Thermal time approach to predicting seedling emergence dates of red clover,white clover and lucerne in farm fields

A practical method for predicting seedling emergence dates of red and white clovers, and lucerne is proposed. The germination response at seven different constant temperatures ranging from 5 to 35°C was examined. Germination rate, which is a reciprocal of the duration for 50% germination of seeds, was linearly regressed against temperature to calculate the base temperature and thermal constant of seed germination. The calculated values were 3·9°C and 15·8 degree days for red clover, 4·2°C and 13·6 degree days for white clover, and 2·9°C and 17·7 degree days for lucerne. Using the base temperatures, thermal constants, and the daily mean air temperatures at the study site, the seedling emergence dates of the three forage legumes were predicted. At the same time, in an outdoor pot experiment, seeds of these legumes were sown approximately every 3 weeks and seedling emergence dates were determined. The predicted dates of seedling emergence generally fitted the observed dates. Another prediction was attempted using the base temperatures, thermal constants, and normal daily mean air temperatures recorded over more than 30 years in the study site. This prediction showed that the seedlings of the three forage legumes began to emerge at the beginning of April and could continue to emerge until the beginning of November when their non‐dormant seeds were present in the site, and that when the seeds were sown from mid‐November of one year to late March of the next year, the emergence of seedlings was delayed until the beginning of April.     

Thermal inactivation of Plasmodiophora brassicae Woron. and its attempted control by solarization in the Salinas Valley of California

Thermal inactivation of resting spores of P. brassicae Woron. in glasshouse soil depended on temperature, duration of treatment, inoculum concentration, and soil moisture. At 42, 44 and 50°C, the relationship between temperature and the time for thermal inactivation plotted on a semi-log scale was linear. Treatment times up to 45 days at 30°C and 37°C did not reduce infectivity. The detection threshold in the system was 10^0·5 spores/g of soil. At all temperatures tested, inactivation was achieved more rapidly in soil infested with 10² spores/g than with 10⁶ spores/g. Heat treatment was more effective in saturated soil than in half-saturated soil. Soil temperatures in the field in the northern Salinas Valley were increased 11–14°C by tarping with clear, polyethylene plastic. The average weekly maximum temperature and minimum temperature at a 10 cm depth under tarps were 38°C and 29°C respectively. Solarization reduced disease development after a 10-week treatment but not after a 5-week treatment.     

南通市粳稻安全齐穗和安全成熟期的时间演变研究

以江苏省南通市1951-2010年9月至11月份日平均温度为资料,根据有关界限温度指标,推测保证率为50%、80%和90%的粳稻安全齐穗期和安全成熟期。结果发现,1991-2010年这20年水稻安全齐穗期和安全成熟期较之前的两个20年均有不同程度延迟,80%保证率的安全齐穗期分别推迟8 d、9 d,80%保证率的安全成熟期分别推迟10 d、5 d;同时发现,在气候变暖形势下以20℃作为安全齐穗的指标已经难以发挥指导生产实际的作用,进而提出以齐穗至成熟期有效积温为参考指标,通过安全成熟期向前累加活动积温（≥10℃）的方法来修正安全齐穗期。修正后的安全齐穗期较原推测日期提早25 d左右,即80%保证率安全齐穗期在9月6日左右。     

Effect of soil solarisation and mouldboard ploughing on black dot of potato, caused byColletotrichum coccodes

Summary Preplant soil solarisation and mouldboard ploughing to a depth of 30 and 60 cm respectively were evaluated in two field experiments for the control ofColletotrichum coccodes causing black dot of potato. Solarisation reduced disease incidence by 45% when tarping was done for eight weeks and temperatures reached 56°C in the top 5 cm of soil. With a six week tarping period and lower maximum temperature (50°C) the reduction in disease was a nori-significant 25%. Mouldboard ploughing to a depth of 30 cm reduced black dot by 34% and was twice as effective as ploughing to a depth of 60 cm.     

