Nitrogen Mineralization as Influenced by Different Organic Manures in an Inceptisol in the Foothill Himalayas

Nitrogen-use efficiency can be enhanced through an understanding of the nitrogen (N) mineralization behavior of organic sources. An incubation study was conducted to assess the impact of organic manures on N mineralization. The manures, farmyard manure (FYM), Leucaena leucocephala, and poultry manure, were applied to the soil alone or along with urea. There was a rapid increase in the amount of mineral N released with a peak appearing either at 14 days (+urea treatments) or 21 days (manure only) of aerobic incubation. Thereafter the net N mineralized decreased gradually and levelled off beyond day 56. Overall the cumulative net N mineralized after 98 days of incubation was in the order urea > Leucaena + urea > poultry manure + urea _> FYM + urea > Leucaena > poultry manure > FYM > zero N. The potentially mineralizable N (N₀) was lower in treatments where urea was not applied.     

Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil II. Effect of organic manures varying in N content and C:N ratio

 Nitrogen and carbon mineralization of cattle manure (N=6 g kg^–1; C:N=35), pressmud (N=17.4 g kg^–1; C:N=22), green manure (N=26.8 g kg^–1; C:N=14) and poultry manure (N=19.5 g kg^–1; C:N=12) and their influence on gaseous N losses via denitrification (using the acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) were investigated in a growth chamber simulating upland, nearly saturated, and flooded conditions. Mineralization of N started quickly in all manures, except pressmud where immobilization of soil mineral N was observed for an initial 4 days. Accumulation of mineral N in upland soil plus denitrified N revealed that mineralization of cattle manure-, pressmud-, poultry manure- and green manure-N over 16 days was 12, 20, 29 and 44%, respectively, and was inversely related to C:N ratio (R ²=0.703, P=0.05) and directly to N content of organic manure (R ²=0.964, P=0.01). Manure-C mineralized over 16 days ranged from 6% to 50% in different manures added to soil under different moisture regimes and was, in general, inversely related to initial C:N ratio of manure (R ²=0.690, P=0.05). Cumulative denitrification losses over 16 days in control soils (without manure) under upland, nearly saturated, and flooded conditions were 5, 23, and 24 mg N kg^–1, respectively. Incorporation of manures enhanced denitrification losses by 60-82% in upland, 52–163% in nearly saturated, and 26–107% in flooded soil conditions over a 16-day period, demonstrating that mineralized N and C from added manures could result in 2- to 3-fold higher rate of denitrification. Cumulative denitrification losses were maximal with green manure, followed by poultry manure, pressmud and cattle manure showing an increase in denitrification with increasing N content and decreasing C:N ratio of manure. Manure-amended nearly saturated soils supported 14–35% greater denitrification than flooded soils due to greater mineralization and supply of C.     

The liming effect of five organic manures when incubated with an acid soil

A laboratory incubation experiment of 6 months duration was carried out to investigate the liming effects of five organic manures (poultry, pig, and cattle manure, soybean residues, and sewage sludge) when added to an acid soil at a rate of 10 mg g^–1. Soils were sampled after 1, 7, 13, 19, and 25 weeks of incubation. For the animal manures and sewage sludge, soil pH was highest after 1 week incubation and it declined thereafter. However, for soybean residues, pH increased over the first 7 weeks of incubation after which it declined. The decreases in pH were accompanied by accumulation of NO ‐N in the soil. The addition of organic residues to the soil resulted in decreases in the concentrations of exchangeable Al and in both total (Al_t) and monomeric (Al_mono) Al present in the soil solution. The effect was most marked for poultry manure, least marked for cattle manure, and more evident after 7 than 25 weeks incubation. Concentrations of soluble C in the soil solution were elevated in manure‐amended soils. Manure additions resulted in a decrease in the percentage of Al_t present in solution as Al_mono, and this was attributed to complexation of Al by soluble organic matter originating from the manures. It was concluded that organic wastes can act as liming materials when added to acid soils and that the resulting increase in pH and decrease in Al_mono concentrations might provide a window of opportunity for establishment and early growth of crop plants.     

