无机氮与蔬菜废弃物耦合对土壤氮矿化的影响

为探明有机废弃物添加量与不同无机氮水平耦合对土壤氮矿化的影响,设计了3个甘蓝废弃叶添加量[B1:200 g.kg 1(土),B2:400 g.kg 1(土),B3:550 g.kg 1(土)]和4个无机氮水平[N0:0 mg.kg 1(土),N1:25mg.kg 1(土),N2:50 mg.kg 1(土),N3:100 mg.kg 1(土)]交互的控制培养试验(25℃,65%的田间持水量)。试验结果显示:各氮处理下土壤净累积氮矿化量是空白对照的4～5倍,N1水平下土壤净累积氮矿化量显著高于其他氮水平。各甘蓝废弃叶添加量处理下土壤净累积氮矿化量是空白对照的3～5倍,且B2添加量下土壤净累积氮矿化量显著高于B1和B3。统计分析表明,氮处理和甘蓝废弃叶添加量之间的交互效应不显著(P=0.275),甘蓝废弃叶的添加是影响氮矿化的主要因素(Eta2=0.16),而供氮水平为次要因素(Eta2=0.07)。B1添加量下,培养前期(0～20 d)土壤净累积矿化量逐渐升高,后期保持稳定水平;但B2和B3添加量下,培养前期(30 d)土壤呈现矿化、固持、再矿化现象,后期土壤净累积矿化量逐渐升高。氮矿化速率结果说明,甘蓝废弃叶添加后氮素矿化主要发生在培养前30 d。对培养期间土壤净累积氮矿化量随时间变化做一级动力方程模拟,拟合效果良好(R2=0.62～0.89)。     

西藏高原日光温室菜地土壤碳、氮矿化特征研究

采用室内培养方法, 以西藏拉萨地区选取的草地、农田为对照, 测定并比较日光温室土壤碳、氮矿化特征, 揭示草地和粮田转变为日光温室菜地后土壤矿化演变过程, 为西藏高原设施菜地土壤管理提供科学依据。结果表明, 草地、农田、1年温室、5年温室土壤有机碳矿化速率均在培养前期(0~7 d)日均矿化量最快, 且草地土壤显著高于农田和5年温室土壤(P<0.05), 温室土壤间无差异(P>0.05); 在培养28 d后, 农田土壤有机碳矿化释放的CO₂-C累积量高于草地, 草地高于1年温室和5年温室, 但不同类型土壤碳矿化释放的CO₂-C累积量间差异不显著(P>0.05)。无论是草地、农田还是温室, 4种土壤氮矿化都主要发生在培养的前期(0~3 d), 之后随着培养时间的延长, 不同利用类型土壤氮素转化以氮素的固定为主; 至培养结束时, 草地、农田、1年温室、5年温室土壤无机氮含量分别为培养0 d的29.04%、75.94%、66.86%、65.70%, 说明草地土壤氮素矿化能力较农田和温室强, 而温室土壤氮素矿化能力随着温室利用年限的延长而不显著升高, 农田氮矿化能力最弱。方差分析表明, 土壤氮矿化能力因土壤类型而异但矿化过程不因土壤类型而存在差异。     

Nitrogen mineralization in a coarse soil of the semi-arid Pampas of Argentina

Use of the nitrogen balance sheet method as a fertilization strategy in the semi-arid Pampas of Argentina is restricted because of a lack of available information regarding nitrogen mineralization in its coarse soils. Our objective was to determine nitrogen mineralization during corn (Zea mays L.) and following wheat (Triticum aestivum L.) growing cycles under contrasting tillage systems in a representative soil of the region. Mineralized nitrogen from decomposing residues was estimated using the litter bag method and mineralization from soil organic matter using a mass balance approach. Soil water content was higher under no-till during the corn growing season and no differences were detected for wheat during this period. Soil temperature was practically not affected by tillage system. Biomass and nitrogen absorption were higher under no-till than under disk till in corn (p ≤ 0.05), as were nitrogen mineralization from residues and organic matter (p ≤ 0.05). In wheat, no differences in biomass, nitrogen absorption and mineralization were detected between treatments. Mineralization during crop growing cycles accounted for 44.8–67.5% of the absorbed nitrogen. Differences in nitrogen mineralization between tillage systems resulted from the greater water availability under no-till than under disk till during the summer.     

