Applying Leaf Compost to Reduce Fertilizer Use In Tomato Production

For two consecutive years, one-inch (50 T/A) of leaf compost was applied to plots on a sandy terrace soil (Windsor, Connecticut) and a loamy upland soil (Mt. Carmel, Connecticut). These compost-amended plots were fertilized with 10-10-10 (N-P₂O_5-K₂O) at three rates: 0, 650 (half), 1300 (full) lb/A and cottonseed meal at a rate of 2166 lb/A. Tomato (Lycopersicon esculentum Miller) yield from compost-amended plots were compared to yield from unamended control plots fertilized with 1300 lb 10-10-10/A. In both years, at both sites, plots only amended with compost had yields equivalent to the fertilized control plots. In both years, the greatest yields at Mt. Carmel were from plots amended with compost and the full rate of inorganic fertilizer. In the second year, yields from compost-amended plots fertilized at half the rate were equivalent to compost-amended plots fertilized at full rate. The yields from the organic plots were similar to the control plots the first year and to plots amended with compost and half the rate of fertilizer the second year. At Windsor, the greatest yields for both years were from plots amended with compost and the full rate of fertilizer. The compost-amended plots fertilized with cottonseed meal produced the lowest yields, both years. Cumulative effects of compost on soils were measured by increases in pH and organic matter percentage at both sites. Tomato fruit in plots amended with compost and no fertilizer developed less blossom-end rot than fruit in all other treatments.     

Effects of manure-based urea pellets on growth,yield, and nitrate content in coriander,garden cress,and parsley plants

Various organic residues and animal manures represent an excellent matrix material for production of natural-based pellet fertilizers. Fully decomposed cow manure with 50% w/w urea was used for pellet production in densities of 400 or 800 kg/m³, representing low and high compact urea pellets. The growth of coriander (Coriandrum sativum L.), garden cress (Lepidium sativum L.), and parsley (Petroselinum crispum Mill.) were then evaluated under application of these pelleted urea compared to urea alone and unfertilized plants. The total amount of applied nitrogen (N) in the form of urea or pelleted urea was 300 mg/kg soil, wherein pelleted urea treatments, 30% of N was incorporated into the soil as urea alone before planting. The results showed that application of pelleted urea in low and high compactness resulted in different plant responses in the three vegetable crops. Plant growth and biomass production was increased in plants treated with urea or low compact urea pellets. Leaf N concentration and the Soil-Plant Analysis Development (SPAD) index were increased by low but not by high compact urea pellet application. Regardless of compactness, pellet treated plants had less nitrate content compared to urea treated plants. Number of flowering plants in coriander and garden cress was higher with high compact urea pellet and in unfertilized plants, whereas plants treated with urea or with low compact urea pellet showed fewer flowering plants. So, for production of these leafy vegetables low compact pellet is preferred.     

Nitrogen losses by volatilization in a corn crop with two tillage systems in the Argentine Pampa

Abstract

Ammonia volatilization from soils is a complex process generally associated with surface applied nitrogen (N) fertilizer. The effect of conventional tillage and no tillage on NH₃ volatilization was evaluated on cultivated corn (Zea maize L.) field in Pampa Húmeda, Argentina. The objectives of this study were a) to determine the amount of N loss by volatilization (NH₃) from urea fertilized soils under two different tillage systems (conventional and no tillage) and two different fertilizer application methods (surface and incorporated application) and b) to relate volatilization losses with environmental factors and biochemical and microbiological properties. This experiment was conducted on a Vertic Argiudoll with a silty clay loam texture in the Argentine Pampa. The site has been in natural grassland for 8 years prior was planted to corn. Following the fertilizer application for conventional tillage and no tillage systems, the daily volatilization loss of NH₃ on the fertilized plots was highest during the first three days. Higher losses of NH₃ occurred in the no‐tillage treatments, with 11.5% and 6.2% of N‐urea lost when the fertilizer was surface applied and incorporated, respectively. For conventional tillage, 8.6 % of the N was lost when the fertilizer was surface applied and 5.4% when the fertilizer was incorporated. Surface application of urea stimulated urease enzyme activity. An opposite effect was observed when the urea was incorporated. Environmental changes conditioned the availability of energy substrates for microorganisms, which resulted in different rates of intensity of biochemical reactions in the soil. Multiple regression equations showed differences between surface applied urea and incorporated urea treatments due to the latter avoiding the direct exposure of the fertilizer to atmospheric conditions.     

