Gas exchange characteristics of wheat stands grown in a closed, controlled environment     

Wheeler RM  Corey KA  Sager JC  Knott WM 《Crop science》1993,33(1):161-168

Information on gas exchange of crop stands grown in controlled environments is limited, but is vital for assessing the use of crops for human life-support in closed habitats envisioned for space. Two studies were conducted to measure gas exchange of wheat stands (Triticum aestivum L. cv. Yecora Rojo) grown from planting to maturity in a large (20 m2 canopy area), closed growth chamber. Daily rates of dark-period respiration and net photosynthesis of the stand were calculated from rates of CO2 build-up during dark cycles and subsequent CO2 drawdown in the light (i.e., a closed-system approach). Lighting was provided as a 20-h photoperiod by high-pressure sodium lamps, with canopy-level photosynthetic photon flux density (PPFD) ranging from 500 to 800 micromoles m-2 s-1 as canopy height increased. Net photosynthesis rates peaked near 27 micromoles CO2 m-2 s-1 at 25 d after planting, which corresponded closely with stand closure, and then declined slowly with age. Similarly, dark-period respiration rates peaked near 14 micromoles CO2 m-2 s-1 at 25 d and then gradually declined with age. Responses to short-term changes in irradiance after canopy closure indicated the stand light compensation point for photosynthesis to be near 200 micromoles m-2 s-1 PPFD. Tests in which CO2 concentration was raised to approximately 2000 micromoles mol-1 and then allowed to draw down to a compensation point showed that net photosynthesis was nearly saturated at > 1000 micromoles mol-1; below approximately 500 micromoles mol-1, net photosynthesis rates dropped sharply with decreasing CO2. The CO2 compensation point for photosynthesis occurred near 50 micromoles mol-1. Short-term (24 h) temperature tests showed net photosynthesis at 20 degrees C > or = 16 degrees C > 24 degrees C, while dark-period respiration at 24 degrees C > 20 degrees C > 16 degrees C. Rates of stand evapotranspiration peaked near Day 25 and remained relatively constant until about Day 75, after which rates declined slowly. Results from these tests will be used to model the use of plants for CO2 removal, O2 production, and water evaporation for controlled ecological life support systems proposed for extraterrestrial environments.  相似文献   

Potato growth and yield using nutrient film technique (NFT)     

Raymond M. Wheeler  C. Ross Hinkle  Cheryl L. Mackowiak  John C. Sager  William M. Knott 《American Journal of Potato Research》1990,67(3):177-187

Potato plants, cvs Denali and Norland, were grown in polyvinyl chloride (PVC) trays using a continuous flowing nutrient film technique (NFT) to study tuber yield for NASs Controlled Ecological Life Support Systems (CELSS) program. Nutrient solution pH was controlled automatically using 0.39M (2.5% (v/v) nitric acid (HNO₃), while water and nutrients were replenished manually each day and twice each week, respectively. Plants were spaced either one or two per tray, allotting 0.2 or 0.4 m² per plant. ALl plants were harvested after 112 days. Denali plants yielded 2850 and 2800 g tuber fresh weight from the one- and two-plant trays, respectively, while Norland plants yielded 1800 and 2400 g tuber fresh weight from the one- and two-plant trays. Many tubers of both cultivars showed injury to the periderrn tissue, possibly caused by salt accumulation from the nutrient solution on the surface. Total system water usage throughout the study for all the plants equaled 709 liters (L), or approximately 2 L m^-2 d^-1 (7.2 mmol m^-2d^-l). Total system acid usage throughout the study (for nutrient solution pH control) equaled 6.60 L, or 18.4 ml m^-2 d^-1 (7.2 mmol m^-2d^-l). The results demonstrate that continuous flowing nutrient film technique can be used for tuber production with acceptable yields for the CELSS program.  相似文献   

An unusual outbreak of contagious ovine ecthyma   总被引：1，自引：0，他引：1  

CD HAWKINS  TM ELLIS  MK DAVIES  RL PEET  J. PARKINSON 《Australian veterinary journal》1991,68(6):210-211

  相似文献   

A STUDY OF THE EPIDEMIOLOGY OF ANAPLASMA MARGINALE INFECTIONS OF CATTLE IN SOUTHERN QUEENSLAND: CLINICAL DISEASE AND THE PREVALENCE OF COMPLEMENT FIXING ANTIBODIES     

R J Rogers  G W Blight  S G Knott 《Australian veterinary journal》1978,54(3):115-120