Study of the Potentially Mineralized Nitrogen Content and Nitrogen Supply by Soil Incubation Method in a Long-Term Field Experiment in East Hungary

The formation and fate of soluble nitrogen (N) forms and their response to organic-matter mineralization is not obvious yet, and results are often inconsistent despite intensive research. The available N supply of the soil is very important for plant nutrition and environmentally sound N fertilization. The determination of actual N supply is very important for sustainable agriculture in Hungary, especially in acidic sandy soils, which are very sensitive to environmental effects and inefficient human treatment. Therefore, the aim of this article is to provide further information about N mineralization processes and organic–mineral interactions of soil. To establish the potentially mineralized N content and available N supply of soil, a biological (incubation) method was carried out an acidic brown forest soil of the Nyírlugos long-term field experiment in Hungary. The incubation was carried out in the laboratory with differently treated soils of the long-term field experiment to investigate the effect of treatments on N mineralization processes of soil. The incubation period was 16 weeks long. The pH and the easily soluble mineralized and organic N fractions of soil were measured periodically from leached solution (0.01 M calcium chloride; CaCl₂). The leaching process was repeated after 2, 3, 5, 7, 9, 12, and 16 weeks. The potentially mineralized N content of soil and the actual rate of N mineralization were calculated from periodically collected data. The results of the incubation method can be summarized as follows: the kinetics of incubation of 0.01 M CaCl₂ soluble organic N is similar to mineral N; 0.01 M CaCl₂–soluble N fractions were mainly in inorganic forms in the incubation period but the content of the organic form was significant too; and the mineralization rate is greater where the microbiological activity of the soil is expressed and the soil properties are more favored as a result of applied treatments.     

不同培肥措施对采煤塌陷区复垦土壤氮素矿化的影响

为揭示不同培肥措施对采煤塌陷区复垦土壤氮素矿化特征,采用间歇淋洗好气培养法,研究了不施肥(CK)、单施化肥(CF)、单施有机肥(M)、化肥配施有机肥(MCF)和化肥配施生物有机肥(MCFB)5种培肥措施对复垦4年和8年土壤矿质态氮和可溶性有机氮变化及氮素矿化特征的影响。结果表明:间歇淋洗好气培养过程中,复垦8年土壤累积NO_3~-—N产生量较4年增加2.63%~26.83%,NH_4~+—N累积产生量增加12.50%~32.14%,可溶性有机氮(SON)累积产生量在CF和M处理下减少31.59%~62.50%,其他处理增加3.44%~34.69%。同一复垦年限下NO_3~-—N、NH_4~+—N和SON累积产生量均以MCFB最高。从矿化参数来看,5种培肥措施土壤矿化势(N_0)均表现为复垦8年高于复垦4年土壤,增加幅度为MCFB(26.9%)CK(15.9%)CF(15.0%)M(12.7%)MCF(4.8%);CK和CF处理下潜在可矿化有机氮(N_0/N)随复垦年限增加而减少,减少率分别为9.4%和13.8%,其余3种培肥措施N_0/N呈增加趋势,增加率表现为MCF(13.2%)MCFB(7.5%)M(2.8%);MCF处理下矿化率(N_t/N)随复垦年限增加而增加,增加率为13.2%,其余4种培肥措施的矿化率(N_t/N)均表现为复垦8年低于复垦4年土壤,减少幅度为CF(12.1%)CK(9.4%)MCFB(7.5%)M(2.7%)。不同处理间N_0、N_0/N和N_t/N值则均以8年复垦土壤的MCFB处理最高。综合来看,经过连续8年复垦,化肥配施生物有机肥较其他培肥措施更大程度上提高了各项矿化参数值,但随着复垦年限的增加,以化肥配施有机肥处理的N_0、N_0/N的增加幅度最大,以化肥配施生物有机肥处理的N_t/N减少率最低,长期单施化肥有降低潜在可矿化有机氮量(N_0/N)的趋势。     