Influence of high rates of topdressed KCl and K2SO4 on recovery of K,Cl, and SO4‐S by alfalfa and residual amount remaining in the soil

Abstract

This study was conducted to ascertain the percent of available K, Cl, and SO₄‐S recovered by alfalfa (Medicago sativa L. cv. ‘Vernal') herbage when various rates of K as KCl and K₂SO₄ were topdressed and also to determine where residual K, Cl, and SO₄‐S accumulated in the soil profile. An established stand of alfalfa growing on low fertility silt loam soil was topdressed in the spring of each of two harvest years with 0, 448, 896, 1344, and 1792 kg/ha of K as KCl or K₂SO₄. Four harvests were taken during each harvest year (1972 and 1973). Soil samples were taken during the autumn of 1973 to a depth of 91.4 cm in KCl‐fertilized plots, and to a depth of 76.2 cm in K₂SO₄‐fertilized and control plots.

Potassium recovery by alfalfa during two harvest years where K as KCl was applied at 448, 896, 1344, and 1792 kg/ha/yr was 56, 33, 20, and 17%, respectively. Recovery of available Cl from those same treatments was 30, 17, 12, and 10%, respectively. Where K as K₂SO₄ was applied at 448, 896, 1344, and 1792 kg/ha/yr, 55, 35, 27, and 22%, respectively, of available K was recovered. Recovery of available SO₄‐S from those same treatments was 16, 9, 7, and 5%, respectively. At the end of two years, a majority of the residual K was in the top 15.2 cm of soil. Residual Cl and SO₄‐S were concentrated at a depth of 30.5 to 76.2 cm in the soil profile.     

SOIL PROPERTY CHANGES FOLLOWING IRRIGATION WITH COALBED NATURAL GAS WATER: ROLE OF WATER TREATMENTS,SOIL AMENDMENTS AND LAND SUITABILITY

Saline‐sodic water is a by‐product of coalbed natural gas (CBNG) production in the Powder River Basin of Wyoming, USA and is being beneficially used in places as irrigation water. This study evaluated effects of 2 years of natural precipitation on soil properties of a hay field after the cessation of managed irrigation with CBNG water. The hay field had been irrigated with only CBNG water [CBNG(NT)], CBNG water amended with gypsum [CBNG(G)] or gypsum plus sulfur via a sulfur burner [CBNG(GSB)] in combination with soil amendments—gypsum ( +G ), elemental sulfur ( +S ), and both ( +GS ). Results indicated that infiltration rates were the lowest on fields irrigated with CBNG(NT), followed by CBNG(G) and CBNG(NT) +G treatments (12·2, 13·2, and 13·5 cm h⁻¹, respectively). The CBNG(GSB) +GS treatment had the highest infiltration rates (33·5 cm h⁻¹). By the second year, salinity and sodicity of treated soils had decreased in the A‐horizon of most CBNG‐water irrigated plots, whereas in Bt₁‐ and Bt₂‐horizons salinity generally decreased but sodicity increased; S and GS soil amended plots had higher profile salinities compared with NT and G soil treatments. Although Na⁺ leaching was observed in all fields that received soil and/or water amendments, CBNG(GSB) +GS plots had the lowest sodicity in the A‐ and Bt₁‐horizons. Effective managed irrigation requires knowledge of site‐specific soil properties, plant suitability, water chemistry, and amendments that would be needed to treat the CBNG waters and soils. This study indicates the greatest success was realized when using both soil and water amendments. Copyright © 2011 John Wiley & Sons, Ltd.     

