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.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.     

Regeneration of Nitrogen Fertility In Disturbed Soils Using Composts

Soil disturbance often results in loss of soil organic matter and nitrogen (N) fertility, making revegetation of barren areas difficult. Yard waste composts are a potential source material to regenerate soil fertility so that revegetation success is improved. The N release behaviors of several compost materials produced within California were evaluated during a long-term, 586-day aerobic incubation. Two general types of compost were tested, including yard waste compost materials (lawn clippings and chipped brush) and cocomposted materials (biosolids bulked and composted with yard waste materials). Nitrogen release from composted material was measured using periodic soil solution extraction and soluble N analysis. Nitrogen release rates varied widely between source materials during the initial portions of the incubation period, with cocomposts having much greater release rates than the yard waste composts. Yard waste composts that were poorly cured or had high woody fiber content showed net immobilization of N during the initial incubation periods, which could potentially lead to N-limitations for plant growth in field conditions. Following additional curing in the soil, however, all yard waste compost materials had positive net N mineralization release rates. Release rates were similar to some of the native soils used as reference materials. The relationship of long-term aerobic N release and several other indicators of mineralizable or “bioavailable” N were evaluated, but the relationship of these other indicators with the aerobic incubation data was low. Because the cumulative N release from yard waste compost materials was a small fraction of the material's total N content, N leaching losses in field conditions are expected to be small and of short duration. Steady, long-term N release patterns were observed from composts throughout the second half of the study and would be expected to continue for an extended period in the field. Composts are shown to provide a suitable replacement source of slowly available N for plant establishment on drastically disturbed, low nutrient soils.     

Nutritional Values of Some Biowastes As Soil Amendments

As a result of increased population, improved standards of living, and strict environmental laws, biowastes have been generated in huge quantities. Thus, land applications of these wastes are desirable, or even necessary, to keep the environment healthy and to conserve natural resources. Yet, the success of such uses requires knowledge of complex biochemical reactions when the wastes are applied to soils. To obtain this knowledge, we evaluated soil amendment properties, primarily nitrogen (N) mineralization/immobilization of six bio wastes when used as plant growth media. An immature yard trimmings compost, ground fresh corn stovers, a commercial peat moss, a chicken manure, and two biosolids were each mixed with a Mollisol at either 25 percent and 50 percent by volume for the plant based wastes, or at 2.5 percent and 5.0 percent by weight for the animal based wastes. Treatments with urea at 0, 70 and 210 mg N kg^?1 were included for comparison. The treated soils were incubated moist for two weeks at which time they were sampled for chemical analysis, and planted to tomatoes. The results showed that those wastes, when added to soil, produced growth media with C/N < 15, and released inorganic N that increased dry matter yield of tomatoes many times over that of the unamended control. In contrast, a waste amended soil with a C/N > 20 immobilized some inorganic N, reduced plant growth, and caused N deficiency in tomatoes. Such a deficiency was characterized by low N concentrations in leaves (< 2.0 percent) and chlorosis, which corresponded to a color index of 0.25 or less. Biowaste amendments also affected soil P extractability differently: Chicken manure increased NaHCO₃-extractable P many fold over the control, whereas corn stover, peat moss and raw biosolids did not. The yard trimmings compost and the anaerobically digested biosolids increased soil P moderately.     

Effect of lignite amendment on carbon and nitrogen mineralization from raw and composted manure during incubation with soil

The application of animal manure as a source of plant nutrients requires the determination of the amount and pattern of nutrient mineralization from manure. A laboratory incubation study was conducted to investigate the influence of lignite amendment and lignite type on carbon (C) and nitrogen (N) mineralization in raw (feedstock) and composted cattle manure following application to soil at 30 and 60 t ha^-1. The mineralization of C and N was determined by measuring changes in CO₂ evolution and mineral N (NH₄⁺ -N + NO₃^- -N) over 40 d. The results showed that lignite amendment suppressed the amount of manure C mineralized in both feedstock and compost, with the effect being more pronounced in the compost. Over the 40-d incubation, the percentage of applied C mineralized was 26.4%-27.8% and 16.3%-21.4% in unamended and lignite-amended feedstocks, respectively. The corresponding C mineralized in the composts was 12.4%-14.1% and 3.5%-6.5%. Lignite had no significant effect on the net N mineralized in compost (4.8%-6.7% and 2.5%-7.8% in unamended and lignite-amended composts, respectively). Lignite had either no effect or increased the net N mineralized in feedstock (from 3.2%-8.7% without lignite to 10.4%-13.5%) depending on the type of lignite used. This study suggests that using lignite-amended manure, especially when composted, has the potential to build up soil organic C without limiting the availability of mineral N.     

