宣城市岗坡地土壤养分特征及其与颗粒组成关系

对宣城市岗坡地土壤养分特征及其与颗粒组成关系进行了分析,结果表明:⑴不同土地利用类型中,林地土壤有机质和全氮含量显著高于其它3种土地利用类型;耕地和新耕地土壤全磷、速效养分含量都高于林地和灌丛;土壤有机质、速效氮和速效磷含量与土地利用类型有显著的相关性。⑵土壤有机质、全氮含量中、上坡位都显著高于下坡位,全磷和速效养分的含量随坡位下降呈显著增加趋势;有机质、全磷和速效磷与坡位有显著的相关性。⑶土壤有机质与粘粒(<0.002 mm)和粉粒(0.002~0.02 mm)的含量均呈显著的正相关,与砂粒(0.02~2 mm)含量呈显著负相关,全氮与粉粒含量呈现显著正相关,全磷与粉粒、砂粒含量显著正相关。     

围栏种植红柳对川西北高寒沙地土壤颗粒组成和矿质养分的影响

为了揭示川西北高寒沙地生态修复过程中土壤颗粒组成和矿质养分的积累和变化特征,以川西北围栏种植红柳生态修复年限分别为0、2、4、6和8年的沙化土地作为研究对象,并结合土壤样品的采集和室内分析化验,研究了川西北沙化土地生态修复过程中土壤颗粒组成及磷、钾养分的变化特征。结果表明,生态修复过程中沙化土地0~20 cm土层土壤全磷和全钾含量略有增加,但不同生态修复年限之间土壤全磷和全钾含量差异未达显著水平(P0.05),而20~40 cm和40~60 cm土层土壤全磷和全钾含量无明显变化特征。随着生态修复年限的增加沙化土地0~20 cm、20~40 cm和40~60 cm土层土壤黏粒、粉粒、速效磷和速效钾含量均呈现逐步增加的趋势,而土壤砂粒含量呈现出逐步下降的趋势,其中0~20 cm土层变化最为明显,生态修复8年后沙化土地粉粒、黏粒、速效磷和速效钾含量分别增加了66.67%、96.30%和109.82%、102.61%,而土壤砂粒含量减少了5.57%,不同生态修复年限沙化土地0~20 cm土层土壤砂粒、粉粒、黏粒、速效磷和速效钾含量差异均达极显著水平(P0.01)。20~40 cm和40~60 cm土层土壤速效磷和速效钾含量增加幅度及差异显著性不及0~20 cm土层。沙化土地植被覆盖度与土壤全磷、全钾呈显著正相关关系(P0.05),与土壤速效钾、速效磷呈极显著正相关关系(P0.01);土壤速效磷、速效钾与土壤砂粒含量呈极显著负相关关系(P0.01),与土壤粉粒和黏粒含量呈极显著正相关关系(P0.01),土壤全磷、全钾含量与土壤颗粒组成相关性未达显著水平。     

荒漠-绿洲边缘区生态过渡带的土壤颗粒分形特征

通过实地采样和实验室分析,测定了黑河中游荒漠绿洲边缘区生态过渡带的土壤粒级分布、有机碳(SOC)、全氮(TN)、全磷(TP)、速效氮(AN)和速效磷(AP)的含量,并采用1993年杨培岭等提出的用粒径的重量分布代替数量分布的土壤分形模型,计算了土壤颗粒分形维数;最后利用统计分析法,研究了颗粒分形维数与土壤粒级分布及各养分指标的关系.结果表明:从荒漠边缘向绿洲延伸的过渡带,土壤中砂粒含量占绝对优势,粉粒居中,黏粒最少,采样区土壤质地较粗;土壤颗粒分形维数在2.105～2.609之间变动,处于极低水平,与土壤各养分指标具有相似的变化趋势,除靠近绿洲区存在一个"生态裂谷"外,整体呈上升趋势;利用相关分析法得出,土壤颗粒分形维数与砂粒含量呈显著负相关,与黏粉粒及各养分指标均呈显著的正相关;利用回归分析法进行定量分析,砂粒含量每增加1g/kg,颗粒分形维数D降低0.0019个单位;粉粒和黏粒含量每增加1g/kg,颗粒分形维数D分别增加0.002和0,023个单位,对土壤颗粒分形维数变化幅度的影响依次为黏粒>粉粒>砂粒,分形维数对黏粒含量的变化最为敏感.因此,可以将土壤颗粒分形维数作为衡量荒漠-绿洲边缘区土壤养分变化状况的指标之一,用于反映荒漠绿洲区土壤的退化状况.     

