G.A. Maddonni

Plant population density, row spacing and hybrid effects on maize canopy architecture and light attenuation

Abstract Light attenuation within a row crop such as maize is influenced by canopy architecture, which has to be defined in terms of the size, shape and orientation of shoot components. Cultural practices that improve the efficiency of light interception affect canopy architecture by modifying such components. Our objectives were to: (i) determine the nature and timing of leaf growth responses to plant population and row spacing; (ii) analyze light attenuation within fully developed maize canopies. Field experiments were conducted at Pergamino (33°56′S, 60°34′W) and Salto (34°33′S, 60°33′W), Argentina, during 1996/1997 and 1997/1998 on silty clay loam soils (Typic Argiudoll) that were well watered and fertilized. Four maize hybrids of contrasting plant type were grown at three plant populations (3, 9 and 12xa0plantsxa0m −2 ) and two row spacings (0.35 and 0.70xa0m). Plant population promoted larger changes in shoot organs than did row spacing. As from early stages of crop growth, leaf growth (V 6 –V 8 ) and azimuthal orientation (V 10 –V 11 ) were markedly affected by treatments. Modifications in shoot size and leaf orientation suggest shade avoidance reactions, probably triggered by a reduction in the red:far-red ratio of light within the canopy. An interaction between hybrid and plant rectangularity on leaf azimuthal distribution was determined, with one hybrid displaying a random azimuthal leaf distribution under most conditions. This type of hybrid was defined as rigid . The other hybrids showed modified azimuthal distribution of leaves in response to plant rectangularity, even at very low plant populations. These hybrids were defined as plastic . Once maximum leaf area index (LAI) was attained light attenuation did not vary among hybrids and row spacing for plant populations ≥9xa0plantsxa0m −2 ( k coefficient: 0.55 and 0.65 for 9 and 12xa0plantsxa0m −2 , respectively). A more uniform plant distribution increased light attenuation ( k coefficient: 0.37–0.49) only when crop canopies did not reach the critical LAI.

Leaf senescence in maize hybrids: plant population, row spacing and kernel set effects

Abstract Maize crop management involves decision making on several cultural practices aimed to maximize grain yield, like plant population and row spacing. These practices affect the light environment perceived by plants and the post-flowering source–sink ratio, but there is scarce information on the way they influence plant leaf senescence. The objectives of our research were to: (i) characterize the development of leaf area senescence for contrasting canopy architectures (i.e. plant population×row spacing), and (ii) analyze the response of leaf senescence to changes in the light environment and the post-flowering source–sink ratio. Field experiments were conducted in Argentina between 1997/1998 and 2000/2001. Four hybrids were grown at a wide range of plant populations (3, 9, 10 and 12xa0plantsxa0m−2), row spacings (0.35, 0.7 and 1xa0m) and pollination treatments (natural and restricted pollination). Senescence development was well described (r2=0.61–0.99,P

Maize Leaves Turn Away from Neighbors

In commercial crops, maize (Zea mays) plants are typically grown at a larger distance between rows (70 cm) than within the same row (16–23 cm). This rectangular arrangement creates a heterogeneous environment in which the plants receive higher red light (R) to far-red light (FR) ratios from the interrow spaces. In field crops, the hybrid Dekalb 696 (DK696) showed an increased proportion of leaves toward interrow spaces, whereas the experimental hybrid 980 (Exp980) retained random leaf orientation. Mirrors reflecting FR were placed close to isolated plants to simulate the presence of neighbors in the field. In addition, localized FR was applied to target leaves in a growth chamber. During their expansion, the leaves of DK696 turned away from the low R to FR ratio signals, whereas Exp980 leaves remained unaffected. On the contrary, tillering was reduced and plant height was increased by low R to FR ratios in Exp980 but not in DK696. Isolated plants preconditioned with low R/FR-simulating neighbors in a North-South row showed reduced mutual shading among leaves when the plants were actually grouped in North-South rows. These observations contradict the current view that phytochrome-mediated responses to low R/FR are a relic from wild conditions, detrimental for crop yield.