Nitrogen Availability Seven Years After a High-Rate Food Waste Compost Application

Long-term effects of compost application are expected, but rarely measured. A 7-yr growth trial was conducted to determine nitrogen availability following a one-time compost application. Six food waste composts were produced in a pilot-scale project using two composting methods (aerated static pile and aerated, turned windrow), and three bulking agents (yard trimmings, yard trimmings + mixed paper waste, and wood waste + sawdust). For the growth trial, composts were incorporated into the top 8 to 10 cm of a sandy loam soil at application rates of approximately 155 Mg ha^?1 (about 7 yd³ 1000 ft²). Tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’) was seeded after compost incorporation, and was harvested 40 times over a 7-yr period. Grass yield and grass N uptake for the compost treatments was greater than that produced without compost at the same fertilizer N rate. The one-time compost application increased grass N uptake by a total of 294 to 527 kg ha^?1 during the 7-yr. field experiment. The greatest grass yield response to compost application occurred during the second and third years after compost application, when annual grass N uptake was increased by 93 to 114 kg ha^?1 yr^?1. Grass yield response to the one-time compost application continued at about the same level for Years 4 through 7, increasing grass N uptake by 42 to 62 kg ha^?1 yr^?1. Soil mineralizable N tests done at 3 and 6 yr. after application also demonstrated higher N availability with compost. The increase in grass N uptake accounted for 15 to 20% of compost N applied after 7-yr. for food waste composts produced with any of the bulking agents. After 7-yr, increased soil organic matter (total soil C and N) in the compost-amended soil accounted for approximately 18% of compost-C and 33% of compost-N applied. This study confirmed the long-term value of compost amendment for supplying slow-release N for crop 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.     

Leaching of Nitrate,Ammonium, and Phosphate From Compost Amended Soil Columns

Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha^?1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha^?1 rate and leached with deionized water (300 ml day^?1, for five days; equivalent to 34 cm rainfall). The concentrations of NO₃-N, NH₄-N, and PO₄-P in leachate reached as high as 246, 29, and 7 mg L^?1, respectively. The amount of N and P leached accounted for 3.3-15.8 percent of total N and 0.2-2.8 percent of total P in the compost. The leaching peaks of NO₃-N occurred following the application of only 300-400 ml water (equivalent to 6.8-9.1 cm rainfall).     

Relating Compost Measures of Stability And Maturity to Plant Growth

Assessment of compost maturity is important for successful use of composts in agricultural and horticultural production. We assessed the “maturity” of four different sawdust-based composts. We composted sawdust with either cannery waste (CW), duck manure (DM), dairy (heifer) manure (HM) or potato culls (PC) for approximately one year. Windrows were turned weekly for the first 60 days of composting, covered for four winter months and then turned monthly for six more months. We measured compost microbial respiration (CO₂ loss), total C and N, C:N ratio, water soluble NO₃-N and NH₄-N, dissolved organic carbon (DOC), pH and electrical conductivity at selected dates over 370 days. Compost effects on ryegrass biomass and N uptake were evaluated in a greenhouse study. We related compost variables to ryegrass growth and N uptake using regression analysis. All composts maintained high respiration rates during the first 60 days of composting. Ammonium-N concentrations declined within the first 60 days of composting, while NO₃-N concentrations did not increase until 200+ days. After 250+ days, DM and PC composts produced significantly more ryegrass biomass than either CW or HM composts. Total C, microbial respiration and water-extractable NO₃-N were good predictors of compost stability/maturity, or compost resistance to change, while dissolved organic carbon, C:N ratio and EC were not. The compost NO₃-N/CO₂-C ratio was calculated as a parameter reflecting the increase in net N mineralization and the decrease in respiration rate. At ratio values >8 mg NO₃-N/mg CO₂-C/day, ryegrass growth and N uptake were at their maximum for three of the four composts, suggesting the ratio has potential as a useful index of compost maturity.     

