Nutrients,Trace Elements and Net N Mineralization in Acidic Kenyan Soils

The nutrients status and properties in Kenyan soils (Kiambu, Mbeere Districts) are reported with the aim to elucidate the factors of productivity decline. According to the FAO (1988) system the studied soils were classified as humic Nitisols, haplic Acrisols or luvic Arenosols. The soils were found acidic, as a result of leaching of exchangeable cations and they are poor in organic carbon. Cation exchange capacity was extremely low in the sandy soils of Mbeere. Available phosphorus and exchangeable K⁺ were low inducing a crucial problem of soil fertility. Among the micronutrients, manganese extracted by DTPA was most abundant element, while micronutrients extracted by 4 M HNO₃ ranked as follows: Fe>Mn>Zn>Cu. Copper (DTPA) was low and manganese was extremely high in Kiambu. Iron content varied greatly, while decreased zinc was observed in Mbeere. Nitrogen mineralization over an incubation period of 30 weeks ranged from 54.64 to 145.50 mg kg^?1 and represents 4.53–21.09% of the total soil nitrogen. Soil nitrogen was associated to soil organic carbon and was strongly correlated to total soil N. Water harvesting, liming, and improved management of composting and manure are amongst the measures to restore soil fertility.     

Nitrogen Mineralization and Nitrification in Two Soils with Different pH Levels

ABSTRACT

Soil pH is one of the properties that mostly influences nitrification rates, and can be used as a tool for controlling this process, seen that depending on its extent it may lead to nitrogen (N) losses and subsequent contaminations. The aims of this study were to evaluate mineralization and nitrification of two soils at different pH levels. The experimental design was factorial with two factors and three replicates, with the first factor referring to two samples of red latosols, one eutrophic (LV1) and the other dystrophic (LV2), and the second factor was soil’s pH, at six levels: 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5. Samples were incubated for 70 days in laboratory conditions. Both nitrate (N-NO₃) and mineral N contents were determined and adjusted to growth models. The eutrophic soil presented higher mineral N and N-NO₃, and the increase of pH levels led to increases of both inorganic N and N-NO₃contents. Increases in pH levels caused N-NO₃levels to increase in both soils, however this occurrence happened because it increased the amount of mineralized N in the soil, seen that in all pH ranges in both soils practically all mineral N was in the form of N-NO₃.     

Mineralization and Nutrient Release of an Organic Fertilizer Made by Flour,Meat, and Crop Residues in Two Vineyard Soils with Different pH Levels

The mineralization and nutrient evolution of an organic fertilizer compost of flour, meat, and crop residues was evaluated in two vineyard soils. A lysimetric testing, using 2.2-L Büchner funnels, was carried out to study the evolution of pH, electrical conductivity, and nutrients during the 400-day experiment. The net mineralization for two different doses of the fertilizer mixed with the soils was compared with an unfertilized control. The pH value of the acidic soil decreased to values less than 4.5 because of the yield of hydrogen (H⁺) in the organic fertilizer mineralization, whereas the soluble aluminium (Al³⁺) increased quickly in the leachates. The mineralization process was quicker in the alkaline soil (with a maximum mineralization rate of 0.83 mg nitrogen (N) kg^?1 day^?1 for the 8 Mg ha^?1 dose and 0.43 mg N kg^?1 day^?1 for the 4 Mg ha^?1 dose) in comparison with the acidic soil, which reduced these rates up to 50%. The N-nitrate (NO₃) amounts yielded in a year were 150 and 79 kg N ha^?1 for the 8 and 4 Mg ha^?1 doses respectively in the alkaline soil, enough to cover the vineyard N demand. These values were reduced to 50% and 60% of N-NO₃ for the acidic soil, indicating the important effect of pH in the mineralization.     

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.     

添加秸秆对土壤矿质氮量、微生物氮量和氮总矿化速率的影响

采用室内恒温培养法,研究了在乌沙土上添加15N标记秸秆后,秸秆15N在矿质氮、微生物氮和土壤不同组分中的分配情况,并应用氮同位素库稀释法测定了秸秆在乌沙土上的氮总矿化速率。结果表明:将秸秆添加到土壤后,微生物氮量显著增加,而土壤矿质氮量在14天时迅速下降。随着秸秆的分解,秸秆15N进入矿质氮库和微生物氮库,矿质15N在第7 d时最高,占到添加秸秆15N的6.7%,微生物15N在第14 d最高,占到添加秸秆15N的18.1%,随后矿质15N和微生物15N量都下降。56 d时,仍有50.8%的秸秆氮没有分解掉,5.4%的秸秆15N进入土壤53μm~2 mm组分,15.5%进入2~53μm组分,14.6%进入小于2μm组分,有13.6%的秸秆氮损失掉。在培养开始时,乌沙土的氮总矿化速率为2.81 mg kg-1d-1,秸秆在乌沙土上的氮总矿化速率分别为2.50 mg kg-1d-1。     

