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1.
Abstract

An upland rice variety IAC‐47 was grown in a greenhouse to determine the effect of foliar nitrogen (N) supplementation during grain development on the activity of the N assimilation enzymes, nitrate reductase (NR) and glutamine synthetase (GS), on free amino‐N content and leaf soluble sugars, and on grain crude protein content. At 10 and 20 days after anthesis (DAA), the leaves were fertilized with a liquid fertilizer containing 32% N as 12.8% urea, 9.6% ammonium (NH4), and 9.6% nitrate (NO3) in increasing rates corresponding to 0,20+20, 40+40, and 60+60 kg N ha‐1. Leaves were collected twice (at 12 DAA and 14 DAA for GS activity, sugar and amino‐N content, and at 11 and 13 DAA for NRA) after each application of leaf N. The late foliar application of N increased significantly grain crude protein without a corresponding decrease in grain weight. The NR activity (NRA) increased after the foliar application of N. In the flag leaf, 60+60 kg N ha‐1 (21 DAA) resulted in higher NRA (20x over the control), while GS activity was smaller than the control. At 22 DAA there was an increase in GS activity in the flag leaf at 20+20 N level. However, the GS activity decreased as applied N levels increased. Also at the 20+20 level, there were increases in free amino‐N in the flag leaf and second leaf at the final harvest. Throughout the experiment, plants at the 60+60 N level had the lowest levels of soluble sugars. Increases in crude protein were highest at 40+40 N level (27.9%), followed by 60+60 (18.7%).  相似文献   

2.
Abstract

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no‐till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split‐split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no‐till corn (split plots) to provide a range of soil N availability. The split‐split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0–300 kg N ha‐1 in 75 kg N ha‐1 increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha‐1 check plots and corn grain yields were determined in all plots. Plant‐available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha‐1 and 9.9 Mg ha‐1 following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha‐1 (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre‐sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover crop‐corn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.  相似文献   

3.
Abstract

Application of soluble forms of nitrogen (N) fertilizers to sandy soils may cause leaching of nitrate N (NO3‐N) resulting in contamination of groundwater. The leaching loss of N may be reduced to a certain extent by the use of controlled‐release N formulations. A leaching column study was conducted to evaluate the leaching of urea, ammonium N (NH4‐N), and NO3‐N forms from selected urea‐based controlled‐release formulations (Meister, Osmocote, and Poly‐S) and uncoated urea under eight cycles of intermittent leaching and dry conditions. Following leaching of 1,760 mL of water (equivalent to 40 cm rainfall) through the soil columns, the recovery of total N (sum of all forms) in the leachate accounted for 28, 12, 6, or 5% of the total N applied as urea, Poly‐S, Meister, and Osmocote, respectively. Loss of urea‐N from all fertilizer sources was pronounced during the initial leaching events (with the exception of Meister). Cumulative leaching of urea‐N was 10% for uncoated urea while <1.7% for the controlled‐release formulations. Cumulative leaching of NH4‐N was 6.2% for uncoated urea while <0.5% for the controlled‐release formulations. Cumulative leaching loss of NO3‐N was 3.78% for Osmocote, 4.6% for Meister, 10.4% for urea, and 10.5% for Poly‐S. This study demonstrates a significant reduction in leaching of N forms from controlled‐release formulations as compared to that from the soluble form.  相似文献   

4.
Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha‐1 or 0, 51, and 102 kg K ha‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.  相似文献   

5.
Nitrogen (N) supply increased yield, leaf % N at 10 days after silking (DAS) and at harvesting, the contents of ribulose‐1,5‐bisphosphate carboxylase (RUBISCO) and soluble protein, and the activities of phosphoenolpyruvate carboxylase (PEPC), and ferredoxin‐glutamate synthase (Fd‐GOGAT), but not of glutamine synthetase (GS) for six tropical maize (Zea mays L) cultivars. Compared to plants fertilized with 10 kg N/ha, plants inoculated with a mixture of Azospirillum sp. (strains Sp 82, Sp 242, and Sp Eng‐501) had increased grain % protein, and leaf % N at 10 DAS and at harvest, but not grain yield. Compared to plants fertilized with either 60 or 180 kg N/ha, Azospirillum‐inoculated plants yielded significantly less, and except for GS activity, which was not influenced by N supply, had lower values for leaf % N at 10 DAS and at harvest, for contents of soluble protein and RUBISCO, and for the activities of PEPC and Fd‐GOGAT. Yield was positively correlated to leaf % N both at 10 DAS and at harvest, to the contents of soluble protein and RUBISCO, and to the activities of PEPC and Fd‐GOGAT, but not of GS, when RUBISCO contents and enzyme activities were calculated per g fresh weight/min. However, when enzyme contents and enzyme activities were expressed per mg soluble protein/min, yield was correlated positively to RUBISCO and PEPC, but negatively to GS. These results give support to the hypothesis that RUBISCO, Fd‐GOGAT, and PEPC may be used as biochemical markers for the development of genotypes with enhanced photosynthetic capacity and yield potential.  相似文献   