Soil restoration in semiarid Patagonia: Chemical and biological response to different compost quality

Restoration of soils burned by a wildfire using composted amendments of different origin (biosolids and municipal organic wastes) and final particle size (screened and unscreened) was studied after 6 and 12 months of application in a field trial in semiarid NW Patagonia. Composts were applied at 40 Mg ha⁻¹. A fertilized treatment with soluble N (100 kg ha⁻¹) and P (35 kg ha⁻¹), and a non-treated control were also included. As indicators of soil response, chemical (electrical conductivity, pH, organic C, total N, extractable P), biological (potential microbial respiration, potential net N mineralization, N retained in microbial biomass) and physical (temperature and soil moisture) properties were evaluated. Plant soil cover was also estimated. Soil chemical and biological properties showed a high response to organic amendment addition, more evident after the wet season (12 months of application). Soil organic C, total N and extractable P increased significantly with biosolids composts (BC), and soil pH with municipal composts (MC). Potential microbial C respiration and net N mineralization were similar for both MC and BC, and significantly higher than in the control and the inorganic fertilized treatment; when calculated on C or N basis the highest values corresponded to MC. Results imply that in terms of organic C accretion, BC were more effective than MC due to higher amounts of total and recalcitrant C. Screened and unscreened composts did not differ significantly in their effects on soil properties. The increase of organic C with BC did not contribute to increase soil moisture, which was even higher in control plots after the wet season; higher plant cover and water consumption in amended plots could also explain this pattern. Inorganic fertilization enhanced higher plant cover than organic amendments, but did not contribute to soil restoration.     

STABILITY,NITROGEN MINERALIZATION CAPACITY AND AGRONOMIC VALUE OF COMPOST-BASED GROWING MEDIA FOR LETTUCE CULTIVATION

Seven composts were used as growing media for lettuce mixed with peat at 25 and 50% (v/v). On the unblended composts and the resulting 14 mixes were determined the main physical-chemical characteristics and the stability by means of a respirometric test in a liquid environment. The potential nitrogen (N)-mineralization capacity of the mixes was measured during the respirometric test solely by the ammonium (NH⁺ ₄-N) determination. The lettuce pot-growing test was performed with and without fertilization; plant biomass and total Kjeldahl nitrogen (TKN) tissue content were measured after cultivation for two months. Compost origin, rate in substrates and fertilization affected plant growth and nitrogen uptake. Multiple regression analysis showed that the stability, proved to be a good predictor for plant growth inhibition. Moreover N-mineralization capacity showed a good fitting with plant uptake. The coupled stability and nitrogen mineralization test gives reliable information about the potential constraints in compost-based growing media.     

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.     

Effects of aeration and moisture during windrow composting on the nitrogen fertilizer values of dairy waste composts

The objective of this work was to evaluate the effects of turning and moisture addition during windrow composting on the N fertilizer values of dairy waste composts. Composted-dairy wastes were sampled from windrow piles, which received four treatments in a 2×2 factorial of turning (turning vs. no turning) and moisture addition (watering vs. no watering) at two stages of maturity (mature vs. immature). Composts were characterized for their chemical properties. An 84-day laboratory incubation of soils with addition of the composts at two levels was conducted to evaluate the inorganic N accumulation patterns from the variously treated composts. Chemical analyses of variously treated composts did not differ between compost treatments or maturity. In contrast, the inorganic N accumulation patterns differed between soils that received immature versus mature turned composted-dairy wastes. The results suggested that turning was a more important factor than moisture addition affecting the composting process. There was no significant difference in inorganic N accumulation patterns among soils that received different immature composts, while the N accumulation patterns observed for soils that received different mature composts depended on compost treatments. Soils amended with mature composts treated by frequent turning had higher N mineralization potentials (N₀), mineralization rate constants (K), and initial potential rates (N₀K) in comparison to soils with composts that had not been turned. Soils with mature composts treated by watering had a higher N₀, lower K, and therefore similar N₀K when compared to soils with composts that had not been watered. Soils that received mature composts treated by watering and frequent turning had higher N mineralization potentials and N₀ to total organic N ratios than soil alone, which suggested that intensive management of composting would ensure positive N fertilizer values of dairy waste composts, if the appropriate composting duration is completed.     

