Rev. Fac. Agron. (LUZ). 1997, 14: 507-516

Phenology and yield of maize for different sowing dates in a tropical mountain environment

Efectos de diferentes fechas de siembra sobre la fenología y producción de maíz en montañas tropicales

Recibido el 24-05-1996 l Aceptado el 24-02-1997
1. Universidad de Los Andes. Facultad de Ciencias Forestales y Ambientales. Instituto de Investigaciones Agropecuarias. Apartado 77 La Hechicera Mérida 5101, Venezuela.

Ramón E. Jaimez

Abstract

Experiments were carried out in order to examine the relationship between leaf appearance and thermal time under field conditions and to improve a model that simulates development and production of maize in tropical mountain environments. The comparative phenology and productivity of the tropical highland maize cultivar Santa Rosa were analized as a function of different sowing dates. The relationships between leaf appearance rate and thermal time for both sowings dates tended to be basically curvilinear and agreed with results shown in the literature. The number of leaves depended on daily maximum and minimum temperature variations and on the stage of plant growth. These affected the timing of anthesis and other development phases. The average yield and number of ears was constant for both sowing dates
Key words: Zea mays, phenology, maize model, sowing dates.

Resumen

Introduction

Maize (Zea mays L.) is the most widely grown cereal in Venezuela producing more than 1.1 million tons over the last few years (6). Maize is mainly produced in the lowland zones during the wet season, while in mountain areas (1500 m elevation), it is planted during both the dry and the wet seasons.

Limited studies about dry matter production and phenology in the wet season have been carried out in lowland regions of Venezuela (10, 13, 14, 8) and little information exists on effects of planting dates on production and phenology. There are also little data available for germplasm growing above 1600 m.a.s.l. under tropical field conditions (1). According to studies in temperate zones, natural changes of temperature and photoperiod have effects on phenology and production (19, 20, 16). Different results were also found for tropical germplasm (7). In temperate regions yearly temperature changes from season to season fluctuate from 8 to 12 °C while in tropical zones the fluctuation is lower (from 3 to 4 °C). Due to this difference, the range of temperature change effects on phenology and yield could vary between tropical and temperate maize.

In spite of adequate nutrients, water and weed control, the effects of temperature on developmental events are difficult to evaluate because phenology is the result of the interaction of other climatic factors. However, several authors have indicated that leaf appearance rate and number of leaves are closely related to temperature (16, 19, 20). They determined more precisely other phenological events such as tassel and silking dates. It is often assumed that there is a linear relationship between leaf appearance and day degrees, but this is not clear. Relationships between accumulated temperature and leaf temperature rate have also been studied in tropical conditions (9,7) and it is necessary that information on phenology and dry matter partitioning is obtained to provide a framework for predicting and validating appropriate maize models for tropical environments. These would lead to improved production.

The main objective of this study was to determine phenological periods and leaf appearance for the Santa Rosa germplasm in a mountain tropical environment and determine how they were influenced by sowing dates. A second objective was to obtain knowledge about yield potential and to generate growth data to validate maize models.

Materials and methods

Experiments were conducted at the Universidad de Los Andes, Agricultural Research Station (IIAP) in Venezuela (latitude 8° 38' N, longitude 71° 10' W, altitude 1 900 m), during June 1991 through July 1992. The soil at this location is a Humitropep Typic (12). Mean annual precipitation is 2 094 mm with a marked dry season from December to March. The natural day length varies between 12.5 h and 11.5 h during the year.

Cultural Practices: The Santa Rosa germplasm showing a high production for mountain zones (1) was planted on June 27, 1991 and January 20, 1992. Two Kernels were sown about 6 cm deep at 25 cm intervals and thinned to 40,000 plants ha^-1. When sowing, the plots were fertilized with 100 kg ha^-1 of N, P and K each. Then, additional fertilization was carried out using 100 kg ha^-1 of N and K at 54 days after sowing (DAS). Plots were irrigated after 3 or 4 rain-free days. Diseases and pests were controlled throughout the experiment. Both trials were replicated three times in a completely randomized block design. Santa Rosa formed part of an experiment with other genotypes of maize.

