土壤水分和氮添加对3种质地紫色土氮矿化及土壤pH的影响

为正确认识土壤水分、质地和外源氮添加对紫色土氮矿化作用和土壤pH的影响,以西南地区典型的紫色土为研究对象,通过90d的室内恒温(25℃)好气培养,研究了3种质地(粘土、粉粘壤土和砂土)紫色土在不同含水量(55%,65%和75%田间持水量)和尿素氮添加水平(0mg/kg土和250mg/kg土.)条件下,土壤氮矿化作用和pH的变化。结果表明:前30d的累积矿化氮量可占培养期间(90d)的78.48%~91.55%,且各处理的土壤累积矿化氮量和净矿化速率均随着培养时间的延长而快速增加;第30~90d,土壤累积矿化氮量增长缓慢,净矿化速率迅速下降并趋于稳定。土壤累积矿化氮量和净矿化速率在各培养阶段均随土壤水分含量的增加而逐渐增大,其中75%WHC(75%田间持水量)和75%WHC+U(75%田间持水量+尿素)处理的矿化作用最强。土壤质地从一定程度上对土壤的矿化产生影响,但其影响并不显著。外源氮添加能促进土壤氮矿化,其净氮矿化量和净矿化速率在各培养阶段均极显著(p0.01)高于未加氮处理,分别为未施氮处理的1.68~4.56倍,0.60~6.47倍。外源氮添加使土壤pH显著下降,55%WHC+U、65%WHC+U和75%WHC+U处理分别下降了0.57,0.66,0.72个pH单位,土壤有酸化趋势。土壤pH值与土壤氮素净矿化速率呈极显著线性相关,净矿化速率对pH变化贡献巨大。总之,土壤含水量增加和外源氮添加均促进了土壤氮矿化,增加了土壤矿质氮含量,同时外源氮添加也加速了土壤pH下降,土壤有酸化趋势。     

祁连山东段青海云杉林区土壤氮矿化与土壤因子的相关性

以祁连山东段青海云杉(Picea crassifolia)林分布带土壤为研究对象,采用顶盖埋管的野外取样法和室内分析法,对海拔梯度上土壤铵态氮(NH+4-N)、硝态氮(NO-3-N)净矿化速率、氮净矿化量和净矿化速率进行测定分析,旨在探讨土壤净氮矿化量与气温降水和土壤理化性质的相关关系,以期建立环境变量与土壤氮矿化量和矿化速率模型,进而提高祁连山青海云杉林生产力及水源涵养能力。其结果表明:(1)土壤硝态氮、铵态氮净矿化速率、土壤净氮矿化量和矿化速率随海拔的升高差异性均极显著;土壤氮净矿化量和矿化速率随海拔梯度的升高呈"W"形变化,与硝态氮净矿化速率随海拔升高的变化规律一致,与铵态氮净矿化速率变化规律相反;在海拔2 800m处,硝态氮净矿化速率、土壤净氮矿化量和矿化速率均达到最大值,为0.372,160.3,0.44 mg/(kg·d),铵态氮净矿化速率出现最低值0.067 mg/(kg·d);在海拔2 900m处出现最低值,为0.155,94.7,0.26mg/(kg·d),在海拔3 100m处,铵态氮的净矿化速率出现最大值0.13mg/(kg·d);(2)回归分析表明,土壤净氮矿化量与年均气温呈极显著负相关(P0.01),R2=0.717 3;与年降水量呈极显著正相关(P0.01),R2=0.383 5;得出气候变化对土壤净氮矿化量的影响程度为:年均气温年降水量;(3)回归分析表明,土壤氮净矿化量与土壤全氮、有机质、含水量、pH值呈极显著正相关(P0.01),其R2依次为0.910 1,0.906 0,0.842 8,0.797 9;与土壤容重呈极显著负相关(P0.01),其R2为0.222 4;由R2值大小可知土壤养分对土壤净氮矿化量的影响程度为:土壤全氮土壤有机质土壤含水量土壤pH土壤容重。     

