Influence of nitrogen forms and levels on the growth and nutrition of cacao

Ammonium and nitrate are the major forms of nitrogen (N) present in tropical soils. An experiment was conducted to assess the influence of nitrate and ammonium forms (NO₃^?, NH₄⁺, and mix of NO₃^? + NH₄⁺), and levels (1.5–12.0 mM) of N on the growth and nutrition of cacao (Theobroma cacao L). Growth parameters were significantly influenced by N forms, and nitrogen supplied as NH₄⁺ proved better for the growth of cacao compared with NO₃^? form and mixtures of these two forms. Irrespective of the forms of N, levels of N had no significant effect on plant growth parameters. Nutrient efficiency ratios (NERs) (shoot dry matter produced per unit of nutrient uptake) for macronutrients were sulfur>phosphorus>calcium>magnesium>nitrogen>potassium (S>P>Ca>Mg>N>K) and for micronutrients NERs were in the order of copper>boron>zinc>iron>manganese (Cu>B>Zn>Fe>Mn).     

Growth Patterns of Jojoba Male and Female Leaf Callus with Various Ammonium and Nitrate Sources

Abstract

Male and female leaf discs of Jojoba [Simmondsia chinensis (Link) Schneider] were cultured on Murashige and Skoog (MS) media supplemented with various nitrate:ammonium ratio and phytohormones concentrations. For the optimum callus growth, hormonal concentrations were remained equal for both male and female leaf tissues i.e., 0.4 mg L^?1 2,4‐dichlorophenoxyaceticacid, 1.25 mg L^?1 6‐benzyladenine and 0.5 mgL^?1 kinetin. However, a statistically significant difference was observed when Murashige and Skoog media was supplemented with an additional nitrogen source. In female leaf tissue, maximum fresh and dry weights were recorded in Murashige and Skoog media supplemented with an additional source of NO₃ ^?:NH₄ ⁺ (60 mM) whereas in male leaf tissue this addition was inhibitory. This study suggests that nitrogen requirement may be different for optimum callus growth in both male and female leaf tissues.     

Growth response of Suaeda salsa (L.) Pall to graded NaCl concentrations and the role of chlorine in growth stimulation

Abstract

Growth response of a halophyte species, Suaeda salsa (L.) Pall, to graded NaCl concentrations was examined under water culture conditions. Growth increased with increasing NaCl concentration from 2 to 200 mol m^?3, but decreased at NaCl concentrations above 200 mol m^?3. Maximum growth was attained at 50 to 200 mol m^?3. The role of Na and Cl in the growth stimulation by NaCl was examined by growing S. salsa in nutrient solutions with or without Na and Cl separately at 5 and 50 mol m^?3. The growth stimulation induced by Cl was greater than that induced by Na, and Na did not significantly induce growth stimulation. The effect of Na or Cl on O₂ evolution from leaves was examined under 5 and 50 mol m^?3 concentrations using an oxygen electrode. Oxygen evolution from leaves in –Cl treatments was smaller than that in +Cl treatments both at 5 and 50 mol m^?3. The O₂ evolution in Na treatments with Cl was similar to that at NaCl. These results indicated that the mechanism of growth stimulation induced by Cl was mainly an increased photosystem II of photosynthesis in leaves. The contribution of Na on the growth stimulation of S. salsa by NaCl was smaller than Cl.     

Sulphur fertilizer effect on cotton: I. Nitrogen and sulphur status and petiole nitrate‐nitrogen

Abstract

The effect of S fertilization on S and N status and petiole NO₃ ^?‐N in cotton was observed during the growing seasons of 1980 and 1981. Four sites representing 2 soil subgroups were studied using a randomized complete block design with 4 replications. Leaf and petiole sampling began one week prior to bloom initiation and continued weekly for eight weeks. Leaf samples were analyzed for S and N and the petioles for NO₃ ^?‐N. Levels of leaf‐S varied directly with amounts of applied S. Leaf‐N and petiole NO₃ ^?‐N varied directly with amounts of applied N. Though not always significant, petiole NO₃ ^?‐N and leaf‐N showed negative correlations with leaf‐S. These results suggest that knowledge of the cotton plant S status may be necessary to interpret petiole NO₃ ^?‐N for N fertilization of cotton.     