Measurements and data analysis: Emergence date was recorded when 50 % of the plants had some part visible at the soil surface. At approximately 15 -17 DAS, 6 plants from each plot were selected and tagged for phenology measurements. From this time to tasseling (50 % of plants with visi-ble tassel) each plant was measured twice a week for last fully expanded leaf (when the ligule is visible). Silking date was recorded when 50 % of the plants had silks outside their husks. Physiological maturity was assumed to be reached when in 50 % of the selected plants, 50 % of the grain possessed a black area (4). Daily thermal time was calculated from maximum and minimum temperatures using 8 °C as the base temperature (5).

Ears were removed and ear number, and potential grain number were determined. Plants were oven dried at 75 °C for 7 days in order to determine dry weights of leaves, stems, roots and grains. In addition, a Student's t test was used for statistical analysis. In order to compare regressions between sowing dates an F test was carried out (15)

Results and discussion

The natural day length for the June sowing was nearly 12.5 h during the first 40 DAS. Daylength gradually decreased to 11.5 h at physiological maturity (158 DAS). The January sowing daylength was approximately 11.5 h but increased later. At 47 DAS daylength was 12 h and at physiological maturity (168 DAS) it was around 12.5 h (2, 3). The average temperature was similar in both sowing dates throughout the life-cycle (17.8 °C, 17.3 °C in the June and January sowings respectively). However, for the June sowing temperatures were higher than for the January sowing during the first 77 DAS (figure 1). From this time until reaching maturity mean temperature of the June sowing decreased while mean temperature for the January sowing increased. Radiation was similar in both experiments (average 14.90 MJ/m²). Lower values were found to be related to days-precipitation days. Soil surface minimun temperature was lower for the first eighty days for the January sowing (figure 2).

Figure 1. Daily minimum and maximum temperatures during sowing on June 20, 1991 and January 21, 1992.

Seedling emergence for the January sowing was reached within six days after planting, while for June it occurred within five days. Corn cultivated in zones above 1 700 m takes around thirty days more to reach physiological maturity than cultivated corn in the lowlands plains (200 - 450 m) (8). Development was slower for the January sowing compared to the June sowing (table 1). Anthesis of the January sowing occurred at 721 ^ocd while for the June sowing it occurred a 705 ocd. This delay was reflected in the greater number of leaves formed during January (table 2). Lower minimum temperatures from sowing to tasseling are related to the greater number of leaves formed. However, the January sowing experienced higher minimum and maximum temperatures from tasseling to physiological maturity. This, however, did not accelerate the phenological events. On the contrary, the duration of phenological stages was longer (table 1).

Although temperature variations from cultivation to anthesis for both planting periods are similar, this minimum variation apparently influences the number of leaves. Average minimum and maximum temperatures for January were from 0.67 to 0.4 °C lower with respect to average minimum and maximum temperatures for the June sowing. These results fit those found by Warrington and Kanemasu (20) who, under controlled conditions, found a curvilinear relationship between the number of total leaves and temperature. For semi-tropical arid regions in Australia Muchow and

Figure 2. Soil temperature for first 80 days after sowing in June, 1991 and January, 1992.

Carberry (9) obtained a greater number of leaves for an August sowing with respect to sowing carried out in October and February. In their experiment minimum temperatures during the first 50 days of the August sowing were less than the minimum temperatures of the October and February sowing. For this study 2.5 more leaves were observed in the January sowing with a difference of 0.5 °C, while Muchow and Carberry (9) showed a 1.7 leaf diffe-rence for the Delkalb XL82 hybrid between August and February with a greater difference of temperature.

Table 1. Duration of phenological events (days and thermal time (°Cd)) of cultivar Santa Rosa sown at two differents dates. Thermal time and days estimated from emergence.

Table 2. Rate of leaf appearance (leaves/day)during four phases of leaf development and final leaf number for two sowing dates for cultivar Santa Rosa. Error indicates standard deviation.

