging weather over these periods and growth that was considered attributable to daily fluctuations in weather ("w" parameters) by the method of Glenday (1955, 1959). These separations, which were made by the use of an IBM 1620 computer program, are shown for each experimental period in Fig. 1.

-GJ '-0 0

.......... ..c ........ (J')

0 -I W

>-a: W I-I-<{

~

>-a: 0

128 W eat her fluctuations and grass growth 500 560

LATE WINTER -

400 EARLY SPRING

400

Growth" curves

300 300

200 200

100 100

.50

~ ·50

~ 0 . PER .. 0

'50

~ '50

0 0 ~ '50 ! 50

CO~ 0 0

-50 - 50 21 AUG 4 SEPT 1B

DEC

MID·WINTER

100 .. Growth" curves. " cJc"''''' 2t)~ ,<'

-50 "w" Paramett"rs

0 ~ '50

~ 0

! 50 1200

C~ MIO-SPRING a - 50 -~- ._---

15 JULY

BOO .. Growth" curves

I 300

1 200- 400

I 100-

----Parometer~ -100- "w:' Parameters

- 50 PER ~-~.~ a .... ------..------- --. f\.,"' . 0_ -- './ ! 50-

.---~~ , 10,(

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co:~ a --~"~Pv a COCKSFOOT -100 -50

22 APR 6 MA'I' 27 OCT 10NOV

DATE Fig. I-Dry matter y~elds (lbjacre) of the three species separated into "growth curves" for smoothly changing weather during the five experimental periods and "w" parameters showing growth attributable to daily fluctuations in weather. The smoothed "growth curves" are plotted cumulatively against arbitrary dates for each period_ The different ordinate scales for the mid-spring data should also

be noted. (PER = perennial ryegrass; SIR = short-rotation ryegrass)

R. W. BROUGHAM AND A. C. GLENDAY 129

Correlation coefficients were then calculated for the "w" parameters of each experimental period and various components of the daily weather. These were maximum and minimum temperatures, relative radiation receipt, and daily rainfall for the last experimental period (early summer). At other periods of measurements soil water levels were adequate for growth. It should also be noted that no attempt was made to evaluate the combined effects of the different weather factors on the growth of the three species.

So that lag responses to weather factors could also be assessed, correlation coefficients were calculated between these and the "w" para­meters 1, 2, 3, and 4 days removed.

The correlation coefficients, where significant, are shown for each species during each experimental period in Table 1. So that correlation patterns could be better determined, coefficients significant at the 10% level or greater are presented.·

To determine the seasonal changes in growth rate of the three species, average and maximum daily growth increments were calculated for each experimental period from the data presented in Fig. 1. These data and some average daily weather data for each experimental period are shown in Table 2.

DISCUSSION

The growth increments measured in this study and the fluctuations in growth attributed to daily changes in weather were determined during the early stages of regrowth after defoliation. Daily growth rates had not reached the maxima possible in any of the experimental periods (Fig. 1), as interception of incident light energy by the foliage in the different stands would not have been complete except perhaps for the last 2 or 3 days in the spring (Brougham 1956). The results obtained therefore apply to the effects of weather changes on growth during the early stages of regrowth.

For all periods except the winter and winter--early spring the smoothed growth curves of the three species conformed to the early stages of the sigmoid pattern of growth previously described (Brougham 1955, 1959). For the other two periods, and particularly in mid-winter, the relationships between growth and time were linear. This is attributed to the marked limits imposed on growth processes such as photosynthesis by the colder temperatures and low radiation that prevailed over the later days of this period (see Table 2), thus restricting daily D.M. increases to constant but reduced increments.

Marked seasonal changes in growth rate have been recorded (Table 2). These ranged from average rates of 8-11lb D.M./acre/day in mid-winter to 77-80 lb in mid-spring. The maximum rates ranged from 14-21 lb D.M./acre/day in mid-winter to 103-134Ib in mid-spring. From previous results (Brougham 1959) these differences are attributed to the seasonal changes in radiation and temperature shown in Table 2.