Amount and quality of grass harvested for first-cut silage for differing spring-grazing frequencies of two mixtures of perennial ryegrass cultivars with contrasting heading date

There are potential advantages and disadvantages associated with grazing spring perennial ryegrass swards designated for first‐cut silage. These may differ for intermediate‐heading (0·50 ear emergence in the second half of May) and late‐heading (0·50 ear emergence in the first half of June) cultivars. The interactions between cultivar type, spring‐grazing frequency, silage‐harvest date and year were examined in an experiment with a randomized complete block (n = 4) design with a factorial arrangement of treatments, conducted in Ireland. The factors were (i) two perennial ryegrass mixtures: intermediate‐ vs. late‐heading cultivars, (ii) three spring‐grazing regimes: no grazing, grazing in mid‐March or grazing in both mid‐March and mid‐April, (iii) four first‐cut silage‐harvest dates that were at c. 10‐d intervals from 19 May and (iv) 2 years (1998 and 1999). The effects of cultivar mixture on herbage mass of the swards in spring were small and not statistically significant. The late‐heading cultivars provided lower amounts of herbage dry matter for harvesting for first‐cut silage but herbage with higher in vitro organic digestibility values compared with intermediate‐heading cultivars. To achieve the same amount of herbage for silage, the late‐heading cultivars needed to be harvested 8 d later than the intermediate‐heading cultivars. Even with this delay in harvest date, the late‐heading cultivars had higher in vitro organic digestibility values than the intermediate‐heading cultivars. The late‐heading cultivars could be harvested up to 30 d later and produce a higher amount of herbage for first‐cut silage with similar digestibility values compared with the intermediate‐heading cultivars.     

Effects on performance and carcass composition of turning beef cattle out to pasture early in the spring

Abstract The effects of turning beef cattle out to pasture earlier in the spring than is conventional in Northern Ireland on performance until slaughter in late summer were examined. Thirty‐eight steers, which were initially 525 kg live weight (LW), were divided into blocks of two according to breed type, previous plane of nutrition and LW and were allocated to two treatments at random within each block. Steers on Treatment 1 were turned out to pasture on 14 March and grazed a permanent perennial ryegrass‐based pasture with a mean sward surface height of 8·4 (s.e. ± 0·36) cm until Treatment 2 steers were turned out on 2 May. Thereafter, all steers grazed as a single group until slaughter at the same estimated carcass fat content, which occurred between June and September. Between the two turnout dates, steers on Treatment 2 were given grass silage ad libitum. For the early and late turnout treatments, respectively, LW gains between the two turnout dates were 1·5 and 0·7 kg d^?1, carcass gains from 14 March until slaughter (mean 143 d) were 0·69 and 0·53 (s.e. ± 0·022) kg d^?1, and carcass weights were 370 and 347 (s.e. ± 2·7) kg. It is concluded that, under the conditions of this experiment, turning beef cattle out to pasture in early spring may offer economic benefits in beef production in situations in which this is practicable.     

Persistence ofCorynebacterium sepedonicum in soil and in buried potato stems

The effect of moisture content and temperature on the persistence, in soil, of cells of the ring rot bacterium,Corynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh., was followed with root-inoculated, rooted potato stem cuttings. Ring rot bacteria were still viable after 284 days in a sterilized Lethbridge silt loam moistened to field capacity and incubated at 15°C. However, the cells did not survive beyond 6 days in two non-sterile silt loams at field capacity and 20°C. In non-sterile Lethbridge silt loam, persistence of the pathogen increased as soil moisture content and temperature decreased. Cells persisted for 10 and 15 days, respectively, in soil at 50% field capacity held at 15 and 10°C. Ring rot bacteria were not recovered after 88 days from a non-sterile Lethbridge silt loam moistened to the wilting point and held at a temperature fluctuating between 10 and 20°C, or from soil at field capacity and at a temperature fluctuating between ?5 and +5°C. They survived for 362 days in soil at the wilting point at mean temperatures of 0 or ?10°C, but were not viable after 278 days in soil at field capacity and a mean temperature of ?10°C. In excised, infected potato stems held in a non-sterile Lethbridge silt loam, the pathogen persisted for 325 days in soil at the wilting point and a mean temperature of 0°C. These results suggest that soil infested with ring rot bacteria should be kept well moistened during warm periods to inactivate these bacteria and to ensure that they do not contaminate healthy tubers that may be stored or grown there later.     