丹江口水库库滨带典型植物群落氮矿化特征

为明确库滨带典型植物群落矿化特征,探究植物化学性质与土壤氮矿化的关系,选取丹江口水库库滨带的苘麻和蛇床群丛.试验采取单一叶处理、单一根处理和根+叶混合等9种处理,分别测定第1、3、7、14、21、31、41、51和61 d的土壤氮矿化量,系统分析添加植物后土壤氮矿化特征.结果表明:1)添加植物后,土壤氮矿化可分为3个阶段,即前期(1 ～7d)各处理矿化量均减小,中期(7 ～41 d)各处理矿化量都有所增加,幅度变化较大,后期(41 ～61d)基本保持平衡,所有处理的土壤矿化量均小于对照(CK)的79.53 mg/kg,单一处理中,苘麻叶(QL)矿化量最高,达到71.62 mg/kg,混合处理最高为苘麻叶+蛇床根(QL+ SR) 26.43 mg/kg;2)添加植物后,土壤微生物的质量分数显著增加(P＜0.05),QL＞4个混合处理＞另外3个单一处理;3)整个试验期间,土壤氮矿化量与植物全碳和全氮质量分数显著相关(P＜0.05),主成分分析(PCA)结果显示全氮质量分数对土壤有机氮矿化影响最明显,重要程度为全氮＞C∶N＞纤维素＞L∶N＞多元酚;4)所有混合处理中,实测氮素矿化量均显著小于预测值(P＜0.01).说明添加苘麻和蛇床后,土壤氮矿化表现为抑制作用,根茎混合处理没有激发效应.该研究为区域植被生态恢复、水土保持与非点源污染治理提供参考依据.     

有机物料和氮添加对宁夏沙化土壤碳矿化的影响

以宁夏当地的枝条、秸秆为材料,通过室内模拟试验设计了不添加(N)、添加枝条(B,5g/kg)、添加秸秆(S,5g/kg)配施不同水平氮肥(N_0,0mg/kg;N_1,40mg/kg;N_2,50mg/kg;N_3,60mg/kg),研究了宁夏沙化土壤碳矿化及土壤微生物性质的影响。结果表明:各类处理均在第一天出现了矿化速率的最大值,到第3天时下降了72.47%~96.54%(N),55.58%~63.43%(B),65.92%~75.38%(S)。各类处理有机碳累积矿化量为0.65~0.88g/kg(N),0.58~0.99g/kg(B),0.63~1.44g/kg(S)。各处理有机碳、全氮、碳矿化量、微生物性质在同一氮水平下呈现SBN趋势,而在同一种有机物料添加处理下,则整体上伴随着施氮水平的提高呈现先增加后降低或提高的趋势(N处理的微生物量氮、脲酶除外)。碳累积矿化量及平均矿化速率与有机碳、全氮、微生物量碳氮、酶活均呈极显著关系(p0.01)。有机物料添加和氮肥添加以及它们的交互作用总体上对有机碳的矿化速率、矿化量有极显著影响(FF0.01)。该研究为宁夏当地及中国北方沙化土壤改良研究提供了参考。     

