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101.
Active crop canopy sensors make possible in-season fertilizer nitrogen (N) applications by using the crop as a bio-indicator of vigor and N status. However, sensor calibration is difficult early in the growing season when crops are rapidly growing. Studies were conducted in the United States and Mexico to evaluate procedures to determine the vegetation index of adequately fertilized plants in producer fields without establishing a nitrogen-rich reference area. The virtual-reference concept uses a histogram to characterize and display the sensor data from which the vegetation index of adequately fertilized plants can be identified. Corn in Mexico at the five-leaf growth stage was used to evaluate opportunities for variable rate N fertilizer application using conventional tractor-based equipment. A field in Nebraska, USA at the twelve-leaf growth stage was used to compare data interpretation strategies using: (1) the conventional virtual reference concept where the vegetation index of adequately fertilized plants was determined before N application was initiated; and (2) a drive-and-apply approach (no prior canopy sensor information for the field before initiating fertilizer application) where the fertilizer flow-rate control system continuously updates a histogram and automatically calculates the vegetation index of adequately fertilized plants. The 95-percentile value from a vegetation-index histogram was used to determine the vegetation index of adequately fertilized plants. This value was used to calculate a sufficiency index value for other plants in the fields. The vegetation index of reference plants analyzed using an N-rich approach was 3–5 % lower than derived using the virtual-reference concept. 相似文献
102.
Karolina Kwasek Konrad Dabrowski Kyle Ware John Mark Reddish Macdonald Wick 《Aquaculture Research》2012,43(9):1384-1391
Formulation of nutritionally complete and cost efficient diets for yellow perch (Perca flavescens) is a prerequisite for successful intensive culture of this species. One of the objectives of this study was to determine the optimum diet for the grow‐out phase of juvenile yellow perch. Fish at the size of 12.9 ± 4 g were individually marked with passive integrated transponders (PIT)‐tags and randomly distributed into six 400 L tanks, 45 fish per tank. This experiment included lysine‐deficient [(?) Lys] and lysine‐supplemented [(+) Lys] wheat‐gluten‐based diets in triplicate groups. Our experiment showed that the mean weight of fish fed (+) Lys diet (83.9 ± 1.5 g) was significantly larger than fish fed (?) Lys diet (68.6 ± 5.2 g) (P < 0.05). This experiment also showed that the blood plasma concentration of free lysine in (+) Lys group was significantly higher than in (?) Lys group (P < 0.05) and the same trend appeared also in methionine concentrations. The concentration of Lys in deficient group of fish, 3 h after a meal was lower compared with levels of Lys 24 h post‐feeding (P < 0.05). Lysine deficiency in diet resulted in significantly higher level of serine, and a similar trend occurred in small and large fish. 相似文献
103.
Variability in microsatellite DNA markers in gynogenetic and backcross progenies obtained from ornamental (koi) carp (Cyprinus carpio L.) × goldfish (Carassius auratus L.) hybrid females
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Inheritance and segregation at five microsatellite loci were studied in diploid gynogenetic and triploid backcross progenies obtained from koi × goldfish hybrid females, which produce diploid eggs. Gynogenetic and backcross progenies were obtained from three individual hybrid females by inseminating eggs with genetically inactivated and intact sperm of parental species respectively; no shock treatments were applied to the early embryos. Complete absence of paternally specific alleles at all investigated microsatellite loci has proven successful genetic inactivation of spermatozoa by irradiation and confirmed gynogenetic origin of progenies. Genotypic segregations at microsatellite loci showed almost complete homogeneity of gynogenetic progenies and their identity to female parents. These results correspond with previous cytogenetic data on the occurrence of premeiotic endomitosis in hybrid females producing diploid eggs. Fish from triploid backcross progenies had genotypes resulting from combination of entire diploid female genome and haploid genome from male. 相似文献
104.
105.
Kyle Andrejczyk Brett J. Butler Brenton J. Dickinson Jaketon H. Hewes Marla Markowski-Lindsay David B. Kittredge Michael A. Kilgore Stephanie A. Snyder Paul F. Catanzaro 《Small-Scale Forestry》2016,15(1):17-28
Using data collected from a series of focus groups, this study examines how landowner assistance programs (which may include management plans, cost-share, technical assistance and advice, and education components) affect family forest owner behaviour in the USA. Not surprisingly, most owners who participated in assistance programs had pre-existing management objectives. Participation in the management plan and cost-share components was found to facilitate the stewardship of private forests by assisting and reinforcing the behaviour of those landowners who already intend to manage their land in some pre-conceived manner. Advice and educational components appeared to do more in terms of introducing owners to new ideas. The mix of components offered as part of a landowner assistance program should consider the goals of the program and which components will be most effective in achieving those goals. 相似文献
106.