Intra-specific competition in maize: early establishment of hierarchies among plants affects final kernel set

Abstract Reduced plant biomass and increased plant-to-plant variability are expected responses to crowding in monocultures, but the underlying processes that control the onset of interplant interference and the establishment of hierarchies among plants within a stand are poorly understood. We tested the hypothesis that early determined plant types (i.e. dominant and dominated individuals) are the cause of the large variability in final kernel number per plant (KNP) usually observed at low values of plant growth rate (PGR) around silking in maize ( Zea mays L.). Two hybrids (DK696 and Exp980) of contrasting response to crowding were cropped at different stand densities (6, 9 and 12xa0plantsxa0m −2 ), row spacings (0.35 and 0.70xa0m), and water regimes (rainfed and irrigated) during 1999/2000 and 2001/2002 in Argentina. The onset of interplant competition started very early during the cycle, and significant differences ( P 4–6 (DK696) and V 6–7 (Exp980). Plant population and row spacing treatments did not modify the onset of the hierarchical growth among plants, but did affect ( P −2 (ca. 0.12xa0g/g per 100xa0°Cxa0day) than at 6xa0plantsxa0m −2 (ca. 0.07xa0g/g per 100xa0°Cxa0day). For all treatments, the largest difference in estimated shoot biomass between plant types took place between 350 (V 7 ) and 750xa0°C day (V 13 ) from sowing, and remained constant from V 13 onwards. Dominant plants always had more kernels per plant ( P P −2 . Our research confirmed the significant ( P P 3 ) reflected the variation in KNP ( r 2 ≥0.62), and was significantly ( P 13 ). This response suggested that the physiological state of each plant at the beginning of the critical period had conditioned its reproductive fate. This early effect of plant type on final KNP seemed to be exerted through current assimilate partitioning during the critical period.

Leaf area, light interception, and crop development in maize

Few models used to estimate the fraction of photosynthetically active radiation intercepted by maize crops (fIPAR) as a function of leaf area index (LAI) account for genotype differences and ontogenetic stage. In this study, the development of the fIPAR/GLAI relationship of three maize hybrids having contrasting plant type and grown in different environmental conditions was characterized. Three field experiments were conducted at Rojas (34°08′S), Argentina, on a silty clay loam soil, without nutrient restriction. The effects of sowing date and water regime were tested. Plant density was always 7 plants m−2. The fIPAR was calculated from measurements above and below the canopy, before and after maximum GLAI was attained. Hybrids differed significantly (P 0.77; n ≥ 15) the fIPAR/GLAI relationship for pre-maximum GLAI data of all hybrids. Nevertheless, maximum fIPAR was always below values quoted in the literature (< 0.90), and differences were detected among hybrids in the attenuation coefficient (k) that were probably related to leaf angle and leaf area. For hybrids with a similar leaf angle at all leaf positions no difference existed in the fIPAR/GLAI relationship along the cycle (pre- and post-maximum GLAI). The relationship changed after tasselling for the hybrid with erect upper leaves. Ignoring such differences could be misleading when fIPAR/GLAI models are used to estimate canopy photosynthesis and hence biomass production, radiation-use efficiency, and kernel set of specific hybrids and growth stages.

Light interception of contrasting azimuth canopies under square and rectangular plant spatial distributions: simulations and crop measurements

Abstract Several studies have considered maize canopy as a homogeneous medium with a random leaf orientation distribution. Recent studies, however, have detected that maize leaf orientation in the horizontal plane (i.e., leaf azimuth distribution) can react filling empty spaces (e.g., intra-row or inter-row) due to plant spatial arrangement. “Rigid” genotypes present a random distribution of leaf azimuth, independent of planting pattern. “Plastic” genotypes have the ability to modify leaf orientation. They generally present a random leaf azimuth distribution under square planting patterns, but tend to align their leaves perpendicularly to the row direction under rectangular planting patterns. We used three-dimensional models to reconstruct canopy architecture, mimicking these two behaviors. We simulated mid-day (maximum sun elevation 79.4° and 65.3°) and daily light interception of fully developed canopies at various plant densities (3, 9 and 12xa0plantsxa0m−2) and row spacings (0.35 and 0.70xa0m), and compared the results of these simulations with data from a field experiment. Simulations and field measurements showed that canopy behavior (plastic or rigid) has a significant (P