TA

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egra

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w

132 Weather fluctuations and grass growth

Marked differences in growth fluctuations attributed to changes in daily weather ("w" parameters) were also obtained (Fig. O. These varied with time of the year. In mid-winter daily fluctuations in the "w" parameters were as great as 30 lb D.M./acre and at the other extreme in mid-spring they were as large as 120-140 lb D.M./acre. In all experimental periods the magnitudes of the fluctuations were usually greater than the growth increments attributed to the average weather during each experimental period. The only exceptions to this were the magnitudes of the fluctuations in the "w" parameters of perennial and short-rotation ryegrass in early summer. For most periods the fluctuations were approximately twice the size of those recorded in a previous study (Brougham 1959) where weekly fluctuations in growth were related to weekly changes in weather. These differences in magnitudes of response between the two studies suggest that fluctuations in the "w" parameters attributed to weekly weather changes in the previous study were masked by the lack of concurrent short-term (daily) changes in other weather factors. The implications of this on the period of adaptation required for changes in weather to influence growth are discussed later.

During the 5 experimental periods a number of significant correla­tions were obtained between the "w" parameters of the different species and the prevailing weather factors (Table 1). These became operative or limited growth at different times of the year. Further, the expression of weather factors through differences in th~ "w" parameters was not always clear-cut, indicating that under field conditions there is often an interplay of all weather factors on growth, with no single factor operating independently of other factors; or that the technique of measurement was not of sufficient accuracy to define weather influences clearly. This aspect of the study is discussed later.

The results presented in Fig. 1 and in Table 1 indicate that in the late autumn changes in day temperatures were associated with changes in growth of all species 1-2 days later, whereas changes in night temperatures had immediate effects on the growth of short-rotation ryegrass and cocksfoot. Daily changes in radiation receipt influenced growth of these two last-named species, but with a time lag in response of 2 days.

During mid-winter the only significant positive correlations obtained indicated that daytime temperatures were high enough on some days to increase the growth of the two ryegrass species significantly. Cocksfoot did not respond to these temperature changes, and none of the species were positively influenced by radiation changes.

In late winter-early spring the average and maximum daily growth rates of the three species were approximately 3-4 times greater than those recorded in mid-winter (Table 2), indicating that weather conditions were generally more favourable for growth. Because of this, all species showed immediate and 2-day lag increases in growth with changes in minimum temperature, indicating that at this time of the year changes in night temperatures had the most marked effect on the growth of the three species. For perennial ryegrass changes in day temperatures were also of significance.

R. W. BROUGHAM AND A. C. GLENDA Y 133

Mid-spring weather conditions were favourable for high daily growth rates of all species. daily maximum temperatures being within the range shown to be optimal for the growth of the three species (Mitchell 1954. 1955). The lack of correlation between the "w" para­meters of the three species and fluctuations in maximum temperatures was therefore not unexpected. Minimum temperatures. however. fre­quently fell below 50°F and were associated with time-lag decreases in growth of perennial ryegrass and cocksfoot. This later correlation was not obtained for short-rotation ryegrass. indicating that this species had a slightly higher tolerance to the colder night temperatures. The delayed positive correlations (4 days) between the "w" parameters of the two ryegrass strains and changes in radiation receipt are of interest and indicate that at this time of the year a relatively long period of adaptation was required before the effects of changes in radiation receipt influenced growth significantly.

Over the early summer the "w" parameters of short-rotation rye­grass were not correlated with changes in any of the weather factors. whereas postive time-lag correlations of 2 days were recorded between the "w" parameters of perennial ryegrass and cocksfoot and rainfall. Perennial ryegrass also showed some immediate and time-lag negative correlations with maximum temperature and a positive 3-day time-lag correlation with minimum temperature. At this time of the year reproductive growth occurs in all species. but short-rotation ryegrass swards normally contain a much higher per­centage of reproductive tillers than perennial ryegrass (Brougham 1961) and cocksfoot (Wilson 1959). Because of this. changes in weather of the magnitude that occurred during this period would have been less likely to affect the growth of the strongly reproductive sward of short­rotation ryegrass than the swards of the other two species. This is shown by the much smaller fluctuations recorded for the "w" parameters of this species compared with the other "w" parameters (Fig. 1). Such a conclusion is also supported by findings of Thorne et al. (1967). who showed that net assimilation rates of barley and sugar-beet respond to temperature changes much more slowly and less definitely at maturity than at other stages of growth.

During December in the Palmerston North environment losses of soil water through evapo-transpiration can be considerable (cf. Table 2). The correlations between rainfall receipt and the "w" parameters of perennial ryegrass and cocksfoot were therefore not unexpected.