东北黑土有机碳、全氮空间分布特征

应用经典统计学方法,分析了东北黑土表层1100个样点的土壤有机碳(SOC)和全氮空间分布规律。结果表明土壤有机碳和全氮平均含量分别为19.25 g kg-1和1.89 g kg-1,从南到北随纬度增加而增加,土壤有机碳和全氮与纬度的相关系数分别为0.70和0.76;土壤有机碳、全氮与黏粒、砂粒在P<0.01水平上显著相关,其中与砂粒为显著负相关,而SOC与粉粒则在P<0.05水平下显著正相关;土壤全氮与粉粒没有相关性。     

北江干流河岸带不同植被类型土壤粒径分形特征

结合野外调查与室内试验,以北江干流河岸带竹林、桉树林、混交林和草地土壤为对象,对比分析了不同植被类型土壤的颗粒组成与分形维数(D)特征及其与其他土壤理化性质的相关性。结果表明:北江干流河岸带土壤结构良好(D=2.79),质地均一,粒径分布均匀(粉粒、砂粒、黏粒百分比分别为40.66%,36.59%,22.75%),但随粒级增大,空间变异增强;D值与土壤颗粒组成显著相关,随黏粒和粉粒含量升高、砂粒含量降低,D值升高;不同植被类型土壤分形与颗粒组成差异明显,其中砂粒含量表现为竹林混交林草地桉树林,D值、粉粒和黏粒含量均表现为桉树林草地混交林竹林,竹林和桉树林对土壤结构的影响差异有显著(p0.05),其他植被类型影响差异不显著;D值、黏粒含量均与硝态氮(NO-3-N)和全磷(TP)含量分别呈显著负相关和显著正相关(p0.05)关系,土壤砂粒含量与含水量(SM)呈显著负相关(p0.05),土壤粉粒含量只与SM呈显著正相关,另外,D值、砂粒、粉粒和黏粒含量与总有机碳(TOC)和全氮(TN)的相关性均不显著。河岸带土壤受多种因素影响,其土壤理化性质间的相互关系与其他景观差异明显。     

伊犁河谷不同森林模式下土壤的养分特征和粒径组成

[目的]对伊犁河谷不同森林模式下土壤粒径组成和养分空间特征进行研究,为科学栽培和可持续经营提供理论依据。[方法]通过野外采样与室内试验,分析伊犁河谷不同模式下土壤粒径分布特征及其与土壤理化性质的关系。[结果]7个模式林地土壤基本集中在细粉粒和粗粉粒两个粒级。主要由细粉粒—粗粉粒—黏粒、细粉粒—粗粉粒—极细砂粒和粗粉粒—细粉粒—极细砂粒为主的质地组成,其中细粉粒—粗粉粒—黏粒土壤养分较佳,相比之下含有砂粒的土壤养分较低。土壤有机质和土壤碱解氮与黏粒和细粉粒含量的关系非常密切,尤其是细粉粒;速效磷与砂粒、黏粒和细粉粒呈正相关;速效钾与黏粒和细粉粒含量的关系密切,随着其含量增加而增加,跟砂粒呈显著负相关,砂粒含量高,速效钾含量降低。[结论]伊犁河谷7个模式林分土壤养分状况各异,养分各项指标含量不同,可根据养分状况进行抚育管理。各模式土壤中粉粒含量占绝对优势。根据各养分含量与各粒径组成之间的相关性分析表明,土壤颗粒越细,与土壤养分的关系越密切。     

祁连山南坡农田土壤碳氮含量垂直分布特征及其影响因素

[目的] 分析农田生态系统土壤碳氮与土壤理化性质的关系,为高寒地区合理利用土地资源提供理论借鉴。[方法] 在祁连山中段南坡选取具有代表性的农田样地共19个,结合野外采样及室内试验,运用回归、通径分析等方法对研究区农田土壤全碳含量（TC）,全氮含量（TN）与有机碳含量（SOC）,含水量（SWC）,土壤容重（ρ_b）,粒度（黏粒、粉砂、砂粒）,pH值等土壤理化性质的关系进行研究。[结果] ①研究区土壤全碳含量、全氮含量随土层的加深而减少,有表聚现象,平均含量分别为35.47,2.41 g/kg。②随着土层的加深,土壤有机碳、含水量、黏粒和粉粒含量减少;土壤容重、pH值和砂粒含量增大。③土壤理化性质因子之间相互联系,共同影响土壤碳氮含量。土壤全碳含量、全氮含量之间直接作用显著,土壤容重对土壤全碳含量产生直接作用效应,土壤含水量通过土壤全氮含量对土壤全碳含量产生间接正效应;土壤粉粒、黏粒含量对土壤全氮含量产生直接作用效应,土壤pH值通过土壤粉粒,黏粒含量对土壤全氮含量产生间接负效应。[结论] 祁连山南坡农田土壤比较肥沃,其土壤全氮含量及有机质含量处于较高水平,可为研究区植被生长提供较为充足的土壤养分。在当前耕作水平下,土壤全氮含量及含水量的增加有利于土壤全碳含量的积累。土壤全碳含量、黏粒及含水量的增加有利于土壤全氮含量的积累。     