施氮量和土壤含水量对黑麦草还田红壤氮素矿化的影响

目标 氮素矿化是决定土壤供氮能力的重要生态过程,养分添加和水分在调节土壤的氮转化方面起着重要的作用。探讨施氮和土壤水分对黑麦草还田过程中土壤氮素矿化的影响有利于进一步优化红壤旱地作物生产的水肥管理。 【方法】 通过室内培养试验,研究了施氮量 (0、60、120 mg/kg) 和土壤含水量 (15%、30%、45%) 对红壤旱地黑麦草还田过程中土壤净硝化量、氨化量和氮矿化量的影响。 【结果】 土壤含水量15%时,施氮有利于提高黑麦草还田初期土壤净硝化量,施氮量120 mg/kg抑制了黑麦草还田后期土壤硝化作用。在30%土壤含水量时,施氮量120 mg/kg明显抑制了黑麦草还田后期土壤硝化作用。土壤含水量45%抑制了黑麦草还田初期不同施氮水平下土壤净硝化量,但增加了黑麦草还田91 d时土壤净硝化量,且施氮量60 mg/kg下的净硝化量显著高于120 mg/kg水平下的。土壤净氨化量在整个黑麦草还田过程中均为正值,且呈现多次升高-降低的往复动态变化。土壤净氨化量在三种土壤含水量下均表现为施氮条件下的显著高于不施氮处理。土壤含水量的增加有利于提高施氮量120 mg/kg下黑麦草还田初期土壤的氨化作用,但降低了黑麦草还田后期土壤净氨化量。相比不施氮,三个含水量条件下的施氮处理在黑麦草还田过程中的大部分阶段都显著增加了土壤净氮矿化量,土壤含水量30%条件下土壤净氮矿化量的变化最大。相比土壤含水量15%,30%含水量促进了黑麦草还田中期 (13～57 d) 土壤净氮矿化量的增加,45%含水量抑制了黑麦草还田后期 (73～91 d) 土壤净氮矿化量。 【结论】 红壤区旱地黑麦草还田时应合理施入化学氮肥 (60 mg/kg),在黑麦草还田初期保持较高的土壤含水量 (45%) 能够抑制土壤的氮矿化作用,还田中后期适当降低土壤含水量 (30%)有利于增加土壤氮素的矿化。      

模拟氮添加对亚热带杉木人工林土壤有机碳矿化的影响

为探讨氮添加对亚热带杉木人工林土壤有机碳矿化的影响，选择福建三明森林生态系统与全球变化国家野外科学观测研究站38年生杉木人工林土壤为研究对象，设置N0(0 mg/kg)、N10(100 mg/kg)、N25(250 mg/kg) 3个氮添加水平，并进行117 d的培养。结果表明：(1)氮添加后，土壤有机碳矿化速率在培养开始(0 d)即达到最大值，在培养前期(0～57 d)这一段时间内N0、N10和N25处理的有机碳矿化速率平均值显著下降了44%、45%、47%，而在整个培养期间3个处理有机碳平均矿化速率分别为9.97、9.27、8.89 mg/(kg·d)；(2)有机碳矿化累积量随培养时间延长显著增加，随氮添加增加显著降低，与N0处理相比，培养117 d后N10、N25处理有机碳矿化累积量平均值分别降低了3.4%、7.4%；(3)微生物生物量对氮添加响应并不显著，但真菌/细菌比随氮添加增加而增大。总体上，氮添加主要是通过改变土壤有机碳和氮抑制了土壤有机碳矿化。因此，氮添加后土壤中碳、氮养分含量的变化是有机碳矿化变化的主要原因，而微生物群落结构变化则不是主要因素。     

无机改良剂对皖南植烟红壤氮矿化的影响

以皖南植烟旱地红壤为研究对象,通过模拟试验分析了无机改良剂(T20、G20、硅藻土)对土壤氮矿化及硝化作用的影响。试验采用室内恒温间歇淋洗好气培养法(Stanford法),研究无机改良剂添加量处理(1%,2%,5%和10%)对皖南植烟红壤氮矿化的影响。结果表明,3种改良剂均可提高土壤淋洗液pH,pH增加幅度与改良剂添加量显著相关,T20、G20与硅藻土的土壤淋洗液pH增加幅度最大可提高0.30,0.50,0.43个单位;利用一级动力学方程N_t=N_0(1-e~(-kt))拟合土壤氮矿化过程,不同处理的相关系数R~2为0.970 9~0.998 0,相关性均达到极显著水平;39个供试土壤样品的有机氮矿化势N0为14.86~177.1mg/kg,平均50.53mg/kg。不同处理的N0均与改良剂添加量显著正相关,对照N0为14.86mg/kg,添加10%硅藻土、T20与G20处理的N0分别为104.1,177.1,26.01 mg/kg,是对照处理的7,11.9,1.75倍。39个土壤样品的供氮指数N0×k为0.66~6.39mg/(kg·d),平均为2.19mg/(kg·d);添加1%,2%的硅藻土处理及添加1%,5%,10%的G20处理的综合指数N0×k均显著高于对照处理。不同处理的土壤硝化累积量随时间变化符合Logistic的"S"形生长曲线,其决定系数R2为0.953 3~0.996 2,达到极显著水平。硅藻土、G20与T20处理的最大氮矿化促进率分别可达27.46%,94.76%,0.63%,而最大硝化促进率分别可达82.83%,136.4%,40.44%;氮矿化促进作用与无机改良剂添加量呈显著正相关。通过对3种改良剂的氮矿化与硝化作用比较,G20较硅藻土与T20在促进氮矿化与硝化方面具有比较优势。可见,合理增加无机改良剂,可以促进土壤有机氮的矿化以及硝化作用的进行,增强皖南旱地植烟土壤氮素的有效利用。     