Response of kentucky‐31 tall fescue to broiler litter and composts made from broiler litter

Abstract

Recycled paper treated with boric acid (BA) is gaining acceptance as bedding in broiler houses. Applying this litter to Kentucky 31 (K‐31) tall fescue, Festuca Arundinacea Shreb, pastures raises the issue of potential boron (B) toxicity. There is also the question of nitrogen (N) availability from composts made with borated paper and broiler manure. The effect of five N sources at 224, 448, and 896 kg N/ha in a factorial arrangement plus an unfertilized control and high nitrogen‐phosphorus‐potassium (NPK) + additional boron at 45 kg B/ha on growth and NPKB uptake of K‐31 tall fescue was determined in a greenhouse during the spring of 1992. The five N sources were (1) inorganic salts, (2) compost made from hen manure, broiler manure, fescue hay and bark (M1), (3) fresh broiler litter (M2), (4) compost made from broiler manure and borated paper bedding (M3), (5) compost from hen manure, oak leaves, broiler litter (M4). The soil was Cecil sandy clay loam subsoil. Six harvests were made at 4‐cm cutting heights for determination of dry matter, N, P, K, and B uptake in tops, stubble, roots, and residue. Relative yield response of M2 was 65% of that from inorganic NPK, whereas the yield of the three composts was 22–30% of that from inorganic NPK. Over 50% of the N applied in compost residue remained at the soil surface. Boron toxicity to K‐31 as estimated from yield reduction or from visual symptoms did not occur from 20 kg B/ha in compost made with borated paper (M3). However, a 12% yield reduction did occur at the 45 kg B/ha rate from inorganic B. Industry efforts to reduce the amount of boric acid used in the treatment of recycled paper, the high mobility of B in humid areas, the apparent ability of K‐31 tall fescue to tolerate massive quantities of compost and high rates of B application suggest that the application of the broiler litter from houses where BA‐treated recycled paper is used as bedding would be environmentally safe at application rates based on N requirements of K‐31 tall fescue.     

Transformations of carbon and nitrogen during composting of animal manure and shredded paper

Composts produced from animal manures and shredded paper were characterized in terms of their carbon (C) and nitrogen (N) forms and C mineralization. Total, water-soluble, acid-hydrolyzable and non-hydrolyzable C and N contents were determined on composts sampled on days 0, 11, 18, 26, 33, 40 and 59 after composting was initiated. Water-soluble and acid-hydrolyzable C and N decreased during composting, whereas non-hydrolyzable C remained relatively constant, and non-hydrolyzable N greatly increased during composting. The water-soluble forms of N were characterized by a decrease of ammomium (NH₄ ⁺-N) at the beginning of composting, followed by an increase of nitrate (NO₃ ^–-N) towards the end of composting. The mineralization of C in composted materials was generally higher at the beginning than at the end of composting, whereas no differences were observed for mineralization of C in non-hydrolyzable materials. The addition of N inhibited C mineralization in composts except in samples collected on days 40 and 59, while C mineralization was strongly stimulated by adding N to the non-hydrolyzable materials. The data suggest that the N forms in the non-hydrolyzable materials were chemically similar and not readily available to microbes, indicating that the C/N ratios often used to assess the biodegradability of organic matter and to develop compost formulations should be based on biologically available N and C and not on total N and C. Received: 12 May 1997     

Nutrient availability of composted and noncomposted residues in a Patagonian Xeric Mollisol

 The main objectives of this study were to determine: (1) the agronomic value of composted and noncomposted residues originated in the Andean-Patagonian region (APR), and (2) whether aerobic incubations provide a reliable index of nutrient availability to estimate application rates. A Xeric Mollisol of the transitional zone between the APR and the Patagonian steppe, amended with composted and noncomposted residues, was employed in laboratory incubations without plants and in a 5-month greenhouse trial with ryegrass. Noncomposted residues were biosolids and fish wastes (FW) collected under farming cages. Composts were obtained from fish offal and biosolids mixed with sawdust, woodshavings and yard trimmings. A commercial compost was also included. In laboratory incubations at similar rates of application (10 g kg^–1), net N mineralization (N_min) was about two-fold higher with the noncomposted (17–23%) than with the composted residues (0–12%) and P release was very high with the FW. Ryegrass yields were closely related to the total Kjeldahl N and mineralized N of the organic residues and weakly related to their P contents (total or extractable). Yields were increased even in the case of composts which exhibited very low values of N_min (and slight N immobilization) during laboratory incubation, suggesting that the presence of plants enhanced N_min at rates of 10–20 g kg^–1. Soil residual extractable P after ryegrass removal was high for fish-derived amendments and the commercial product, suggesting a potential risk of P pollution when these are applied according to N requirements. Aerobic incubations provided a relatively good index with which to assess adequate rates of application. Received: 17 July 1999     

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.     

