PG99S智能型喷灌机的调试及维护

在蔬菜、花卉的工厂化育苗生产中,准确控制肥水的浓度和喷洒的均匀性显得尤为重要,而喷灌设备作为智能型连栋育苗温室的主要浇灌设备,被广泛应用于现代化育苗温室中。该设备自动作业,水量控制精准。本文就PG99S型智能喷灌机介绍其调试方法和故障维修。     

The effect of seed pretreatment and sowing date on the nursery emergence of Sitka spruce (Picea sitchensis [Bong.] Carr.) seedlings

Sitka spruce seeds which had been: (1) untreated (U), (2) prechilled(P), or (3) prechilled and then redried and stored for 16 months(R), were sown into progressively warmer seed beds on four datesat monthly intervals from March to June. At each sowing date,samples of seed were germinated in the laboratory at optimum(20°C) and sub-optimum (10°C) temperatures. Prechillingand prechilling + redrying both increased the rate and totalamount of germination compared with untreated seed at each testtemperature. However in the nursery, the beneficial effectsof pretreating Sitka spruce seed were restricted to sowing inMarch and April when soil temperatures were sub-optimal forthe germination of untreated seeds. Pretreatment resulted inrapid seedling emergence at soil temperatures between 10°Cand 15°C, whereas untreated seed germinated slowly and seedlingemergence continued until high soil temperatures in June killedungerminated seeds. The pattern of seedling emergence from theredried seed was similar to that from the prechilled seed, exceptfor a lag in the start of seedling emergence probably due tothe extra time needed for redried seed to imbibe water in theseed beds. Thus redrying caused insignificant loss of seed performanceon the nursery. Seed sown in May and June experienced average temperatures closeto the optimum for germination of 20°C, however daily maximaregularly exceeded 35°C resulting in the cessation of seedlingemergence in all three seed treatments, and the loss of newlyemerged seedlings. Periods of warm weather from June onwardswere the main factors limiting the final number and size ofseedlings.     

Extraction and characterization of water–repellent materials from Australian soils

Organic materials responsible for water–repellency in some Australian soils were extracted with an amphiphilic mixture of iso -propanol/15.7 m ammonia (7:3, v:v) in a Soxhlet apparatus, after which the water–repellent soils were rendered wettable. The successful extraction by an organic solvent system indicates that the bulk of hydrophobicity in these soils is not covalently linked to the surface of the sand. The extracted materials restored hydrophobicity on acid washed sands or ignited sands at levels comparable to the original soils.
Spectroscopic and chromatographic examination of the extracted materials indicated that both free and esterified long–chain, 16–32 carbon atom, fatty acids were present with a bimodal distribution showing maxima at C₁₆ and C₂₂. The ¹³C–NMR and infrared spectra of the most hydrophobic extract suggest that hydrophobicity is caused by molecules with extensive polymethylene chains. Calculations with model compounds indicate that at least a close packed monolayer is required before measurable hydrophobicity can be detected with the molarity of ethanol droplet penetration test.     

Trivalent metal (Cr, Y, Rh, La, Pr, Gd) sorption in two acid soils and its consequences for bioremediation

The recent addition of trivalent metals to soil and their subsequent movement within the biosphere are of concern. For this reason, the sorption of chromium (Cr), yttrium (Y). rhodium (Rh), lanthanum (La), praseodymium (Pr) and gadolinium (Gd) in two contrasting acid soils has been determined. Except for Rh, the sorption of the other trivalent metals conformed well to the Langmuir equation with derived sorption parameters similar for all the trivalent species tested. Calculation of the buffer powers indicated that under both small (0·01 mmol kg^?1) and large (1 mmol kg^?1) trivalent metal soil loadings > 99·5% of the metals will be associated with the exchange phase with small quantities present in the bulk soil solution (<0·5%). It seems that the slight availability of metals within the bulk soil solution will slow the rate of trivalent metal bioremediation of contaminated sites.     

Drivers,challenges and opportunities of forage technology adoption by smallholder cattle households in Cambodia

Forage technology has been successfully introduced into smallholder cattle systems in Cambodia as an alternative feed source to the traditional rice straw and native pastures, improving animal nutrition and reducing labour requirements of feeding cattle. Previous research has highlighted the positive impacts of forage technology including improved growth rates of cattle and household time savings. However, further research is required to understand the drivers, challenges and opportunities of forage technology for smallholder cattle households in Cambodia to facilitate widespread adoption and identify areas for further improvement. A survey of forage-growing households (n = 40) in July–September 2016 examined forage technology adoption experiences, including reasons for forage establishment, use of inputs and labour requirements of forage plot maintenance and use of forages (feeding, fattening, sale of grass or seedlings and silage). Time savings was reported as the main driver of forage adoption with household members spending approximately 1 h per day maintaining forages and feeding it to cattle. Water availability was reported as the main challenge to this activity. A small number of households also reported lack of labour, lack of fencing, competition from natural grasses, cost of irrigation and lack of experience as challenges to forage growing. Cattle fattening and sale of cut forage grass and seedlings was not found to be a widespread activity by interviewed households, with 25 and 10% of households reporting use of forages for these activities, respectively. Currently, opportunities exist for these households to better utilise forages through expansion of forage plots and cattle activities, although assistance is required to support these households in addressing current constraints, particularly availability of water, if the sustainability of this feed technology for smallholder cattle household is to be established in Cambodia.     