秸秆还田对土壤氮素转化的影响

利用原状土柱田间培养法 ,测定了冬小麦、夏玉米农田土壤氮 (N)素的年净矿化量 ;利用氯仿熏蒸浸提茚三酮反应氮法测定了土壤微生物量氮的数量 ;利用连续流动分析仪测定了土壤表层无机氮的含量。结果表明 ,在冬小麦秸秆覆盖、夏玉米秸秆翻埋的土壤中 ,第 1年土壤氮净矿化量为N 210kg/hm2,第 2年为 179kg/hm2,2年的净矿化量均基本与同期施氮量相当。在秸秆不还田的土壤中 ,第 1年土壤氮净矿化量为N 164kg/hm2,第 2年为248kg/hm2,年际变化较大。翻埋玉米秸秆导致小麦季土壤表层无机氮数量增加 ,引发土壤氮矿化的正激发效应 ;表层覆盖小麦秸秆对玉米季土壤表层无机氮的影响不明显。秸秆还田后 ,每个生育期开始时 ,土壤微生物量氮比不还田土壤的增加 72 %～ 2.34% ,每个生育期结束时增加 34%～ 72%。在实施秸秆还田的最初 2年内 ,土壤微生物量但氮处于动态调整阶段 ,尚未达到新的稳定状态     

华中地区两种典型菜地土壤中氮素的矿化特征研究

以华中地区两种典型的菜地土壤——黄棕壤和潮土为研究对象,利用室内连续培养试验研究了菜地土壤氮素的矿化规律和矿化特征.结果表明,黄棕壤和潮土氮素的矿化以硝态氮量较多,铵态氮较少.两种土壤的矿化速率随培养时间的延长而降低,培养13周以后黄棕壤的矿化速率为N 0.13 mg/(kg.d),潮土为N 0.32 mg/(kg.d).随着培养时间的延长,黄棕壤和潮土的累计氮矿化量缓慢增长.培养结束时黄棕壤矿化量为N 68.65 mg/kg,潮土矿化量为N109.37 mg/kg,分别占土壤全氮量的24.52％和21.45％.黄棕壤和潮土氮素的矿化势分别为N 74.63 mg/kg和123.45mg,/kg,分别占土壤全氮量的26.65％和24.21％.     

