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排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Summary Standard local practice in Northern India is to continue irrigation of winter wheat crop almost up to harvest, based on the farmer's belief that this treatment increases grain weight and yield. The effect of an early cut-off of irrigation on the water use was studied in a three-year experiment on a deep, sandy-loam soil.Wheat, sown during the second or third week of November, received its first irrigation four weeks later. Subsequently treatments included irrigations of 7.5 cm water depth applied after 10 cm of cumulative pan evaporation minus rainfall had elapsed since the previous irrigation up till mid-April; irrigations of 7.5 cm up till mid-February and thereafter irrigation equal to 75 and 100% soil-water deficit in the 0–180 cm profile around March 10 with no later irrigation; and a similar treatment with one additional irrigation after making up the water deficit.Least irrigation water was used from the treatment in which 75% water deficit was restored around March 10 and no further irrigation was applied. This treatment increased the average extraction of profile water by 4 cm compared to treatments in which irrigation was continued until mid-April. Profile water depletion was inversely related to the amount of irrigation. Grain weight and yields from the various treatments harvested in the last week of April were unaffected by the treatments.The authors are grateful to the ICAR for financing this research 相似文献
942.
Production and water use in lettuces under variable water supply 总被引:3,自引:0,他引:3
M. Gallardo L. E. Jackson K. Schulbach R. L. Snyder R. B. Thompson L. J. Wyland 《Irrigation Science》1996,16(3):125-137
The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m–2 mm–1 and for fresh weight of 48 g m–2 mm–1 . For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications. 相似文献
943.
A field experiment was conducted with a bunched variety of peanut (Arachis hypogaea L.) cv. JL-24 during the summer seasons (March–June) of 1992 and 1993 in the humid tropical canal command area at the University Experimental Farm, Memari (23°1 N, 88°5 E and 21.34 m a.s.l) in West Bengal of eastern India. The soil at the site is of sandy loam (Typic Fluvaquent) texture and the area has a shallow water table. Weekly and seasonal field water balance components of actual evapotranspiration (ETa) including the capillary contribution into root zone were determined. Peanut yield and water productivity were determined for three ratios of irrigation water and cumulative pan evaporation (CPE) of 0.9, 0.7 and 0.5. Mean crop coefficients were determined for each 7-day period of growth and were related to leaf area index and growing degree-days. Average seasonal values of ETa of peanut were 434, 391 and 356 mm for the three treatments, respectively, for 115 days of growth. The total pod yield and WP were significantly higher in 0.9 IW:CPE treatment in the 1992 season. On an average, 0.9 IW:CPE treatment had 7 and 11% higher yields in 1992 and 1993, respectively, over treatments 0.7 and 0.5 IW:CPE. The maximum average Kc of 1.19 occurred about 9 weeks after sowing relative to grass reference ET (ETo). 相似文献
944.
Operational limits to the Priestley-Taylor formula 总被引:4,自引:0,他引:4
945.
Summary An investigation was made of the irrigation requirements of cotton grown in a sub-humid environment with significant but highly variable rainfall. In the first year of the study, no additional yield benefits accrued to subsequent irrigations following a pre-emergent irrigation due to above average rainfall (550 mm) throughout the growing season. In the second year a similar rainfall amount (502 mm) fell but significant yield increases to irrigation resulted due to the uneven distribution of the rainfall. The main effect was associated with later rains which influenced the number of bolls set. The maximum amount of water extracted by cotton from a deep grey cracking clay was 178 mm. It was found that 70% of this amount could be depleted before irrigation without loss of yield. Crop evapotranspiration varied from 607 mm with no irrigation after emergence to 775 mm following three irrigations. Irrigation was associated with significant losses from rainfall runoff. Too frequent irrigation creates a risk that soil will be too wet to permit utilisation of natural rainfall. Therefore, the use of soil water information to maximise the interval between irrigation is proposed as a necessary basis for efficient irrigation management. 相似文献
946.