Variation in spring temperatures, grass production and response to nitrogen over twenty years in the uplands

Large between-year variation was observed in spring air and soil temperatures at Pant-y-dwr Hill Centre (305 m altitude) from 1967 to 1984 and at Bronydd Mawr Research Centre (330 m) from 1985 to 1986 in Powys. The mean date of attaining T-sum 200°C accumulated air temperature was 13 March (range 9 February to 23 April) and that of soil temperature at 100 mm depth permanently above 5 5°C was 9 April (range 7 March to 4 May). Net herbage accumulation and response to applied N from Aberystwyth S23 perennial ryegrass (Lolium perenne L.) swards during April were also highly variable and were correlated with the date of reaching target soil temperatures of above 5 5°C for 5 consecutive days ( r =−0·68, P < 0·001 for net herbage accumulation and r =−0·70, P < 0·001 for response to N).
The use of early flowering varieties of perennial ryegrass gave a significant increase of herbage growth in spring compared with late varieties. From 1979 to 1980 net herbage accumulation during April from the early variety Frances was 94% more than from Perma (late) and 55% more than from Talbot (intermediate) varieties. Under conservation management more winter hardy and persistent varieties of Italian and hybrid ryegrasses ( L. multiflorum L. and L. multiflorum X L. perenne ) gave higher quantities of firstcut silage crops in early June than RvP Italian ryegrass.
After the severe winters of 1978–79 and 1985–86, subsequent spring production from a wide range of ryegrasses was shown to be affected by sward survival, highlighting the value of winter hardy varieties when resowing in the uplands     

THE INFLUENCE OF DATE OF SOWING AND OF STRAIN ON HEAD PRODUCTION IN TIMOTHY

Heading behaviour of eight strains of timothy was observed in the sowing and first harvest years, after sowing on a series of dates between March and August.
All strains produced heads in the sowing year. Only a very few plants failed to head when sown between 18 March and 29 April. With subsequent sowing dates the proportion of heading plants progressively declined, most markedly in S.50 Phleum nodosum , least in the early-heading P. pratense strains. No heading occurred in the sowing year after the mid-August sowing.
The environment to which the later sowings are exposed differs from that of the earlier sown lots in that (a) the initial temperatures and daylengths are higher and (b) the decline in daylength occurs earlier in their development. One or both of these factors must be responsible for failure of heading among plants of the later sowings.
The sequence of heading dates among the strains in the sowing year differed considerably from that in the same plants after overwintering, suggesting the action of some factor other than photo-period in determining heading date in the sowing year.
Variability in heading date within the strains was much greater in the sowing year than after overwintering, and increased with lateness of sowing.     

Influence of energy-saving night temperature regimes on Botrytis cinerea in an early-season glasshouse tomato crop

Night minimum temperatures of 9°C and a regime with periods of one month at 16°C,and 5°C, followed by 13°C, were compared with a night regime of 13°C for their effects on Botrytis cinerea Pers. in an early-season glasshouse tomato crop. Day temperatures were the same in all treatments. Nine independent compartments were used in a randomized block design in which sub-plots were treated with or without a programme of fungicidal sprays of iprodione started at one of three stages in relation to the first infection by B. cinerea. The low-temperature regime of 9°C significantly increased numbers of lesions caused by B. cinerea on stems and leaves during April and May, but not in subsequent months. Increases during May and June of fallen fruits from 9°C plants were not statistically significant. Stem and leaf infections were not increased by the 16/5/13°C energy-saving regime, although losses due to fallen fruit were greater during May. Treatment with iprodione sprays caused significant decreases in disease in all night temperature regimes and was similar in effect to an increase in night temperature from 9°C to 13°C. Responses to the timing of the first application of iprodione were never significant and differed during the first month of disease assessment only. Yields were significantly lower in the first month of cropping at 9°C but there were no differences in yield between the 13°C and the 16/5/13°C regimes.     

Relationships between stem number,tuber set and yield of Russet Burbank potatoes

Five storage temperatures and three planting dates were used to obtain differences in seed performance. As seed storage temperature increased, average stem number per seed piece significantly increased. Stem number also increased with later planting dates. Germination tests, conducted under controlled temperatures, resulted in a curvilinear response with the least stems per seed piece at 10°C. a maximum stem number at 16°C and a slight decline in number at 21°C. The major effect of planting date was manifested through differences in germinating temperatures which resulted in increased stem number with later plantings. Yield of U.S. No. 1 tubers (5cm or 112 gm minimum) declined significantly as stem number increased. In the first planting, the correlation coefficient between stem number per seed piece and yield was r = ?0.95. Increased stem number and declining yield were attributed to advanced physiological age resulting from exposure to higher temperatures in storage and in the field. As stem number increased with planting date, tuber number also increased. The correlation coefficient between stem and tuber number for the first planting date was r = 0.92. The relationship declined significantly on the third planting date to r = 0.46. From these results it was concluded that economic yields are influenced by stem and tuber number which in turn can be manipulated by control of seed storage temperatures and planting dates.     

