Growth of Rudbeckia and Leaching of Nitrates in Potting Media Amended with Composted Coffee Processing Residue,Municipal Solid Waste and Sewage Sludge

Composts made from coffee processing residue (CFPR), source separated municipal solid waste (MSW), sewage sludge and wood chips (SSWC), and sewage sludge, wood ash, wood chips and leaves (SSACL) were examined as replacements for the peat, perlite and sand found in a conventional potting medium. The perennial flower Rudbeckia hirta L. ‘Goldilocks’ (Black-Eyed Susan) was grown in media composed of 0, 10, 25, 50, 80, and 100 (percent by vol) of each compost. Leachate from media containing 0, 25, 50, and 100% compost was tested for NO₃-N and NH₃-N + NH₄-N to determine if compost would increase the potential for potting media to be a source of nitrate in surface and ground water. The effects of two mid season applications of liquid fertilizer on plant growth and nitrogen leaching were also examined.

Compared to a conventional medium without compost, differences in the growth of Rudbeckia in media with compost were few. Statistically significant decreases in growth occurred in media containing 80 and 100% CFPR, and 80% SSACL. None of the composts caused a statistically significant increase in growth. Leaching of nitrogen increased from media containing 100% CFPR, SSWC and SSACL compared to the medium with no compost. Media containing 25, 50, and 100% MSW leached less N the conventional medium. Liquid fertilizer did not significantly change the growth of Rudbeckia or the amount of nitrogen found in the leachate from any medium.     

Growth of Rhododendron,Rudbeckia and Thujia and the Leaching of Nitrates as Affected by the pH of Potting Media Amended with Biosolids Compost

A conventional potting media containing peat moss, softwood bark and sand was amended to contain 0,25,50,75 and 100 (percent vol^?1) municipal compost made from yard waste and biosolids. Each medium was adjusted with limestone and sulfur to an approximate pH of 5.0, 6.0 or 7.0. Rhododendron Panticum L. ‘Anah Kruschke’ (Rhododendron), Thujia occidentalis L. (Arborvitae) and Rudbeckia hirta L. ‘Goldilocks’ (Black-eyed Susan) were grown in each medium and pH level for 18 months. Leachate from pots was tested for NO₃-N and NH₃-N+NH₄-N to determine how media pH and the amount of compost effected the potential for potting media to be a source of nitrate in surface and ground water.

Media pH affected plant growth more than the percent compost. Compared to media with a pH of 7.0, statistically significant increases in the growth of Rhododendron occurred in media with a pH of 5.0 or 6.0. This pH effect was similar but less pronounced for Thujia. Growth of Rudbeckia was not effected by media pH or percent compost. Media with 0 and 25 percent compost leached the least nitrogen regardless of pH. Media with 75 and 100 percent compost at pH 5.0 and 6.0 leached the most nitrogen. The increase in nitrogen leaching in the more acidic media was associated with higher concentrations NH₃-N+NH₄-N. Nitrogen in leachate was greatest during the four weeks immediately after the pots were placed in the field and four weeks after fertilizer was applied in June of the second year of the experiment.     

Evaluation of New Container Media for Aglaonema Production

Mandated processing of waste by‐products in the United States has inspired national interest in addressing the effectiveness of using composted biosolids and yard trimmings to grow containerized plants. Diamond bay Chinese evergreen (Aglaonema ‘Diamond Bay’) was transplanted in containers filled with one of eight formulated media (components added by volume). Medium 1 was a standard mix commonly used in Aglaonema production (5:2:3 peat–vermiculite–perlite); medium 2 was formulated on site to contain peat–bark–stalite–rice hulls–coir (2:2:3:1:2); media 3 and 4 contained 40% biosolid–yard waste compost instead of peat and with or without 20% stalite, respectively; and media 5, 6, 7, and 8 were commercially formulated to contain peat–bark–perlite–rice hulls–coir (4:1.5:2.5:1:1, 4:1.5:2.5:1:1, 4:2:2:1:1, and 3.0:2.5:2:1:1.5, respectively). Physical and chemical properties of the eight media were in ranges 50–65% container water‐holding capacity, 2.9–7.8% air‐filled porosity, 55–80% moisture (w/w), 0.11–0.37 g·cm³ bulk density, 0.34–0.96 g·cm³ particle density, 4.2–7.2 pH, 0.12–4.4 dS·m^?1 electrical conductivity (EC), 27.3–54.5 meg/100 g cation exchange capacity (CEC), 17.9–39.0% carbon (C), and 0.22–1.7% nitrogen (N). Medium 4 (40% compost) had 5.5 times more ammoniacal N (NH₄‐N) and 1.7 times more nitrate N (NO₃‐N) than that of the standard commercial mix. At week 8, plants grown in media 2 and 5 were 8.9% to 9.5% taller than plants grown in medium 1 (commercial standard). At week 16, there were no significant differences in plant heights or growth indices among media. At week 24, there were no significant differences in plant height, growth index, visual quality, shoot dry weight, and root dry weight among media. However, cumulative phosphorus (P) leaching from media 1, 4, and 5 was significantly more than leaching from media 2 and 8. This study suggests that compost may serve as a horticulturally suitable and cost‐effective alternative to peat‐based media for Aglaonema production.     

