Maize Shoot Growth Research Articles

Pre-emergent shoot growth of maize ( Zea mays, L.) as a function of soil strength

Poor crop establishment is a common problem in summer cropping regions. The physical environment predisposes seedbeds to high soil strength and temperature. It is frequently difficult, however, to determine the relative contributions of these stresses to emergence failure. Our capacity to determine the effect of soil strength is limited by: (a) a limited understanding of the effect of soil strength on pre-emergent shoot growth, and whether there is an interaction with soil temperature and (b) difficulty in measuring the mechanical stresses experienced by the pre-emergent seedling in a way that is applicable to a wide range of soils. We used a uniaxial compression cell to quantify the rate of shoot growth of maize as a function of soil strength (0 to 956 kPa), and to assess if temperature affected this relationship. Soil strength was calculated as spherical cavity expansion pressure, with field estimates taken from blunt penetrometer readings adjusted for soil friction. Coleoptile and first internode growth rates fell by more than 50% when strength increased from 0 to 118 kPa. By combining functions describing the strength dependence of shoot growth with functions developed previously to describe the temperature dependence of shoot growth, a model was developed to predict the response of shoot growth to strength at a range of temperatures. The model successfully predicted the outcomes of laboratory experiments where seedlings were grown at 118 kPa and exposed to diurnally varying temperatures in both the physiological temperature range (10–40°C) and at supra-maximum temperatures (> 40° C). This suggested that at low soil strengths, temperature did not interfere with the shoot growth response to strength. However, when seedbed strength increased to 174 kPa, and seedlings were exposed to supra-maximum temperatures, the model significantly overestimated first internode growth, suggesting that high temperature stress had reduced the expansion pressure of the first internode. Maize shoot growth in the laboratory was more than five times as sensitive to cavity expansion pressure, than in field measurements. One factor which may have contributed to this is the increase in second node width in response to high temperature and/or high strength. As a result, the theoretical analysis used may have underestimated the mechanical forces imposed on the elongating shoot.

Pre-emergent shoot growth of maize (Zea mays, L.) as a function of soil strength

Pre-emergent shoot growth of maize (Zea mays, L.) as a function of soil strength

Simulating Maize Emergence Using Soil and Climate Data

AbstractExperimental programs aimed at improving seedling establishment in the semiarid tropics require quantitative information concerning the interaction between the seedbed environment and preemergent seedling growth. The model here described links a soil heat and water model, a soil strength model, and a temperature‐dependent maize (Zea mays L.) shoot growth model to predict the response of preemergent maize seedlings to a physical environment typical of the semiarid tropics. In comparisons with field measurements taken in the semiarid tropics under high drying rate conditions, the model simulations yielded accurate representations of soil water, temperature, strength, and preemergent shoot growth of maize. The model was also used to compare the effects of radiation‐ vs. wind‐dominated evaporative demand on preemergent seedling growth in a hardsetting seedbed. Results showed that under radiation‐dominated conditions, the early onset of high soil temperature limited seedling growth, while under wind‐dominated conditions, the early development of high soil strength affected seedling growth first. Simulations using surface mulch as an ameliorative management practice showed that mulch greatly reduced soil evaporation, thereby eliminating high soil strength as a limitation to seedling establishment. Results indicate that the model is a potentially useful tool for investigating the likely effects of soil and climate on seedling emergence.

Modeling Preemergent Maize Shoot Growth: II. High Temperature Stress Conditions

AbstractHigh soil temperatures are a significant constraint to crop establishment. Exposure of preemergent maize (Zea mays L.) to temperatures in excess of 40°C stops shoot elongation and may also damage the seedling, reducing subsequent shoot growth in the physiological temperature range (9 to 40°C). At present, there is little quantitative understanding of the effects of high temperature stress on preemergent maize shoot growth. Consequently, existing maize emergence or preemergent maize shoot growth models are restricted to the physiological temperature range. The work described in this paper quantified the effect of supramaximum temperatures (temperatures greater than 40°C) on maize shoot growth, and in particular on its component parts, the coleoptile and first internode. The major impact of supramaximum temperatures on shoot growth was due to a severe reduction in the first internode growth rate, which was correlated with the maximum temperature reached during the day. We also found that, under diurnally varying temperature conditions, coleoptile growth ceased only at 45°C, rather than at 40°C as found previously in constant temperature experiments. Inhibition of shoot growth due to high temperature damage was alleviated when seedlings were grown in the physiological temperature range for 33 h. Based on these findings, a model was developed that can predict shoot growth of seedlings exposed to supramaximum temperatures. The model successfully predicted shoot growth of seedlings exposed to supramaximum temperatures as a part of the diurnal cycle. The model was unable, however, to predict seedling recovery from high temperature damage.