DEVELOPMENT OF A SOIL N TEST FOR FERTILIZER REQUIREMENTS FOR WHEAT

Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO^? ₃)- N, soil ammonium (NH ⁺ ₄)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO^? ₃-N and NH ⁺ ₄-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH ⁺ ₄-N and NO^? ₃ -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO^? ₃-N.     

Effect of Chloride and Sulfate Salinity on Micronutrients Release and Uptake from Different Composts Applied on Total Phosphorus Basis

Generation of different biowastes is increasing day by day, and ultimate load on agricultural lands has increased. Concerns over increased phosphorus (P) application with nitrogen (N)–based compost application shifted the trend to P‐based applications. But focus on only one or two nutritional elements will not serve the goals of sustainable agriculture. Full insight into nutrient availability from different composts is necessary. The need to understand the nutrient release and uptake from different composts has increased because of the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, current greenhouse studies were designed to evaluate the bioavailability and leachability of some micronutrients [calcium (Ca), magnesium (Mg), and zinc (Zn)] from different biocomposts under chloride (Cl^?) and sulfate (SO₄ ^?2) saline environment. In the first pot experiment, soil was amended with livestock compost (AC), poultry compost (PC), and composted sludge (SC) at the rate of 200 kg P ha^?1 equivalent bases. Pots were irrigated with artificial saline water of sodium chloride (NaCl) or sodium sulfate (Na₂SO₄; 60 mmol_c L^?1), and leachates were collected for Ca and Mg analysis. As composts were applied on total P bases, which left varying amounts of nutrients in each treatment, it was observed that nutrient uptake and release differed greatly regardless of the total amount applied with each compost type. Amount of Ca applied with PC (3.9 g pot^?1) was greater, but Ca concentration in leachate was greater under AC‐amended treatments. Magnesium concentration also varied greatly under compost types. Among the saline irrigation, Ca and Mg concentration in leachate increased under both saline irrigations compared to nonsaline treatment, and SO₄ ^?2 had relatively greater ionic strength to replace cations than Cl^?. Calcium, Mg, and Zn uptake by maize stem and leaves were greater from SC‐amended pots followed by PC, SC, and control. Irrespective of the salt types, Ca and Mg uptake reduced under both saline irrigations, whereas Zn uptake increased as compared to nonsaline treatment. Among the salt types, it was observed that plant growth and nutrient uptake was more influenced by Cl^? than SO₄ ^?2 saline irrigation. In the second experiment, soil was saturated with NaCl and NaSO₄ (75 mmol_c L^?1) and amended with AC. The trend of nutrient uptake under both salt types was similar to first experiment, and the results of AC amendments have been discussed. It can be inferred from the results that regardless of the total amount applied, nutrient uptake greatly varies under different composts and their availability depends upon the source rather than total amount applied. Analogously, sulfate‐dominated irrigation water can increase the leaching of Ca and Mg from root zone more than chloride.     

Growth,Nitrate Accumulation,and Macronutrient Concentration of Pakchoi as Affected By External Nitrate-N: Amino Acid-N Ratio

ABSTRACT

A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO₃ ^?) accumulation, and macronutrient concentrations of pakchoi (Brassica chinensis L.) in hydroponics. Plants were supplied with NO₃ ^? and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO₃ ^?-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO₃ ^?-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO₃ ^?-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO₃ ^?-N/AA-N ratios reduced NO₃ ^? concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO₃ ^?-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO₃ ^? concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields.     

Nitrate leaching,nitrous oxide emission and N use efficiency of aerobic rice under different N application strategy

