Growth and nutrient and nitrate accumulation of lettuce under different regimes of nitrogen fertilization

Abstract

For plant growth and composition, the effects of fertilizers including blood meal (BLO), cottonseed meal (CSM), dehydrated cow manure (COW), and urea (UREA) factored with lettuce (Lactuca sativa L.) of different morphological phenotypes including iceberg, romaine, loose head, and loose leaf were studied in a greenhouse. Lettuce growth increased with increasing nitrogen (N) applications from 0 to 800?mg N/pot (kg), but the top application of BLO, CSM, or UREA suppressed yields. Lettuce grown with BLO, CSM, or UREA had higher concentrations of N than with COW. Nitrate-N concentration in leaves of all varieties exceeded some standards at high application of organic fertilizer or urea except for COW. In general, increasing N application resulted in higher concentration of NH₄-N in lettuce with increases in applications of fertilizers. Organic fertilizers and urea were equally effective in supporting growth and affecting nutrient accumulation in lettuce if sufficient N was supplied.     

Influence of the Modification of Nutritional Parameters in Aglaonema commutatum: K+, Ca2+, Mg2+ and Na+

Abstract

This trial was carried out to establish an appropriate nutrient solution for Aglaonema commutatum and to investigate the nutritional effects generated by modifications in the solution. Six treatments were tested: control (T₀; pH 6.5, E.C. 1.5 dS m^?1, 6 mmol L^?1 NO₃ ^?‐N, and 6 mmol L^?1 K⁺); high nitrogen (N) level (T₁; 9 mmol L^?1 6:3 NO₃ ^?–NH₄ ⁺); N form (T₂; 6 mmol L^?1 N‐NH₄ ⁺); high K⁺ level (T₃; 12 mmol L^?1 K⁺); high electrical conductivity (T₄; E.C. 4 dS m^?1, 25 mmol L^?1 NaCl), and basic pH (T₅; pH 8). At the end of the cultivation, leaf, shoot, and root dry weights and elemental concentrations were determined. Nutrient contents and total plant uptake were calculated from the dry weights and nutrient concentrations. Plant K⁺ uptake increased with application of K⁺ or basic nutrient solution. The uptake and transport of calcium (Ca) were enhanced by the use of NO₃ ^?‐N and inhibited by the presence of other cations in the medium (NH₄ ⁺, K⁺, Na⁺) and by basic pH. Magnesium (Mg) uptake increased with NO₃ ^?‐N application and with pH. Sodium (Na) uptake was the highest in the saline treatment (T₄), followed by the basic pH treatment. Sodium accumulation was detected in the roots (natrophobic plant), where the plant generated a physiological barrier to avoid damage. Dry weight did not differ significantly (p<0.05) among treatments except in the NaCl treatment. These results may help in the formulation of nutrient solutions that take into account the ionic composition of irrigation water and the physiological requirements of plants.     

Growth and nutrition of pansy as influenced by N‐form ratio and temperature

Abstract

Pansy (Viola xwittrockiana Gams.) producers often observe nutrient disorders among plants grown during warm periods (>18°C) of the growing season. These disorders typically are not seen when production temperatures are optimal (≥18°C) even though fertility regimes may remain the same. Our objectives were to assess the effects of temperature and nitrogen (N) fertility on growth and nutrition of pansy. Pansies cultivar ‘Crown White’ were grown until lateral branches had open flowers. Treatments consisted of two temperatures (12 and 22°C) and three NO₃ ^?:NH₄ ⁺ molar % ratios (100:0, 62:38, and 25:75) with a total concentration of 100 mg N L^?1. A modified Hoagland's solution was used with NO₃ ^?‐N supplied as Ca(NO₃)₂ and KNO₃ and with NH₄ ⁺‐N as (NH₄)₂SO₄. Cumulative nutrient absorption and foliar nutrient content were determined when plant lateral branches flowered. Root and shoot growth were limited when NH₄ ⁺ was present in solutions at high ambient air temperature (22°C), but not at low temperature (12°C). Individual absorption and accumulation of plant nutrients varied with N regimes and temperatures. Overall, pansies absorbed more total N, NH₄ ⁺, NO₃ ^?, calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P), zinc (Zn), and less iron (Fe) and manganese (Mn) at 12°C than at 22°C. In addition, absorption of NO₃ ^? by pansy was negligible if any NH₄ ⁺ was present in solutions at 22°C. Results suggest that pansy growers should adjust fertility programs according to production temperatures to avoid possible nutritional disorders and maximize plant growth. If maximum growth is to be obtained in warm temperatures, the use of NH₄ ⁺‐containing fertilizers should be reduced or eliminated. However, the choice of NO₃ ^?:NH₄ ⁺ ratio for nutrition may be less important under cool growing conditions.     