Leachability of Arsenic from Field Containers Filled With Plant Growth Medium Amended With Biosolids Compost

The leaching of arsenic (As) from plant growth medium, admixed with different proportions of composted biosolids in field containers, was determined over a four-month period. Eight-week-old perennial flowers, Coreopsis grandiflora L, were transplanted in the field in 2-L containers filled with plant growth media. The treatments were replicated three times and rainfall was supplemented to supply 2 cm of water per day. Water percolating through potted plant containers was collected biweekly and analyzed for As using graphite furnace atomic spectrometry. The concentrations of As in the leachates increased with increasing proportions of compost in the medium and decreased with time of leaching, generally remaining below the drinking water standard of 50 μg/L after two months. Leaching of As occurred at a rapid rate initially but then continued at a slow rate. Compared to other metals of concern, as Cd, Cr, Ni and Pb, As in the compost appeared more mobile.     

Relationships between electrical conductivity and fertilizer levels in an azalea Liner growing medium

Abstract

Regression analyses were used to survey the effects of extractable NO₃‐N, P, K, Ca, Mg, and soil pH on electrical conductivity (EC) in a 1: 1: 1 (v/v/v) peat‐sand‐perlite azalea (Rhododendron sp.) growing medium amended with soluble 21–3–6 (N‐P‐K) or slow‐release 18–3–6 fertilizer sources. Simple linear correlations indicated a high degree of relationship between NO₃‐N, P, and K versus EC (r=0.95**, 0.79**, and 0.79**, respectively). Partial regression coefficients suggested that NO.‐N was the primary ionic species affecting EC. The correlations between EC versus P and K were apparently related to their intercorrelation with NO₃ ‐N, associated with the use of N‐P‐K fertilizers. These relationships were constant across fertilizer sources. The results demonstrate a potential for the use of soil EC in the estimation of NO₃‐N in soilless rooting media.     

Pathways of different forms of nitrogen and role of ammonia‐oxidizing bacteria in alkaline residue sand from bauxite processing

Nitrogen (N) dynamics and associated processes are often overlooked in the rehabilitation protocols of disturbed landscapes. This study reports on the transformations of N fertilizers and the microbial community, and plant growth responses in rehabilitated strongly alkaline residue sand from bauxite processing (BRS). Ryegrass was grown in specifically designed growth chambers in a two‐factorial completely randomized design. Different forms of N fertilizer, such as ammonium sulphate (AS), potassium nitrate (KN) and glycine (GL), were applied at two rates. Nitrogen uptake by plants, residual inorganic N and N losses through leaching and volatilization were determined and quantified throughout the growing period. The abundance of both ammonia‐oxidizing archaea (AOA) and bacteria (AOB) was determined by quantitative polymerase chain reaction. The results showed that N uptake was greater with KN fertilizer (31.3–56.4%) than with AS (23.4–47.8%) and GL (16.4–38.1%), in spite of the substantial leaching loss of NO₃^?. Combined N losses by volatilization and leaching with GL (39–53%) and AS (40–60%) fertilizers indicated both physico‐chemical and biological transformations of N by mineralization and nitrification. Ammonia‐oxidizing bacteria, rather than AOA, were the dominant nitrifiers that colonized the freshly rehabilitated BRS growth media. The gene copy number of AOB correlated with both soil extractable NO₃^?‐N (r = 0.92, P < 0.001) and ryegrass leaf biomass N (r = 0.89, P < 0.001). We concluded that AOB play a pivotal role in the cycling of N in BRS, whereas NO₃^?‐N is critical for plant N nutrition and rehabilitation in the alkaline BRS disposal areas.     