A field study was conducted in the sub-humid tropical region of India to examine the effect of different nitrogen (N) management strategies on nitrate leaching, nitrous oxide (N₂O) emission and N use efficiency in aerobic rice. Treatments were: control (no N), 120 kg N ha^?1 applied as prilled urea (PU) in conventional method, 120 kg N ha^?1 applied as neem coated urea (NCU) in conventional method, N applied as PU on the basis of leaf colour chart (LCC) reading, N applied as NCU on the basis of LCC reading, and 120 kg N ha^?1 applied as PU and farm yard manure (FYM) in 1:1 ratio. Results showed that 3.4–16.1 kg NO₃-N ha^?1 was leached below 45 cm depth and 0.61–1.12 kg N₂O-N ha^?1 was emitted from aerobic rice during the growing season. NCU when applied conventionally reduced nitrate-nitrogen (NO₃-N) leaching and N₂O emission by 18.6% and 21.4%, respectively However when applied on the basis of LCC reading NCU reduced NO₃-N leaching by 39.8% as compared to PU applied in conventional method. NCU when applied on the basis of LCC reading synchronized N supply with demand and reduced N loss, which resulted in higher yield and N use efficiency.     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

Changes in Properties of Composting Rice Husk and Their Effects on Soil and Cocoa Growth

The worldwide production of rice husk, a by‐product and agrowaste that causes serious environmental problems, may reach 116 million t y^?1. The objectives of this study were (i) to determine the physicochemical changes of rice husk and its structural chemistry during composting using ¹³carbon nuclear magnetic resonance (¹³C NMR) and (ii) to determine the effect of the composted rice husk (CRH) on the properties of Oxisol and cocoa (Theobroma cacao L.) growth under glasshouse conditions. Results showed an active composting phase occurred at the first 53 days as revealed by high carbon dioxide (CO₂)‐C (40–71 µg g^?1 h^?1) production, followed by a matured composting phase occurring at 54–116 days as revealed by decreasing in CO₂‐C production (10 µg g^?1 h^?1). The active composting was accompanied by increases in electrical conductivity (EC), pH, ammonium (NH₄ ⁺), and nitrate (NO₃), whereas during the matured composting phase, the EC and cation exchange capacity increased but pH, NH₄ ⁺, and NO₃ ^?1 decreased. The ash of the produced compost contains mainly calcium (Ca), potassium (K), sulfur (S), magnesium (Mg), and phosphorus (P) as essential nutrients. The CP/MAS ¹³C NMR spectra before and after various composting times indicated the dominance of sharp and well‐resolved signal peaks at O‐alkyl C and di‐O‐alkyl C regions (67–73%), which are characteristic of cellulose. The percentage of N‐alky/methoxyl was 23–26% whereas phenolic, carboxyl, and alkyl C types were less than 3% each. The application of the CRH to an Oxisol significantly increased soil pH and Ca, Mg, K, sodium (Na), and silicon (Si) ions of in situ soil solution but decreased the amounts of toxic ions [aluminum (Al), manganese (Mn), and iron (Fe)]. The CRH was found to increase cocoa growth up to 37%.     

Development of a Soil N Test for Fertilizer Requirements for Corn Production in Quebec

Corn requires high nitrogen (N) fertilizer use, but no soil N test for fertilizer N requirement is yet available in Quebec. Objectives of this research were (1) to determine the effects of soil nitrate (NO₃ ^?)-N, soil ammonium (NH₄ ⁺)-N, and N fertilizer rates on corn yields and (2) to determine soil sampling times and depths most highly correlated with yields and fertilizer N response under Quebec conditions. Soil samples were taken from 0- to 30-cm and 30- to 60-cm depths at seeding and postseeding (when corn height reached 20 cm) to determine soil NH₄ ⁺ and NO₃ ^? in 44 continuous corn sites fertilized with four rates of N in two replications using a quick test (N-Trak) and a laboratory method. The N-Trak method overestimated soil NO₃ ^?-N in comparison with the laboratory method. Greater coefficients of determination were observed for soil NO₃ ^?-N analyses at postseeding compared with seeding.     

Emissions of Nitrous Oxide,Ammonia, and Carbon Dioxide from a Cambisol at Two Contrasting Soil Water Regimes and Urea Granular Sizes