玉米秸秆不同构件混合分解的非加和效应及其对土壤有机碳矿化的影响

[目的]研究玉米秸秆不同构件混合分解的非加和效应及其对黄绵土土壤有机碳矿化的影响,为秸秆还田背景下坡地土壤CO2排放提供理论支撑。[方法]采用室内模拟试验,试验设置无玉米秸秆土壤对照(CK)及4种玉米秸秆添加处理:茎+土壤(CKS)、叶+土壤(CKL)、鞘+土壤(CKLS)、混合玉米秸秆+土壤(CKM)。[结果]培养结束土壤有机碳矿化累积排放量实测值显著高于预测值,且促进作用主要是由培养初期快速分解阶段(1~28d)导致的。培养结束后混合玉米秸秆剩余质量预测值明显高于实测值,且元素含量发生明显改变,其中全氮含量预测值明显低于实测值,C/N预测值明显高于实测值。培养结束后CKS处理土壤微生物碳含量明显高于其他几种处理,其他几种处理差异不显著;添加玉米秸秆处理土壤微生物量氮明显降低,相应的土壤微生物量C/N增大,CKS,CKL和CKM处理与CK处理差异达到显著水平。土壤可溶性有机碳(DOC)含量CKLS和CKM处理明显高于其他3种处理,CKS与CKL处理与对照差异不显著。[结论]玉米秸秆不同构件按比例混合对玉米秸秆分解产生协同促进作用,混合分解过程促进氮累积。     

Nitrogen mineralization and nitrogen uptake by maize as influenced by light and heavy organic matter fractions

On a sandy tropical soil, organic materials (prunings of Leucaena leucocephala, Senna siamea and maize stover) with contrasting C/N ratio (13, 18 and 56, respectively) were applied at the rate of 15 t ha^?1a^?1 in order to increase the amount of soil organic matter. Two light fractions (LF1 = LF > 2 mm and LF2 = 0.25 mm < LF < 2 mm) and the heavy fraction (HF) of the soil organic matter pool were determined by means of a combined density/particle size fractionation procedure and data obtained were related to soil nitrogen mineralization under controlled conditions and to nitrogen uptake by maize under field conditions. Under controlled conditions and when the LF1 fraction was excluded, nitrogen mineralization was found not to be correlated to total organic carbon content in the soil (R²=0.02). The R²-value of the linear regression increased considerably, when amount and C/N ratio of the LF2 fraction was taken into account in the regression analysis (R² = 0.88). Under field conditions, a multiple linear regression with amount and C/N ratio of HF, LF1 and LF2 better explained variation in crop nitrogen content and nitrogen uptake of maize (R² = 0.78 and 0.94) than a simple linear regression with total organic carbon (R² = 0.48 and 0.76). The results illustrate the importance of the two light and heavy organic matter fractions for estimating soil nitrogen mineralization. Determination of light and heavy soil organic matter fractions by density/particle size fractionation seems to be a promising tool to characterize functional pools of soil organic matter.     

pH change, carbon and nitrogen mineralization in paddy soils as affected by Chinese milk vetch addition and soil water regime

Purpose

The aim of the research was to explore the effect of Chinese milk vetch (CM vetch) addition and different water management practices on soil pH change, C and N mineralization in acid paddy soils.

Materials and methods

Psammaquent and Plinthudult paddy soils amended with Chinese milk vetch at a rate of 12 g?kg^?1 soil were incubated at 25 °C under three different water treatments (45 % field capacity, CW; alternating 1-week wetting and 2-week drying cycles, drying rewetting (DRW) and waterlogging (WL). Soil pH, dissolved organic carbon, dissolved organic nitrogen (DON), CO₂ escaped, microbial biomass carbon, ammonium (NH₄ ⁺) and nitrate (NO₃ ^?) during the incubation period were dynamically determined.

Results and discussion

The addition of CM vetch increased soil microbial biomass concentrations in all treatments. The CM vetch addition also enhanced dissolved organic N concentrations in all treatments. The NO₃–N concentrations were lower than NH₄–N concentrations in DRW and WL. The pH increase after CM vetch addition was 0.2 units greater during WL than DRW, and greater in the low pH Plinthudult (4.59) than higher pH Paleudalfs (6.11) soil. Nitrogen mineralization was higher in the DRW than WL treatment, and frequent DRW cycles favored N mineralization in the Plinthudult soil.

