Four New Planets Orbiting Metal-enriched Stars

Peer reviewe

Spatial variation in the effects of size and age on reproductive dynamics of common coral trout Plectropomus leopardus

The effects of size and age on reproductive dynamics of common coral trout Plectropomus leopardus populations were compared between coral reefs open or closed (no-take marine reserves) to fishing and among four geographic regions of the Great Barrier Reef (GBR), Australia. The specific reproductive metrics investigated were the sex ratio, the proportion of vitellogenic females and the spawning fraction of local populations. Sex ratios became increasingly male biased with length and age, as expected for a protogyne, but were more male biased in southern regions of the GBR (Mackay and Storm Cay) than in northern regions (Lizard Island and Townsville) across all lengths and ages. The proportion of vitellogenic females also increased with length and age. Female P. leopardus were capable of daily spawning during the spawning season, but on average spawned every 4·3 days. Mature females spawned most frequently on Townsville reserve reefs (every 2·3 days) and Lizard Island fished reefs (every 3·2 days). Females on Mackay reefs open to fishing showed no evidence of spawning over 4 years of sampling, while females on reserve reefs spawned only once every 2–3 months. No effect of length on spawning frequency was detected. Spawning frequency increased with age on Lizard Island fished reefs, declined with age on Storm Cay fished reefs, and declined with age on reserve reefs in all regions. It is hypothesized that the variation in P. leopardus sex ratios and spawning frequency among GBR regions is primarily driven by water temperature, while no-take management zones influence spawning frequency depending on the region in which the reserve is located. Male bias and lack of spawning activity on southern GBR, where densities of adult P. leopardus are highest, suggest that recruits may be supplied from central or northern GBR. Significant regional variation in reproductive traits suggests that a regional approach to management of P. leopardus is appropriate and highlights the need for considering spatial variation in reproduction where reserves are used as fishery or conservation management tools

Zone production system for cotton: soil response

In a three-year study, the major advantage of a zone cotton production system with controlled traffic was determined to be reduction in tractor operations for field preparation and crop management without a reduction in yield. The study indicates that tillage is required under any surface where wheels are operated to return the soil to a low impedance for root exploration and to a conductive state for water infiltration. However, the soil managed with a zone system, with no traffic or tillage after initialization, was stable with lower soil impedance and higher water infiltration than soil in tilled and trafficked plots. Adoption of these findings will reduce unit production costs

Bulk density of a sandy loam: traffic, tillage, and irrigation method effects

Modern crop production creates a cycle between soil compaction caused by traffic and alleviation of this condition by tillage or natural processes such as freezing and thawing. The objective of this study was to evaluate important management practices as they relate to changes in bulk density of a tilled sandy loam soil. Practices evaluated were irrigation method, time between tillage and traffic, tire pressure and wheel load of applied traffic, and controlled traffic. Relationships among bulk density, penetration resistance, and infiltration rate were determined. Experiments were conducted in the San Joaquin Valley of California, on a sandy loam soil (Entisol) with an organic-matter content of <1%. After tillage, settling and trafficking of a soil resulted in rapid changes in its bulk density until a new equilibrium was reached. Tire pressure of 408 kPa and wheel weight of 2724 kg applied at moisture contents near field capacity resulted in a bulk density of 1.92 Mg m-3 , compared with a value of 1.67 for no traffic. The time interval between tillage and traffic did not affect final bulk density. Drip irrigation, which did not saturate the soil, resulted in a bulk density of ?0.1 Mg m-3 lower than flood irrigation, which saturated the soil surface. Wheel traffic in the furrow resulted in only small changes in the bulk density within the row. When tillage did not occur between cropping seasons, traffic caused high bulk densities in the furrow but only small changes in the row. An increase in bulk density from 1.7 to 1.89 Mg m-3 decreased the infiltration rate by four times and increased resistance to penetration at the end of the season by three times. Knowledge of how management practices affect bulk density can aid growers in reducing recompaction following tillage

Fine root development of alfalfa as affected by wheel traffic

Root development in alfalfa (Medicago satire L.) is dependent of many factors including the soil environment which is influenced by crop management procedures. Soil compaction, which is unavoidable under current management procedures, can have a detrimental effect on root development. The purpose of this field experiment was to compare the effects of controlled and conventional traffic management on alfalfa fine root growth in a Wasco sandy loam (coarse-loamy, mixed, nonacid thermic Typic Torriorthent). No wheel traffic and traffic only before planting were compared to two conventional systems that varied in the amount of traffic applied during crop production. Twenty months after planting, there was a significant decrease in fine root density (FRD) from single passes of traffic after each harvest down to a 0.45-m depth while several passes after each harvest significantly decreased FRD down to 1.8-m depth. Regardless of treatment, root density was greatest in the upper 0.1 m of soil decreasing to 1.8 m in the first summer. By the second summer FRD showed bimodal distribution with significantly fewer roots at 0.3 to 0.6 m compared to layers above and below this depth. Seasonally there was a significantly higher root density during the winter than the summer in the upper 0.3 m of soil. The results of this study shows that alfalfa fine roots more thoroughly exploit the soil volume in the absence of wheel traffic and that compaction from traffic diminished root growth to different depths depending on its intensity

Alfalfa yield as affected by harvest traffic and soil compaction in a sandy loam soil