THE NATURE OF THE NITROGEN COMPOUNDS IN SOIL ORGANIC MATTER EXTRACTED BY ANHYDROUS FORMIC ACID

Organic matter extracted with 9 : 1 formic acid : acetylacetone from twenty-five soils of widely varying organic content and precipitated with excess di-isopropyl ether was hydrolysed with 6N HC1. The relationships between the proportions of acid-soluble N, acid-insoluble N, amino-N, and ammonium-N thus produced, and the properties of the original soil were examined. The distribution of N in acid hydrolysates was similar to that reported in the literature for material isolated by neutral and alkaline extractants. The relatively large proportion of N released as ammonium-N from organic matter obtained from soils of high pH and low C : N ratio may derive from organically fixed ammonia. The low levels of amino-N in organic matter extracted by formic acid from soils of high clay content imply the existence of clay-amino complexes that resist extraction although formation of such complexes during extraction cannot be ruled out.     

SENSITIVITY OF LOW‐FIELD T2* IMAGES FOR DETECTING THE PRESENCE AND SEVERITY OF HISTOPATHOLOGIC MENISCAL LESIONS IN DOGS

The sensitivity of low‐field magnetic resonance (MR) T2^* images for predicting the presence of meniscal lesions was determined in 12 dogs with naturally‐occurring cranial cruciate ligament rupture and three control dogs, using histopathology as the reference standard. Previously published grading systems were used to grade the severity of meniscal lesions on MR images, gross inspection and histopathology. Focal areas of increased signal intensity were detected in 11/12 symptomatic dogs and 3/3 control dogs. Lesions mimicking meniscal tears (pseudotears) were identified at junctions between meniscal margins and adjacent connective tissue in control dogs and dogs with naturally occurring disease. Histopathologic lesions were present in all menisci of both symptomatic and control dogs, including the menisci from two affected dogs that appeared grossly normal but were removed and submitted based on MR imaging findings. Histopathologic lesions identified included hyaline cartilage metaplasia and changes in the amount of ground substance and cellularity. The sensitivity of MR imaging for detecting the presence of meniscal histopathologic lesions was 90% in symptomatic dogs and 91% in control dogs. However, agreement between severity scores for the different tests was poor. Low‐field MR imaging is a sensitive test for predicting the presence but not severity of meniscal histopathologic lesions in dogs with naturally‐occurring cranial cruciate ligament rupture. Findings also supported previous studies indicating that histopathologic lesions can be present in dogs with grossly normal menisci. An improved grading system for comparing MR images and histopathologic severity of meniscal lesions in dogs is needed.     

A proposed framework for accelerating technology trajectories in agriculture: a case study in China

Precision agriculture (PA) technologies have great potential for promoting sustainable intensification of food production, ensuring targeted delivery of agricultural inputs, and hence food security and environmental protection. The benefits of PA technologies are applicable across a broad range of agronomic, environmental and rural socio-economic contexts globally. However, farmer and land-manager adoption in low to middle income countries has typically been slower than that observed in more affluent countries. China is currently engaged in the process of agricultural modernisation to ensure food security for its 1.4 billion population and has developed a portfolio of policies designed to improve food security, while simultaneously promoting environmental protection. Particular attention has been paid to the reduction of agricultural inputs such as fertilisers and pesticides. The widespread adoption of PA technologies across the Chinese agricultural landscape is central to the success of these policies. However, socio-economic and cultural barriers, farm scale, (in particular the prevalence of smaller family farms) and demographic changes in the rural population, (for example, the movement of younger people to the cities) represent barriers to PA adoption across China. A framework for ensuring an acceptable and accelerated PA technology trajectory is proposed which combines systematic understanding of farmer and end-user priorities and preferences for technology design throughout the technology development process, and subsequent end-user requirements for implementation (including demonstration of economic and agronomic benefits, and knowledge transfer). Future research will validate the framework against qualitative and quantitative socio-economic, cultural and agronomic indicators of successful, or otherwise, PA implementation. The results will provide the evidence upon which to develop further policies regarding how to secure sustainable food production and how best to implement PA in China, as well as practical recommendations for optimising end-user uptake.     

A study of fluctuations in Escherichia coli sensitivity patterns from pigs fed a halquinol supplemented diet

Escherichia coli isolated from pigs fed on a medicated diet containing 120 p.p.m. halquinol did not develop any resistance to this addition over a 6-week period.
Sensitivity patterns of the E. coli isolates to eight antimicrobial substances, although fluctuating slightly during the test period (but no more than a control group), did not significantly alter. However, the patterns did change significantly when for 17 days after the completion of the halquinol trial the pigs were fed a normal commercial ration medicated with a commonly used feed additive containing chlortetracycline hydrochloride, procaine penicillin and sulphadimidine.