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 Fractions in Arable Soils in Relation to Nitrogen Mineralization and Plant Uptake

Abstract

Nitrogen (N) as a major constituent of all plants is one of the most important nutrients. Minimizing input of mineral nitrogen fertilizer is needed to avoid harm to the environment. Optimal input of mineral nitrogen should take the nitrogen supply of the soil into account. Many different soil tests have been proposed for determining soil nitrogen availability. In this article we present a new approach that is based on the measurement of nitrate, ammonium, and dissolved organic nitrogen (DON) in a 0.01 M CaCl₂ soil extract. Eighteen agricultural soils, differing widely in the availability of nitrogen were used, fertilized and unfertilized. It is shown that the nitrogen uptake by maize plants (Zea Mays L.) in both “N‐fertilized” and “N‐unfertilized” soils as measured in a pot experiment can be described with a simple model using the measured nitrogen fractions in the extract. The main source of nitrogen uptake by the plants is the mineralized organic nitrogen during the growing period. It is shown that the initial measured DON fraction is a good indicator of the nitrogen mineralized during plant growth.     

设施和露天栽培下有机菜地土壤氮素矿化和硝化作用的比较研究

矿化作用和硝化作用是土壤氮素转化的主要途径,通过室内培养试验,对设施和露天栽培方式下有机菜地土壤氮素的矿化与硝化作用进行了比较研究。结果表明,除培养第1d外,设施有机菜地土壤氮素矿化量、矿化率在整个培养期间都显著高于露天有机菜地土壤;设施有机菜地土壤硝化量、硝化率在培养前两周内高于露天有机菜地土壤;设施有机菜地土壤矿化与硝化作用总体比露天有机菜地土壤强烈。矿化作用可能与全氮、C/N、微生物活性关系密切,而硝化作用强弱可能与微生物活性有关。无论施肥与否,设施有机菜地土壤N2O排放速率在培养期间总体高于露天有机菜地土壤,前者N2O累积排放量显著高于后者,这可能与土壤C/N有关。     

勐海县甘蔗土壤养分空间分布特征及肥力评价

对勐海县10个甘蔗生产乡镇进行土壤调研取样,共采集0～20 cm土层样品200份,测定了土壤pH、有机质、碱解氮、有效磷、速效钾、交换性钙和交换性镁含量,运用ArcGIS的Kriging插值法分析了蔗区土壤肥力现状与空间分布特征,并采用改进后的Nemerow综合指数法评价了土壤的肥力等级.结果表明:勐海县蔗区土壤主要为...     

Nutrient Mineralization from Deoiled Neem Seed in a Savanna Soil from Nigeria

Abstract

The mineralization of nutrients from deoiled neem seed (neem seed cake), the residue left after oil extraction, was examined in a typical savanna soil with a view to determining its potential for fertility improvement. The neem seed cake (NSC) application rates were 0, 2.5, and 5.0 g kg^?1 soil (0, 5, and 10 tons ha^?1). The concentrations of ammonium‐nitrogen (NH₄‐N) and nitrate (NO₃)‐N mineralized from the neem‐amended soil were two to three times greater than the control. Similarly, exchangeable potassium (K), magnesium (Mg), and cation exchange capacity were significantly greater than the control. The neem‐amended soil maintained organic carbon (OC) at the pre‐incubation level, whereas OC in the control soil declined to significantly less than the pre‐incubation concentration. The electrolytic conductivity of the soil saturation extract with neem application was 8–10 times greater than the control soil. However, the NSC increased exchange acidity markedly and decreased the soil pH significantly. Thus, the benefits of NSC in increasing the concentrations of N, K, and Mg and maintaining OC of the soil must be weighed against the consequences of soil acidity, though it is unlikely that NSC can acidify the soil to the same extent under field conditions as it did in this closed‐system incubation study.     

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.     