Mineralization and N Fertilizer Equivalent Value of Composts as Assessed by Tall Fescue (Festuca arundinacea)

The capability to determine nitrogen availability of composts is necessary to ensure that such materials will provide sufficient fertilization to the growing crop and cause minimal environmental degradation. A greenhouse study using tall fescue as a bioindicator was used to evaluate nitrogen availability of two biosolids composts, two mixed yard waste-poultry manure composts, and one commercially-processed poultry litter. Five inorganic nitrogen (as NH₄NO₃-N) treatments applied at 0, 22.5, 45, 67.7, and 90 mg N/kg soil were employed to establish an N calibration curve. Yield, fescue biomass total nitrogen (as total Kjeldahl N (TKN)), and soil TKN and KCl extractable NO₃^?-N and NH₄⁺-N concentrations of the organically amended treatments were compared to the inorganically fertilized treatments to determine amendment N mineralization rates and N fertilizer equivalent values (NFEV). Nitrogen mineralization rates were greatest in the poultry litter (21%) and Panorama yard waste compost (5%) amended pots. The NFEV of these amendments were 49% and 10%, respectively. Wolf Creek biosolids compost and Huck's Hen Blend yard waste compost immobilized N (?5% and 0.18%, respectively), and had percent NFEV of ?0.66% and 0.19%, respectively. Rivanna biosolids compost immobilized N (?15%), but the NFEV was 30% due to the relatively high inorganic N content in the amendment. Nitrogen mineralization and NFEV were generally greater in amendments with greater total N concentrations and lower C:N values. The total N concentration and C:N values were less reliable variables in predicting N mineralization and percent NFEV when a significant portion of the total N was in the inorganic form. Nitrogen equivalency value and N mineralization for each amendment increased with time of sampling, indicating the potential for early season N insufficiency to plants fertilized with compost due to lack of synchrony between N mineralization and plant N needs.     

Comparison of Herbaceous Perennial Plant Growth in Seaweed Compost and Biosolids Compost

Liners of angelonia ‘Pink’ (Angelonia angustifolia Benth.), shooting star (Pseuderanthemum laxiflorum), coreopsis ‘Early Sunrise’ (Coreopsis grandiflorum Hogg ex Sweet.), and scutellaria ‘Purple Fountains’ (Scutellaria costaricana H. Wendl.) were transplanted into containers filled with, by volume, 1) 100% compost; 2) 60% compost, 25% vermiculite, 15% perlite; 3) 30% compost, 30% sphagnum peat, 25% vermiculite, 15% perlite; 4) 0% compost, 60% sphagnum peat, 25% vermiculite, 15% perlite. Two compost products were evaluated: SW, a 1:1 by volume mixture of partially composted seaweed and partially composted yard trimmings and SYT, a 1:1 by weight mixture of biosolids compost and yard trimmings compost. There was no difference in angelonia shoot dry mass among the different percentages of SW compost but angelonia plants grown in 0 and 30% SYT had greater shoot dry mass than plants grown in 60 or 100% SYT. Shoot dry mass of shooting star plants increased as the percentage of SYT compost increased from 0 to 30 % and then decreased while shoot dry mass of plants grown in SW compost decreased as the percentage of compost increased. There was no difference in coreopsis shoot dry mass or scutellaria shoot dry mass between the two compost products and there also was no difference in shoot dry mass among the different percentages of either compost product.     