Arbuscular mycorrhizal fungi mitigates heavy metal toxicity adverse effects in sewage water contaminated soil on Tagetes erecta L

The aim of this experiment was to evaluate the impact of colonization with arbuscular mycorrhizal (AM) fungus Glomus constrictum on the biomass production, flower quality, chlorophyll content, macronutrients and heavy metals content of marigold (Tagetes erecta L.) planted under uncontaminated soil and watered with various rates of sewage water. Sewage water utilization significantly decreased biomass production, characters of flower, nutrient concentration and rates of mycorrhizal colonization of mycorrhizal (M) and non-mycorrhizal (NM) marigold as compared to control untreated plants especially at the higher rates, but the reduction rate was proportionally higher in non-AM treatments. Mycorrhizal plants had significantly greater yield, relative chlorophyll content, leaf area, flower quality and element (P, N, K and Mg) content compared to non-inoculated marigold plants irrigated with or without sewage water. Furthermore, AM inoculation had highly decreased heavy metal (Zn, Co, Mn, Cu) content in tissues as compared to equivalent non-inoculated plants grown under sewage water application. Growing marigold with AM inoculum can reduce toxicity of heavy metals and enhance biomass production and P uptake. The results support the view that AM have a protective function for the host plant, hence playing a potential function in soil polluted immobilization processes, and thus are of assessing the potential of phytoremediation of heavy metals in sewage water contaminated soil.     

INFLUENCE OF A MYCORRHIZAL FUNGUS AND/OR RHIZOBIUM ON GROWTH AND BIOMASS PARTITIONING OF SUBTERRANEAN CLOVER EXPOSED TO OZONE

The influence of soilborne symbionts such as rhizobia or mycorrhizal fungi on plant response to ozone (O₃) has not been well defined. Leguminous plants in the field are infected by both types of organisms, which influence plant nutrition and growth. We studied the effects of infection with Rhizobium leguminosarum biovar trifolii and/or Gigaspora margarita on response of subterranean clover (Trifolium subterraneum L. cv Mt. Barker) to O₃. Exposures were conducted in greenhouse CSTR chambers using four O₃ concentrations [charcoal-filtered (CF), 50, 100, or 150 ppb; 6 h day^-1, 5 day wk^-1 for 12 weeks] as main plots (replicated). Four inoculum types were subplot treatments, i.e., inoculated with one, both, or neither microorganisms. At 2-wk intervals, plants were exposed to ¹⁴CO₂ and harvested 24 h later for determination of biomass and ¹⁴C content of shoots and roots. Ozone at 100 or 150 ppb suppressed clover growth during the experiment. Inoculation with G. margarita alone suppressed clover growth by the last two harvests, whereas R. leguminosarum alone enhanced growth during this time period. When both symbionts were present, the plants grew similarly to the noninoculated controls. Shoot/root ratios were increased by 100 or 150 ppb O₃ compared to that for CF-treated plants. Shoot/root ratios were greater for all inoculated plants compared to noninoculated controls. Under low O₃ stress (CF or 50 ppb), plants inoculated with both R. leguminosarum and G. margarita transported a greater proportion of recent photosynthate (¹⁴C) to roots than did noninoculated plants; we attribute this to metabolic requirements of the microorganisms. At the highest level of O₃ stress (150 ppb), this did not occur, probably because little photosynthate was available and the shoots retained most of it for repair of injury. Statistically significant interactions occurred between O₃ and inoculum types for shoot and total biomass. When averaged across harvests, 50 ppb O₃ suppressed biomass in the plants inoculated with G. margarita alone. Apparently, the mycorrhizal fungus is such a significant C drain that even a small amount of O₃ stress suppresses plant growth under these conditions.     

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.     

EFFECT OF THE APPLICATION OF SILICON HYDROXIDE ON YIELD AND QUALITY OF CHERRY TOMATO

Silicon (Si) plays an important role in the structural rigidity of cell walls. When plants have a passive or selective assimilation or they are poor accumulators as solanaceae, the percentage of silicon absorbed and present in the plants is lower than 1%, but its presence can provide significant benefits to the plant before it undergoes biotic and abiotic stresses. The objective of this work was to assess the effect of fertilization with monosilicic acid on yield and quality of cherry tomato crops (Lycopersicon esculentum var. cerasiforme cv. ‘Salomee’) grown on rockwool in a greenhouse. Two types of treatments were investigated: control test (conventional fertilization) and fertilization with silicic acid [Si(OH)₄] [seven applications of 250 mL of Si(OH)₄·ha^?1 for each crop cycle]. Significant differences were observed, including a higher number of fruits (fruits/plant) and a larger yield (kg m^?2) in the plots that were fertilized with silicon.     