温度对不同年限日光温室土壤氮素矿化特性的影响

【目的】日光温室作为具有我国特色的一种高强度的栽培方式,过量施肥问题突出。随着温室栽培在我国北方地区规模的不断扩大,由此带来的土壤退化和地下水污染问题值得关注。不少研究表明,随着日光温室栽培年限的增加,土壤有机质含量不断增加;且温室栽培中的土壤温度与露地存在很大差异,其土壤氮素矿化特性如何,尚缺乏研究。【方法】本研究以位于黄土高原南部陕西省杨凌示范区不同栽培年限的日光温室土壤为研究对象,采用室内好气培养法(84 d)测定不同培养温度(20℃和30℃)对不同年限温室(0 3年)土壤0—20 cm及20—40cm土层氮素矿化量,采用一级动力学方程拟合土壤氮素矿化曲线,根据土壤氮矿化势(N0)评价不同栽培年限温室土壤氮素矿化特性。【结果】1)随着日光温室栽培年限的增加,土壤有机质、全氮含量和氮素累积矿化量随之显著增加。2)30℃的土壤氮素累积矿化量高于20℃的矿化累积量;栽培年限长的日光温室矿化作用对温度的敏感程度高于年限短的温室。3)若温度和栽培年限同时增加,土壤氮素累积矿化量随之增加,说明温度和栽培年限对土壤氮素净矿化量有一定的交互作用,但差异不显著(P0.05)。4)日光温室栽培年限越长,土壤氮矿化势(N0)越大;与种植前相比,第2a、3a温室土壤氮矿化势增加了5.59和11.48倍。5)回归分析表明,0—20 cm土层土壤有机质含量每增加1 g/kg,20℃和30℃条件下土壤氮矿化势(No)分别增加2.70及3.18 mg/kg;土壤全氮含量每增加1g/kg,No分别增加37.28及43.12 mg/kg。【结论】日光温室土壤氮素矿化量随其栽培年限的增加显著增加;培养温度由20℃增加到30℃,土壤氮素矿化量也明显增加,日光温室栽培年限和温度对土壤氮矿化有一定的正交互效应。因此,在日光温室氮素管理中应考虑栽培年限和温度对土壤氮素矿化的影响,以采取针对性的氮素管理措施。     

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.     

Comparison of buried bag and PVC core methods for in situ measurement of nitrogen mineralization rates in an agricultural soil

Abstract

We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core methods in an ongoing investigation of the effects of earthworms and N fertilizer sources on agroecosystem N dynamics. Over a seven‐month period, we paired monthly buried bag and PVC core soil incubations within research plots receiving one of three N treatments (inorganic, legume, or manure fertilizers) and with manipulated earthworm populations (reduced, ambient, or increased numbers). Soil moisture within both the buried bags and the PVC cores fluctuated in response to changes in the surrounding soil, violating assumptions of the buried bag method that soil moisture remains constant during incubation. For both methods, overall CV's for net ammonification, nitrification, and N mineralization rates were very high (104 ‐ 628%). Overall, results for the two methods were significantly correlated for net ammonification (r = 0.89), net nitrification (r = 0.58), and net N mineralization (r = 0.24). In general, the two methods yielded similar seasonal estimates of net N mineralization and nitrification. However, on one occasion in the plots with the inorganic N treatment, buried bag estimates of net N mineralization were significantly higher than the PVC core estimates (1.5 versus ‐0.4 mg N‐kg^‐1 soil‐d¹, respectively). Under some conditions, the two methods may lead to quite different interpretations of soil N mineralization processes.     

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.     

施入~(15)N标记氮肥在长期不同培肥土壤的残留及其利用

采用盆栽试验和短期矿化培养相结合的方法,研究了施入15N标记氮肥(+N)及其与秸秆配施(+1/2N+1/2S)在3种长期(19年)不同培肥土壤(即:No-F,长期不施肥土壤;NPK,长期施用NPK化肥土壤;MNPK,长期有机无机肥配施土壤)中的残留及其矿化和作物吸收特性。结果表明,第一季小麦收获后,+1/2N+1/2S处理下三供试土壤和+N处理下的NPK和MNPK土壤残留肥料氮(残留15N)中有82.6%~95.1%以有机态存,而+N处理下No-F土壤残留15N有47.7%以矿质态存在。经过28 d矿化培养后,与NPK土壤相比,MNPK土壤氮素净矿化量显著增加,增幅为39%~49%;NPK和MNPK土壤残留肥料氮(残留15N)矿化量为1.23~1.90 mg kg-1,占总残留15N的2.78%~5.53%,均显著高于No-F土壤。与+N处理相比,+1/2N+1/2S处理显著提高了3供试土壤氮素净矿化量,但两施肥处理对NPK和MNPK土壤残留15N矿化量无显著影响。+N处理下No-F土壤残留15N的利用率为20%,显著高于NPK(9%)和MNPK(12%)土壤。两种施肥处理下,MNPK土壤残留15N的利用率均显著高于NPK土壤。短期培养期间土壤氮素矿化量和第二季小麦生育期作物吸氮量呈显著性正相关,而残留15N矿化量和第二季小麦吸收残留15N量间无显著性相关关系。长期有机无机配施可以提高土壤残留肥料氮的矿化量及有效性。     