SUMMARY A total of 386 clinical outbreaks of anaplasmosis were confirmed in Queensland south of the 22nd parallel over the period 1967 to 1976. Seventy-eight per cent of these outbreaks occurred during autumn and winter and only 6.8% involved cattle less than 1 year of age compared with 54.8% for cattle more than 3 years old. Dairy breeds were involved in 48.1% of 258 outbreaks compared with 51.9% for beef breeds. Bos taurus beef breeds were involved in 90.7% of 118 outbreaks compared with 9.3% for Bos indicus crossbreds. Approximately 3 times as much clinical disease per head of population was confirmed in tick (Boophilus microplus) infested southern Queensland south of the 25th parallel (south zone) than in areas between the 25th and 22nd parallel (north zone). A survey was conducted during 1975 in which 3,810 cattle from 241 herds were sampled on the basis of the distribution of the cattle population. The prevalence of CF reactors in tick-infested areas was 42.1% of 3,026 samples compared with 0.4% of 784 samples from tick-free areas. The prevalence in the north zone was 52.3% compared to 30.2% for the south zone and it also varied with the type of animal sampled. The prevalence in Bos taurus cattle was significantly greater than in Bos indicus types and it increased with age of the animal. No significant difference in susceptibility to infection attributable to sex could be demonstrated. Animals exposed to heavy to medium tick infestations had significantly more CF reactors than those exposed to light infestation. Higher stocking densities were associated with higher prevalence levels. Thus anaplasmosis is predominantly a disease of autumn and winter and of cattle greater than 1 year of age. Both clinical and subclinical infection occur only in tick-infested areas and B. microplus is considered to be the main, if not the only vector. Both clinical and inapparent infection are more frequent in Bos taurus than in Bos indicus types.  相似文献   

HAEMOLYTIC DISEASE OF NEWBORN CALVES IN A DAIRY HERD IN QUEENSLAND     

G. Langford  B.V.Sc.  S. G. Knott  B.V.Sc.  Corinne K.  Dimmock B.Sc.† P. Derrington  B.V.Sc.†† 《Australian veterinary journal》1971,47(1):1-4

  相似文献   

Keith McDonald Grant     

SG Knott  BA Woolcock 《Australian veterinary journal》2003,81(3):166-166

  相似文献   

The Effect of Post-Ovulatory Artificial Insemination on Sow Reproductive Performance     

CD Castagna  CH Peixoto  FP Bortolozzo  I Wentz  F Ruschel  GB Neto 《Reproduction in domestic animals》2003,38(5):373-376

In order to increase reproductive performance, sows are usually inseminated several times during oestrus. In practice, this results in a significant number of sows receiving one or more post‐ovulatory inseminations. This study was carried out to determine the percentage of sows that receive one or more post‐ovulatory inseminations and the effect of such treatment on reproductive performance. The results were analysed from a total of 1298 sows on two farms. It was observed that more than 70% of the sows received at least one post‐ovulatory insemination and approximately 20% received two or more. There was no observed effect on the rate of return to oestrus, farrowing rate or litter size (p > 0.05).  相似文献   

The Structure of the Harderian Gland of the Guinea Fowl at Embryonic and Post Embryonic Stages     

B.I. Onyeanusi    A.N. Ema    CD. Ezeokoli  J.C. Onyeanusi 《Anatomia, histologia, embryologia》1993,22(2):183-190

The Harderian gland of the guinea fowl is a bright, pink and relatively large orbital organ situated at the ventromedial aspect of the orbit. It possesses a single duct that has its exit on the convex medial surface. The outline is irregular with its caudal half narrower than the rostral half, and possessing a slight constriction about the mid point. Histologically, the gland had been outlined with the existence of a large contorted lumen by day 18 of incubation. The surface epithelial lining showed two layers of cells all through and lymphocytes were also present. By day 19 of incubation, certain zones of the surface epithelium had become pseudostratified and some of these cells contained vacuoles indicative of secretory materials within their cytoplasm. By day 21, few definitive acini with lumina had been observed and at day 23, the epithelium had assumed only a single layer of cells that were tall columnar cells, except at the junctions of the folds. By day 24, the tunica propria seemed to have completely disappeared with the acini occupying every available space. Plasma cells were seen three days after hatching.  相似文献   

Outcome of phacoemulsification in 71 cats: A multicenter retrospective study (2006‐2017)     

Elena Fenollosa‐Romero  Emily Jeanes  Ines Freitas  Andra‐Elena Enache  Rachel Lockhart  Lorraine Fleming  Timothy N. L. Knott  Charlotte Dawson  Kerry Smith  Claudia Busse 《Veterinary ophthalmology》2020,23(1):141-147

  相似文献   

VITAL RESEARCH OF AGRICULTURE     

Macgillivray JH  Hanna GC  Knott JE  Weier TE 《Science (New York, N.Y.)》1945,101(2615):143-144

  相似文献