辽东山区天然次生栎林土壤有机碳含量及其与理化性质的关系

通过对设置在辽东山区本溪市草河口镇和庄河市仙人洞镇两个典型天然次生栎林(Quercus spp.)样地内的土样进行分层(0—10,10—20,20—30,30—40cm)采集和室内分析,研究了0—40cm土层土壤有机碳、全氮、全磷等含量的剖面分布特征,探讨了有机碳与理化性质间的关系。结果表明:土壤有机碳及全氮、全磷、全钾、碱解氮、速效磷、速效钾、阳离子交换量的含量均随土层加深而降低,而土壤容重随土层加深而增加,由t检验和方差分析得知,各指标含量在土层间差异均达到5%显著水平;土壤有机碳与粉粒、pH、全氮、全磷、全钾、碱解氮、速效磷、速效钾、阳离子交换量间均呈显著正相关(r=0.430 9~0.919 0,n=44,P0.01),与土壤容重、砂粒间均呈显著负相关(r=0.388 3~0.670 6,n=44,P0.01),而与黏粒间无显著相关性;由逐步回归分析得知土壤碱解氮、碳氮比、全钾、pH、全氮与有机碳间关系最为紧密。土壤有机碳与其他理化性质间关系密切,且以全氮、碱解氮、碳氮比、全钾和pH对其影响最大;同时,各指标均具有明显的剖面分布规律。     

平顶山矿区丘陵坡地土壤理化性质及质量评价

以平顶山矿区丘陵坡地土壤为供试材料,通过采样、测试分析,分析了坡面不同海拔与矿区下风向不同距离处土壤的理化性质及重金属Cu,Zn,Cr,Ni和Pb含量,并采用熵权TOPSIS法进行土壤质量评价。结果表明:(1)不同海拔坡面土壤中的砂粒含量显著高于黏粒,其中矿区附近砂粒含量最高而黏粒含量最低,矿区以上砂粒减少而黏粒增多,且在近坡顶附近最高。矿区附近坡面土壤呈碱性,矿区以上海拔高于356m的坡面土壤呈酸性,且随海拔上升而酸性增强。土壤电导率、有机质、速效磷、全磷与速效磷含量在矿区附近含量最高,矿区以上坡面最低,但在近坡顶附近略有富集。土壤全氮沿坡面波动较大,但近坡顶附近富集明显。全钾与碱解氮在矿区附近含量最低,近坡顶附近最高。(2)矿区下风向距离矿区越近,砂粒含量越高,黏粒含量越低,反之则砂粒含量趋于减小,而黏粒含量趋于增大。土壤pH值、电导率、有机质、全氮及全磷随距离增大而减小,全钾、碱解氮、速效磷及速效钾在距离矿区100~200m的范围内含量最高,之后趋于波动性减小。(3)不同海拔下,矿区周边坡面土壤质量较好,坡底附近一般,而矿区以上则较差;矿区下风向随着距离增大,土壤质量趋于波动性变差。其质量变化除了与土层浅薄及土壤自身特点有关以外,还主要与矿区长期的煤炭开采活动对周边土壤的扰动及其释放的粉煤灰、粉尘、重金属元素等的坡面径流迁移、高空气流传输、地形阻滞、沉降有关,而且与耕地农业活动也有一定关系。     