Utilization of Compost Increases Organic Carbon And Its Humin,Humic and Fulvic Acid Fractions In Calcareous Soil

Organic carbon sustainability in a gravelly calcareous soil is a great challenge under the humid conditions of south Florida. The beneficial effects of compost utilization on soil fertility prompted an investigation on (i) accumulation of total organic carbon and (ii) the soil organic carbon (SOC) in humin, humic acid (HA) and fulvic acid (FA) fractions in a gravelly calcareous soil amended with composts or inorganic fertilizer. In 1996 and 1998, compost from municipal solid waste (MSW) (100% MSW), Bedminster cocompost (75% MSW and 25% biosolids) and biosolids compost (100% biosolids) at 72, 82.7 and 15.5 Mg ha^?1, respectively, were each incorporated in soil beds and inorganic fertilizer (6-2.6-10) NPK at 2.8 Mg ha^?1. A control (no amendment) treatment was also included. Total organic carbon and various fractions of soil organic carbon were determined in two depths (0-10 and 10-22 cm) for both soil particles (< 2mm) and pebbles (> 2mm). Inorganic and organic soil amendments had decreased soil pH and increased soil electrical conductivity (EC) 19 months from initial application. Total organic carbon contents in soil particle were 4-, 3-, and 2-fold higher in MSW compost, Bedminster cocompost and biosolids compost treatments, respectively, than those in fertilizer treated or non-treated soils. MSW compost increased total organic carbon in pebbles by 4- and 3-fold in the 0-10 and 10-22 cm deep layers, respectively, more than other treatments. The soil organic carbon accumulation decreased with depth in all treatments in soil particles, but did not in pebbles. Amending soils with MSW compost significantly increased the organic carbon in humin, HA and FA fractions more than those treated with inorganic fertilizer or non-amended. MSW compost has a potential to be used as a soil amendment to increase and sustain the organic carbon in calcareous soils of south Florida.     

Use of mineralization kinetics to estimate the potentially mineralizable nitrogen of rock phosphate-enriched composts-amended soil

Predicting nitrogen (N) mineralization has been one of the greatest challenges to improving N management in agriculture. A laboratory incubation experiment was conducted to study the N mineralization of soil amended with rock phosphate (RP)-enriched composts. The RP-enriched rice straw compost amended soil mineralized highest N as compared to compost prepared from mustard stover and tree leaves. The first-order model was found to be the most suitable for N because it provided the best fit to the experimental data and for its simplicity. The model predicted that potentially mineralized N (N₀) was varied from 4.0 to 52.1 mg kg^?1 and the mineralization rate k varied from 0.015 to 0.066 day^?1. The rice straw compost amended soil had higher N₀ value than mustard stover and tree leaves compost amended soil. This study demonstrated the importance of application of rock phosphate-enriched composts in improving N supplying capacity of soil.     

Soil‐microbial response to sugarcane filter cake and biogenic waste compost

An incubation experiment was carried out to examine the N‐immobilizing effect of sugarcane filter cake (C : N = 12.4) and to prove whether mixing it with compost (C : N = 10.5) has any synergistic effects on C and N mineralization after incorporation into the soil. Approximately 19% of the compost‐C added and 37% of the filter cake–C were evolved as CO₂, assuming that the amendments had no effects on the decomposition of soil organic C. However, only 28% of the added filter cake was lost according to the total‐C and δ¹³C values. Filter cake and compost contained initially significant concentrations of inorganic N, which was nearly completely immobilized between day 7 and 14 of the incubation in most cases. After day 14, N remineralization occurred at an average rate of 0.73 µg N (g soil)^–1 d^–1 in most amendment treatments, paralleling the N mineralization rate of the nonamended control without significant difference. No significant net N mineralization from the amendment N occurred in any of the amendment treatments in comparison to the control. The addition of compost and filter cake resulted in a linear increase in microbial biomass C with increasing amounts of C added. This increase was not affected by differences in substrate quality, especially the three times larger content of K₂SO₄‐extractable organic C in the sugarcane filter cake. In most amendment treatments, microbial biomass C and biomass N increased until the end of the incubation. No synergistic effects could be observed in the mixture treatments of compost and sugarcane filter cake.