Amelioration of Acidic Soil and Production Performance of Cowpea by the Application of Different Organic Manures in Eastern Himalayan Region,India

Acidic soils are limiting the production potential of the crops because of low availability of basic ions and excess of hydrogen (H⁺), aluminium (Al³⁺), and manganese (Mn²⁺) in exchangeable forms. Therefore, a field study was conducted to know the ameliorating effect of organic manures on acidic soils and production performance of cowpea (Vigna unguiculata L., Walp.) by using different locally available organic manures. Growth and yield attributes were observed to be significantly greater with vermicompost (VC) followed by poultry manure (PM). Porosity, maximum water-holding capacity (MWHC), and organic carbon were greater with farmyard manure (FYM) and cow dung manure (CDM). However, water retention at field capacity (FC), permanent wilting point (PWP), bulk density (BD), pH, and availability of nitrogen (N), phosphorus (P), and potassium (K) were greater with VC. However, physical and chemical properties were deteriorated in control plots.     

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

Abstract

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

Effects of Temperature,Moisture, and Chemical Composition of Organic Substrates on C Mineralization in Soils

Laboratory experiments were conducted to (i) study the influence of chemical composition of organic substrates (green manure, rice straw, wheat straw, and farmyard manure) and temperature on carbon (C) mineralization under flooded and nonflooded moisture conditions, (ii) study the relationship between C mineralization and chemical composition of organic materials, and (iii) model C mineralization kinetics under different temperature and moisture conditions. The proportion of added C mineralized under nonflooded conditions ranged between 45 and 66% at 35 °C compared to 18 to 42% at 15 °C. Flooding the soil reduced the proportion of added C mineralized, which ranged between 25 to 47% at 35 °C and 6 to 20% at 15 °C. Water-soluble components, cellulose, lignin, and nitrogen content of the organic source significantly influenced C mineralization. Temperature sensitivity of decomposition depended on the quality of the organic substrate with relatively less decomposable farmyard manure (FYM) being more sensitive (Q₁₀ ?3.0) than the easily decomposable green manure (Q₁₀ ?2.5). A first-order monocomponent model that is based on relative rate of mineralization and includes a parameter for speed of aging best described C mineralization under both the temperature and moisture conditions. It was concluded that FYM with preponderance of recalcitrant components and low decomposability provides greater C sequestration potential than green manure and crop residues.     

Soil Organic Carbon Sequestration by Long-Term Application of Manures Prepared from Trianthema portulacastrurm Linn

ABSTRACT

A 6-year field experiment was conducted at Maharashtra, India, from 2011 to 2017 on a silty clay soil, to study the impact of organic manure prepared from common weed Trianthema portulacastrurm Linn. on soybean-fodder maize crop system and soil organic carbon (SOC) sequestration. Organic manures were prepared from Trianthema as compost, vermicompost, dry leaf powder and were compared with application of Farm Yard Manure (FYM), chemical fertilizer treatment (NPK), and control. All treatments were repeated to same earlier treated plots every year for subsequent 6 years. Soil samples were analyzed before experiment and after harvesting of crops at the end of 6 years. All organic manures prepared from Trianthema and FYM increased SOC, nitrogen, phosphorus, and potassium content in the soil as compared to chemical fertilizer treatment and control. The overall increase in SOC content in the 0–60-cm soil depth in vermicompost treatment was 3.51 Mg C ha^?1 as compared to control at the end of this 6 years experiment at the carbon sequestration rate of 585 kg ha^?1 year^?1. Preparation and use of different manures from Trianthema will increase the carbon sequestration in soil, a measure to mitigate global warming.     