Conclusions

The addition of CM vetch increased soil pH, both under waterlogging and alternating wet–dry conditions. Waterlogging decreased C mineralization in both soils amended with CM vetch. Nitrogen mineralization increased in the soils subjected to DRW, which was associated with the higher DON concentrations in DRW than in WL in the acid soil. Frequent drying–wetting cycles increase N mineralization in acid paddy soils.     

不同有机肥对采煤塌陷区土壤氮素矿化动态特征研究

为揭示不同有机肥对煤矿复垦土壤氮素矿化特性的影响,以山西省孝义市水峪煤矿采煤塌陷复垦土壤为研究对象,采用室内好气培养法,研究在40%含水量和30℃培养条件下,施用3种有机肥(鸡粪、猪粪、牛粪)后在0~161天的氮素矿化动态特征,以明确不同有机肥对该矿区复垦土壤氮素矿化特征,从而预估不同有机肥的供氮特性,为合理施用有机肥进行低产农田的培肥改造提供科学依据。结果表明:(1)各处理0~14天铵态氮含量均随培养时间的延长迅速下降,与培养时间呈极显著负相关关系(P<0.01),14~161天土壤铵态氮含量维持在较低水平,培养结束时,各处理铵态氮含量均低于1.31mg/kg。(2)各处理土壤硝态氮含量、累积量及矿质氮累积量变化均呈近似的“S”形曲线递增,表现为0~56天缓慢增加,56~84天迅速增加,84天至培养结束(161天)其含量基本不变。培养结束时不同处理间硝态氮含量、累积量及矿质氮累积量整体上均表现为鸡粪>猪粪>牛粪>空白,且鸡粪较猪粪和牛粪处理间存在显著差异,猪粪和牛粪较空白处理间存在显著差异(P<0.05)。(3)不同施肥处理出现氮素净矿化的时间点不同,其中鸡粪处理在第14天时最早出现净矿化现象,而猪粪和牛粪在培养28天后才出现明显的氮素净矿化。(4)不同施肥处理在培养的不同阶段硝态氮和矿质氮累积速率不同,但整体趋势一致,表现为培养0~84天各处理土壤累积矿化波动较大,56~84天达到峰值,培养84~161天各处理矿化速率平稳下降。总体来看,有机肥的施入能有效促进煤矿复垦土壤氮素矿化,从而提高土壤氮素有效性。其中,施鸡粪较猪粪和牛粪对提高矿区复垦土壤有效氮效果更好。4种处理的氮素矿化效果总体表现为鸡粪>猪粪>牛粪>空白。     

Net Nitrogen and Sulfur Mineralization in Mountainous Soils Amended with Indigenous Plant Residues

Abstract

Mineralization of nitrogen (N) and sulfur (S) were examined over a 31‐week incubation period under aerobic conditions in 13 soils selected from the mountainous district of Pertouli, central Greece. The main native plant species are turf, forage crops, forest trees, herbs, and shrubs. Net mineralization and immobilization of N and S by indigenous plants were estimated. Most soils are acidic in this xeric, mesic climatic regime, and organic carbon (C), organic nitrogen (N), and sulfur (S) appreciably varied in soils and plant species. The cumulative net mineralization of N is much higher in comparison to the amount of mineralized S. Release of N is curvilinear with time and associated with a declining mineralization in the later stages of the incubation. Close relationships exist between soil organic S and N and between organic C and N, indicating that these elements are mainly bound in the organic matter. The cumulative net mineralization from soils varies greatly and ranges between 36.6 and 212.8 (average 104.8) mg/kg for N and between 21.4 and 45.2 (average 31.8) mg/kg for S. Immobilization occurs in most soils amended with indigenous plant residues, with the amount of immobilized N varying between 14.8 and 49.5 mg/kg and that of immobilized S ranging from 2.6 to 30.7 mg/kg. However, the estimated rates of N and S mineralization are not negligible and can be taken into account as potential sources in the management of the upland soils.     