Iron Metabolism in Tomato and Watermelon Plants: Influence of Nitrogen Source

Abstract

Tomato and watermelon plants were grown in nutrient solutions in which nitrogen (N) was supplied as NO₃ ^? (6 mM‐N) or NH₄ ⁺ (6 mM‐N). The experiments were conducted to evaluate the effect which different N sources exert on iron (Fe) uptake and accumulation, on the enzymatic activities of aconitase (Aco), chelate reductase (FeCH‐R), peroxidase (POD), catalase (CAT), and Fe‐superoxide dismutase (FeSOD), and on biomass production. For both species of plants, fertilization with NH₄ ⁺ caused the total Fe concentration to be lower, in the roots and in the leaves in relation to the concentrations recorded in plants fertilized with NO₃ ^?. The response of the enzymes related to Fe correlated with their concentration. The plants treated with N?NO₃ ^? registered the highest activities in Aco, FeCH‐R, POD, and CAT for both tomato and watermelon. On the other hand, only in the tomato plants was the superoxide dismutase (SOD) activity appreciably influenced primarily by NH₄ ⁺, due possibly to the toxic effect of this N source. Finally, in relation to biomass production, fertilization with NH₄ ⁺ drastically reduced growth in the tomato plants, while in watermelon plants, no significant alteration was detected in dry‐matter production, regardless of the N form used. It was concluded that the response of the parameters analyzed to NH₄ ⁺ fertilization, in tomato and watermelon, compared to fertilization with NO₃ ^? was similar. By contrast, tomato plants, but not watermelon plants, were negatively influenced by NH₄ ⁺.     

Relationships between microbial biomass nitrogen,nitrate leaching and nitrogen uptake by corn in a compost and chemical fertilizer-amended regosol

Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO₃-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L^?1 K₂SO₄ extractable N (extractable N), NO₃-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha^?1 containing 158 kg N ha^?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO₃-N leaching were monitored in soil treated with SDC (20 Mg ha^?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha^?1 containing 0, 15, 29, 44 and 59 kg N ha^?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH₄)₂SO₄ at rates of 220 kg N ha^?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha^?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha^?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha^?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO₃-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO₃-N leaching in the CF treatment was 146 kg N ha^?1, which was equal to half of the applied N, but only 53 kg N ha^?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO₃-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO₃-N leaching without impacting negatively on N uptake by plants.     

Rhizosphere effects of maize hybrids and N forms on Cd bioavailability in a limed soil

Replacing new corn genotypes in agricultural practices requires adequate information on the reaction of the selected hybrids to Cd uptake in Cd-polluted soil and an understanding of interactions with N fertilizers. A 2 × 2 × 3 factorial pot experiment with limed soil (pH 8), two maize (Zea mays) hybrids (Pioneer cultivar yellow and Pioneer cultivar white), two N fertilization forms (NH₄ ⁺ and NO₃ ^?) and three Cd exposures (0, 2 and 5 mg kg^?1 soil) was conducted under greenhouse conditions. Shoot dry mass increased significantly with NH₄ ⁺ nutrition compared with NO₃ ^? nutrition in both maize hybrids, with greater negative influence of Cd application combined with NH₄ ⁺ nutrition. The yellow cultivar had significantly greater shoot dry mass and lower Cd uptake than the white cultivar. Both hybrids exhibited similar N uptake in shoots and roots, with the exception of yellow cultivar with NH₄ ⁺ nutrition without Cd application. NO₃ ^? nutrition always decreased Cd uptake in both cultivars compared with NH₄ ⁺ nutrition. The N balance (mean across cultivars and Cd supply) after harvest showed most N uptake with NH₄ ⁺ nutrition (63.4%) and N_min remains in the soil with NO₃ ^? nutrition (48.7%). Soil pH decreased more with NH₄ ⁺ (?0.95 pH units) than NO₃ ^? nutrition (?0.21).     