SOIL POTENTIALLY MINERALIZABLE NITROGEN AND ITS RELATION TO RICE PRODUCTION AND NITROGEN NEEDS IN TWO PADDY RICE SOILS OF CHILE

Rice is an important food in the world population's diet. As nitrogen (N) is the principal nutrient associated with the yield and its mineralization from the soil contribute to plant-available N, the use of biological or chemical methods are necessary for its estimation. Two paddy rice soils types of Chile were used for laboratory (anaerobic incubation) and field experiments: Quella (Vertisol) and Quilmen (Inceptisol), fertilized with three N rates - ureas of 0, 80 and 160 kg ha^?1. The mineralized inorganic N was measured and potentially mineralizable N (N₀) was calculated based on the first-order kinetic model. N mineralization was positively affected by N fertilization, but only affected grain yield in the Quilmen soil with a negative effect on the crop N recovery. Furthermore, crop N uptake was related with the incubation time at 14 and 21 days for the Quilmen and Quella soils respectively. Finally an N optimization model for those soils was proposed.     

Sequential extractions and 31P-NMR spectroscopy of phosphorus forms in animal manures, whole soils and particle-size separates from a densely populated livestock area in northwest Germany

The solubility and forms of phosphorus (P) were investigated in manures from chicken and pigs, eight whole soil samples and clay-, silt-, and sand-size separates from an arable and a grassland soil. Total P (P_t) in liquid pig manure (16.2 g kg^–1) and dry chicken manure (26.2 g kg^–1) was distributed between residual P (39–41% P_t), H₂SO₄–P (17–27% P_t), labile resin- and NaHCO₃–P (24–39% P_t), and NaOH-P (3–10% P_t). Most soils had larger proportions of NaOH-P and residual P, indicating reactions of manure-derived P compounds with pedogenic oxides and humic substances. Clay-size separates had the highest P-concentrations in all fractions and were particularly enriched in exchangeable and labile P forms. Solution ³¹P-nuclear magnetic resonance (NMR) spectra of 0.5 M NaOH extracts from manures and some soil samples showed greater signal intensities for orthophosphate and monoester P than 0.1 M NaOH extracts. This can be explained by alkaline hydrolysis phosphate diesters at higher NaOH concentrations and/or by preferential extraction of diesters at lower concentrations. The ³¹P-NMR spectra showed differences between the two manures and confirmed that increasing proportions of ester-P can be expected if they are spread to soils. The NaOH extracts of soil samples were characterized by large proportions of orthophosphate-P (mean 77% of assigned P compounds), which seemed to be slightly enriched in clay fractions whereas the extracts from silt contained more ester-P. Sequential extractions and ³¹P-NMR spectroscopy both showed that these excessively manured soils are likely to lose large amounts of P. Received: 15 July 1996     

Continuous Cropping,Fertilization, and Organic Manure Application Effects on Potassium in an Alfisol under Arid Conditions

Effects of continuous cropping and addition of organic manures (farmyard manure, FYM, and groundnut shells, GNS) along with inorganic fertilizers on nonexchangeable potassium (K) release kinetics in a K-deficient Alfisol were studied in a 20-year manurial experiment under arid conditions. There was a depletion in available K under continuous cropping without K input (control) as compared to other treatments such as 100% nitrogen–phosphorus–potassium (NPK), 50% NPK + 4 metric tons (MT) groundnut shells ha^?1, 50% NPK + 4 MT FYM ha^?1, and 100% organic (i.e., 5 MT FYM ha^?1). Over 20 years of cropping without K input, available K was reduced from 155 kg ha^?1 (in 1985) to 82 kg ha^?1 (in 2005), showing a negative balance of 73 kg ha^?1. Soil in control plots showed available K in the deficient range (<50 mg kg^?1), whereas four other fertilizer and manurial treatments were greater than the critical limit. Considerable improvements in nonexchangeable K-release parameters such as step K and cumulative K release were observed in manured plots over control. Parabolic diffusion and first-order kinetic equations explained K release from soils. Potassium-release rates were drastically reduced in control plots, and there were increased release rates with continuous addition of manures. Results suggest that soils with groundnut shells or FYM (4 MT ha^?1) along with 50% inorganic fertilizer additions could maintain greater K release rates after 20 years of cropping as compared to cropping without K input.     