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.     

Mineralization of soil organic nitrogen solubilized by aqua ammonia fertilizer

Organic N solubilized by NH_3(aq) was extracted from ¹⁵N-labelled or unlabelled soil, concentrated and added to non-extracted soil, which was incubated under aerobic conditions at 27±1°C. Gross N mineralization, gross N immobilization, and nitrification in soils with or without addition of unlabelled soluble organic N were estimated by models based on the dilution of the NH ₄ ⁺ or NO _inf3 ^sup- pools, which were labelled with ¹⁵N at the beginning of incubation. Mineralization of labelled organic N was measured by the appearance of label in the mineral N pool. Although gross N mineralization and gross N immobilization were increased in two soils between day 0 and day 7 following addition of unlabelled organic N solubilized by NH_3(aq), there was no increase in net N mineralization. Solubilization of ¹⁵N-labelled organic N increased and the ¹⁵N enrichment of the soluble organic N decereased as the concentration of NH_3(aq) added increased. A constant proportion of approximately one-quarter of the labelled organic N added at different rates to non-extracted soil was recovered in the mineral N pool after an incubation period of 14 days, and the availability ratios calculated from net N mineralization data were 1.1:1 and 2.1:1 for 111 and 186 mg added organic-N kg^-1 soil, respectively, indicating that the mineralization of organic N was increased by solubilization.     

Interaction effects of nitrogen and phosphorus fertilizer on nitrogen mineralization of wheat residues in a calcareous soil

Abstract

Because of the high pH of the soil in semiarid regions, phosphorus adsorption is unfavorable. So, considerable amounts of phosphorus fertilizers are used annually, where this fertilizer may affect the plant residues' decomposition. To examine the interaction effects of nitrogen and phosphorus on nitrogen mineralization in calcareous soil, a factorial experiment was performed in a completely randomized design with three replications. The first factor consisted of various C:N ratios (20, 40, and 60 or three levels of nitrogen N₁:0, N₂:11, and N₃:43?kg N ha^?1, respectively) and the second factor consisted of various C:P ratios (87, 174, and 260 or three levels of phosphorus P₁:0, P₂:12, and P₃:45?kg P ha^?1, respectively), under incubation conditions. The results indicated that the cumulative mineral nitrogen content in all treatments, except for N1P2 and N1P3 treatments, started from a positive amount and remained positive until the end of the incubation period. The highest amount of cumulative mineral nitrogen among treatments was related to N3P1 treatment, while the lowest was associated with N2P3 treatment. Mineralization of nitrogen during 60?d of incubation was the dominant phenomenon, except for the N1P2 and N1P3 treatments which remained in the organic phase. The effect of phosphorus on the cumulative mineralization of nitrogen was significant. With increasing the amount of phosphorus, the total inorganic nitrogen diminished. Nitrogen release begins earlier with lower C:N ratios, and therefore the available nitrogen can be released more quickly to the plant. It is generally concluded that, in calcareous soil, the use of nitrogen fertilizer to adjust C:N ratio and to improve the mineralization of wheat residues will be a suitable option.     

Soluble organic nitrogen in temperate forest soils

Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K₂SO₄) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K₂SO₄₎ were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K₂SO₄ solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K₂SO₄-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.     

