No abstract
High population densities have been proposed as one way of achieving earlier maturity in cotton (Gossypium hirsutum L.) by increasing the potential number of early fruiting points. But competition among closely spaced plants may adversely affect initiation and set of fruit. Theoretically, competition can be reduced by improving the uniformity of plant distribution. A year field study was conducted to determine the morphological and agronomic reactions of cotton to intraspecific competition over a wide range of plant populations within equidistant spacing configurations. Response to equidistant plant spacing was studied using two genotypes of upland cotton (Gossypium hirsutum L.) with contrasting plant types and five population densities ranging from 38,750 to 620,000 plants/ha in patterns where distance between plants within the row equaled the distance between rows. Vegetative and fruiting components were measured and dry weight determinations were made after destructive fractionation at three harvest dates. Yield, earliness, and fiber quality data were accumulated from weekly harvests of mature bolls. As plant population increased, dry weight per unit land area of all plant components increased except vegetative branches, which decreased. Leaf area index and the number of nodes to the first fruiting branch also increased with higher populations. A smaller, more compact plant developed as plant density increased, which was indicated by reductions in plant height, stem diameter, and number of branches. Boll size, number of seed/boll, seed index, and lint index were all reduced as plant spacing decreased. Retention rate of fruiting forms was apparently much lower in the very high plant densities. Population levels of 79,000 and 155,000 plants/ha were earlier maturing and produced higher lint yield than population levels on either side of this range. These results generally agree with those of investigations of cotton spaced in 1‐m rows. There was no evidence that high population densities in equidistant spacing patterns improve earliness or yield.
Crambe (Crambe abyssinica Hochst. ex R.E. Fries) is a potential oilseed crop for semiarid and arid environments where saline irrigation waters and soils are common. Crambe tolerance to salinity during germination is unknown. A laboratory experiment was designed to determine salinity tolerance of crambe during germination and salinity ✕ temperature interactions that may influence germination and stand establishment. Treatment solutions were prepared using NaCl and CaCl2 in a 2:1 molar ratio. Salinity (electrical conductivities of 0.03, 6.3, 12.1, 17.3, 22.5, 27.1, 32.0 and 36.3 dS m−1) and temperature (5, 10, 15, 20, 25 and 30 °C) effects on germination of ‘Meyer’ crambe seed were determined over a 12 d period. Counts were taken at 3 d intervals and germination percentages and rate indexes were determined. Germination declined with increasing salinity at each counting date and salinity ✕ temperature interactions were highly significant. Germination was severely limited at 5 °C with only 22% germination in the salinity control (0.03 dS m−1) after 12 d. The optimum germination temperature for all salinity levels fell in the 15 to 25 °C range, with the final cumulative germination percentage peaking at 20 °C for most treatments. Germination decreased on either side (10 and 30 °C) of the optimum. Germination rate was drastically reduced at 5 °C at all salinity levels, with an intermediate effect at 10 and 30 °C at the lower salinity levels decreasing with increasing salinity at all temperatures. These results suggest that crambe is moderately tolerant to salinity stress during germination over the 10 to 30 °C temperature range.
Alterations of plant architecture in narrow‐row cotton (Gossypium hirsutum L.) using management and genetic strategies to improve light penetration into the canopy may increase crop yields. The objective of this study was to quantify how plant architecture changes affect light penetration into the canopy, yield, and yield components of narrow‐row cotton. The study was conducted on a Glendale clay loam soil (fine montmorillonitic, thermic Typic Torrert). Two field experiments were established on 0.76‐m rows in 1995 and 1996. Treatments consisted of the following plant architecture modifications: pruning leaves throughout the canopy, mechanical topping, trimming of branches, and temporarily opening the canopy during boll production. Photosynthetic photon flux density (PPFD) interception and PPFD penetration into the canopy were measured when the canopy was fully developed. Seed‐cotton yield and yield components by plots, fruiting positions, and strata by four main‐stem node groups were obtained. Early canopy modifications simulating plant characteristics such as reduced plant height, short branches, and modified leaf shape increased light availability at the medium and upper part of the canopy. Modified canopy treatments grown at 97 000 plants ha−1 reached high PPFD interception (90–97%), with leaf area index from 3.7 to 5.2. Treatments to increase light distribution in the canopy while maintaining a high PPFD interception increased seed‐cotton yield by 34% due to a 26% increase in number of bolls per square meter. A canopy light environment improved during the first 3 wk after canopy closure (86–107 d after sowing) increased number of bolls per square meter by 33%.
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