The superiority of mixing and deep placement of prilled urea (PU) or urea supergranules (USG) over surface‐broadcast application for reducing nitrogen (N) loss from lowland rice is well established. In upland agricultural systems, rainfall and/or the application and loss of irrigation water from soil systems may regulate urea N transformations and gaseous losses, depending on the method of fertilizer application and the particle size. To develop further insights into these processes, experiments were carried out in a silt loam soil mixed with PU or amended with point‐placed USG at a depth of 7.5 cm. Two soil water regimes were used: around field capacity (AFC) with low evaporative conditions (depletion: 77 to 69% water‐filled pore space, WFPS) and below field capacity (BFC) with high evaporative conditions following two irrigations (depletion: 70 to 55% WFPS). The nitrous oxide (N₂O) emission was greater at AFC than at BFC, where nitrification was more rapid. The N₂O peaks appeared mostly after the disappearance of nitrite (NO₂ ^?), presumably dominated by nitrifier and/or chemodenitrification and the degree of emissions probably depended on the stability period and the reduction of NO₂ ^? induced by the soil water regimes. The relative N₂O losses from the added N were small (?0.20%) for all treatments after 21 days. The point at which 50% of its emissions (t_½) occurred was delayed up to 6 days longer than found from the application of PU. The differences between PU and USG application were likely linked with the concentrations of ammonium (NH₄ ⁺), NO₂ ^?, and pH. These high concentrations continued longer at AFC than at BFC and were limited to a distance of <5.0 cm from the application zone. Similarly, the relative losses of the added N ranged from 0.19 to 0.56% at AFC and 0.08 to 0.37% at BFC, the highest being with USG application. Based on the areas receiving equal N, the N₂O and ammonia (NH₃) emissions from USG differed marginally with PU. Carbon dioxide (CO₂) release was higher at AFC than BFC, in which the USG application probably limited microbial respiration preferentially to methane oxidation. A correlation study showed that the N₂O flux was best explained together with CO₂, nitrate (NO₃ ^?), NO₂ ^?, and WFPS (R ² = 0.67***). This indicates the influence of both auto‐ and heterotrophic microbial activities toward N₂O emission, with soil water being an important regulatory factor.     

Leaf litter C and N cycling from a deciduous permanent crop

Our understanding of leaf litter carbon (C) and nitrogen (N) cycling and its effects on N management of deciduous permanent crops is limited. In a 30-day laboratory incubation, we compared soil respiration and changes in mineral N [ammonium (NH₄⁺-N) + nitrate (NO₃^–-N)], microbial biomass nitrogen (MBN), total organic carbon (TOC) and total non-extractable organic nitrogen (TON) between a control soil at ¹⁵N natural abundance (δ¹⁵N = 1.08‰) without leaf litter and a treatment with the same soil, but with almond (Prunus dulcis (Mill.) D.A. Webb) leaf litter that was also enriched in ¹⁵N (δ¹⁵N = 213‰). Furthermore, a two-end member isotope mixing model was used to identify the source of N in mineral N, MBN and TON pools as either soil or leaf litter. Over 30 d, control and treatment TOC pools decreased while the TON pool increased for the treatment and decreased for the control. Greater soil respiration and significantly lower (p < 0.05) mineral N from 3 to 15 d and significantly greater MBN from 10 to 30 d were observed for the treatment compared to the control. After 30 d, soil-sourced mineral N was significantly greater for the treatment compared to the control. Combined mineral N and MBN pools derived from leaf litter followed a positive linear trend (R² = 0.75) at a rate of 1.39 μg N g^?1 soil day^?1. These results suggest early-stage decomposition of leaf litter leads to N immobilization followed by greater N mineralization during later stages of decomposition. Direct observations of leaf litter C and N cycling assists with quantifying soil N retention and availability in orchard N budgets.     

Analysis of NO3 interception of the parasitic angiosperm Orobanche spp. using a positron-emitting tracer imaging system and 13NO− 3: A new method for the visualization and quantitative analysis of the NO3 interception ratio

Abstract

The root parasitic plants Orobanche spp. (broomrapes) seriously affect agricultural production. A visualization and quantitative analytical method for the interception of nutrients was established using a positron-emitting tracer imaging system and ¹³NO^? ₃. By using this analytical method that involves volume normalization with ¹⁸F^? images, the nitrogen nutrient interception ratio of the Orobanche spp. was calculated to be 73.6 ± 3.9% in a host–parasite system of red clover (Trifolium pratense L.).     