No conclusive explanation is offered for the temperature correlations with the "w" parameters of perennial ryegrass during early summer. except that towards the end of this measurement period these "w" parameters were all strongly negative. whereas day temperatures showed appreciable increases and night temperatures appreciable decreases. However. these correlations could have been dependent on the correla­tions with rainfall. and more particularly with the low soil moisture levels. Under such conditions fluctuations in the "w" parameters of perennial ryegrass were more likely to be strongly negative than those of cocksfoot (Fig. I). Perennial ryegrass is less well adapted to tolerate

134 Weather fluctuations and grass growth

low soil water levels than cocksfoot because of the much higher concen­tration of roots that normally occurs in the top few inches of soil than in cocksfoot swards (Klapp 1943).

The correlations between the various weather factors and the "w" parameters that have been discussed above are of interest in determining the relative importance of the weather factors on the growth of swards of the three species in this environment from April to December. They show that daily changes in temperatures were generally more critical and influenced growth more rapidly than changes in radiation receipt or rainfall. These responses were probably influenced by the stage of regrowth, as in all periods light interception by the leaf canopies of the swards would have been incomplete. Full expression of radiation responses would therefore not have occurred, whereas growth processes such as remobilisation of energy substrates and cell division and elonga­tion associated with early regrowth would have been markedly dependent on temperature. Nevertheless these results indicate that from April to November in this environment growth responses were often very sensitive to changes in day and night temperatures.

The period of adaptation required before changes in weather factors were expressed as changes in D.M. increments varied. This is illustrated by the fact that immediate and time-lag correlations were obtained between the "w" parameters and the different weather factors, and that these varied during the year and with the different weather factors. Examples are the immediate responses to changes in night temperatures by all species in the late winter when low temperatures limited growth, and at the other extreme the relatively long periods of adaptation (up to 4 days) required for response to changes in weather during the mid­spring when no single factor limited growth. These differences in periods of adaptation which were dependent on the time of the year when the weather factor was operative and on the interplay of the other weather factors and growth extend results previously obtained for the growth of pasture (Brougham 1959). They also illustrate that whereas under controlled environment conditions changes in growth in response to changes in climatic factors may be immediate (Mitchell and Coles 1955), under field conditions such changes are not always so definite and immediate. Of particular interest in this context was the complete lack of immediate response in mid-spring, a time of the year in this environ­ment when weather. conditions are generally very favourable for the growth of all species.

Some of the correlations obtained are difficult to interpret, which suggests that the technique used, though adequately determining large weather influences on growth, was not sensitive enough to determine smaller but critical weather influences. Examples of these are the lack of correlation between the "w" parameters of perennial ryegrass and minimum temperatures in late autumn compared with short-rotation ryegrass and cocksfoot, the lack of response of cocksfoot to weather influences in mid-winter, the lack of response of short-rotation ryegrass .and cocksfoot to changes in maximum temperatures in late winter and early spring, the negative correlations with radiation levels and perennial ryegrass in mid-winter and short-rotation ryegrass in late winter--early

R. W. BROUGHAM AND A. C. GLENDAY 135

spring, and to a less extent the very significant negative correlations between the "w" parameters of perennial ryegrass and changes in maximum temperature in early summer. The negative correlations outlined, and particularly those related to radiation receipt, are difficult to interpret, although in the winter in this environment frosty nights (low minimum temperatures) are usually associated with relatively sunny days, and cloudy and rainy days often follow slightly warmer nights. This suggests an interplay between weather factors and growth of the three species that was not elucidated in this study.

The lack of correlations obtained when these would have been predicted applied to growth in the colder periods of the year when the growth increments measured were relatively small. This would indicate that the area of pasture cut daily for each species (80 sq ft) was insufficient to determine weather influences accurately over these periods, and this would have applied' particularly for cocksfoot during the winter when the average daily growth increment was only 8 lb D.M. per acre.

In spite of this limitation it is considered that the technique employed, and the results obtained by its use, are of value in assessing the relative importance of weather factors on growth of pasture species. The value of the results in assessing growth potentials of three grass species commonly used in pastures in this environment should also be obvious.

Acknowledgment

The technical assistance of Mr L. E. Madgwick is greatly appreciated.