James H. Tidwell Oluwapelumi O. Odeyemi Shawn D. Coyle Kyle J. Schneider Leigh A. Bright 《Journal of the World Aquaculture Society》2014,45(5):595-603
Three genetic strains (Texas [cultured], Hawaii [cultured], and Myanmar [wild]) of freshwater prawn, Macrobrachium rosenbergii, were characterized and compared under two pond grow‐out management technologies using a 3 × 2 factorial design. Juvenile prawns (45 d nursed juveniles) from each strain were stocked at individual average weights of 0.4 ± 0.3 g (Texas), 0.3 ± 0.2 g (Hawaii), and 0.3 ± 0.2 g (Myanmar). The low input management technology prawns were stocked at 24,700 /ha with no added substrate. The high input management technology prawns were stocked at 74,100 /ha with the addition of artificial substrate. Each of the six treatment combinations were replicated in three, 0.04 ha earthen ponds (total of 18 ponds). Prawns were fed a sinking pellet (32% protein) once daily at a standardized rate. After 112 d, prawns were harvested, bulk weighed, and counted. Survival of Texas strain (95%) was significantly higher (P ≤ 0.05) than Myanmar strain (77–80%) under both management technologies with survival of Hawaii strain (86–91%) intermediate and not significantly different (P > 0.05) from other strains. Under both management technologies, average weight, total production, and marketable percentage (>20 g) was significantly better (P ≤ 0.05) in Texas and Hawaii strains in comparison to the Myanmar strain. These data appear to indicate that the cultured strains evaluated in this study demonstrate positive impacts of domestication and do not indicate inbreeding depression. 相似文献
107.
Vegetation control (VC) in forest plantations often increases growth of crop trees but can also affect biomass and nutrient
partitioning to tree components. We examined above-ground biomass and macronutrients, leaf area and crown structure in 5-year
old Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco) growing with VC and with no vegetation control (NVC) in coastal Washington, United States of America. Trees
in VC had larger stem, branch, foliage and total biomass than trees of equal stem diameter at 1.3 m above ground in NVC. The
difference in component biomass between treatments was in the order: branch > foliage > stem. Trees in the VC regime did not
differ in macronutrient concentration in stem, branch and foliage except for branch N which was greater in NVC than in VC.
Differences in tree macronutrient stores between VC and NVC ranged from 2.2 times for Mg to 2.6 times for N and K. The relationship
between stem diameter and leaf area was linear in both VC treatments. The relationship between stem diameter and foliage biomass
was curvilinear for both VC treatments. Results of this study support the need for separated allometric equations to estimate
biomass for young Douglas-fir growing in areas with and without VC. 相似文献
108.
109.
Effects of fragmentation on the seed predation and dispersal by rodents differ among species with different seed size
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Fragmentation influences the population dynamics and community composition of vertebrate animals. Fragmentation effects on rodent species in forests may, in turn, affect seed predation and dispersal of many plant species. Previous studies have usually addressed this question by monitoring a single species, and their results are contradictory. Very few studies have discussed the fragmentation effect on rodent–seed interaction among tree species with different seed sizes, which can significantly influence rodent foraging preference and seed fate. Given that fruiting periods for many coexisting plant species overlap, the changing foraging preference of rodents may substantially alter plant communities. In this study, we monitored the dispersal and predation by rodents of 9600 seeds, belonging to 4 Fagaceae species with great variation in seed size, in both the edge and interior areas of 12 tropical forest fragments ranging in area from 6.3 to 13872.9 ha in Southwest China. The results showed that forest fragmentation altered the seed fates of all the species, but the intensity and even the direction of fragmentation effect differed between species with large versus small seeds. For the seeds harvested, fragment size showed negative effects in forest interiors but positive effects at edges for the 2 large‐seeded species, but showed little effect for the 2 small‐seeded species. For the seeds removed, negative effects of fragment size only existed among the small‐seeded species. The different fragmentation effect on seed dispersal and predation among plant species may, in turn, translate into the composition differences of the regeneration of the whole fragmented forest. 相似文献
110.