Estimating theoretical radiation‐use efficiency for kale crops

Establishing the radiation‐use efficiency (RUE) of forage brassica crops will aid our understanding of their photosynthetic performance. The concept of RUE has been developed for cereals and legumes, but there is limited information for forage brassica crops. Three experiments defining the influence of different sowing dates on ‘Gruner’ kale (Brassica oleracea acephala L.) dry matter production were conducted at Hastings (Hawkes Bay) and Lincoln (Canterbury) in New Zealand between 2002 and 2009. These trials were also evaluated for radiation interception and RUE. Delayed sowing increased RUE in two out of three experiments across sites: from 1·93 g MJ^?1 photosynthetically active radiation (PAR) for December‐sown crops to 2·72 g MJ^?1 PAR (P < 0·001) for January‐sown crops at Hastings and from 1·50 for September‐sown crops to 2·00 g MJ^?1 PAR (P < 0·001) for November‐sown crops at Lincoln. The different sowing dates and years of experimentation provided a range of mean temperatures (from 13 to 16°C) during the vegetative period. Across years and sowing dates, RUE was strongly correlated with mean temperature (R² = 0·81) and sowing date (R² = 0·64), but weakly correlated with season length (R² = 0·11) and dry matter (R² = 0·002). There was also a strong correlation (R² = 0·83) between sowing date and mean temperature. The increase in RUE with delayed sowing was therefore mainly attributed to increased mean temperatures. Radiation‐use efficiency increased at about 0·41 g MJ^?1 for each 1°C increase from 13 to 16°C.     

Temperature-dependent fecundity of overwintered Unaspis yanonensis (Hemiptera: Diaspididae) and use of degree-days for the prediction of first crawler

The longevity and fecundity of the overwintered arrowhead scale, Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae), was examined at constant temperatures. The total fecundity increased up to 24 °C and declined thereafter. Total fecundity reached a maximum of 260.9 eggs per female at 24 °C. Females demonstrated periodic oviposition activity but the pattern differed with temperature. The first cycle of fecundity was not significantly different between 16 and 28 °C. However, fecundity in the latter cycles, measured at rearing temperatures of 16, 20 and 32 °C, was lower than at 24 and 28 °C. The pre-oviposition period ranged from 49.0 d at 16 °C to 19.7 d at 32 °C, and was shortest (19.4 d) at 28 °C. The longevity was found to be greatest (87.3 d) at 16 °C and was as short as 48.9 d at 32 °C. Regression of the mean development rate vs. temperature provided a low-threshold temperature estimate of 8.7 °C for the pre-oviposition stage and a thermal constant of 358.4 degree days. The theoretical low threshold temperature and thermal constant applied to the calculation for the completion of the U. yanonensis pre-oviposition period predicted the appearance of first crawlers in the field.     

普通气候年景下江汉平原超级杂交稻结实率及其与气候条件的关系

采用扬两优6号等9个湖北目前推广的超级杂交稻组合,以汕优63为对照,从2008年4月19日起采用分期播种法每10d播种1次,考查品种结实率变化及其与结实前后主要气象因子的相关关系。结果表明,2008年水稻生育期间的气象条件总体为雨日阴天稍多,但仍属于普通气候年景。9个超级杂交稻组合7个播期结实稳定、正常,各播期间结实率最高与最低相差6.1个百分点。但各播期的结实率总体上仍表现为越早播,结实率越高(日均温为24～29℃时),结实率随孕穗和开花结实期日均温降低而降低,每降低1℃结实率约降低0.8个百分点。同组合同播期不同抽穗批次茎蘖结实率在前4个播期差别较小,但从第5播期后,部分组合的第3抽穗批次分蘖的结实率出现明显下降。结实率在不同播期间的差异与抽穗后15d期间的日平均气温、抽穗前后40d期间日照时数和抽穗前后7d期间最高气温呈极显著正相关。     

Effects of Early- and Late-Sowing on Starch Accumulation and Associated Enzyme Activities During Grain Filling Stage in Rice