Effect of Raw and NH4+-enriched Zeolite on Nitrogen Uptake by Wheat and Nitrogen Leaching in Soils with Different Textures

Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH₄⁺)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z₀: (100 kg (N) ha^?1) as urea, two levels of raw zeolite; Z₁:(0.5 g kg^?1 + 100 kg ha^?1) and Z_2: (1 g kg^?1 + 100 kg ha^?1), and two levels of NH₄⁺-enriched zeolite; Z₃: (0.5 g kg^?1 + 80 kg ha^?1) and Z₄: (1 g kg^?1 + 60 kg ha^?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO₃^?) and NH₄⁺ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH₄⁺ and NO₃^? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH₄⁺-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH₄⁺-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH₄⁺-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.     

Fluid Catalytic Cracking Unit Emissions and Their Impact

A constructed wetland composed of a pond- and a marsh-type wetland was employed to remove nitrogen (N) and phosphorus (P) from effluent of a secondary wastewater treatment plant in Korea. Nutrient concentrations in inflow water and outflow water were monitored around 50 times over a 1-year period. To simulate N and P dynamics in a pond- and a marsh-type wetland, mesocosm experiments were conducted. In the field monitoring, ammonium (NH ₄ ⁺ ) decreased from 4.6 to 1.7 mg L^?1, nitrate (NO ₃ ^? ) decreased from 6.8 to 5.3 mg L^?1, total N (TN) decreased from 14.6 to 10.1 mg L^?1, and total P (TP) decreased from 1.6 to 1.1 mg L^?1. Average removal efficiencies (loading basis) for NO ₃ ^? , NH ₄ ⁺ , TN, and TP were over 70%. Of the environmental variables we considered, water temperature exhibited significant positive correlations with removal rates for the nutrients except for NH ₄ ⁺ . Results from mesocosm experiments indicated that NH ₄ ⁺ was removed similarly in both pond- and marsh-type mesocosms within 1 day, but that NO ₃ ^? was removed more efficiently in marsh-type mesocosms, which required a longer retention time (2?C4 days). Phosphorus was significantly removed similarly in both pond- and marsh-type mesocosms within 1 day. Based on the results, we infer that wetland system composed of a pond- and a marsh-type wetland consecutively can enhance nutrient removal efficiency compared with mono-type wetland. The reason is that removal of NH ₄ ⁺ and P can be maximized in the pond while NO ₃ ^? requiring longer retention time can be removed through both pond and marsh. Overall results of this study suggest that a constructed wetland composed of a pond- and a marsh-type wetland is highly effective for the removal of N and P from effluents of a secondary wastewater treatment plant.     

Evaluating Bearberry Nitrogen Nutrition Using Hydroponic Cultures: Establishing Preliminary DRIS Norms

Abstract

This study was designed to explore nitrogen (N) nutrition in bearberry plants (Arctostaphylos uva‐ursi L.) using a hydroponic culture system. Two experiments were performed in which the total N concentration (34, 52, and 73 mg L^?1) and N‐NO₃ ^?:N‐NH₄ ⁺ ratio (50/50, 60/40, and 70/30 in %) in the nutrient solution were varied and effects on nutrient uptake [N, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)] and foliar composition determined. Highest‐quality plants were yielded using a N level of 73 mg L^?1 and a N‐NO₃ ^?:N‐NH₄ ⁺ ratio of 50/50. Standard nutrient values for foliar tissue were obtained for bearberry plants growing in these hydroponic cultures for their use as preliminary norms in the diagnosis and recommendation integrated system (DRIS). In a subsequent complementary experiment, these norms were used in the DRIS procedure and applied to plants growing in solutions of varying K concentrations. It was found that the DRIS norms established in the hydroponic experiments were able to account for changes in nutrient limiting factors produced in response to the varying K concentrations in the nutrient solution. The results obtained will be useful for the nutritional diagnosis of bearberry plants.     