INFLUENCE OF CLAY SOIL ON TWO PROTEA CULTIVARS PLANTED DIRECTLY OR GRAFTED ON CLAY-SOIL RESISTANT ROOTSTOCK. STUDY OF SOIL FERTILITY,FOLIAR NUTRITION,AND NUTRIENT CONTENT OF CUT FLOWERS

Leucospermum is a genus of the Proteaceae family that has achieved an increasing importance in the market of cut flowers worldwide. Some Leucospemum plants do not grow properly in clay soils, but grafting on a clay-soil resistant rootstock could provide better performances. The nutrient composition of two cultivars of Leucospermum (‘High Gold’ and ‘Succession II’) cultivated in clay soil was evaluated planting them directly or grafting on Leucospermum patersonii rootstock. The assay consisted of four treatments, T1 = ‘High Gold’ planted directly, T2 = grafted ‘High Gold’, T3 = ‘Succession II’ planted directly, and T4 = grafted ‘Succession II’. The experiment was carried out over three years, following a randomized block design with four replications per treatment. Foliar calcium (Ca) decreased in grafted plants of both cultivars. Nitrogen, phosphorus, potassium, Ca, and magnesium contents of the cut-flowers of ‘High Gold’ treatments were higher than those of ‘Succession II’, though in the third year no comparison with T3 plants was possible because most of them had died. The studied nutrients removal by ‘High Gold’ exceeded those of ‘Succession II’.     

Pelletized sewage sludge as a fertilizer for containerized plants: Plant growth and nitrogen leaching losses

To evaluate the effectiveness of sewage sludge pellet fertilizers (SPFs) for growing containerized greenhouse crops and their potential for nitrogen (N) leaching, three experiments were conducted where SPFs were compared to conventional water‐soluble fertilizer (WSF) and controlled‐release fertilizer (CRF). In different experiments ‘First Lady’ marigold (Tagetes erecta L.) and ‘Selenia’ New Guinea Impatiens (Impatiens sp. hybrids) (NGI) were grown in 0.5‐liter pots of soilless growth medium and plants were fertilized with 20N‐ 4.3P‐16.6K WSF, 14N‐6.2P‐11.6K CPF, or two types of SPF, 3N‐1.0P‐0.1K or 5N‐1.3P‐0.1K. CRF and SPFs were incorporated in the growth medium at planting. In each experiment, treatments received the same amount of N and volume of irrigation water. Leachate was analyzed for ammonium‐nitrogen (NH₄‐N) and nitrate‐nitrogen (NO₃‐N) at regular intervals and shoot dry weight was measured at the end of each experiment. SPFs alone as the sole source of N resulted in less N leaching compared to WSF or CRF alone but did not provide adequate N for marigold as shoot dry weight was reduced compared to WSF and CRF and foliar N deficiency symptoms developed. However, SPFs alone caused no such effects on NGI and shoot dry weight was equal to WSF and CRF with less N leaching. Growth of marigold increased and N deficiency symptoms were prevented by combining SPFs with a dilute solution of WSF, but the same treatment did not affect NGI. Combining SPFs and WSF in this manner for marigold resulted in less N leaching than SPFs alone, however with NGI more N leaching occurred, but not to the level of WSF and CRF. Results suggest that SPFs can provide adequate N for slow‐growing plants with low N uptake rates like NGI, but for fast‐growing plants with high N uptake rates, SPFs must be combined with more soluble fertilizers.     