The environmental temperature occurring during the grain filling stage is an important factoraffecting starch synthesis and accumulation in rice. We investigated starch accumulation, amylaseactivity and starch granule size distribution in two low-amylose japonica rice varieties, Nanjing 9108 andFujing 1606, grown in the field at different filling temperatures by manipulating sowing date. The two ricevarieties exhibited similar performances between two sowing dates. Total starch, amylose andamylopectin contents were lower at the early-filling stage of T1 treatment (Early-sowing) compared withthose at the same stage in T2 treatment (Late-sowing). In contrast, at the late-filling stage, when fieldtemperatures were generally decreasing, total starch and amylopectin contents in T1 were highercompared to those in T2. The ideal temperature for strong activity of ADP-glucose pyrophosphorylaseand soluble starch synthase was about 22℃. A higher temperature from the heading to maturity stagesin T1 increased the activities of starch branching enzyme and suppressed the activities of granule boundstarch synthetase and starch debranching enzyme. We found that rice produced larger-sized starchgranules under the T1 treatment. These results suggested that due to the early-sowing date, the hightemperature (30℃) occurring at the early-filling stage hindered starch synthesis and accumulation,however, the lower temperatures (22 ℃) at the late-filling stage allowed starch synthesis and accumulationto return to normal levels.     

Calendar and degree-day requirements for emergence of adult Macroglenes penetrans (Kirby), an egg-larval parasitoid of wheat midge, Sitodiplosis mosellana (Géhin)

The chalcidoid wasp, Macroglenes penetrans (Kirby), is an important parasitoid of wheat midge, Sitodiplosis mosellana (Géhin), in Europe and western Canada. Emergence of adult wasps was evaluated at 12 sites in Saskatchewan in 1991-2000. Emergence was assessed in relation to calendar days and accumulated degree-days above five different threshold air temperatures. Male wasps emerged 1-2 days before the female wasps. Dates for 10%, 50% and 90% emergence of both wasp sexes were July 16, July 21 and July 30, respectively. Standard deviations (SD) indicated that emergence dates varied by 6.2-7.7 days. The variation in dates related to degree-day accumulations between March 1 and July 31. Wasps emerged 2-12 days earlier than expected at sites with the highest accumulation and 2-17 days later than expected at sites with the lowest accumulation. Accumulated degree-days above 9 °C provided the most accurate estimate of 10% emergence (450 DD, SD = 2.4 days) and 90% emergence (579 DD, SD = 5.0 days). Accumulated degree-days above 5 or 9 °C provided the most accurate estimate of 50% emergence (823 DD, SD = 3.0 days; 503 DD, SD = 3.1 days, respectively). Deviations between observed and expected emergence were greatest at sites with either low or high precipitation. In most instances, wasps emerged 1-8 days earlier than expected at sites that received 20-40 mm rain in May and 1-11 days later than expected at sites that received more than 145 mm rain in May and June. Degree-days above 5 or 9 °C minimized the variation at these sites. Emergence was re-assessed in 2008 and 2009. In both years, accumulated degree-days above 9 °C predicted 10%, 50% and 90% emergence within 0.1-2.2 days. Forecast maps, based on daily degree-day accumulations above 9 °C, would assist producers in monitoring their fields for the presence of wasps. Producers could also adjust the timing, rate and placement of sprays for control of wheat midge to protect and conserve the parasitoid.     

Correlation and Regressive Model Between Spikelet Fertilized Rate and Temperature in Inter-Subspecific Hybrid Rice

To study the sensitivity of inter-subspecific hybrid rice to climatic conditions, the spikelet fertilized rate (SFR) of four types of rice including indica-japonica hybrid, intermediate hybrid, indica and japonica were analyzed during 2000-2004. The inter-subspecific hybrids showed lower SFR, and much higher fluctuation under various climatic conditions than indica and japonica rice, showing the inter-subspecific hybrids were sensitive to ecological conditions. Among 12 climatic factors, the key factor affecting rice SFR was temperature, with the most significant factor being the average temperature of the seven days around panicle flowering (T7). A regressive equation of SFR-temperature by T7, and a comprehensive synthetic model by four important temperature indices were put forward. The optimum temperature for inter-subspecific hybrids was estimated to be 26.1-26.6℃, and lower limit of safe temperature to be 22.5-23.3℃ for panicle flowering, showing higher by averagely 0.5℃ and 1.7℃, respectively, to be compared with indica and japonica rice. This suggested that inter-subspecific hybrids require proper climatic conditions. During panicle flowering, the suitable daily average temperature was 23.3-29.0℃, with the fittest one at 26.1-26.6℃. For an application example, optimum heading season for inter-subspecific hybrids in key rice growing areas in China was as same as common pure lines, while inferior limit for safe date of heading was about a ten-day period earlier than those of common pure lines.     