6.
Plant roots are exposed to a variety of nitrogen forms (e.g., nitrate, ammonium, amino acids) and take up these forms at different rates. Many studies have investigated whether plants prefer nitrate, ammonium, or amino acids; but studies may not be comparable because they used substrate concentrations between 100 and 2000 μmol L–1. This study tests the hypothesis that substrate concentrations from 10 to 1750 μmol L–1 affect plant preference for N forms. Nitrogen uptake by the herb Ocimum basilicum and the evergreen tree Eucalyptus regnans was examined by placing roots of intact seedlings in equimolar mixtures of nitrate, ammonium, and glycine in which one of the N forms was 15N‐labelled (and 13C‐labelled in the case of glycine). In both species, preference for N forms was affected by substrate concentration. At 10 μmol L–1 (O. basilicum) or 10 and 50 μmol L–1 (E. regnans), rates of N uptake did not differ among N forms. At substrate concentrations of 50 μmol L–1 and greater O. basilicum took up ammonium the fastest, glycine the slowest, and nitrate at an intermediate rate. At substrate concentrations from 100 to 1750 μmol L–1, E. regnans took up ammonium the fastest with glycine and nitrate taken up at slower rates. The absence of significant differences at lower concentrations was a true biological effect rather than a function of larger relative errors. This study demonstrates that substrate concentration has a large effect on plant preference for N forms, and sounds a warning for studies of N nutrition that do not consider the concentration‐dependence of plant preference for N forms.  相似文献   

7.
Abstract

Pearl millet and annual ryegrass were continually doubled‐cropped on Olivier silt loam soil for seven years at six levels of N, applied as ammonium nitrate in three applications to millet and in two applications to ryegrass. Forage yields increased as N application rates increased. During seven years at the 0 and 448 kg/ha N rate, millet produced 35% and 95%, respectively, as much yield as it produced at the 800 kg/ha N rate, while comparable values for ryegrass were 19% and 83%. At 448 kg/ha of N the two grasses produced a combined yield of over 20 Mg/ha of dry forage per year. Ryegrass yields following millet were consistently lower than yields previously obtained at this site.

Nitrogen applications consistently increased concentrations of N, Ca, and Mg in both forage grasses, while effects on P and K were variable and S concentrations were unaffected. The amounts of all nutrients removed in the forages were increased as yields increased with N application rates. Nitrate‐N levels considered to be toxic to ruminant animals occurred only where N applications exceeded 170 kg/ha at any one time. In vitro digestibility of each grass was consistently increased by N applications.

The percentage of fertilizer N that was removed in the crops ranged from 66% to 68% for millet and from 35 to 52% for ryegrass as N applications increased up to 448 kg/ha. Residual ammonium and nitrate levels in the top 1.2 m of soil were not increased by N rates of 448 kg/ha or lower. At the 800 kg/ha N‐rate, the apparent N recovery rate decreased and residual ammonium and nitrate levels increased throughout the soil profile.  相似文献   