Nutrients transport through variably structured soils

Abstract

Contribution of sesbania green manure, rice straw, and FYM (farm yard manure) was studied along with that of urea and A/SO₄ (ammonium sulphate) for the cultivation of lowland rice and for the residual soil fertility. The results revealed that A/SO₄ application resulted in a larger number of productive tillers, higher straw production, and higher grain yield compared to urea. Among the organic manures, sesbania green manure and FYM exerted almost similar effects on the number of productive tillers and paddy yield while the yield increase compared to the incorporation of rice straw. A similar affect of these organic manures on nitrogen uptake by rice straw, grain, and straw + grain was observed. Additional uptake of N due to the application of sesbania green manure, FYM and rice straw amounted to 15, 13, and 2.85 kg ha^?1, respectively. Residual N fertility was the highest when of sesbania green manure was applied followed by FYM and rice straw. Residual P fertility was higher in the case of FYM than other treatments whereas the residual K fertility was the highest in the case of rice straw incorporation.     

Carbon mineralization in soils of different textures as affected by water-soluble organic carbon extracted from composted dairy manure

The water-soluble organic C in composted manure contains a portion of labile C which can stimulate soil microbial activity. The objective of this experiment was to evaluate the effects of water-soluble organic C extracted from composted dairy manure on C mineralization in soil with different textures. Three soils with textures varying from 3 to 54% clay were amended with 0 to 80 mg water-soluble organic C kg^–1 soil extracted from a composted dairy manure and incubated for 16 weeks at 23°C. The total amount of C mineralized was greater than the amount of C added in the three soils. Differences in mineralizable C with and without added water-soluble organic C were approximately 13–16 times, 4.8–8 times, and 7.5–8 times greater than the amount of C added to clay, loam, and sand soils, respectively. The results of this experiment suggest that immediately following composted manure applications, C mineralization rates increase, and that most of the C mineralized comes mainly from the indigenous soil organic C pool.CLBRR contribution No. 94-71     

Impact of organic manures with and without mineral fertilizers on soil chemical and biological properties under tropical conditions

Soils receiving organic manures with and without chemical fertilizers for the last 7 yr with pearlmillet–wheat cropping sequence were compared for soil chemical and biological properties. The application of farmyard manure, poultry manure, and sugarcane filter cake alone or in combination with chemical fertilizers improved the soil organic C, total N, P, and K status. The increase in soil microbial‐biomass C and N was observed in soils receiving organic manures only or with the combined application of organic manures and chemical fertilizers compared to soils receiving chemical fertilizers only. Basal and glucose‐induced respiration, potentially mineralizable N, and arginine ammonification were higher in soils amended with organic manures with or without chemical fertilizers, indicating that more active microflora is associated with organic and integrated system using organic manures and chemical fertilizers together which is important for nutrient cycling.     

Availability of organic nutrient sources and their effects on yield and nutrient recovery of tef [Eragrostis tef (Zucc.) Trotter] and on soil properties