Simulation study of past climate change effect on chickpea phenology at different sowing dates in Gorgan, Iran

This simulation study was mainly aimed to find the probable difference between sowing dates for response of four chickpea cultivars to past climate change. Firstly, the model CYRUS was recoded in QBASIC programming. Then phenology of cultivars Jam, Hashem, Arman and Beauvanij, seeded at day of year 50, 70 and 90, was evaluated during years 1961 to 2003 in Gorgan, Iran. The changes in some climatic variables were also studied. Results revealed that the solar radiation has been decreased for month December. Although the value of maximum temperature appeared to be the same across years 1961 to 2003 for all months, that of minimum temperature tended to show increasing trend for May and August. The increase in number of days with temperature higher than 35 degrees C was considerable for April and October, but negligible for other months. The warming of night temperature was significant only for May and August. It found about 34 mm per 43 years decrease in monthly rainfall for March. The rate of increase in number of days with rainfall was 0.0737 day per year for December. Nearly similar situation was found for number of days with rainfall lower than and/or equal to 10 mm. The change in number of days with rainfall higher than 10 mm and lower and/or equal to 30 mm was in decreasing manner (March, October and December). The length of time from sowing to emergence appeared to be constant across past years. The advance in flowering (R1) was true only for cultivar Jam seeded at day of year 70. The length of period from R1 to pod initiation (R3) has been diminished for sowing at day of year 70 (Jam and Arman). Only cultivar Hashem seeded at day of year 90 tended to have decreasing trend for length of period between R3 and pod filling. It found one day (per 43 years) decreases from pod yellowing to maturity for cultivar Beauvanij seeded at day of year 70. Based on these findings and on the fact that future climate change is predicted using past changes, it seems that the adaptation strategies for future, including agronomy and/or breeding programs, may be not the same for different sowing dates of chickpea.     

Influence of high daytime temperature during the grain filling stage on fissure formation in rice

High daytime temperatures during the grain filling stage in rice have negative impacts on milling quality traits. In this study, we used growth chambers to evaluate the influence of high daytime temperature (33 °C) during grain filling, together with grain moisture content at harvest (26%, 18% and 15%), on grain fissure formation. Varietal susceptibility to fissure formation was also evaluated by exposing grains to high temperature at different grain filling stages (milky, dough, maturing). Two fissure resistant varieties: Cypress (long-grain) and Reiziq (medium-grain) and susceptible varieties: YC53-00-7 (long-grain) and Baru (medium-grain) were compared. The average head rice yield (HRY) of Cypress declined from 62.7% at 25 °C to 53.5% at 33 °C, while Reiziq declined from 56.2% (25 °C) to 47.4% (33 °C). Both were significantly higher than the HRY of YC53-00-7 (39.2% and 24.9%) and Baru (39.3% and 31.7%) at 25 °C and 33 °C, respectively. When grains were drier at harvest (15% cf. 26%) there was a greater reduction in HRY. When the four varieties were exposed to high temperature, the highest average reduction of HRY was recorded at 21 days after heading. It is important to choose an optimal sowing date to avoid coincidence of the final grainfilling stage with high temperatures, in order to minimize milling quality losses.     

Modelling leaf production and crop development in maize (Zea mays L.) after tassel initiation under diverse conditions of temperature and photoperiod

Prediction of the initiation, appearance and emergence of leaves is critically important to the success of simulation models of crop canopy development and some aspects of crop ontogeny. Data on leaf number and crop ontogeny were collected on five cultivars of maize differing widely in maturity and genetic background grown under natural and extended photoperiods, and planted on seven sowing dates from October 1993 to March 1994 at Gatton, South-east Queensland. The same temperature coefficients were established for crop ontogeny before silking, and the rates of leaf initiation, leaf tip appearance and full leaf expansion, the base, optimum and maximum temperatures for each being 8°C, 34°C and 40°C. After silking, the base temperature for ontogeny was 0°C, but the optimum and maximum temperatures remained unchanged. The rates of leaf initiation, appearance of leaf tips and full leaf expansion varied in a relatively narrow range across sowing times and photoperiod treatments, with average values of 0.040 leaves (°Cd)⁻¹, 0.021 leaves (°Cd)⁻¹, and 0.019 leaves (°Cd)⁻¹, respectively. The relationships developed in this study provided satisfactory predictions of leaf number and crop ontogeny (tassel initiation to silking, emergence to silking and silking to physiological maturity) when assessed using independent data from Gatton (South eastern Queensland), Katherine and Douglas Daly (Northern Territory), Walkamin (North Queensland) and Kununurra (Western Australia).