渭北旱塬区不同坡向土地利用类型对土壤性质的影响

为了研究不同坡向土地利用类型对土壤性质的影响,以渭北旱塬区5种土地利用类型(不同坡向)为研究对象,系统分析该区不同坡向土地利用类型剖面土壤物理、化学和生物性质的差异。结果表明:(1)除土壤pH和土壤颗粒组成外,5种土地利用类型土壤含水量、总孔隙度、有机质、全氮、微生物量碳和氮含量总体随土层加深呈下降趋势,土壤容重则相反。(2)0-30cm土层,阳坡农用地土壤含水量、黏粒含量和pH最高,粉粒和全氮含量最低;人工草地砂粒和全氮含量最高,黏粒含量最低;人工林地土壤总孔隙度、土壤有机质、微生物量碳和氮含量最高,土壤含水量、土壤容重和pH最低;天然草地土壤容重和粉粒含量最高,总孔隙度和砂粒含量最低;退耕地有机质、微生物量碳和氮含量最低。阴坡农用地土壤含水量、粉粒含量和pH最高,黏粒和全氮含量最低;人工草地土壤容重、黏粒和微生物量氮含量最高,土壤总孔隙度、粉粒、砂粒和有机质含量最低;人工林地有机质含量和微生物量碳含量最高;天然草地土壤总孔隙度、砂粒和全氮含量最高,土壤容重和pH最低;退耕地土壤含水量、微生物量碳和氮含量最低。(3)5种土地利用类型中,土壤容重、细黏粒、粗黏粒、细粉粒、粗砂粒、土壤pH和有机质(退耕地除外)表现为阳坡阴坡,土壤含水量(退耕地和农用地除外)、总孔隙度、粗粉粒、细砂粒、土壤质地粗化度、全氮(人工草地除外)、土壤微生物量碳和氮含量则为阴坡阳坡。     

聚丙烯酸钠对3种土壤持水能力及作物产量的影响

在离心机模拟不同水吸力条件下,研究了聚丙烯酸钠(sodium polyacrylate记作SP)5种使用浓度(占干土质量0,0.01%,0.08%,0.2%与1%)对3种土壤(砂土、壤土、黏土)持水能力的影响;采用大田试验研究了地表撒施2 g/m2SP对冬小麦与下季玉米产量及WUE影响。结果表明:3种土壤在0.01 MPa至1.5 MPa水吸力下的持水能力随着SP用量的增加而增加,砂土的作用效果较壤土、黏土更显著;3种土壤适宜浓度为0.08%~0.2%,最佳用量为0.2%,此用量条件下砂土、壤土、黏土的最大毛管持水量分别较对照增加了138.61%,7.22%,62.70%;不灌水条件下,SP处理较不施用SP冬小麦增产4%,WUE增加5.7%,灌浆期灌水28.5 mm条件下SP处理较不施用SP增产1%,WUE降低1%;SP处理的玉米产量较对照降低0.5%,WUE提高3%,效果明显低于对冬小麦效果。     

基于土壤水分空间变异的变量灌溉作物产量及节水效果

提高整个田块作物生长指标和产量的均匀性是实施变量灌溉水分管理的目标之一。该研究基于土壤可利用水量(available water holding capacity,AWC)将试验区划分为4个水分管理区,利用相同的灌水控制指标(0.45AWC)进行分区变量灌溉水分管理;作为对照,基于最小AWC区的土壤水分进行均一灌溉水分管理。对比变量灌溉和均一灌溉条件下冬小麦、夏玉米生长指标(株高、叶面积指数、地上部分干物质质量)、叶片相对叶绿素含量、产量及其均匀性,分析AWC对作物生长和产量的影响。结果表明,与均一灌溉相比,夏玉米变量灌溉节水14.1%,冬小麦灌水量相同。与均一灌溉相比,变量灌溉对冬小麦、夏玉米生长指标、叶片相对叶绿素含量和产量的影响均未达到显著水平,而不同AWC管理区之间作物生长指标和产量的差异均达到了显著水平。为获得更高的作物产量,建议不同AWC管理区内采用不同的灌水控制指标。研究可为大型喷灌机变量灌溉水分管理决策提供依据。     

Spatial variability of Southeastern U.S. Coastal Plain soil physical properties: Implications for site-specific management

Our objectives were to describe the field-scale horizontal and vertical spatial variability of soil physical properties and their relations to soil map units in typical southeastern USA coastal plain soils, and to identify the soil properties, or clusters of properties, that defined most of the variability within the field. The study was conducted on a 12-ha field in Kinston, NC. A 1:2400 scale soil survey had delineated three soil map units in the field: Norfolk loamy sand, Goldsboro loamy sand, and Lynchburg sandy loam. These are representative of millions of hectares of farmland in the Coastal Plain of the southeastern USA. Sixty soil cores were taken to ∼ 1-m depth, sectioned into five depth increments, and analyzed for: soil texture as percentage sand, silt, and clay; soil water content (SWC) at − 33 and − 1500 kPa; plant available water (PAW); saturated hydraulic conductivity (Ksat); bulk density (BD); and total porosity. A penetrometer was used to measure cone index (CI) at each sample location. Variography, two mixed-model analyses, and principal components analysis were conducted. Results indicated that soil physical properties could be divided into two categories. The first category described the majority of the within-field variability and included particle size distribution (soil texture), SWC, PAW, and CI. These characteristics showed horizontal spatial structure that was captured by soil map units and especially by the division between sandy loams and finer loam soils. The second class of variables included BD, total porosity, and Ksat. These properties were not spatially correlated in the field and were unrelated to soil map unit. These findings support the hypothesis that coastal plain soil map units that delineate boundaries between sandy loams versus finer loam soils may be useful for developing management zones for site-specific crop management.     