We undertook a mark–recapture study of three pool‐dwelling balitoroid loaches and a nonmigratory goby in a Hong Kong hillstream, which extended over a 35‐week period. The target species were Pseudogastromyzon myersi and Liniparhomaloptera disparis (Balitoridae), Schistura fasciolata (Nemacheilidae) and Rhinogobius duospilus (Gobiidae). Recapture rates of tagged individuals were high (58% overall), especially for the abundant R. duospilus (70% of 412 tagged) and P. myersi (57% of 762 tagged). At the end of the study, most recaptured individuals (78% of gobies, 62% of P. myersi, 42% of L. disparis and 67% of S. fasciolata) were within the pools where they had been released. Of those that had moved elsewhere, maximum displacements ranged from 46 m (R. duospilus) to 101 m (P. myersi), giving rise to a strongly leptokurtic distribution of movement distances. Mean displacements after 35 weeks ranged from only 2.9 m (R. duospilus) to 10.0 m (L. disparis). The sedentary behaviour of these species was more marked than most other small benthic fishes, although our study excluded the breeding period and wet season when high flows might have stimulated movement. Among the mobile P. myersi individuals, most travelled upstream, whereas mobile gobies tended to move downstream. Juveniles of P. myersi and R. duospilus, as well as large adult P. myersi, were especially sedentary, while mobile adult P. myersi that travelled further showed smaller growth increments. The highly sedentary habits of all four fishes suggest that they may exert persistent local top‐down control of benthic communities within pools in Hong Kong streams. 相似文献
947.
948.
I. Placha M. Pogany Simonova K. Cobanova A. Laukova S. Faix 《Research in veterinary science》2010,89(2):257-261
We investigated the effect of Enterococcus faecium on phagocytic activity, antioxidative status in vivo and the effect of E. faecium and 0.4% concentration of Thymus vulgaris essential oil (EO) on the duodenal tissue integrity in vitro in laying hens. The birds were fed the same standard diets and were divided into four groups. E. faecium was added to the drinking water for the second and fourth groups. EO was added to special chambers for measuring trans-epithelial electrical resistance (TEER) for the third and fourth groups only. TEER was lower in groups where EO was added, but in the group with E. faecium TEER was not changed significantly. Our results show that EO at 0.4% concentration may negatively affect intestine integrity, and the probiotic strain E. faecium AL41 is able to eliminate this effect and can strengthen non-specific immunity. To confirm our findings further histopathological investigations of intestinal tissue are needed. 相似文献
949.
The probabilistic approach methodology that assesses the permissible level of heavy metal (HM) pollution of agricultural land according to sanitation and hygiene principle is developed. Application of the methodology is illustrated by using information from the database, which characterize parameters of zinc transition from the soil to agricultural plants. 相似文献
950.
The raspberry varieties Mailing Jewel and Mailing Exploit were used to study growth and crop responses to mulching and irrigation from 1957 to 1962 inclusive.Treatment A consisted of a wheat straw mulch applied deeply enough to form a complete surface cover; treatments B and C of water applications on unmulched cultivated soil at soil moisture tensions of 20 cm. and 50 cm. of mercury respectively, measured at 1 ft. depth. Treatment B was changed after i960 to a single 2-in. water application given when the raspberry fruits began to ripen. Plots under treatment D were cultivated, unwatered and unmulched.Irrigation greatly increased the rate of cane growth but this was found to be a disadvantage in raspberries grown as continuous rows because the new cane tended to chafe and obscure ripe berries. Restricting irrigation to the pre-picking period reduced height growth but did not appear to reduce cane numbers or crop yield. Crop yield was increased by irrigation to about 30% more than was produced on the unwatered and unmulched plots, mainly as a result of increased berry size, but the full effect of irrigation on yield was not realized because cane numbers and height were restricted. Under the conditions of this experiment, in which the canes were thinned to a given density and tipped to a given height, a single 2-in. application of water at the commencement of ripening, i.e. when the berries showed the first tinge of pink, was a very economic irrigation treatment. Irrigation slightly delayed ripening, probably because of the harder tipping required by the irrigated canes.The mulch conserved the equivalent of 2 in. of moisture and was intermediate in effect between the irrigation treatments B and C and treatment D in height growth, crop yield and berry size, but had a depressing effect on the production of new canes by the weaker-growing variety Mailing Jewel. 相似文献