Reducing nitrogen leaching‐losses from containerized plants: The effectiveness of controlled‐release fertilizers

Abstract

To evaluate the effectiveness of controlled‐release fertilizer (CRF) for reducing nitrogen (N) leaching‐losses from containerized greenhouse crops, three experiments were conducted where CRFs were applied in different ways and compared to water‐soluble fertilizer (WSF). In each experiment, ‘First Lady’ marigold (Tagetes erecta L.) plants in 0.5‐liter pots of a soilless growth medium were fertilized with the same amount of ? from 20N‐4.3P‐16.6K WSF, Osmocote 14N‐6.2P‐11.6K CRF, or Nutricote 14N‐6.2P‐11.6K CRF fertilizers. The volume of irrigation water applied to all treatments was the same in each experiment. Nitrogen content, as NH₄‐N and NO₃‐N in container leachates, and plant growth were measured and used to compare WSF with CRFs incorporated in the growth medium, or as applied to the surface, in either one large application or two small doses. A single large application of CRF at planting resulted in as much or more ? leaching than the regular application of WSF. Effectiveness of CRFs in limiting ? leaching was greatly increased by making two smaller applications, the first at planting and the second 15 to 35 days later. More ? was recovered in the leachate when CRFs were incorporated in the growth medium compared to surface application. Regardless of fertilizer type, application method, timing of application, or for each individual experiment, NO₃‐N was the predominant ? form found in the leachate and more than one‐half of the total amount of ? leached during each experiment was recovered within 30 days of planting.     

Ryegrass Utilization of Nutrients Released from Composted Biosolids and Cow Manure

Use of composts as soil amendments to enhance crop growth requires a knowledge of rates and amounts of nutrients released. A greenhouse study was conducted using ryegrass (Lolium perenne L.) as a test plant to evaluate this release from composts. The experimental design consisted of four blocked replicates in a complete factorial with two types of compost (wastewater treatment plant biosolids and cow manure), four application rates (1, 2, 5 and 10 percent of weight of sand), and three fertilizer treatments (0, 100 mg N/kg mixture, and 100 mg P/kg mixture). Rye-grass top growth was harvested after 21 days. The regrowth was harvested three additional times. Roots were recovered after the fourth harvest. Total N uptake was significantly and positively affected by the total amount of N supplied by the compost or compost plus N fertilizer (r² values ranged from 0.992 to 0.999). Initial N uptake depended on the mineral N concentration in the compost and was higher from biosolids than from cow manure compost. Biosolids compost contained 10 times more mineral N and this N was primarily taken up in the first two harvests. Cow manure compost, however, provided N gradually over the entire 84 day test. In addition to N, both composts also supplied P, K, and other major and minor nutrients essential for plant growth.     

Nitrogen and Phosphorus Availability in Groundfish Waste and Chitin-Sludge Cocomposts

Seafood processing generates a substantial volume of wastes. This study examined the feasibility of converting the fish waste into useful fertilizer by composting. Groundfish waste and chitin sludge generated from the production of chitin were composted with red alder or a mixture of western hemlock and Douglas-fir sawdust to produce four composts: alder with groundfish waste (AGF); hemlock/fir with groundfish waste (HGF); alder with chitin sludge (ACS); and hemlock/fir with chitin sludge (HCS). The resulting AGF had a higher total N and a lower C:N ratio than the other three composts. A large portion of the total N in the AGF, HGF, and HCS composts was in inorganic forms (NH₄⁺-N and NO₃^?-N), as opposed to only two percent in the ACS compost. Alder sawdust is more quickly decomposed, which favored N retention and limited nitrification during the composting period. It was less favorable than the hemlock/Douglas fir sawdust for composting with chitin sludge. Corn growth on soil amended with compost was dependent upon both compost type and rate. Nitrogen and P availabilities in all composts except the ACS were high and compost addition enhanced corn yields, tissue N and P concentrations, and N and P up-take. Neither the total N concentration nor the C:N ratio of the composts was an effective measure of compost N availability in the soil. Because soil inorganic N test levels correlated well with the corn biomass, tissue N and N uptake, they should be an effective measure of the overall compost effects on soil N availability and corn growth response. Phosphorus concentration, which increased linearly with increasing compost rates, was related to soil P availability from compost additions and correlated well with corn biomass, tissue P concentration and P uptake under uniform treatments of N and K fertilizers. Composting groundfish waste with alder or hemlock/Douglas-fir sawdust can produce composts with sufficient amounts of available N and P to promote plant growth and is considered to be a viable approach for recycling and utilizing groundfish waste.     