8.
Abstract

The effect of four consecutive years of tillage method [conventional tillage (CT) or no‐tillage (NT)] and fertilizer N rate (84, 168, 336 kg N·ha‐1·yr) on soil carbon, nitrogen and and gaseous profiles was examined in a Wharton‐Cookport (Aquic Hapludults‐Aquic Fragiudults) silt loam soil in West Virginia cropped to continuous maize (Zea mays L.). At midseason (July) of the last cropping year, soil mineral N profile differences were generally discernible only at the high N (336 kg·ha‐1) rate in the topsoil (0‐ to 30‐cm layer). Ammonium (NH4 +‐N) levels at this time were significantly (p ≤ 0.05) higher under CT, while NO3 ‐‐N levels were the same under both tillage methods. However, after silage harvest in September NH4 +‐N levels were the same under both tillage systems, while NO3 ‐‐N levels were significantly higher under CT. Although no significant (p ≥ 0.05) tillage effects were found for TC, the level was increased by ～16% under NT in the surface soil (0 to 15‐cm) layer at the low N (84 kg·ha‐1) rate treatment. Total N (TN) was significantly (p ≤ 0.05) increased under NT compared to CT only in the soil surface layer at the high N rate treatment. Soils under both tillage methods after cropping appeared to be equally well aerated to the deepest layer (60 cm) as O2 levels were near atmospheric concentrations, and no gases commonly associated with more anaerobic environments (CH4, C2H4) were detected. Carbon dioxide (CO2) levels increased 30‐ to 40‐times atmospheric levels in the deepest layers, and were generally higher under NT. The incidence of detectable N2O (‐0.36 × 10 ‐2μg·ml‐1) was two‐ to seven‐times more numerous at the high N rate, and twice as numerous under NT compared to CT. These results generally corroborate previous results for soil mineral N changes as related to tillage method, but not for organic C, N and microbial activity, as has usually been reported, especially for more arid region soils.  相似文献   

9.

Purpose  

Up to date, most studies about the plant photosynthetic acclimation responses to elevated carbon dioxide (CO2) concentration have been performed in temperate areas, which are often N limited under natural conditions and with low ambient N deposition. It is unclear whether photosynthetic downregulation is alleviated with increased N availability, for example, from increased N deposition due to fossil fuel combustion in the tropics and subtropics. Awareness of plant photosynthetic responses to elevated CO2 concentration will contribute to the better understanding and prediction of future forest productivity under global change.  相似文献   

10.
Abstract

Nitrogen (N) in forest soil extracts and surface waters may be dominantly in organic compounds as dissolved organic nitrogen (DON). Due to various difficulties associated with measuring total N (as TKN) by the Rjeldahl digest, this important vehicle for nutrient movement is rarely monitored. By coupling two relatively new methods and optimizing them for use in soil studies, we developed an alternative method for measuring DON. Analysis of pure compounds and field samples shows that persulfate oxidation combined with conductimetric quantification of nitrate (NO3) provides a highly accurate measure of dissolved N content. With relatively inexpensive equipment and reagents, a single technician can digest and assay over a hundred samples a day. This rapid, simple, and accurate assay may make it possible to routinely monitor DON where it had previously been impractical. This in turn could substantially enhance understanding about the form and quantity of N involved in nutrient fluxes.  相似文献   

11.
Growth of vinca [Catharanthus roseus (L.) G. Don ‘Grape Cooler'] was compared under several cultural conditions. Conditions investigated included two types of media (a peat‐lite mix and a mix containing 25% pine bark) and five types of nutrient charges in the peat‐lite media (sulfated micros, chelated micros, sulfated or chelated micros with pH adjustment to 5.5, and no charge). Nitrogen (N) source effect on growth was also investigated. Plants were grown at five different ratios of nitrate‐N to ammonium‐N. Greatest growth as measured by shoot length and shoot dry weight occurred in the peat‐lite media at either the sulfated micro or chelated micros adjusted to pH 5.5 and at the highest ratios of nitrate‐N to ammonium‐N. Root dry weight and growth were negatively affected by high levels of ammonium‐N in the fertilizer solution.  相似文献   

12.
Does net soil nitrogen (N) mineralization change if N‐fertility management is suddenly altered? This study, conducted in a long‐term no‐tillage maize (Zea mays L.) fertility experiment (established 1970), evaluated how changing previous fertilizer N (PN) management influenced in situ net soil N mineralization (NSNM). Net soil N mineralization was measured by incubating undisturbed soil cores with anion and cation exchange resins. In each of three PN fertilizer application plots (0, 84, and 336 kg N ha?1), another three fertilizer application rates (0, 84, and 336 kg N ha?1) were imposed and considered the current fertilizer N (CN) management. Generally, PN‐336 (336 kg N ha?1) had significantly greater NSNM than PN‐0 (0 kg N ha?1) or PN‐84 (84 kg N ha?1), which reflected differences in soil organic‐C (SOC) and soil total‐N (STN). The three CN rates had no significant effect on NSNM when they were applied to PN‐0 or PN‐84, but CN‐336 (336 kg N ha?1) had significantly higher NSNM than CN‐0 (0 kg N ha?1) or CN‐84 (84 kg N ha?1) in the PN‐336 plots. The CN or “added N interaction” used the indigenous soil organic matter (SOM) pool and the added sufficient fertilizer N. Environmental factors, including precipitation and mean air temperature, explained the most variability in average daily soil N mineralization rate during each incubation period. Soil water content at each sampling day could also explain NSNM loss via potential denitrification. We conclude that “added N interaction” in the field condition was the combined effect of SOM and sufficient fertilizer N input.  相似文献   