Grain yield components in maize: II. Postsilking growth and kernel weight

Maize kernel weight (KW) results from kernel growth during two stages of grain filling, the lag phase (formative period) and the effective grain-filling phase. Environmental conditions may affect kernel biomass accumulation in each phase. This work analyzed: (1) changes in duration and rate of kernel growth on a thermal time (°C day) basis; and (2) KW response to postsilking biomass production kernel−1 (source:sink ratio). Sowing date, plant population, and nitrogen fertilization experiments were conducted in France and Argentina to induce changes in assimilate availability per kernel. Hybrids of different KW were tested. Hybrids differed in the duration of the lag phase, which determined kernel growth rate during the effective grain-filling period for hybrids with similar grain-filling duration (ca. 745°C day). Environments with low air temperature ( 300 mg) with reduced kernel number (2800 to 4000 kernels m−2). For the former, grain yield increments should not be based on increased kernel number but on increased biomass production.

Crop water stress index of three maize hybrids grown in soils with different quality

Maize production in Argentina is obtained mostly under dryland conditions and grain yield is highly related to water availability around silking. Drought, and differences in soil quality caused by intensive land use, sometimes limit water availability for the crop. Field experiments were performed on silty clay loam soils in the temperate humid region of Argentina (32° to 35°S, 58° to 62°W), to (i) validate a methodology to determine maize water stress (Crop water stress index, CWSI), (ii) describe the behavior of CWSI along the crop cycle of three maize hybrids growing in environments with different soil quality, and (iii) establish the effect of soil quality and hybrids on the relationship between CWSI and available soil water. The CWSI methodology was satisfactorily validated. Crop water stress increased along the growing season in all environments and hybrids. No interactions between soil quality and hybrid on CWSI were found. The effect of soil quality on CWSI did not present a single and clear trend. Differences between hybrids in CWSI were detected. A relationship between CWSI and available soil water was fitted for all hybrids and environments (r2 = 0.52, n = 51, P < 0.001). The threshold below which crops presented symptoms of water stress was 60% of available soil water.

Modeling grain yield and grain yield response to nitrogen in spring wheat crops in the Argentinean Southern Pampa

Agronomic efficiency (kg grain yield kg−1 N applied) is conditioned by environmental factors and nitrogen availability during the growing period. Hence, a fertilization model that considers environmental factors affecting wheat crop growth and effective N supply should be based on crop N demand. In this work, a simple model based on N balance during the growing season is used as the frame to simulate both the demand and the availability of N, and to determine grain yield. Fertilization experiments were conducted under different environments (50 sites, 8 y) of the Southern Pampa of Argentina. Nitrogen fertilization rates ranged between 25 and 125 kg N ha−1. Soil initial conditions and water balance during the crop cycle were found to modify both N demand and soil N supply. The amount of N taken up by crops, water balance during the crop growth period and mean maximum temperature during grain filling, all affected grain yield components. The proposed model provided a good agreement between observed independent data sets and simulated values of grain yield (root mean square error = 9% of the mean value). Model operation was performed for one site within the region using climatic records to estimate annual grain yield variability under three levels of N availability.

Analysis of the climatic constraints to maize production in the current agricultural region of Argentina—a probabilistic approach

A simple method of analysis was proposed to characterize the impact of climatic conditions of a wide region of Argentina (from 27°05′S to 35°48′S, from 61°5′W to 64°21′W) on potential maize (Zea mays L.) grain yield, and the occurrence of various climatic constraints (low temperatures and low soil water content, frost, drought stress and heat stress) along the cycle. The analysis was based on previous studies of the eco-physiology of maize crops and the use of climatic records of six locations in the region under study. Results were analyzed using a probabilistic method, later organized as a checklist to consider when deciding on sowing date in a location of the region. Thus, for each production scenario (combination of location and sowing date), farmers would have a tool enabling them to pay particular attention to the restrictions more likely to occur, to include some cultural practices to avoid or mitigate the most severe climatic constraint to maize production.