Ammonia Volatilization from Soil,Dry-Matter Yield,and Nitrogen Levels of Italian Ryegrass

Nitrogen (N) loss by ammonia (NH₃) volatilization is the main factor for poor efficiency of urea fertilizer applied to the soil surface. Losses can be suppressed by addition of zeolite minerals to urea fertilizer. The objective of this study was to evaluate ammonia volatilization from soil and dry-matter yield and nitrogen levels of Italian ryegrass. A greenhouse experiment was carried out with the treatments of urea, urea incorporated into soil, urea + urease inhibitor, urea + zeolite, ammonium nitrate, and unfertilized treatment. Ammonia was captured by a foam absorber with a polytetrafluoroethylene tape. There were few differences between zeolite and urease inhibitor amendments concerning NH₃ volatilization from urea. Results indicate that zeolite minerals have the potential to improve the N-use efficiency and contributed to increasing N uptake. Zeolite and urea mixture reduced 50% the losses by volatilization observed with urea.     

Extraction, characterization, and nematicidal activity of chitin and chitosan derived from shrimp shell wastes

Chitin has been chemically extracted from the Egyptian shrimp shell waste. The obtained chitin was transformed into the more soluble chitosan. Chitin and chitosan were characterized using Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance spectrometry. These products were also characterized by their nematicidal potential against the root-knot nematode, Meloidogyne incognita, infecting tomato in a glasshouse. Chitin or chitosan was incorporated into the soil at the rate of 1, 3, 5, and 10 g/kg, and their nematicidal activity was compared with that of the synthetic nematicide oxamyl at the rate of 0.01 g a.i./kg. The effects of the treatments on the growth of tomato were also examined. The obtained results show that chitin and chitosan reduced tomato root galls and J₂ of M. incognita in the soil in a dose-dependent manner. Chitosan was more effective in the reduction of galls and J₂ in the soil than chitin. However, the efficacy of chitin and chitosan in reducing the number of J₂ in the soil was less than that of oxamyl. As compared to the untreated inoculated plants, the length of shoots and roots was significantly (p ≤ 0.05) increased in soil amended with either chitin or chitosan, whereas both treatments did not significantly (p > 0.05) differ with respect to the inoculated control on the effect on the dry weight of shoot and root systems. Furthermore, neither chitin nor chitosan treatments at the tested rates were phytotoxic to tomato plants.     

Effects of chloride and partial substitution of reduced forms of nitrogen for nitrate in nutrient solution on the nitrate,total nitrogen,and chloride contents of onion

An experiment was conducted to determine the effects of chloride (Cl) and reduced forms of nitrogen (N) on the nitrate (NO₃), total N, and Cl concentrations in onion (Allium cepa L.) plants using a non‐recirculating nutrient film growing system. The reference treatment was a nutrient solution containing 19 mM NO₃ and 1.25 mM ammonium (NH₄). The results from this treatment were compared with that obtained using mixed amino acid, urea, and glycine treatments with or without additional Cl (10 mM) in which 20% of the NO₃ in the reference treatment was substituted with one of these reduced forms of N. Fresh and dry weights of the onion plants were not affected by the treatments. The NO₃ content was considerably lower in the mixed amino acid treatment, being 4236 mg NO₃/kg FW as compared to either the reference, urea, or glycine treatments. The NO₃ contents of the plants in these treatments were 5393, 5339, and 5261 mg NO₃/kg FW, respectively. The presence of Cl in the nutrient solution also reduced the NO₃ content of the plants from 5816 to 4299 mg NO₃/kg FW. The reduced‐N treatments increased the total N contents of the plants. The Cl content of the plants was increased by the Cl supplied and by the reduced forms of N in the nutrient solution.     

Influence of Azolla (Azolla microphylla Kaulf.) compost on biogenic gas production,inorganic nitrogen and growth of upland kangkong (Ipomoea aquatica Forsk.) in a silt loam soil