REFERENCES

ALLAN, A. H.; McCREE, K. I. 1954: A daylight integrator for con­tinuous use. Rep. Dam. phys. Lab. (N.Z.) 220.

BLACK, I. N. 1955: The interaction of light and temperature in deter­mining the growth rate of subterranean clover (Trifolium subtcrraneum L.). Aust. J. bioi. Sci. 8: 330-43.

BLACKMAN, G. E.; BLACK, J. N.; KEMP, A. W. 1955: Physiological and ecological changes in the analysis of plant environment. 10. An analysis of the effects of seasonal variation in daylight and temperature on the growth of Helianthus annuus in the vegetative phase. Ann. Bot. n.s. 19: 527-48.

BROUGHAM, R. W. 1955: A study in rate of pasture growth. Aust. J. agric. Res. 6: 804--12.

----- 1956: Effect of intensity of defoliation on regrowth of pasture. Ibid. 7: 377-87.

-------1959: The effects of season and weather on the growth rate of a ryegrass and clover pasture. N.Z. JI agric. Res. 2: 283-96.

1961: Some factors affecting the persistency of short­rotation ryegrass. Ibid. 4: 516-22.

136 Weather fluctuations and grass growth

DE WIT, C. T. 1959: Potential photosynthesis of crop surfaces. Neth. J. agric. Sci. 7: 141-9.

1965: Photosynthesis of leaf canopies. Agric. Res. Rpt. No. 663, Centre of agricultural publications and documentation, Wageningen.

EVANS, L. T. 1963: "Environmental control of plant growth". Academic Press, Inc.; New York.

GAASTRA, P. 1958: Light energy conversion in field crops in comparison with the photosynthetic efficiency under laboratory conditions. Meded. LandbHogesch., Wageningen 58: 1-12.

GLENDAY, A C. 1955: The mathematical separation of plant and weather effects in field growth studies. Aust. J. agric. Res. 6: 813-22.

~~~~-1959: Mathematical analysis of growth curves replicated in time. N.Z. Jl agric. Res. 2: 297-305.

KLAPP, E. 1943: Concerning the spread of roots in grass turf as a result of different methods of utilization and plant associations. Pflanzenbau. 19: 221-36.

LEMON, E. R. 1963: Energy and water balance of plant communities. In "Environmental Control of Plant Growth". Ed. L. T. Evans. Academic Press, Inc.; New York.

LooMIS, R. S.; WILLIAMS, W. A 1963: Maximum crop productivity: an estimate. Crop Sci. 3: 67-72.

MITCHELL, K. J. 1954: Growth of pasture species. I. Short-rotation and perennial ryegrass. N.Z. Jl Sci. Techno!. 36A: 193-206.

1955: Growth of pasture species. II. Perennial ryegrass, cocksfoot, and paspalum. Ibid. 37 A: 8-26.

1956: The influence of light and temperature on the growth of pasturt' species. Proc. 7th into Grassld Congress: 58--69.

MITCHELL, K. J.; CoLES, S. T. J. 1955: Effect of defoliation and shading on short-rotation ryegrass. N.Z. Jl Sci. Techno!. 36A: 586--604.

MONTEITH, J. L. 1965: Light distribution and photosynthesis in field crops. Ann. Bot. n.s. 29: 17-37.

MURAMOTO, H.; HESKETH, I.; EL-SHARKAWY, M. 1965: Relationships among rate of leaf area development, photosynthetic rate, and rate of dry matter production among American cultivated cottons and other species. Crop Sci. 5: 163--6.

SLATYER, R. O. 1965: Measurements of precipitation interception by an arid zone plant community (Acacia aneura F. Muel!). Proc. Montpel/ier Symposium. "Methodology of Plant Eco-Physiology". 181-92.

THORNE, G. N.; FORD, M. A; WATSON, D. J. 1967: Effect of tem­perature variation at different times on growth and yield of sugar-beet and barley. Ann. Bot. n.s. 31: 71-101.

WATSON, D. I. 1958: The dependence of net assimilation rate on leaf area index. Ibid. n.s. 22: 37-54.

WENT, F. W. 1958: The physiology of photosynthesis in higher plants. Preslia. 30: 225-49.

WILSON, J. R. 1959: The influence of time of tiller origin and nitrogen level on the floral initiation and ear emergence of four pasture grasses. N.Z. Jl agric. Res. 5: 915-32.