On the other hand, the relationship between the number of leaves and the variation in temperature is a characteristic of the cultivar (17, 20), wich also depends on the daily minimum and maximum temperature variations of each region. Lower soil surface minimum temperatures registered during the first 45 DAS for the January sowing days (figure 2) probably have a greater effect on the number of leaves. This coincides with the temperature sensitive phase which influences the total number of leaves (17). For the June sowing, soil surface temperatures were similar to the minimum air temperatures (figure 1).

Leaf number and leaf appearance showed a curvilinear relationship with thermal time (figure 3), consistent with findings by Muchow and Carberry (9) for the semiarid tropical zone in Australia but not with findings by Manrique and Hodges (7) who encountered a linear relationship in Hawaii for the hybrid Pioneer X304C. Until the appearance of leaf number 12, for both trials, rates were maintained constant and did not present significant differences. From the twelfth leaf, rates were around 38 % faster. These variations are consistent with those found for hybrids in the field as well as laboratory conditions in temperate zones (16, 18). However Tollenaar et al. (18) found appearance rates to be 10 % lower from the third to the sixth leaf. Rates found for this study's cultivar were higher than those reported by Warington and Kanemasu (19) and Muchow and Carberry (9); that is, they were higher for the first twelve leaves as well as for the apppearance rate after the twelfth leaf. Depending on minimum and maximum temperature variation, the maximum appe-arance rate changes. Possibly such a variation will be exaggerated as differences between minimum and maximum temperatures increase.

The relationship between thermal time and leaf appearance rate on the cultivar has yet to be established. Equations which differentiate behaviors of leaf appearance rate should form part of growth models and corn phenology in order to take in account faster rates in the last formed leaves. F test showed no differences in linear or exponential regressions, although the fitted exponential regression has a standard error of estimate 10 times better for both sowings of Santa Rosa and all germplasms (table 3). For the relationship between thermal time and number of fully expended leaves (NEFL) the use of the exponential regression equation (NEFL = 1.16 exp (0.00245CTT), where CTT is cumulative thermal time (table 3) is advisable. The incorporation of this equation could improve the prediction of maize phenology for tropical areas. The equation found is similar to that of Muchow and Camberry (9) for maize in semiarid tropical zones in Australia.

Figure 3. Relation between expanded leaf number and accumulative thermal time from emergence in June and January sowing. Each point is an average of 15 plants selected.

Biomass accumulation and yield. Significant differences were not found in weight accumulation for expanded leaves, stalks (weight of the rest of the plant minus expanded leaves and grains), and roots (data no showed). Leaf weight for the final harvest was an exception although the differences were not significant for the two sowing dates (table 4). The number of grains per ear was not significantly different for the two sowing dates. A significant effect was not established between sowing time with production, number of grains and harvest index (HI). (table 4). The average production of both trials was 685 g/m². This is similar to production rates of other corn varieties grown at lower altitudes (between 60 - 500 m) where greater extensions were utilized for cultivating corn and where production was between 400 - 694 g/m2 (10,13,14). Although most of the sowing is done in the rainy season (April to October), the wide production range may be attributed to the availability of soil water which depends on unpredictable precipitation schedules. The number of ears of corn was relatively constant for both crop periods (1.6 ears/plant). This gives approximately 581 potential grains per plant. This value is high compared to other tropical hybrids (11, 8).

Table 4. Effect of sowing date on dry yield (g m^-2), grain number per ear and harvest index. (error indicates standard deviation). values with same letter are not significantly different at P = 0.05 according to Student's test.

Table 3. Regression analysis for linear and exponential models for June and January sowing of Santa Rosa germplasm.

Finally, the present work adds new information which may be included in corn growth and development models adapted to the characteristics of tropical genotypes. Furthermore, it demonstrates the need to develop a broader data base to elaborate coefficients more in line with the phenological characteristics which tropical varieties present.

Acknowledgements

The author gratefully acknowledges Lic. Fernando Castro, Eng. Ciro Dávila and their group of workers for their assistance in the field work at the IIAP station Santa Rosa. My appreciation also goes to researchers of the PAN EARTH project; Venezuela case study. This work was supported in part by the Universidad de Los Andes (CDCH-I328-90) and CONICIT (S1-2123)

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