Harvesting alfalfa (Medicago saliva L.) results in plants being subjected to traffic at different times during the growth cycle with equipment having different wheel sizes and loads. The affect of this traffic could have important ramifications on yield. The objectives of this study were to determine the long-term effects of harvest traffic and soil compaction on alfalfa yield. In the first experiment, two conventional traffic systems were compared to alfalfa production with no traffic. A single traffic event, that covered 100% of the plot area 3 to 5 d after each swathing, compared to no traffic significantly decreased yield by 20% in the 1st yr, 16.5% in the 2nd yr, 14% in the 3rd yr, with no significant difference the 4th yr. There was no difference in total yield between nontrafficked and a typical grower's traffic pattern the 1st yr, but in the succeeding 3 yr there was a 5 to 17% reduction. The effects of soil compaction and harvest traffic on yield were separated in the second experiment. Alfalfa grown in moderately and heavily compacted soil had a 12 and 26% decrease respectively in seasonal total yield compared to the yield from plants grown in noncompacted soil the 1st yr. Annual yields were the same regardless of the degree of soil compaction in the 3rd yr. When harvest traffic was applied to alfalfa grown in extremely compacted soil there was an additional decrease in yield. It was not statistically significant the 1st yr, but in the following 2 yr, 1987 and 1988, yield was significantly reduced by 17.8 and 19.1%, respectively. Alfalfa yields were significantly reduced both by harvest traffic and compacted soil. To achieve optimum long-term alfalfa yields compacted soil must be tilled before planting and operations that reduce the area of the field subjected to traffic must be implemented

Alfalfa (Medicago sativa L.) water use efficiency as affected by harvest traffic and soil compaction in a sandy loam soil

Traffic during alfalfa harvest operations can cause soil compaction and damage to newly growing stems. Root exploration for soil water and nutrients, forage growth dynamics, and final yield can all be affected. The objectives of this study were to determine the long-term effects of harvest traffic and soil compaction on water-use efficiency (WUE) of alfalfa grown in a Wasco sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents). Alfalfa was planted into tilled soil and managed with or without harvest traffic. Plants subjected to traffic during harvest had a significantly lower WUE two out of the three years studied compared to plants that were never subject to traffic. The second experiment examined whether planting alfalfa into compacted soil and managed with or without harvest traffic altered WUE. Soil compaction had no affect on alfalfa WUE. It was significantly lower when grown in compacted soil and subjected to harvest traffic. It is suggested that the decrease in WUE caused by harvest traffic may be explained by plants allocating carbohydrates to damaged shoots and crowns instead of to above ground forage production. The area of the field affected by harvest traffic, which damages newly growing stems, should be minimized to increase crop water use efficiency

Root-zone mineral nitrogen changes as affected by crop sequence and tillage

Crop sequence and tillage affect soil mineral N (NH4 plus NO3) and NO3 leaching below the root zone following alfalfa (Medicago sativa L.). A 2-yr field experiment was conducted in south-central Idaho to determine the effect on soil NO3 levels of a corn (Zea mays L.)- wheat (Triticum aestivum L.) rotation compared with a bean (Phaseolus vulgaris L.)-bean rotation and to demonstrate improved N utilization with a corn-wheat rotation. Alfalfa, growing on an irrigated Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid), was killed in October 1989 with herbicide. Treatments were: (i) BT-BT: conventional tilled bean grown in 1990 and 1991; (ii) CNT-WNT: no-till silage corn grown in 1990, and no-till winter wheat grown in 1990-1991; and (iii) CT-WT: same as CNT-WNT but under conventional tillage. Similar amounts of soil N were mineralized the first (275 kg N ha-1) and second (213 kg N ha-1) year after killing the alfalfa in all treatments. The BT-BT treatment had the highest growing-season soil mineral N (up to 251 kg ha-1, 0-0.45-m depth) because the N uptake by bean was lower (187 kg N ha-1) than corn (252 kg N ha-1, average of CT-WT and CNT-WNT treatments) in 1990 and later than winter wheat uptake in 1991. Most wheat N uptake had occurred by late June when bean uptake was just starting. A rotation that follows alfalfa with corn or a crop with a similar N uptake pattern, instead of bean, will save N fertilizer, lower soil NO3 levels, and reduce NO3 leaching potentia

Changes in infiltration under alfalfa as influenced by time and wheel traffic

Infiltration rates were measured for alfalfa, (Medicago saliva L., cv. WL514) subjected to treatments where wheel traffic was varied in terms of area covered and time of application on a Wasco sandy loam (coarse-loamy, mixed, nonacid thermic Xeric Torriorthent). Traffic treatments were (i) No-traffic, (ii) Preplant, (iii) Repeated, and (iv) traffic similar to what a grower would apply. Infiltration rates increased for all treatments, with increases being 240% for treatments without harvest traffic and 140% for treatments with harvest traffic Increases in infiltration were related to decreases in stand density. Slight packing (traffic) applied before the soil was flood-irrigated in 1983 increased infiltration rates 20% compared to flooding loosened soil (no traffic). Harvest traffic resulted in slower water movement in the soil

Infiltration rate as affected by an alfalfa and no-till cotton cropping system

Previous studies measured a long-term increase in infiltration rate in a sandy loam soil with time when alfalfa (Medicago saliva L., cv. WL514) was grown. Cotton (Gossypium hirsutum L.) was direct-planted into alfalfa to determine if the high infiltration rates measured under alfalfa culture could be maintained in cotton under either a till or no-till system. Treatments were no-till or tillage to the 0.15 - m depth just before the cotton was planted. Prior compaction levels created by harvest traffic applied to the alfalfa made the soil loose or compacted. Cotton was planted flat and irrigated as a basin. Infiltration rates measured 2 h after water was applied and averaged for the season were 101 (no-till, loose), 56 (till, loose), 82 (no-till, compacted), and 42 mm/h (till, compacted). All the infiltration rates were much higher than normally measured for cotton in these soils. Water flow in the 5-yr-old alfalfa was determined to be mainly through the soil macropore system. High infiltration rates measured in the no-till cotton were also probably the result of flow through the macropores