Modeling Preemergent Maize Shoot Growth: I. Physiological Temperature Conditions

AbstractPrediction of seedling emergence is an important first step in predicting crop establishment. There are numerous models that, under nonlimiting seedbed physical conditions, can adequately predict time to emergence using heat sums based on average daily temperatures. Under more adverse seedbed physical conditions, however, such as occur in the semiarid tropics, use of such coarse indices will tend to obscure the strong influence that even temporary extremes in soil temperature or strength can have on the time and extent of emergence, yet it is in these situations that final crop establishment and ultimately yield will be particularly sensitive to emergence predictions. One way to quantify the effect that temporary extremes in seedbed conditions have on emergence is to model the emergence process (namely, preemergent shoot growth). In this paper, we model preemergent maize (Zea mays L.) shoot growth as a first step in characterizing seedling response to a high soil temperature and strength environment. The model, developed from shoot length data obtained under constant temperature conditions ranging from 20 to 40°C, uses an exponential function that predicts coleoptile and first internode growth rates as a function of temperature and sums the output to predict shoot length. Comparison of model predictions with independent measurements carried out in the 20 to 40°C range show that the model is capable of accurately simulating preemergent shoot growth under conditions where (i) temperatures are constant with time, (ii) temperatures of the whole seedbed vary diurnally, and (iii) temperatures within the seedbed vary with time and depth in the seedbed. However, the model was unable to predict shoot growth in situations where seedlings had been exposed to temperatures in excess of 40°C, indicating that further work is needed to assist modeling within the high temperature range.

Effects of soil structural discontinuity on root and shoot growth and water use of maize

The role of roots penetrating various undisturbed soil horizons beneath loose layer in water use and shoot growth of maize was evaluated in greenhouse experiment. 18 undisturbed soil columns 20 cm in diameter and 20 cm in height were taken from the depths 30–50 cm and 50–70 cm from a Brown Lowland soil, a Pseudogley and a Brown Andosol (3 columns from each depth and soil). Initial resistance to penetration in undisturbed soil horizons varied from 2.5 to 8.9 MPa while that in the loose layer was 0.01 MPa. The undisturbed horizons had a major effect on vertical arrangement of roots. Root length density in loose layer varied from 96 to 126 km m-3 while in adjacent stronger top layers of undisturbed horizons from 1.6 to 20.0 km m-3 with higher values in upper horizons of each soil. For specific root length, the corresponding ranges were 79.4–107.7 m g-1 (on dry basis) and 38.2–63.7 m g-1, respectively. Ratios of root dry weight per unit volume of soil between loose and adjacent undisturbed layers were much lower than those of root length density indicating that roots in undisturbed horizons were produced with considerably higher partition of assimilates. Root size in undisturbed horizons relative to total roots was from 1.1 to 38.1% while water use from the horizons was from 54.1 to 74.0%. Total water use and shoot growth were positively correlated with root length in undisturbed soil horizons. There was no correlation between shoot growth and water use from the loose layers.

Preemergent Shoot Growth of Maize under Different Drying Conditions

AbstractPoor establishment of seedlings is a problem in semi‐arid cropping regions. High drying rates that are characteristic of these regions can result in the early onset of high soil strengths and high soil temperatures, which are detrimental to seedlings. In this study, we examined the response of preemergent shoot growth of maize (Zea mays L.) to differences in the drying rate of a hardsetting red‐brown earth (fine, mixed, thermic Typic Paleustalf or Calcic Luvisol). We examined the impact of high soil strength on the constituent shoot parts (coleoptile and first internode), and used a temperature‐based shoot‐growth model to separate the effects of soil temperature and soil strength on preemergent shoot growth.Preemergent shoot growth was sensitive to small differences in drying rate. Rapid drying resulted in no emergence, moderate drying in 52% emergence, and slow drying in 78% emergence. Soil strength impeded shoot elongation at a cone index of 1.1 MPa and, at 2 MPa, growth and emergence ceased. Differences in soil strength development reflected not just the total amount of water removed from the profile, but also the distribution of water remaining within the profile. Rapid drying quickly reduced soil water content near the surface and led to the immediate development of high soil strength there.Reduction in shoot elongation at high soil strengths was largely due to the sensitivity of the first internode. The coleoptile elongation rate showed no response to treatment differences in soil strength although twisting, buckling, and rupture was more prevalent at high soil strengths.