Inadequate nutrient and organic‐matter supply constitutes the principal cause for declining soil fertility and productivity in much of sub‐Saharan Africa (SSA). In a survey in Gare Arera, the central Ethiopian highland, farmyard manure (FYM) and compost enriched with ash were identified as underutilized organic nutrient sources. Mustard meal, a by‐product of mustard‐seed oil production, is also locally available. On‐farm experiments were carried out on two major soil types (Nitisol and Vertisol) to study effects of the organic fertilizers, synthetic fertilizer (urea + triple superphosphate) and an unfertilized control on the yield and yield components of tef [Eragrostis tef (Zucc) Trotter] and selected soil properties. Application of organic fertilizers at an N rate equivalent to that of urea produced grain yields of 82% and 99% of that produced with urea on Nitisol and Vertisol, respectively. The apparent N recovery from urea, mustard meal, FYM, and compost was, respectively, 31%, 25%, 16%, and 28% on Nitisol and 23%, 17%, 26%, and 21% on Vertisol. The mean agronomic efficiency for the organic and synthetic fertilizers on Nitisol was 20 and 24 kg grain (kg N)^–1 applied, respectively, whereas on the Vertisol, it was 13 kg grain (kg N)^–1 for both. On Vertisol, tef was most responsive to FYM and on Nitisol, it was most responsive to compost. Soil N and P contents increased due to organic‐fertilizer application. The results showed that compost enriched with ash is a good choice on Nitisol while FYM works well on Vertisol. Mustard meal can be applied on both soils.     

Effect of addition of organic residues,farmyard manure and fertilizer nitrogen on soil fertility in rice‐wheat cropping system

A field experiment was conducted for 3 crop years (July‐June) at the Indian Agricultural Research Institute, New Delhi to study the effects of Sesbania and cowpea green manuring (GM) and incorporation of mungbean residues after harvesting grain, Leucaena loppings, FYM and wheat straw incorporation before planting rice and application of 0,40,80 and 120 kg N ha^?1 to rice on the soil organic carbon (SOC), alkaline permanganate oxidizable N (APO‐N), 0.5 M sodium bicarbonate extractable P (SBC‐P) and 1N ammonium acetate exchangeable K (AAE‐K) in surface 0–15 cm soil after the harvest of rice and wheat grown in sequence. Green manuring and addition of organic residues prevented the decline in SOC. On the other hand addition of N fertilizer tended to decrease SOC after rice harvest. On the contrary application of green manures, organic residues, FYM and fertilizer N increased APO‐N, which indicates the benefit of these treatments to a more labile soil organic N pool. Also application of green manures, organic residues, FYM and fertilizer N increased SBC‐P. Not much change was observed in AAE‐K by the treatments applied.     

Comparison of N Mineralization Rate and Pattern in Different Manure- and Sewage Sludge-Amended Calcareous Soil

A 12-week incubation experiment was conducted to determine the pattern and rate of N mineralized from organic materials. Treatments consisted of sheep manure (SM), cattle manure (CM), poultry manure (PM), sewage sludge (SS) at 1% (W/W) level, and unfertilized treatment with three replications. The concentrations of nitrate (NO₃)- nitrogen (N) and ammonium (NH₄)-N were determined in day 1 and 1, 2, 4, 8, and 12 weeks after the beginning of incubation. Results indicated that the magnitude of N mineralized during the incubation time periods was in the order of CM (134 mg kg^?1) > PM (83 mg kg^?1) > SS (56 mg kg^?1) > SM (55 mg kg^?1), and different management is required for obtaining optimum N-use efficiency. In conclusion, improving N-uptake efficiency in manure- and SS-amended soils depends on the pattern and rate of N mineralization to synchronize N released with crop N demand periods.     

Influence of Long‐Term Sodic‐Water Irrigation,Gypsum, and Organic Amendments on Soil Properties and Nitrogen Mineralization Kinetics under Rice–Wheat System

Abstract

Influence of long‐term sodic‐water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice–wheat cropping in a sandy loam soil in northwest India. Long‐term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg^?1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW‐irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS‐amended plots but increased it under GM‐treated, FYM‐treated, or unamended plots. Nitrogen mineralization potential (N_o) ranged from 62 to 543 mg N kg^?1 soil. In the first‐order zero‐order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg^?1 soil. Compared to the first‐order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in N_o were influenced more by changes in pH, SAR, and ESP induced by long‐term SW irrigations and amendments rather than by soil OC.     