Mineralization of Three Organic Manures Used as Nitrogen Source in a Soil Incubated under Laboratory Conditions

Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg^?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH₄ ⁺–N+NO₃ ^?–N)], NH₄ ⁺–N, and accumulation of NO₃ ^?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg^?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg^?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg^?1 soil day^?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO₃ ^?–N was 13.2, 10.6, and 14.6 mg kg^?1 soil relative to 7.4 mg NO₃ ^?–N kg^?1 in the control soil, indicating that manures accumulated NO₃ ^?–N almost double than the control. The proportion of total mineral N to NO₃ ^?–N revealed that a total of 44–61% of mineral N is converted into NO₃ ^?–N, indicating that nitrifiers were unable to completely oxidize the available NH₄ ⁺. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.     

Microbial decomposition of leached or extracted dissolved organic carbon and nitrogen from pasture soils

Microbial decomposition of extracted and leached dissolved organic carbon (DOC) and nitrogen (DON) was demonstrated from three pasture soils in laboratory incubation studies. DOC concentration in water extracts ranged between 29 and 148 mg C L^?1 and DON concentration ranged between 2 and 63 mg N L^?1. Between 17 and 61 % of the DOC in the water extracts were respired as CO₂ by microbes by day 36. DON concentrations in the extracts declined more rapidly than DOC. Within the first 21 days of incubation, the concentration of DON was near zero without any significant change in the concentration of NO₃ ^? or NH₄ ⁺, indicating that microbes had utilized the organic pool of N preferentially. Decomposition of leached DOC (ranged between 7 and 66 mg C L^?1) and DON (ranged between 6 and 11 mg N L^?1) collected from large lysimeters (with perennial pasture; 50 cm diameter?×?80 cm deep) followed a similar pattern to that observed with soil extracts. Approximately 28 to 61 % of the DOC in leachates were respired as CO₂ by day 49. The concentration of DON in the leachates declined to below 1 mg N L^?1 within 7–14 days of the incubation, consistent with the observations made with extractable DON. Our results clearly show that DOC and DON components of the dissolved organic matter in pasture soils, whether extracted or leached, are highly decomposable and bioavailable and will influence local ecosystem functions and nutrient balances in grazed pasture systems and receiving water bodies.     

N,P, K and S uptake response to various levels of CO2 assimilation and growth rate in lettuce

Under conditions of limited nutrient supply, plant nutrient uptake is controlled by the external concentration of the ions. Limited information exists about the whole-plant regulation of nutrient uptake when the supply is adequate. To study the relationship between growth rate and carbon dioxide (CO₂) assimilation with nutrient uptake, growth chamber experiments were conducted with temperatures ranging from 10 to 35°C at medium (600 µmol m^?2 s^?1) and high (1200 µmol m^?2 s^?1) light intensities. Nutrient solution samples were collected every 24 hours and the concentration of ions was analyzed by Inductively coupled plasma -atomic emission spectroscopy (ICP-AES) and nitrate and ammonium (NO₃^?/NH₄⁺) conductivity. Leaf photo-synthesis was measured using a closed gas exchange system and the total amount of CO₂ assimilated was calculated from dry weight increases. The daily absorption of NO₃^?, Total nitrogen (N), dihydrogen phosphate (H₂PO₄^?) and potassium (K⁺) responded linearly to plant growth, while ammonium (NH₄⁺) and sulfate (SO₄^2?) uptake showed a curvilinear response. All the ions studied showed a curvilinear relation with CO₂ assimilation.     

Evaluating Inorganic Nitrogen and Rye-Crimson Clover Mixture Fertilization of Spring Broccoli and Lettuce by 15Nitrogen Tracing and Mass Balance