Dynamics and Model Fitting of Nitrogen Transformations in Pig Slurry Amended Soils

Abstract

To optimize the efficient use of nutrients in pig slurry by crops and to reduce the pollution risks to surface and groundwater, a full knowledge of the fate of nitrogen (N) in amended soils is needed. A 120 day laboratory incubation experiment was conducted to study the effects of pig slurry application on soil N transformations. Pig slurry was added at the rates of 50 and 100 g kg^?1. A nonamended soil was used as a control treatment. Soil samples were taken after 0, 7, 14, 30, 45, 60, and 120 days of incubation and analyzed for NH₄ ⁺‐N and NO₃ ^?‐N. Initially, the application of pig slurry produced significant increases in NH₄ ⁺‐N, especially at the highest application rate, whereas NO₃ ^?‐N content was not affected. Nitrification processes were active during the entire incubation time in the three treatments. In the control soil, the net N mineralization rate was highest during the 1st week (5.7 mg kg^?1 d^?1), followed by a low‐steady phase. Initially, net N mineralization rate was slower in soil with the lowest slurry rate (2.7 mg kg^?1 d^?1), whereas in the treatment with the highest slurry rate, a net N immobilization was observed during the 1st week (4.8 mg kg^?1 d^?1). Mineral‐N concentrations after 120 days were 180, 310, and 475 mg kg^?1 in soils amended with 0, 50, and 100 g kg^?1 of pig slurry, respectively. However, when results were expressed as net mineralized N, the opposite trend was observed: 74, 65, and 44 mg kg^?1. Of the six kinetic models tested to describe the mineralization process, a two‐component, first exponential model (double model) offered the best results for all treatments.     

Peanut residues supply minimal plant-available nitrogen on a major soil series in the USA peanut basin

Field observations have shown that a substantial portion of peanut leaves abscise in windrows during pod curing, leading to an uneven distribution of leaves and stems when intact residues are spread during harvest. Possible differences in nitrogen (N) mineralization rates between peanut leaf and stem residues may lead to spatial and temporal variability in available N during subsequent crops. The objective of this study was to quantify N mineralization in soil amended with different peanut residue components under simulated conventional and conservation tillage practices. A 252-day microlysimeter incubation was conducted in which peanut leaves, stems and a 1:1 mixture of leaves:stems from three varieties were incorporated or placed on the soil surface to simulate conventional or conservation tillage, respectively. Soils were periodically leached to assess N mineralization compared with a soil-only control. Nitrogen mineralization was only affected by residue component. Averaged over variety and residue placement, soil amended with leaves mineralized 10% more N relative to the control or soil containing stems. It was estimated that leaves supplied 25 kg N ha⁻¹ over 252 days at 0–15 cm soil depth, which would likely be insufficient to induce a yield response by a subsequent crop. This study suggests that uneven distribution of peanut leaf and stem residues following harvest causes only minor spatial and temporal variability in available N during subsequent crop growth. These results support the growing body of evidence indicating that peanut residue N contributions to subsequent crops are negligible in the peanut basin of the south-eastern USA.     