13.
Three‐week‐old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 20 and 10%) for five weeks. Half of the stressed plants was treated with potassium chloride (KC1) at 10 (K1) and 150 mg (K2)/kg soil at the beginning of water deficit. Nodulation was examined and some nodule activities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stress. Soluble carbohydrate contents of nodules, however, was significantly increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was accumulated. The results indicate that K supply, particularly at the 150 mg/kg soil level, increased faba bean resistance to water stress.  相似文献   

14.
Abstract

Nitrogen (N) or growth regulator application to small grain cereals near anthesis has been demonstrated to alter grain fill and grain yield, the protein yield and nutritional quality may also be modified by these management factors. The objective of this study was to determine whether delivery of N, growth regulator, or sucrose solutions into greenhouse‐grown barley (Hordeurn vulgare L. cv. Leger) or wheat (Triticum aestivum L. cv. Katepwa), plants through peduncle perfusion altered the amino acid composition of the grain. The following treatments were tested: N (25 and 50 mM), chlormequat (30 μM), ethephon (15 μM), N + chlormequat, N + ethephon, detillering + N, sucrose (250 mM), distilled water check, and non‐perfused check. Perfusion lasted 30 d beginning 5 to 8 d after spike emergence. Addition of N via peduncle perfusion increased protein concentrations and concentrations of all amino acids in both barley and wheat when expressed in terms of grain dry matter. Protein yield and lysine content were also increased. However, the increase in essential amino acids such as lysine, methionine, threonine, isoleucine, arginine, and leucine was relatively small, and the proportions of these amino acids in the grain protein were actually reduced. The sucrose treatment only affected wheat, increasing lysine concentration and decreasing the total protein concentration. Growth regulators used in this study did not alter protein yield or amino acid composition in either crop.  相似文献   

15.
Under greenhouse conditions, a study was made on the effects of nitrogen (N) source (N)O3 or NH4), mode of application (single vs. split) and nitrification inhibition on the N‐uptake and metabolism, of bahiagrass.

Variations in light and temperature in the greenhouse affected the N‐metabolism of bahiagrass plants. Nitrate fed plants had nitrate reductase activity (NRA) pattern different from that of NH4‐fed plants. Amino‐N accumulation patterns were similar for plants under both N‐sources, although amino‐N levels in leaves of NH4‐fed plants were much smaller than that of NO3 plants. Nitrate accumulation in leaves showed inverse trend to that of roots in plants fed both NO3 or NH4. To the sharp peaks in NO3 levels in roots due to increases in light and temperature corresponds a sharp decrease of its levels in leaves.

For both both NO3 or NH4 treatments, soluble‐N accumulated most in the rhizomes of bahiagrass plants, whereas protein N accumulated most in leaves, suggesting that rhizomes had a buffering effect on the NO3 fluxes to leaves. This presumably resulted in a lag in the NRA response of the NO3‐fed plants to increases in light and temperature.  相似文献   


16.
Abstract

Efficient soil fertility management is essential for sustained production of high crop yields. Field experiments were conducted on an Entisol soil during 1984 to 1987 at Bidhan Chandra Agricultural University, West Bengal, India, to study the changes in soil N, P, and K in sub‐humid tropics under irrigated intensive cropping in rice‐potato‐mung bean (Oryza sativa L.‐ Solanum tuberosum L.‐ Vigna radiatus Roxb.) and rice‐potato‐sesame (O. sativa L.‐ S. tuberosum L.‐ Sesamum indicum L.) cropping sequences. The crops were grown with or without application of farmyard manure and with or without incorporation of crop residues. Different quantities of inorganic fertilizers based on locally recommended practices for fertilization were applied to rice and potato, and their residual effects on succeeding mung bean or sesame crops were assessed. At the end of experimentation, the total N status of soil improved more under the rice‐potato‐mung bean sequence than under the rice‐potato‐sesame sequence. The available phosphorus status of soil showed a positive balance in both sequences except in the treatment receiving 50% of the recommended amounts of N, P, and K. A reduction in the recommended fertilization without a compensating application of manure or crop residues resulted in the depletion of soil‐available K. All treatments reduced nonexchangeable K, and depletion was low wherever manure or crop residues were added into the cropping system. Integration of inorganic fertilizers with organic fertilizers, such as manure or crop residues, maintained soil N, P, and K under intensive agriculture and sustained soil productivity.  相似文献   