室内恒温条件下稻田土壤中菌渣的分解过程及CO2释放特征

菌渣是栽培食用菌后的下脚料,可作为有机肥再利用。本文通过实验室条件下培养不同比例的菌渣和稻田土壤混合物[不施用菌渣(TS),土壤与菌渣质量比为10∶1(SM1)、5∶1(SM2)和2∶1(SM3),全部菌渣(TM)],研究不同处理有机碳和全氮的变化,探讨菌渣在稻田土壤中的分解过程,并分析CO_2释放特征,为菌渣合理利用提供参考。结果表明,在相同培养时间,添加不同比例菌渣处理有机碳和氮含量均比TS处理高,其中TM处理的有机碳和全氮分别比TS处理提高了10.7倍和11.0倍。有机碳、氮含量的提高量主要依赖于菌渣的添加量。总体来说,各处理随培养时间的延长,由于碳氮的分解,有机碳、氮均有下降趋势;在35 d后TM处理有机碳氮下降较快。添加菌渣越多,有机碳残留率也越大。在培养63 d后,菌渣有机碳(YC)和氮(YN)的分解残留率与菌渣添加量(X)的关系式分别为:YC=71.26X-0.607 5,r2=1.000 0**和YN=74.039X-0.413 3,r2=0.999 9**。各处理土壤CO_2释放速率均表现出先增后降然后趋于稳定趋势。菌渣用量越高,CO_2释放速率越高,各处理在不同培养时间CO_2释放速率均表现为TMSM3SM2SM1TS。在第7 d时各处理CO_2释放速率最高,在第14 d时渐渐处于平稳下降状态,培养35 d后,各处理土壤有机碳矿化强度很小,大部分有机碳被固定在土壤中,其中TM处理有机碳矿化强度最小。总之,还田菌渣越多,土壤中被固定的碳越多。     

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 of Nitrogen in Soils Amended with Dairy Manure as Affected by Wetting/Drying Cycles

Abstract

Interest in manure management and its effects on nitrogen (N) mineralization has increased in recent years. The focus of this research was to investigate the N‐mineralization rates of different soil types in Coastal Plain soils and compare them to a soil from Illinois. Soils with and without dairy composted manure addition were subjected to different wetting/drying cycles [constant moisture at 60% water‐filled pore space (WFPS) and cycling moisture from 60 to 30% WFPS] under laboratory conditions at three different temperatures (11°C, 18°C, and 25°C). Samples were collected from three different soil types: Catlin (Mollisols), Bama (Ultisols), and Goldsboro (Utilsols). Soil chemical and physical properties were determined to help assess variations in N-mineralization rates. Addition of composted manure greatly impacted the amount of N mineralized. The amount of manure‐derived organic N mineralized to inorganic forms was mainly attributed to the soil series, with the Catlin (silt loam) producing the most inorganic N followed by the Goldsboro (loam) and then Bama (sandy loam). This was probably due to soil texture and the native climatic conditions of the soil. No significant differences were observed between the constant and cycling moisture regimens, suggesting that the imposed drying cycle may not have been sufficient to desiccate microbial cells and cause a flush in N mineralization upon rewetting. Nitrogen mineralization responded greatly to the influence of temperature, with the greatest N mineralization occurring at 25°C. The information acquired from this study may aid in predicting the impact of manure application to help increase N‐use efficiency when applied under different conditions (e.g., climate season) and soil types.     

Nitrogen Mineralization Potential as Influenced by Microbial Biomass,Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha^?1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.     

Nitrogen Mineralization in Soils Used for Biofuel Crops

Perennial biofuel crops such as Miscanthus and switchgrass are thought to increase soil organic matter and therefore may increase soil nitrogen (N) mineralization rates. Our objective was to evaluate a range of N-mineralization indices for soils with established biofuel crops and compare these results with soils in a traditional corn and soybean rotation. We sampled surface soil (0–10 cm deep) from switchgrass (6 years after establishment) and Miscanthus plots (5 years) in a high-organic-matter Mollisol. The longest potential N mineralization index, a 24-day incubation, was significantly greater in Miscanthus soils compared to switchgrass and corn–soybean. In addition, 7-day anaerobic N and potassium chloride–extractable ammonium N were both greater in Miscanthus soils compared to switchgrass and corn–soybean. Our results do support our hypothesis that N-mineralization rates are greater in soils under biofuel production.     

Decomposition of rice residue in tropical soils

Nitrogen mineralization and immobilization of rice residue in Maahas clay soil under lowland and upland conditions were investigated by using ¹⁵N-labelled rice straw. The mineralization of residue-nitrogen was taking place even though the net mineralization was depressed by incorporation of rice residue.

There were some significant differences in the pattern of nitrogen transformation between lowland and upland soil conditions. The nitrogen transformation measured by mineralization of soil nitrogen and rice-residue nitrogen and the nitrogen immobilization into rice residue were more active under lowland conditions than under upland conditions, during the earlier period of residue decomposition.