Salinity effects on nitrogen metabolism in plants – focusing on the activities of nitrogen metabolizing enzymes: A review

Nitrogen (N) metabolism is of great economic importance because it provides proteins and nucleic acids which in turn control many cellular activities in plants. Salinity affects different steps of N metabolism including N uptake, NO₃^? reduction, and NH₄⁺ assimilation, leading to a severe decline in crop yield. Major mechanisms of salinity effects on N metabolism are salinity-induced reductions in water availability and absorption, disruption of root membrane integrity, an inhibition of NO₃^? uptake by Cl^?, low NO₃^? loading into root xylem, alteration in the activities of N assimilating enzymes, decrease in transpiration, and reduction in relative growth rate which results in a lower N demand. However, the effects of salinity on N metabolism are multifaceted and may vary depending on many plant and soil factors. The present review deals with salinity effects on N metabolism in plants, emphasizing on the activities of N metabolizing enzymes in a saline environment.     

The effect of N and NaCl on growth,yield, and nitrate content of salad rocket (Eruca sativa Mill.)

Hydroponic production of rocket as a salad vegetable has become increasingly important in recent years. Rocket is known to be a high nitrate (NO₃^–)-accumulating vegetable, which can be grown throughout the year. In the present study, rocket was grown in a floating hydroponic system at three levels of nitrogen (N) and sodium chloride (NaCl). The highest yield was obtained at 14 mM N, whereas the yield was lower at 20 mM and 40 Mm NaCl. Leaf elongation was more sensitive to salinity than leaf differentiation. Adding NaCl to the nutrient solution increased the relative chlorophyll content. Na⁺ and Cl^– concentrations increased as salinity increased. NO₃^? levels in fresh biomass increased with increased amounts of NO₃^? in the nutrient solution, and plants at 18 mM N were able to maintain a higher NO₃^? : Cl^? ratio than those at 10 mM N.     

Nitrite and Ammonium Toxicity on Lettuce Grown under Hydroponics

Abstract

Nitrite (NO₂ ^?‐N) toxicity symptoms have been observed on lettuce (Lactuca sativa) at various locations in California. The objective was to evaluate the symptoms of ammonium (NH₄ ⁺‐N) and nitrite (NO₂ ^?‐N) toxicity on Sundevil iceberg lettuce and Paragon romaine lettuce and to determine lettuce growth and biomass production under different levels of NO₂ ^?‐N. Hydroponic studies under greenhouse conditions were conducted using nutrient solutions containing nitrate (NO₃ ^?‐N) and two other forms of nitrogen (NO₂ ^?‐N and NH₄ ⁺‐N) applied at a constant concentration (50 mg NL^?1) or using different NO₂ ^?‐N levels (0, 5, 10, 20, 30, and 40 mg N L^?1) and a constant NO₃ ^?‐N level (30 mg N L^?1). Crown discoloration (brownish color) was observed for lettuce grown in both NO₂ ^?‐N and NH₄ ⁺‐N solutions approximately 3 weeks after transplanting into the hydroponic systems. Lettuce grown in NO₃ ^?‐N solution produced larger biomass and greater number of leaves per plant than lettuce grown in NO₂ ^?‐N or NH₄ ⁺‐N solutions. Increasing the concentration of NO₂ ^?‐N suppressed plant height, fresh and dry biomass yield, and number of leaves and increased the root vascular discoloration. Lettuce growth was reduced more than 50% at NO₂ ^?‐N concentrations greater than 30 mg N L^?1. Even at 5 mg NO₂ ^?‐N L^?1, growth was reduced 14 and 24% for romaine and iceberg lettuce, respectively, relative to that obtained in nitrate solution. Although concentrations between 5 and 40 mg NO₂ ^?‐N L ^?1 reduced dry biomass similarly for both lettuce types, toxicity symptoms were more severe in iceberg lettuce than in romaine.     