25年来褐土区土壤养分演变特征

褐土是中国小麦与玉米产区的重要土壤类型之一。为了探明我国褐土养分和肥力的演变特征,科学合理地指导褐土施肥,本研究分析了1988-2013年间褐土中的有机质(SOM)、全氮(TN)、碱解氮(AN)、有效磷(AP)和速效钾(AK)含量以及土壤p H值演变特征,并运用主成分分析法(PCA)分析了6个肥力指标对褐土综合肥力的作用和影响。结果表明,褐土有效磷含量从8.8 mg·kg~(-1)上升到30.9mg·kg~(-1),显著上升(P0.05)。土壤速效钾含量从监测初期70.75 mg·kg~(-1)上升到162.20 mg·kg~(-1),显著增加(P0.05)。土壤p H值下降了0.35个单位(P0.05),土壤有机质和全氮含量也显著增加(P0.05)。褐土肥力主要贡献因子为有机质、全氮和碱解氮。褐土区土壤养分含量基本呈上升趋势,说明土壤肥力总体上得到了改善。土壤有机质和全氮含量是褐土区农业生产和可持续发展的重要影响因素,加大有机肥的投入,对提高褐土的综合肥力具有重要意义。     

黄土区几种土壤培养过程中可溶性有机氮的变化及其与土壤矿化氮的关系

研究了黄土高原12种土壤(农地和林地)35 d好气培养过程中可溶性有机氮(SON)含量及其占可溶性全氮(TSN)的比例,以及SON与土壤矿化氮间的关系。结果表明,随着培养过程的进行,不同类型土壤SON的含量均呈明显增加;土壤SON占TSN的比例在培养的前3 d内明显下降,随后这一比例基本保持在24%左右。根据总可溶性氮确定的供试土壤氮素矿化势No平均为45.8 mg/kg,较由矿化的无机氮确定的土壤氮素矿化势No(平均36.5 mg/kg)高约1/4左右;培养过程中土壤SON含量与利用无机氮拟合得到的土壤氮素矿化势No间的相关性未达显著水平。研究表明,评价土壤氮素矿化特性时仅仅测定矿化的无机氮数量,可能会低估土壤氮素矿化潜力和氮素损失的数量和效应。     

Nitrogen Mineralization in Soils Related to Initial Extractable Organic Nitrogen: Effect of Temperature and Time

An important source of nitrogen (N) for crops is mineralization of soil organic matter during the growing season. Awareness is growing that dissolved organic nitrogen (DON) plays an important role in mineralization and plant uptake. We studied the influence of temperature and time on extractable organic nitrogen (EON) levels, which is a measure of DON, and their relationship with N mineralization. Aerobic incubation experiments were conducted in the laboratory for five soils at different temperatures (4 20, and 30 °C) and different time intervals with optimal water content (60% of its water-holding capacity). Net N mineralization ranged between 14 and 155 mg kg^–1 within 84 days and was correlated with the initial amount of EON. Net N mineralization among the soils, time, and incubation temperatures was linearly related to the square root of time multiplied by temperature, with mineralization rate k being independent of time and temperature. Because initial EON values were also related to these kvalues, we were able to describe the net N mineralization at different temperatures based on an analysis of initial EON. Preliminary validation with results from pot experiments in the literature suggests that the approach is promising, although the proposed model needs to be calibrated with more soils.     

Variation in content of available P and K (bray I) in soil samples from a cropped N,P, and K fertility experiment over 8 years

Abstract

Plots from a N, P, and K field fertility experiment were soil sampled each spring and fall from 1971 to 1979 to study the effect of cropping and different rates of added P and K on the content of available soil P and K (Bray I). Phosphorus and K fertilization was in the spring after soil sampling and before planting in 1971, 1972,and 1973 and in the fall after sampling in 1974, 1975, 1976, 1977, and 1978. Over the 8‐year period, available soil P increased 1 kg/ ha for every 2.3 kg/ha of added P; while available soil K increased 1 kg/ha for every 5.7 kg/ha of added K. However, within a growing season and between growing seasons, contents of available soil P and K showed cyclic patterns, increasing and decreasing to a greater extent than the long‐term response. Changes in available P and K from spring to fall and from fall to spring are presented. Variability in the content of available soil P and K for 32 plots receiving a similar treatment of either P or K was greater for P as compared to K.     

横垄覆膜对丹江口库区土壤净氮矿化的影响

以丹江口库区五龙池小流域玉米黄棕壤为例,利用原位矿化试验,通过与横垄无覆膜土壤比较,研究横垄覆膜对土壤净氮矿化的影响。结果表明:玉米苗期中期和拔节期前期,横垄覆膜土壤净氮矿化量与无覆膜土壤相比分别降低7.8%~57.0%和2.2%~52.8%;玉米拔节期后期、抽穗期和成熟期,横垄覆膜土壤净氮矿化量比无覆膜土壤分别提高352.9%~703.3%,52.5%~311.0%和15.2%~334.8%。横垄覆膜土壤净氮矿化量在玉米苗期、拔节期、抽穗期和成熟期与土壤含水量、温度和全氮间均存在较强度关联关系(0.6灰色关联度≤0.8)。逐步回归分析表明,横垄覆膜土壤净氮矿化量在玉米苗期与土壤温度间呈最优线性关系(F=7.205,P=0.023);在玉米拔节期与土壤含水量和温度间呈最优线性关系(F=36.861,P=0.001);在玉米成熟期与土壤含水量间呈最优线性关系(F=42.438,P=0.007)。     