Mineralization of nitrogen in permanent pastures amended with fertilizer or dung

 Nitrogen mineralization was measured in three permanent pastures – either fertilized or unfertilized grass, or a mixed grass-clover sward – which were further amended with either fertilizer or cattle dung over a summer growing season. Measurements were made at 4-weekly intervals from June to October. Rates of net mineralization were similar in each of the background treatments (overall mean 0.99±0.091 kg N ha^–1 day^–1) and did not change markedly during the experiment. From the second sampling (July) onwards, rates of mineralization in all the dung treatments were higher than in the control by a factor of up to 2. In the fertilizer-amended treatments, rates were also consistently (but not significantly) higher than in the control. However, the relatively small effect of fertilizer detected at each sampling had a significant cumulative effect by the end of the experiment. There was no interaction between the background and current treatments. Potential mineralization, measured by anaerobic incubation, increased in all the treatments over the period of the experiment, showing an accumulation of readily mineralizable residues. Total N mineralized and the N accumulated during the experiment were calculated and compared. This approach suggests that potential measurements could provide a good estimate of changes in soil N supply that would not be otherwise detectable in changes in soil total N in the short-term. Received: 12 June 2000     

Nutrient Mineralization from Nitrogen- and Phosphorus-Enriched Poultry Manure Compost in an Ultisol

The combination of inorganic fertilizers and compost is a technique aimed at improving crop growth and maintaining soil health. Understanding the rate of nutrient release from enriched compost is important for effective nutrient management. A laboratory incubation study was conducted for 112 days to study the nutrient mineralization pattern of poultry manure compost enriched with inorganic nitrogen (N) and phosphorus (P) fertilizer nutrients in an Ultisol. Compost applied at the rate of either 5 or 10 g kg^?1 was blended with N (50 kg N ha^?1) and P (30 kg P ha^?1). Carbon dioxide evolution and N and P mineralization were measured fortnightly. The bacterial and fungal populations were determined at the mid and end of the experiment. The combination of compost and inorganic N and P increased carbon (C) and P mineralization by 4?8% and 56?289%, respectively, over the application of either compost or inorganic N and P. However, P addition influenced the amount of C mineralized. Inorganic N and P, on the other hand, were better at increasing N mineralization than compost blended with inorganic N and P over a short time. The addition of compost stimulated bacterial and actinomycete populations, while fungal populations were unaffected. Actinomycetes and bacteria had similar and higher relationship trend with C (R² = 0.24) and P (R² = 0.47) mineralization and were key determinants in nutrient mineralization from compost in this Ultisol. Integrating compost with inorganic fertilizers improves nutrient availability through the growth and activities of beneficial microorganisms.     

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.     

Controlled‐release urea decreased ammonia volatilization and increased nitrogen use efficiency of cotton

Excessive nitrogen (N) fertilizer input leads to higher N loss via ammonia (NH₃) volatilization. Controlled‐release urea (CRU) was expected to reduce emission losses of N. An incubation and a plant growth experiment with Gossypium hirsutum L. were conducted with urea and CRU (a fertilizer mixture of polymer‐coating sulfur‐coated urea and polymer‐coated urea with N ratios of 5 : 5) under six levels of N fertilization rates, which were 0% (0 mg N kg⁻¹ soil), 50% (110 mg N kg⁻¹ soil), 75% (165 mg N kg⁻¹ soil), 100% (220 mg N kg⁻¹ soil), 125% (275 mg N kg⁻¹ soil), and 150% (330 mg N kg⁻¹ soil) of the recommended N fertilizer rate. For each type of N fertilizer, the NH₃ volatilization, cotton yield, and N uptake increased with the rate of N application, while N use efficiency reached a threshold and decreased when N application rates of urea and CRU exceeded 238.7 and 209.3 mg N kg⁻¹ soil, respectively. Ammonia volatilization was reduced by 65–105% with CRU in comparison to urea treatments. The N release characteristic of CRU corresponded well to the N requirements of cotton growth. Soil inorganic N contents, leaf SPAD values, and net photosynthetic rates were increased by CRU application, particularly from the full bloom stage to the initial boll‐opening stage. As a result, CRU treatments achieved significantly higher lint yield by 7–30%, and the N use efficiency of CRU treatments was increased by 25–124% relative to that of urea treatments. These results suggest that the application of CRU could be widely used for cotton production with higher N use efficiency and lower NH₃ volatilization.