Crop nitrogen recovery and soil nitrogen dynamics in a 10‐year field experiment with biowaste compost

When fertilizing with compost, the fate of the nitrogen applied via compost (mineralization, plant uptake, leaching, soil accumulation) is relevant both from a plant‐production and an environmental point of view. In a 10‐year crop‐rotation field experiment with biowaste‐compost application rates of 9, 16, and 23 t ha^–1 y^–1 (f. m.), the N recovery by crops was 7%, 4%, and 3% of the total N applied via compost. Due to the high inherent fertility of the site, N recovery from mineral fertilizer was also low. In the minerally fertilized treatments, which received 25, 40, and 56 kg N ha^–1 y^–1 on average, N recovery from mineral fertilizer was 15%, 13%, and 11%, respectively. Although total N loads in the compost treatments were much higher than the N loads applied with mineral fertilizer (89–225 kg N_tot ha^–1 y^–1 vs. 25–56 kg N_tot ha^–1 y^–1; both on a 10‐year mean) and the N recovery was lower than in the treatments receiving mineral N fertilizer, soil NO ‐N contents measured three times a year (spring, post‐harvest, autumn) showed no higher increase through compost fertilization than through mineral fertilization at the rates applied in the experiment. Soil contents of N_org and C_org in the plowed layer (0–30 cm depth) increased significantly with compost fertilization, while with mineral fertilization, N_org contents were not significantly higher. Taking into account the decrease in soil N_org contents in the unfertilized control during the 10 years of the experiment, 16 t compost (f. m.) ha^–1 y^–1 just sufficed to keep the N_org content of the soil at the initial level.     

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO₃-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO₃-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH₄-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH₄-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.     

Nitrapyrin effect on corn N‐15 uptake efficiency,denitrification and nitrate leaching

Abstract

The effect of nitrapyrin on the fate of fertilizer nitrogen (N) applied to soil needs further investigation. Our objective was to determine the effect of nitrapyrin under two different leaching regimes on the fate of ammonium sulfate‐nitrogen [(NH₄)₂SO₄‐N] added to the soil, namely corn N uptake, denitrification, nitrate leaching and soil residual N. A Nunn sandy clay loam soil (fine, montmorillonitic, mesic, aridic, argiustoll), low in residual inorganic N was used. Nitrogen‐15 enriched (NH₄)₂SO₄ (5 atom% N‐15) was applied at five rates (0, 50, 100, 200, and 400 mg/kg), nitrapyrin at three rates 0, 1.3, and 2.6 μL/kg (0, 2.36, and 4.72 L/ha) and leaching at two rates (0 and 1000 mL over field capacity in two 500‐mL increments at 3 and 6 weeks after planting) in a complete factorial arrangement with three replications. Corn (Zea mays L.) seeds were planted in pots (2 kg soil/pot) and allowed to grow for 80 days in a greenhouse. The atom% N‐15 values were determined in plant tops, leachates and soil samples using a mass spectrometer. The results showed that N fertilizer increased dry matter production, plant N concentration, leaching of nitrates and denitrification significantly. The effect of nitrapyrin on yield was not statistically significant, but, it at a rate equivalent to 4.72 L/ha reduced denitrification and nitrate (NO₃) leaching and increased N uptake efficiency. Application of 4.72 L/ha of nitrapyrin versus control showed the following results respectively, N uptake: 46.3 versus 39.6%, denitrification: 26.3 versus 35.3% and NO₃ leaching: 2.7 vesus 6.7% of fertilizer N‐15. Nitrapyrin increased soil residual fertilizer N‐15 in organic matter and roots. The result of this study show that application of nitrapyrin at an adequate rate decreases denitrification and NO₃ leaching and increases N uptake efficiency.     

Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal

Leaching losses of N are a major limitation of crop production on permeable soils and under heavy rainfalls as in the humid tropics. We established a field trial in the central Amazon (near Manaus, Brazil) in order to study the influence of charcoal and compost on the retention of N. Fifteen months after organic‐matter admixing (0–0.1 m soil depth), we added ¹⁵N‐labeled (NH₄)₂SO₄ (27.5 kg N ha^–1 at 10 atom% excess). The tracer was measured in top soil (0–0.1 m) and plant samples taken at two successive sorghum (Sorghum bicolor L. Moench) harvests. The N recovery in biomass was significantly higher when the soil contained compost (14.7% of applied N) in comparison to only mineral‐fertilized plots (5.7%) due to significantly higher crop production during the first growth period. After the second harvest, the retention in soil was significantly higher in the charcoal‐amended plots (15.6%) in comparison to only mineral‐fertilized plots (9.7%) due to higher retention in soil. The total N recovery in soil, crop residues, and grains was significantly (p < 0.05) higher on compost (16.5%), charcoal (18.1%), and charcoal‐plus‐compost treatments (17.4%) in comparison to only mineral‐fertilized plots (10.9%). Organic amendments increased the retention of applied fertilizer N. One process in this retention was found to be the recycling of N taken up by the crop. The relevance of immobilization, reduced N leaching, and gaseous losses as well as other potential processes for increasing N retention should be unraveled in future studies.     

