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71.
72.
73.
Summary Ammonium nitrate fertilizer, labelled with15N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates
of application were respectively 95 and 102 kg N ha−1 in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years
were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments
the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another
labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop
to study further the uptake of nitrogen fertilizer in relation to waterlogging.
In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied
to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer,
and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam
soils respectively.
In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water,
and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer.
Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller.
Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application.
On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter
waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging
promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications. 相似文献
74.
Summary The formation of mineral nitrogen species and of organic nitrogen was studied in three different types of soils in relation
to the application of the nitrification inhibitor nitrapyrin. The results indicate that nitrification brings about a deficit
in total mineral nitrogen and a concomitant surplus in non biomass organic nitrogen. This phenomenon increases with increasing
levels of applied ammonium nitrogen and soil organic matter. The phenomenon is considered to be due to the reaction of the
transient nitrite formed with soil phenolic compounds and appears to be of significance in all soils in which nitrification
occurs, even neutral to alkaline and low carbon soils. 相似文献
75.
76.
Analysis of total nitrogen, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [ Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above-mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid-development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics. 相似文献
77.
Electron transport system (ETS) activity, CO2 evolution, O2 consumption, N2-fixation (C2H2 reduction) and methanogenesis were appropriately measured in aerobic and anaerobically incubated sediment at 4, 10 and 20 ° C to better characterize these activities under different incubation conditions. ETS activity was always higher in the aerobically incubated sediment at all three incubation temperatures, whereas (C2H2 reduction was always greater in the anaerobic sediment. Carbon dioxide evolution was detected only in the aerobic sediment at 10 and 20 ° C but not at 4 ° C. Methane evolution in anaerobic sediment increased gradually with an increase in the incubation temperature. 相似文献
78.
79.
Corrado Fogher Ilona Dusha∗ Patricia Barbot Claudine Elmerich∗ 《FEMS microbiology letters》1985,30(1-2):245-249
Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains. 相似文献
80.
Effects of phosphorus and nitrogen enrichment on the phytoplankton in a tropical reservoir (Lobo Reservoir,Brazil) 总被引:2,自引:2,他引:0
The effects of enrichment with phosphate (0–500 µg. 1–1) and forms of nitrogen (nitrate, nitrite, ammonia an and urea) (0–3500 µgg. –1) on the phytoplankton growth of Lobo Reservoir (Brazil) were studied in July, 1979. Suspended matter, chlorophyll a, cell concentrations and the carotenoid:cchlorophyll ratio were estimated following 14 days of in situ incubation. Phosphate alone caused no significant effects, but enrichment with nitrogen caused a substantial increase on the growth of phytoplankton. Comparison between the different forms of nitrogen showed insignificant effects after their additions with 350 µg. –1 and in combination with phosphate. However, when nitrogen was added in large quantities (3 500 µg. –1), significant differences between the nitrogeneous forms were found, with urea causing the strongest effect. In July, nitrogen is mhe main limiting nutrient to phytoplankton growth of Lobo Reservoir.Supported by CNPq and FAPESP. 相似文献