Azolla microphylla Kaulf. (Azolla) biomass was composted to create a high nitrogen (N) organic matter amendment (Azolla compost). We examined the effect of this Azolla compost on carbon (C) and N mineralization and the production of biogenic gases, nitrous oxide (N₂O) and carbon dioxide (CO₂), in a soil incubation experiment. A pot experiment with upland kangkong (Ipomoea aquatica Forsk.) examined plant growth in silt loam soil treated with three levels of Azolla compost. The results showed that N₂O production from soil increased with urea amendment, but not with Azolla compost treatments. The Azolla-amended soil showed enhanced CO₂ production throughout the 4-week incubation. The Azolla-treated soils showed a 98% lower global warming potential compared to urea treatment over the 4-week incubation. However, Azolla-amended soil had higher nitrate (NO₃^–) levels compared to urea-fertilized soil at 1 week of incubation, and these were maintained until the fourth week. Soils amended with Azolla compost showed lower ammonium nitrogen (NH₄-N) levels than those in the urea-fertilized soils. The height and dry weight of upland kangkong fertilized with Azolla compost were similar to plants receiving urea fertilization. Therefore, the use of Azolla compost as a substitute for urea fertilizer would be beneficial for reducing the production of N₂O while maintaining plant growth.     

EFFECT OF VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI ON THE RELATIONS OF PLANT GROWTH, INTERNAL PHOSPHORUS CONCENTRATION AND SOIL PHOSPHATE ANALYSES

The effect of infection by vesicular-arbuscular mycorrhiza on the predictive value of soil analysis for available P was tested in a glasshouse experiment. Leeks (Allium porrum) were grown on ten Rothamsted soils with a wide range of initial NaHCO₃-soluble P, each of which also received 5 levels of added P. Soils were partially sterilized with 1 Mrad of γ-radiation, or left untreated; plants on sterilized soil were infected with yellow-vacuolate endophyte (Glomus mosseae) or left non-mycorrhizal. The NaHCO₃-soluble P in the soils was measured 5 days after phosphate addition. Yields from all P levels on all soils were plotted against soil NaHCO₃-soluble P content and separate smooth response curves were obtained for non-infected and artificially-infected plants. Infection increased yield only on soils with less than 100 mg P kg^?1. In contrast, naturally-infected plants gave no clearly defined response curve to P, and on three soils the yields were consistently low. These soils gave very low natural infections and had low spore densities probably due to the cropping history of the sites. Artificially-infected plants had much higher shoot P concentrations than did uninfected plants of similar dry weight, over a large range of soil phosphate levels; this effect was also noted with the endophyte G. fasciculatus. Naturally-infected plants showed a poor relationship between shoot P concentration and yield.     

在DAP-CaCO3体系与DAP-石灰性土壤体系中NH3的挥发与磷的吸附之间的关系

本工作是研究在CaCO₃体系和石灰性土壤体系中NH₃的挥发与磷的吸附之间相互作用的化学变化,结果表明:在NH₄Cl—CaCO₃体系中,通气的pH值比不通气的低,但溶液中Ca²⁺浓度正好相反。在K₂HPO₄-CaCO₃体系中,在24小时内,通气与不通气的,CaCO₃吸附磷没有差异。在24小时反应期间,在DAP-CaCO₃体系中,因溶液pH值不断增高,NH₃的挥发对CaCO₃吸附磷的影响也就逐渐降低。在石灰性土壤体系中,施用尿素加过磷酸钙或单施尿素时,几乎没有发现NH₃的挥发,而施DAP时,在6天后,NH₃的挥发损失占加入的56%,且DAP处理的土壤,其水溶性磷未通气比通气的高。尿素加过磷酸钙处理的,其水溶性磷通气与未通气的没有差异。另外,尿素加过磷酸钙或过磷酸钙单独处理的土壤,水溶性磷含量均相同。所有这些均表明,在石灰质体系中,NH₃的挥发(如果发生的话)能够加强CaCO₃对磷的吸附,而磷的吸附又能加强NH₃的挥发,两者是相互影响和相互促进的过程。     

ARBUSCULAR MYCORRHIZA,AZOSPIRILLUM AND CHEMICAL FERTILIZERS APPLICATION TO BABY CORN (ZEA MAYS L.): EFFECTS ON PRODUCTIVITY,NUTRIENTS USE EFFICIENCY,ECONOMIC FEASIBILITY AND SOIL FERTILITY