17.
Two rates of broiler litter (20 and 40 mt/ha) were compared to recommended rates of inorganic nitrogen (N), phosphorus (P), and potassium (K) in a double cropping system of spring sweet corn (Zea mays L. ‘Silverqueen') and fall broccoli (Brassica oleracea L, ‘Southern Comet')‐ Sweet corn matured one week earlier both years when fertilized with 40 mt/ha of broiler litter compared to commercial fertilizer. The early maturity may be due to improved P nutrition. Similar or higher yields of fall broccoli were produced with broiler litter following sweet corn than with commercial fertilizer.  相似文献   

18.
Abstract

A new method for microsite assessment of soil nutrient supply in forest soil was developed. The method involves the use of ion exchange membranes to assess differences in soil nitrogen (N), phosphorus (P), and potassium (K) supply rates in‐field over small depth increments in the forest floor (i.e., the L, F, and H horizons). Ion exchange membranes were buried and retrieved from the forest floor in an aspen forest stand in Saskatchewan, Canada. Small (6 mm diameter) sections of the membrane were cut out and ion concentration on the sections measured to provide a nutrient supply rate at that location. Soil nutrient supply rates at the site ranged from 4.6–6.0, 7.3–8.5, 11.6–21.5, and 122–196μg 10 cm2#lb2 h‐1 for NH4 +‐N, NC3 ‐‐N, P, and K, respectively. On average, the highly humified H horizon had the highest N and P supply rates, followed by the F horizon, with the surface litter (L horizon) having the lowest N supply rates. The simplicity and sensitivity of the procedure make this method appropriate for in‐field assessment of differences in soil nutrient supply over small vertical and horizontal distance and was especially appropriate for the forest floor horizons in forest soils.  相似文献   

19.
Soybean plants [Glycine max (L.) Merr.] were grown in pots and inoculated with Rhizobium japonicum and/or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, either at planting or 20 days later. Nitrogen was supplied in the nutrient solution to plants without nitrogen‐fixing bacteria, and P was added to those without the mycorrhizal fungus. At harvest, 50 days after planting, all plants had leaves of similar dry mass. Each root symbiont grew best in the absence of the other. Growth of Glomus reflected the duration of its growing time and the presence and duration of competition from Rhizobium. Nodule weight in the tripartite associations, on the other hand, was inhibited only by the earlier introduction of Glomus.

Dipartite associations and the plants inoculated with both root symbionts at planting had the highest concentration of leaf N, and the lowest was in those inoculated with both organisms at d 20. Leaf P was highest in plants inoculated only with Rhizobium, and lowest in those tripartite associations involving any inoculation at day 20. The low values were presumably a result of the short duration of endophyte‐mediated P uptake before the plants were harvested.

Although there was almost no difference in leaf sugar concentrations, starch concentrations reflected the duration of Glomus growth, and were greatest in those plants that had supported it for the least time. Uninoculated plants contained the least starch, but produced a greater fresh mass of leaf tissue than any of the tripartite symbionts.  相似文献   


20.
Abstract

Diffusion methods for quantitative determination and isotope‐ratio analysis of inorganic N in soil extracts were modified for use with Kjeldahl digests. The digest was diluted to 25 mL with deionized water, and an aliquot (to 6 mL) was transferred in a shell vial (17 mm dia., 60 mm long) to a 473‐mL (1‐pint) wide‐mouth Mason jar containing 15 mL of 8 M NaOH. The NH3 liberated by overturning the vial inside the sealed jar was collected for 48 h at room temperature (24 h with orbital shaking) in 3 mL of boric acid‐indicator solution in a Petri dish, or in an acidified glass‐fiber disk, suspended from the Mason‐jar lid. Determinations of N and 15N by diffusion were in close agreement with analyses using conventional steam‐distillation and concentration techniques.  相似文献   

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