ABSTRACT

Broccoli (Brassica oleraceaL. var. italica) and lettuce (Latuca sativaL.) were grown under greenhouse conditions with nitrogen (N) from a cover crop mixture of rye (Secale cerealeL.) and crimson clover (Trifolium incarnatumL.) and ammonium nitrate (NH₄NO₃). Individual cover crop species were produced with non-enriched or enriched (5 atom % NH₄ ¹⁵NO₃) Hoagland Nutrient Solutions resulting in enriched rye [0.799% atom % ¹⁵N, 24:1 carbon (C):N ratio] and enriched clover (0.686% atom % ¹⁵N, 19:1 C:N ratio). Cover crops were applied as an equal mixture of rye and clover at 1884, 3768, and 5652 kg·ha^{? 1} dry weight to supply 26, 52, and 78 kg·ha^{? 1} N. Enriched materials were only applied at the 3768 kg·ha^{? 1} rate, either as enriched rye plus non-enriched clover or non-enriched rye plus enriched clover. Additional treatments consisted of an unfertilized control and three NH₄NO₃ fertilizer rates; 112, 224, and 336 kg·ha^{? 1} N for broccoli and 70, 140, and 210 kg·ha^{? 1} N for lettuce. Combination treatments were the standard cover crop rate (3768 kg·ha^{? 1}) plus the lowest N fertilizer rate for each vegetable. Cover crops did not increase yield of either broccoli or lettuce, and contributed only 17% of the N in broccoli and 15% of the N in lettuce. The majority of cover crop ¹⁵N remained in the soil: 54.8% and 81.3% of rye and clover N, respectively, after broccoli harvest; and 68.1% and 79.2% of rye and clover N, respectively, after lettuce harvest. Broccoli plant tissue recoveries were 8.0% of the rye and 11.0 % of the clover ¹⁵N; while lettuce plant tissue recoveries were 6.3% (rye) and 4.1% (clover). Broccoli yield could not be assessed due to lack of floret development, but dry matter accumulation was maximized at 224 kg·ha^{? 1}N. Lettuce yield and fertilizer N recovery efficiency (by mass balance) was maximized at 140 g·ha^{? 1} N.     

EFFECT OF NITROGEN APPLICATION ON GROWTH PARAMETERS,YIELD AND LEAF NITRATE CONTENT OF GREENHOUSE LETTUCE CULTIVATED DURING THREE SEASONS

Lettuce (Lactuca sativa L., cv. ‘Parris Island’) was grown hydroponically in autumn, winter and spring under five levels of nitrogen (N) fertilization. Plant biomass was highest in spring and lowest in autumn at N rates of 200 and 260 mg L^?1, respectively. Increasing N application correlated positively with rates of photosynthesis, transpiration, stomatal carbon dioxide (CO₂) conductance and leaf chlorophyll concentration. Photosynthetic rate, stomatal CO₂ conductance, and chlorophyll a/b ratio were higher in spring than in autumn or winter. Nitrate concentrations within the leaves increased with increasing N application in all seasons. It is concluded that lettuce growth and yield is higher in spring than in winter or autumn due to enhanced photosynthesis thanks to increasingly favorable photoperiod. Regardless of season, high N rates promote yield but increase leaf nitrate concentrations. Therefore, for the production of healthy produce the recommended N rate should be based not just on yield but also on the nitrate content.     

Leaching Methods Can Underestimate Mineralization Potential of Soils

Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl₂), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH₄⁺)-N and nitrate + nitrite (NO₃^?+ NO₂^–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH₄⁺-N (1 g kg^?1) and NO₃^–-N (0.6 g kg^?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH₄⁺-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH₄⁺.     

Effect of NO3 and NH4 concentrations in nutrient solution on yield and nitrate concentration in seasonally grown leaf lettuce

The effect of suboptimal supply of nitrogen (N) and of replacing nitrate in the nutrient solution with ammonia on growth, yield, and nitrate concentration in green and red leaf lettuce was evaluated over two seasons (autumn and spring) using multiple regression analysis. The plants were grown in a greenhouse on a Nutrient Film Technique (NFT) system. Nitrogen concentrations in the nutrient solution were either 3?mM or 12?mM, and the form of N was varied as follows: 100% NO₃, 50% NO₃?+?50% NH₄, and 100% NH₄. In both seasons, the biomass (fresh weight) of lettuce heads increased with increasing NO₃ concentrations and in autumn, NO₃ even at 1.5?mM was sufficient for high yield. However, head dry weight was affected neither by the season nor by changes in the composition of the nutrient solution. The concentration of NO₃ had no effect on root dry weight, but it decreased at higher concentrations of NH₄. The number of leaves increased as the ratio of NO₃ to NH₄ in the nutrient solution increased and was higher in autumn because of the longer growth period. Increasing the concentration of NO₃ in nutrient solution increased both total N and nitrate concentration in lettuce heads (dry weight) but decreased the concentration of total C. Also, leaf nitrate concentration was lower in spring than in autumn and decreased with increasing NH₄ concentration. Nitrogen utilization efficiency was maximum when NH₄ levels in the nutrient solution were either 0% or 50% irrespective of the season. Our results thus show that suboptimal N supply in autumn will not affect lettuce yield, and that nitrate concentration in leaves is lower when NH₄ concentrations in nutrient solution are higher and also much lower in red lettuce than in green lettuce.     