The study was investigated at Agricultural Experimental Farm, Giridih, India during winter seasons of 2007–2008 and 2008–2009. Plants grown with 100% recommended dose of fertilizer (RDF) [nitrogen (N): phosphorus pentoxide (P₂O₅): potassium oxide (K₂O) = 150:60:60 kg ha^?1] + AM + Azospirillum (T₁₅) produced maximum chlorophyll, baby cob, and green fodder yield. Root biomass was highest with application of 150% RDF + arbuscular mycorrhizae (AM) + Azospirillum (T₁₆). Co-inoculated plants produced higher chlorophyll, root biomass resulted higher cob and green fodder yield. Biofertilizers supplied along with chemical fertilizers saved 70, 29, and 33 kg N, P₂O₅ and K₂O per hectare, respectively. Nutrient (NPK) uptake was greatest in T_15. Residual soil fertility in terms of NPK was recorded maximum in T_16. Although, co-inoculated plots built up higher residual soil fertility as compare to sole inoculation. Nutrients use efficiency and benefit cost ratio were higher due to application of 50% RDF with co-inoculants. T₁₆ was most costly whereas T₁₄ (50% RDF + AM + Azospirillum) was most beneficial.     

Fate of Azolla spp. and urea nitrogen applied to wetland rice (Oryza sativa L.)

Summary Using ¹⁵N, the fate of N applied to wetland rice either as Azolla or urea was studied in a field at the International Rice Research Institute (IRRI). In bigger plots nearby, yield response and N uptake were also determined with unlabelled N sources. Azolla microphylla was labelled by repeated application of labelled ammonium sulfate. Labelled and unlabelled N were used alternately in applications of Azolla or urea 0 and 42 days after transplanting, in order to determine the effect of the time of application on the availability of Azolla N. The quantities of Azolla N incorporated were 23% more than those of urea N (30 kg N ha^–1) in the isotope plots or 7% less in the yield response plots. Grain yield and total N uptake by the rice plants in the yield-response plots were higher in the urea-treated plots than in the Azolla-treated plots, but the physiological effect of Azolla N (grain yield response/increase in N uptake) was higher than that of rea. The labelled N balance was studied after the first and second crops of rice. Losses of labelled N after the first crop were higher from urea (30%–32%) than from Azolla (0%–11 %). Losses in N applied as a side dressing 42 days after transplanting were less than those of N applied basally. No further losses of ¹⁵N occurred after the first crop. The recovery of Azolla ¹⁵N in the first crop of rice was 39% from the basal application and 63% from the side dressing. The recovery of urea ¹⁵N was 27% from the basal application and 48% from the side dressing. Recoveries of residual N from both Azolla and urea during the second rice crop were similar. Laboratory incubation of the Azolla used and the changes in labelled exchangeable N in the soil showed that at least 65% of Azolla N (4.7% N content) was mineralized within 10 days.     

Efficiency of nitrogen-15-labelled fertilizers for rice and rye-grass cultivated in an Ultisol of Brazilian Amazonia

 The objective of this study was to determine the efficiency of two N fertilizers, (NH₄)₂SO₄ and urea, for rice (Oryza sativa L.) and rye-grass (Lolium multiflorum L.) cultivated in an Ultisol of central Amazonia using ¹⁵N as a tracer. Rice was cultivated in the field, while rye-grass was grown in a phytotron. Fertilization with (NH₄)₂SO₄ caused a 16% increase in the yield of rice grains and urea a 36% increase. In both crops total N uptake and N use efficiency of the fertilizers were higher for urea than for (NH₄)₂SO₄. The low values for N derived from fertilizer showed that the fertilizers contributed little to the total N absorbed by the plants. The "priming effect" or positive added N interaction (ANI) between the fertilizer N and soil organic N was observed, especially with urea. Immobilization by soil microorganisms was greater in the presence of urea, while losses were always higher with the (NH₄)₂SO₄ treatments. These losses were significant, and their reduction should allow more efficient use of this N fertilizer. It is possible that the N use efficiency was higher for urea due to a pH increase, caused by urea hydrolysis, which in turn may have favoured the activity of nitrifying bacteria in this extremely acid soil. Received: 6 April 1999