Evaluation of Coconut Wastes as an Amendment to Acidic Soils in Low-Input Agricultural System

The effectiveness of plantation wastes along with locally available organic materials in ameliorating acidic soil was studied by conducting an experiment with coconut husk, poultry manure, vermicompost, and compared with limestone. Application of organic amendments significantly increased the soil pH, and it was greatest in poultry manure–amended soils followed by vermicompost and coconut husk + poultry manure treatments. The relative liming efficiency was greatest for poultry manure through out the observation period of 180 days. The coconut husk alone showed the least liming effect and its liming efficiency had increased when applied in combination with poultry manure and or vermicompost. This increase in soil pH was mirrored by significant reductions in exchange acidity, exchangeable aluminum (Al³⁺), diethylenetriaminepentaacetic acid (DTPA)–extractable iron (Fe²⁺), and manganese (Mn²⁺) and increases in cation exchange capacity, exchangeable bases, especially calcium (Ca), and Olsen-extractable phosphorus (P) by addition of organic amendments and lime. This study indicated the potential of using coconut husk along with poultry manure for managing acidic soils in low-input agricultural systems, especially in tropical islands.     

不同处理池塘底泥氮矿化机制及有机氮组分矿化特征研究

采用Warning等的淹水培养法,研究了不同处理池塘底泥氮素的矿化特征,并对可矿化氮进行一级动力学方程模拟;采用Bremner法测定了底泥培养前后各有机氮组分含量,并通过通径分析确定了可矿化氮与各有机氮组分之间的关系。研究结果表明,采用不同处理组的底泥氮矿化的强度和容量都小于对照组,其中加入沸石的矿化容量最小,强度也最低,其次是加入微生物的处理,再次是加入脲酶抑制剂的处理;上覆水中氨态氮主要来自底泥酸解氮的矿化,其中氨基酸态氮矿化最大,酰胺态氮和氨基糖态氮次之,水解未知态氮降低最小;通径分析结果表明,在酸解氮中,酸解未知态氮与可矿化氮不相关,而氨基酸态氮、铵态氮、氨基糖态氮和未知态氮与可矿化氮的直接通径系数较大,说明这几种形态氮对可矿化氮皆有贡献。酰胺态氮对可矿化氮有很高的通径系数,表明了它对上覆水氨态氮的贡献最大。     

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％.     

水分条件对不同类型土壤氮矿化及酶活性的影响

针对凉攀烟区立体气候特征明显，干湿分明特征，从水分变化角度研究植烟土壤氮素矿化及其酶活变化特征，为合理调控土壤氮素供应提供科学依据。以凉攀烟区土壤为研究对象，通过室内培养法研究了不同水分条件培养下（60%田间持水量（60%WHC），淹水状态（FS）），土壤（红壤、紫色土）氮矿化动力学及酶活性特征。结果表明，（1）与60%WHC相比，FS培养条件提高了土壤NH4+-N含量，且培养期内紫色土NH4+-N平均含量较红壤增加6.0%~9.0%； 60%WHC培养下土壤NO3--N含量明显高于FS，且培养期内红壤NO3--N平均含量（40.7~64.1 mg/kg）高于紫色土（38.0~56.4 mg/kg）；（2）FS培养提高了土壤氨化速率，紫色土平均氨化速率均高于红壤，60%WHC培养提高了土壤硝化速率，且红壤平均硝化速率高于紫色土；（3）培养期内，60%WHC培养下土壤无机氮累积矿化量明显高于FS，红壤氮矿化潜力强于紫色土，其中红壤在60%WHC培养下的土壤无机氮累积矿化量最大（42.12~394.06 mg/kg），其次是同一水分条件培养下的紫色土；（4）土壤脲酶、蛋白酶和亚硝酸还原酶的活性与土壤无机氮矿化累积量存在显著的相关性，红壤的脲酶活性强于紫色土，尤其是在60%WHC培养的效果更为显著；紫色土的蛋白酶活性和亚硝酸还原酶活性高于红壤，尤其是在FS培养下的效果显著。总体上，凉攀烟区红壤氮矿化潜力强于紫色土，尤其是在60%WHC条件下，在推荐氮肥施用量时，不仅要考虑不同土壤类型，而且还应该注意土壤水分状况的调控，防止烤烟生长后期氮素供应能力过强，影响烟叶成熟落黄和香气物质形成。