Nitrogen mineralization potential of dairy manures and its relationship to composition

The objectives of this study were to determine the variability in mineralization of dairy manure N, to determine if N mineralization can be predicted by compositional factors or by near- or mid-infrared reflectance spectroscopy. Dairy manures (n =107) were collected from farms in Maryland, Virginia, Pennsylvania, New York, and Connecticut. The composition of these manures ranged from 14 to 386 g dry matter kg^-1, 0.9 to 9.5 kg total N/m³, and 0.3 to 4.7 kg NH₄⁺-N/m³. Manure-amended soil was aerobically incubated at 25°C and concentrations of NH₄⁺-N and NO₃^--N were determined at day 2 and day 56. The manures were highly variable in their N mineralization characteristics, ranging from a net mineralization of 54.9% to a net immobilization of 29.2% of the organic N. When compositional parameters were individually regressed against percentage mineralized organic N, the highest correlation coefficient (r) was 0.164. A stepwise regression of all 11 variables yielded a maximal r of 0.486. These results suggest that the availability of dairy manure organic N is highly variable and that the availability cannot be predicted from simple compositional parameters. No relationship was found between near-infrared spectral characteristics and N mineralization suggesting that no simple relationship exists between N mineralization and compositional characteristics. There appears to be some potential for the use of mid-infrared for determining the mineralization potential of manures.     

Long-Term Effect of Lime,Mycorrhiza, and Inorganic and Organic Sources on Soil Fertility,Yield, and Proximate Composition of Sweet Potato in Alfisols of Eastern India

A field experiment was conducted for five kharif seasons (2006–2011) in an Alfisol to study the effect of integrated use of lime, mycorrhiza, and inorganic and organics on soil fertility, yield, and proximate composition of sweet potato. Application of graded doses of nitrogen, phosphorus, and potassium (NPK) significantly increased the mean tuber yield of sweet potato by 44, 106, and 130 percent over control. Green manuring along with ½ NPK showed greater yield response over that of ½ NPK. The greatest mean tuber yield was recorded due to integrated application of lime, farmyard manure (FYM), NPK, and MgSO₄ (13.69 t ha^?1) over the other treatments. Inoculation of mycorrhiza combined with lime, FYM, and NPK showed a significant yield response of 10 percent over FYM + NPK. Conjunctive use of lime, inorganics, and organics not only produces sustainable crop yields but also improve soil fertility, nutrient-use efficiency, and apparent nutrient recovery in comparison to NPK and organic manures.     

Effect of organic manures,crop residues and green manure (Sesbania aculeata) on nitrogen and phosphorus transformations in a sandy loam at field capacity and under waterlogged conditions

Summary The influence of the water regime on mineralization and immobilization of N and P was investigated in a calcareous sandy loam incubated with cattle, poultry and green manure (Sesbania aculeata), and wheat and rice straw in a pot experiment. At field capacity, N released from poultry and green manure during the first 4 weeks of incubation was 45% and 59%, respectively. During the next 12 weeks, only around 40% more organic N was mineralized from both sources. In contrast, addition of cattle manure resulted in a period of net N immobilization lasting up to 4 weeks. By the end of 16 weeks of incubation only about 19010 of the added N was mineralized. High rates of N immobilization were observed during the first 4 weeks of incubation of rice or wheat straw with C/N ratios of 78 and 85, respectively. The N mineralization kinetics of poultry and green manure and of untreated soil showed an initial fast reaction followed by a slow release of inorganic N and could be described by two simultaneous first-order reactions. Under waterlogged conditions mineralized N was lost simultaneously in significant amounts possibly through nitrification — denitrification reactions. At field capacity, the largest amount of Olsen P was accumulated in the soil amended with poultry manure, followed by cattle manure. Results from other treatments did not differ much from those of the untreated soil. About 15% of P from poultry manure was mineralized during the 1st week of incubation. In contrast to the field-capacity moisture regime, marked increases in Olsen P in the soils amended with green manure and crop residues were observed under water-logged conditions.