Effects of Fertilizer Nitrogen on Short‐Term Nitrogen Loss in Bypass Flow in a Vertisol

Bypass flow, the vertical flow of free water along the walls of macropores or preferential flow paths in the soil, can lead to movement of fertilizer nutrients beyond the reach of plants. Fertilizer type and the rate of application, as well as the amount, frequency, and intensity of rainfall, can influence the amount of fertilizer nitrogen (N) loss in leaching or bypass flow. The effect of fertilizer N form and rate of application on N recovery in bypass flow in a Kenyan Vertisol was determined. Calcium nitrate and ammonium sulfate, used to supply nitrate (NO₃ ^?)‐N and ammonium (NH₄ ⁺)‐N, respectively, were surface‐broadcast to 40‐cm‐long undisturbed soil columns at equivalent rates of 50, 100, and 200 kg N ha^?1. Using a rainfall simulator, two rainfall events (30 mm of water applied in 1 h) were applied to the soil columns, one before and the other after fertilizer application. Total N, NO₃ ^?‐N, and NH₄ ⁺‐N concentrations in the bypass flow were determined after the second rainfall event. The application of NH₄ ⁺‐N, regardless of the rate, had no effect on N recovery in the bypass flow. When nitrate N was applied, the amount of fertilizer N recovered in the bypass flow significantly increased with the rate of NO₃ ^?‐N application. Of the total N in the bypass flow, 24 to 48% was derived from the soil, the bulk of which was organic N. It is concluded that following the application of NO₃ ^?‐N, bypass flow is an important avenue of loss of both fertilizer and soil N from Vertisols.     

The effect of form and level of inorganic N on nitrogen use efficiency of sugarcane grown in pots

To-date, assessments of nitrogen use efficiency (NUE) of sugarcane have not included the contribution of its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). This study determined these values, based on biomass and plant nitrogen (N) content, in two four-month-old pot-grown genotypes. The treatments included six N regimes, with nitrate (NO₃^—N) or ammonium (NH₄⁺-N) supplied alone, or as NO₃^?-N for the first 6 weeks and then NH₄⁺-N until harvest, each as 4 or 20 mM. Regardless of the N form, NUE was higher at four than at 20 mM due to significantly higher NUpE at low N supply. The results indicated that there was luxury N uptake and preference for NH₄⁺-N nutrition, which resulted in the highest determined NUE. There were significant differences between genotypes in biomass, morphological growth parameters, N uptake, total plant N and NUE, the latter matching previously established sucrose yield-based NUE field rankings.     

A field trial to evaluate the pollution potential to ground and surface waters from woodchip corrals for overwintering livestock outdoors

Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH₄‐N L^?1, 372–1078 mg dissolved organic carbon (DOC) L^?1, 3–13 mg NO₃‐N L^?1, 8 × 10⁴–1.0 × 10⁶Escherichia coli 100 mL^?1 and 2.8 × 10²–1.4 × 10³ faecal enterococci 100 mL^?1. Little influence of design features could be observed. DOC, NH₄ and (in most cases) E. coli and faecal enterococci concentrations decreased 10²–10³ fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day^?1 for DOC, 0.014–0.045 day^?1 for E. coli and 0–0.022 day^?1 for faecal enterococci). The mean [NO₃‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO₃‐N L^?1, when compared with 59 ± 15 mg NO₃‐N L^?1 from a field overwintering area and 47 ± 40 mg NO₃‐N L^?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha^?1 day^?1, 3–23 kg C ha^?1 day^?1, and 5–340 g C ha^?1 day^?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH₄‐N m^?3.     

Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature,pH, organic carbon,and substrates

Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N₂ production in a paddy soil were investigated via slurry incubation combined with ¹⁵N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g^?1 h^?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g^?1 h^?1). The presence of glucose and acetate (5–100 mg C L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (V_max) of 4.4 nmol N g^?1 h^?1 and an affinity constant (K_m) of 6.3 mg NH₄⁺-N L^?1. Whereas, nitrate addition (5–15 mg ¹⁵NO₃^?-N L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.