Effect of liming and micronutrient application on the growth and occurrence of sterility in maize and tomato plants in a Malaysian deep peat soil

Abstract Two field experiments were conducted in a deep woody peat soil located at Pontian in the south western part of Peninsular Malaysia to determine the effect of graded levels of liming with and without micronutrient application on the growth and performance of maize and tomato plants. The results obtained revealed that the growth of the maize and tomato plants was extremely poor in the unlimed treatment (pH 3.8 to 4.0). When micronutrients were applied, the growth was enhanced and the yield increased with the increase of the lime level and reached a maximum value at the lime level of 8 t/ha (pH 5.0 to 5.3) in both plants. There was no difference in the yield above the lime levels of 8 t/ha. When micronutrients were not applied, shoot growth of maize was enhanced with the increase of the lime level up to 8 t/ha in the same manner as in the treatments with micronutrient application. However, grain formation was inhibited while in the case of tomato the shoot growth was extremely inhibited and no fruit...

Gibberellins and Heterosis in Maize: Quantitative Relationships

To investigate the possible relationship between gibberellins (GA) and heterosis, a diailel from four elite maize, Zea mays L., inbreds (A632, B73, CH807 [from Mo17], and CO109) was studied under controlled environment conditions. Heterosis for plant growth was substantial at 25/15 °C (day/night), as hybrid seedlings emerged more rapidly, were taller, had heavier shoots, and larger leaf areas than the parental inbreds. Gibberellic acid (GA3) at 0.1, 0.5, or 1.0 mg per plant was pipetted into the leaf whorls of 14‐d‐old seedlings. The exogenous GA3 promoted ligule and total height in all genotypes, but the inbreds were maximally influenced. Consequently, potence ratios, representing the overall degree of dominance, were reduced from an average of 7.7 to 1.7 following GA3 application, indicating decreased heterosis. In an experiment at 15 °C, imbibition of seeds in GA3 accelerated germination and seedling growth, particularly shoot elongation of the parental inbreds. Endogenous concentrations of GA1 and GA19 were determined by gas‐chromatography‐selected ion monitoring using [2H]GAs as quantitive internal standards. Highly significant regressions of height, leaf area, relative growth rate, and height increment versus the log of GA concentration were observed. These results are consistent with the theory that GA are one factor involved in the regulation of heterosis of shoot growth in maize, a theory that suggests that a partial deficiency in endogenous GA in maize inbreds limits their growth, and is a contributing cause of inbreeding depression.

Gibberellins: A Phytohormonal Basis for Heterosis in Maize

Four commercially important maize parental inbreds and their 12 F(1) hybrids were studied to investigate the role of the phytohormone gibberellin (GA) in the regulation of heterosis (hybrid vigor). All hybrids grew faster than any inbred. In contrast, all inbreds showed a greater promotion of shoot growth after the exogenous application of GA(3). Concentrations of endogenous GA(1), the biological effector for shoot growth in maize, and GA(19), a precursor of GA(1), were measured in apical meristematic shoot cylinders for three of the inbreds and their hybrids by gas chromatography-mass spectrometry with selected ion monitoring; deuterated GAs were used as quantitative internal standards. In 34 of 36 comparisons, hybrids contained higher concentrations of endogenous GAs than their parental inbreds. Preferential growth acceleration of the inbreds by exogenous GA(3) indicates that a deficiency of endogenous GA limits the growth of the inbreds and is thus a cause of inbreeding depression. Conversely, the increased endogenous concentration of GA in the hybrids could provide a phytohormonal basis for heterosis for shoot growth.

The effect of compaction of the arable layer in sandy soils on the growth of maize for silage. 1. Critical matric water potentials in relation to soil aeration and mechanical impedance.

A new approach in defining the range of soil structure for optimal maize production is proposed. The effect of different degrees of compaction of ploughed sandy soils on soil aeration and mechanical impedance and on root and shoot growth of maize was tested in 5 model field experiments in the eastern Netherlands. In this first paper the effects on soil aeration and penetration resistance are described. The narrower the range of matric water potentials which allow unimpeded root growth, the greater the potential risks for plant growth and the greater the need for a controlled supply of water. Soil structures which substantially impede root growth even at the most favourable water potential are classified as dangerous. (Abstract retrieved from CAB Abstracts by CABI’s permission)