模拟干旱和盐碱胁迫对碱蓬、盐地碱蓬种子萌发的影响

为研究干旱和盐碱胁迫对碱蓬(Suaeda glauca)、盐地碱蓬(Suaeda salsa)种子萌发的影响,比较碱蓬和盐地碱蓬逆境生理特性的异同,本研究利用PEG6000、NaCl和Na_2CO_3分别模拟干旱、盐和碱胁迫,配制相同渗透势的PEG6000、NaCl、Na_2CO_3处理液,以蒸馏水处理为对照,对碱蓬、盐地碱蓬种子的萌发与胚的生长进行比较研究。结果表明:1)低渗处理(-0.46 MPa)对碱蓬、盐地碱蓬种子的萌发无显著影响;高渗处理(-1.38MPa、-1.84 MPa)抑制碱蓬、盐地碱蓬种子的萌发。2)当溶液渗透势相等时,NaCl处理下碱蓬种子的萌发率显著大于PEG、Na_2CO_3处理;而等渗PEG、NaCl、Na_2CO_3处理对盐地碱蓬种子萌发率的影响无显著差异。3)PEG、NaCl、Na_2CO_3处理组碱蓬、盐地碱蓬种子的最终萌发率与对照无显著差异。4)在幼苗形成阶段,PEG、Na_2CO_3处理对碱蓬、盐地碱蓬胚的抑制作用显著大于等渗NaCl处理。5)碱蓬、盐地碱蓬胚的生长对NaCl、Na_2CO_3胁迫的响应存在差异。-0.92 MPa NaCl处理抑制碱蓬胚的生长,却对盐地碱蓬产生促进作用;-0.46 MPa Na_2CO_3处理对碱蓬胚的抑制作用小于盐地碱蓬。综合分析表明:碱蓬、盐地碱蓬均具有很强的抗盐性。在种子萌发阶段,碱蓬种子的抗旱、抗碱能力低于盐地碱蓬;在幼苗形成阶段,碱蓬胚的抗盐性小于盐地碱蓬,但对轻度碱胁迫的抗性高于盐地碱蓬。     

Soil N Losses by Denitrification Evaluated Using the 15N Tracer Method

Molecular nitrogen (N₂) and nitrous oxide (N₂O) generated by denitrification increase N losses in the soil–plant system. This study aimed to quantify N₂ and N₂O from potassium nitrate (K¹⁵NO₃) applied to soils with different textures and moisture contents in the absence and presence of a source of carbon (C) using the ¹⁵N tracer method. In the three soils used (sandy texture (ST), sandy clay loam texture (SCLT), and clayey texture (CT)), three moisture contents were evaluated (40%, 60%, and 80% of the water holding capacity (WHC)) with (D⁺) and without (D^?) dextrose added. The treatments received 100 mg N kg^?1 (KNO₃ with 23.24 atom% ¹⁵N). N₂ emissions occurred in all of the treatments, but N₂O emissions only occurred in the D⁺ treatment, showing increases with increasing moisture content. SCLT with 80% WHC in the D⁺ treatment exhibited the highest accumulated N emission (48.26 mg kg^?1). The ¹⁵N balance suggested trapping of the gases in the soil.     

Nitrate accumulation,productivity and photosynthesis of Brassica alboglabra grown under low light with supplemental LED lighting in the tropical greenhouse

Abstract

Vegetables are a large source of nitrate (NO₃^?) in our diet. As NO₂^? is toxic to humans, it is undesirable to consume vegetables with high NO₃^? content. Therefore, this study aimed to investigate the effect of supplementing of red- and blue-LED lighting to B. alboglabra grown in the tropical greenhouse in terms of moderating NO₃^? accumulation, improving photosynthesis, and enhancing productivity. All plants were grown hydroponically in full nutrients under prevailing greenhouse conditions for 20?days (full sunlight). Thereafter, plants were subjected to three different light treatments for 12?days: full sunlight, shade, and shade supplemented with LEDs. The average midday photosynthetic photon flux density (PPFD) during the light treatment periods were 220?μmol m^?2 s^?1 (full sunlight), 55?μmol m^?2 s^?1 (shade), and 220?μmol m^?2 s^?1 (shade supplemented with LEDs). Shoot nitrate (NO₃^?) concentration increased significantly in plants grown in the shade. However, shoot NO₃^? concentration was reduced when plants were supplemented with red- and blue-LED lighting. Photosynthetic CO₂ assimilation, stomatal conductance, and productivity also improved in these plants. Our results suggest that supplemental red- and blue-LED lighting in a tropical greenhouse during periods of cloudy and hazy weather could improve productivity and nutrient quality of Chinese broccoli.