Phytotoxicity of Biosolids Compost at Different Degrees of Maturity Compared to Biosolids and Animal Manures

Biosolids compost is a good organic amendment but immature compost can exhibit phytotoxic behavior which can be attributed to different toxic substances. Our objective was to determine the phytotoxicity of: i) Biosolids; ii) Mix of biosolids and wood sawdust sampled a day after composting started; iii) The same material sampled at the end of the thermophilic stage; iv) cured compost; v) cow manure and vi) horse manure A germination bioassay was carried out using Lolium perenne (ryegrass) seeds: germination and root growth percentage were determined as well as electrical conductivity, pH, phenol content and volatile organic acids. In three treatments, Ni, Pb, Zn, Cu and Cd were also determined. Ammonia volatilization was determined during biosolids composting. The germination percentage varied from 67% to 95% but the inhibition of root growth appears to be a more sensitive phytotoxicity indicator (18% to 74%. Phytotoxic effects on germinating ryegrass were mainly related to extract pH and electrical conductivity. Potentially toxic elements, volatile organic acids, phenolic compounds and ammonia were not related to germination.     

Soil Inorganic Nitrogen Content and Indices of Red Raspberry Yield,Vigor, and Nitrogen Status as Affected by Rate and Source of Nitrogen Fertilizer

Abstract

The single‐year response of soil inorganic nitrogen (N) content and indices of red raspberry (Rubus ideaus L.) yield, vigor, and N status to rate and source of fertilizer N were determined. Twenty‐nine trials were conducted in commercial plantings from 1994 to 1996. Treatments were 0, 55, or 110 kg N ha^?1 as ammonium nitrate or 55 kg N ha^?1 as a slow‐release fertilizer product containing 60% polycoated sulfur‐coated urea and 40% urea. Soil nitrate (NO₃) content frequently increased during the growing season, indicating that soil N supply was nonlimiting. The plant indices were generally insensitive to fertilizer‐N rate under these high‐N fertility conditions. Soil nitrate content measured after berry harvest was frequently excessive even at the recommended N rate and can be used to identify fields with excess N fertility. The slow‐release N fertilizer provided limited benefits compared with use of ammonium nitrate.     

Effects of Slow‐Release Fertilizers on Tomato Growth and Nitrogen Leaching

Tomatoes (Lycopersicon esculentum Mill.) were grown in 9.46‐L plastic pots in a glasshouse for evaluation of their growth and nitrogen (N) losses through leaching. Plants were fertilized with either ammonium nitrate (AN) or one of three slow‐release N fertilizers. The slow‐release N fertilizers were Georgia Pacific liquid 30‐0‐0 (L30), Georgia Pacific granular 42‐0‐0 (N42), and Georgia Pacific granular 24‐0‐0 (N24). Each fertilizer was applied at 112 low N rate (L) and 224 high N rate (H) kg N ha^?1. The pots were filled with either a sandy soil from Florida or a loam soil from Georgia. Increasing the N rate did not influence shoot biomass at 19 days after transplanting (DAT) and increased biomass production at 77 DAT. Shoot biomass differed significantly among fertilizer treatments. The accumulation of N in shoots was significantly influenced by fertilizer source, rate, and soil type. The plants grown in the loam soil accumulated significantly more N than those grown in the sandy soil with the same treatment. In the loam soil, the highest and lowest N accumulations occurred in the N42‐H and N24‐L treatments, respectively; and in the sandy soil the corresponding treatments were AN‐H and N24‐L. The amount of N leached varied with the different fertilizers, soils, and time. The net leaching of N ranged from ?0.4% to 6.3% of the fertilizer N applied for the loam soil and 6.5% to 32.9% for the sand soil. The net amount of N leached from the loam soil at both high and low application rates declined in the following order: AN > N24 > N42 > L30; the corresponding order for the sandy soil was AN‐H > N42‐H > L30‐H > N24‐H. L30 had the least leaching potential, and ammonium nitrate had the most. Slow‐release fertilizers had significantly less leaching N than did ammonia nitrate.     

Effects of amendments and fertilization on plant growth,nitrogen and phosphorus availability in rehabilitated highly alkaline bauxite‐processing residue sand

The effects of organic–inorganic amendments and nitrogen‐phosphorus (NP) fertilization (NH₄NO₃ plus Ca (H₂PO₄)₂) on ryegrass (Lolium rigidum) growth, and nitrogen (N) and phosphorus (P) availability in highly alkaline bauxite‐processing residue sand (BRS), were examined in a pot experiment. The BRS used was either unamended (control) or amended with organic (e.g. greenwaste compost and biochar) or inorganic (e.g. zeolite) materials at a rate of 10% v/v. BRS from 15 years of rehabilitation (15YRRH) was also used as the second control. NP fertilizer was applied at different rates. The experimental set up was arranged in a two factorial complete randomized design. BRS with zeolite and 15YRRH at NP fertilizer rates of 2.0 and 2.5 t/ha produced the highest dry matter, leaf N concentration and N uptake by ryegrass, which were significantly higher (P < 0.05) than the other treatments, suggesting the potential of zeolite in providing stability of applied N fertilizer in BRS. Further, BRS with biochar at NP rates 2.0 and 2.5 t/ha can also be suitable amendments as they enhance growth and also improved the N and P supplying capacity of BRS. Ryegrass leaf P concentration and P uptake were above the critical P values in the 15YRRH compared with organic–inorganic amended BRS, suggesting that time is important for better P uptake from the residue. It is concluded that zeolite and biochar combined with appropriate NP fertilizer rates can improve plant growth and provide a source of nutrients for ryegrass establishment in bauxite residue storage areas. The results need to be tested in field conditions before being advised in farming practice.     

Effects of biochar compared to organic and inorganic fertilizers on soil quality and plant growth in a greenhouse experiment

Our contemporary society is struggling with soil degradation due to overuse and climate change. Pre‐Columbian people left behind sustainably fertile soils rich in organic matter and nutrients well known as terra preta (de Indio) by adding charred residues (biochar) together with organic and inorganic wastes such as excrements and household garbage being a model for sustainable agriculture today. This is the reason why new studies on biochar effects on ecosystem services rapidly emerge. Beneficial effects of biochar amendment on plant growth, soil nutrient content, and C storage were repeatedly observed although a number of negative effects were reported, too. In addition, there is no consensus on benefits of biochar when combined with fertilizers. Therefore, the objective of this study was to test whether biochar effects on soil quality and plant growth could be improved by addition of mineral and organic fertilizers. For this purpose, two growth periods of oat (Avena sativa L.) were studied under tropical conditions (26°C and 2600 mm annual rainfall) on an infertile sandy soil in the greenhouse in fivefold replication. Treatments comprised control (only water), mineral fertilizer (111.5 kg N ha^–1, 111.5 kg P ha^–1, and 82.9 kg K ha^–1), compost (5% by weight), biochar (5% by weight), and combinations of biochar (5% by weight) plus mineral fertilizer (111.5 kg N ha^–1, 111.5 kg P ha^–1, and 82.9 kg K ha^–1), and biochar (2.5% by weight) plus compost (2.5% by weight). Pure compost application showed highest yield during the two growth periods, followed by the biochar + compost mixture. biochar addition to mineral fertilizer significantly increased plant growth compared to mineral fertilizer alone. During the second growth period, plant yields were significantly smaller compared to the first growth period. biochar and compost additions significantly increased total organic C content during the two growth periods. Cation‐exchange capacity (CEC) could not be increased upon biochar addition while base saturation (BS) was significantly increased due to ash addition with biochar. On the other hand, compost addition significantly increased CEC. Biochar addition significantly increased soil pH but pH value was generally lower during the second growth period probably due to leaching of base cations. Biochar addition did not reduce ammonium, nitrate, and phosphate leaching during the experiment but it reduced nitrification. The overall plant growth and soil fertility decreased in the order compost > biochar + compost > mineral fertilizer + biochar > mineral fertilizer > control. Further experiments should optimize biochar–organic fertilizer systems.