Straw incorporation and soil organic matter in macro-aggregates and particle size separates

Two field experiments in which straw has been removed or incorporated for 17 yr (loamy sand) and 10 yr (sandy clay loam) were sampled to examine the effect of straw on the C and N contents in whole soil samples, macro-aggregate fractions and primary particle-size separates. The particle size composition of the aggregate fractions was determined. Aggregates were isolated by dry sieving. Straw incorporation increased the number of 1–20 mm aggregates in the loamy sand but no effect was noted in the sandy clay loam. Straw had no effect on the particle size composition of the various aggregate fractions. After correction for loose sand that accumulated in the aggregate fractions during dry sieving, macro-aggregates appeared to be enriched in clay and silt compared with whole soil samples. Because of the possible detachment of sand particles from the exterior surface of aggregates during sieving operations, it was inferred that the particle size composition of macro-aggregates is similar to that of the bulk soil. The organic matter contents of the aggregate fractions were closely correlated with their clay + silt contents. Differences in the organic matter content of clay isolated from whole soil samples and aggregate fractions were generally small. This was also true for the silt-size separates. In both soils, straw incorporation increased the organic matter content of nearly all clay and silt separates; for silt this was generally twice that observed for clay. The amounts of soil C, derived from straw, left in the loamy sand and sandy clay loam at the time of sampling were 4.4 and 4.5 t ha^?1, corresponding to 12 and 21% of the straw C added. The C/N ratios of the straw-derived soil organic matter were 11 and 12 for the loamy sand and sandy clay loam, respectively.     

The distribution of native and labelled carbon between soil particle size fractions isolated from long-term incubation experiments

Four soils with 6, 12, 23 and 46% clay were fractionated according to particle size after incubation for 5–6 years with ¹⁴C labelled straw, hemicellulose or glucose: 6–23% of the ¹⁴C was still present and the amount increased with increasing content of fine particles. clay fractions contained 66–84% of the ¹⁴C and the silt fractions accounted for 4–19%. <2% was found in the sand fractions and 4–9% was water soluble. The distribution of the native C was: clay, 46–68%; silt, 20–31%; sand, 2–7%. The clay fractions had higher relative proportions of ¹⁴C than of native C, the reverse being true for the silt fractions. This distribution pattern was not directly related to soil clay content or to kind of organic amendment. The C enrichment factor of clay and silt fractions (per cent C in fraction/per cent C in whole soil) increased with decreasing fraction size for both native and ¹⁴C. However, clay enrichment factors were higher for ¹⁴C than for native C, whereas silt enrichment factors were lower. A soil (9% clay) that had been incubated in the field for 18 years with ¹⁴C labelled straw was also analysed. Labelled C content at sampling was 9% of the initial value. In contrast to the other soils the distribution of labelled and native C was similar in the clay and silt fractions, which contained 55% and 33% of the whole soil C, respectively. The results indicate that clay-bound organic matter may be important in mediumterm organic matter turnover, whereas silt-bound organic matter may participate in longer-term organic matter cycling.     

Nitrogen in particle size fractions of soils incubated for five years with 15N-ammonium and 14C-hemicellulose

Four soils with a range of clay and silt contents were incubated for 5 a with ¹⁵N-labelled (NH₄)SO₄ and ¹⁴C-labelled hemicellulose and then fractionated according to particle size by ultrasonic dispersion and sedimentation. The distribution of labelled and native N between clay, silt and sand fractions was determined and elated to previous results on the C distributions. Between 29% and 48% of the added N was found in organic form. The ¹⁵N atom percentage excess decreased in the order: clay > whole soil > silt > sand. For both clay and silt, the enrichment factor for labelled and native N decreased with increasing fraction weight. Clay enrichment was higher for labelled than for native N, the converse being true for silt. The distribution of whole soil labelled organic N was: clay 77–91%, silt 4–11%, and sand <0.5%. Corresponding values for native N were 69–74%, 16–22%, and 1–2%, respectively. All soils had higher proportions of labelled than of native N in the clay, the converse was true for the silt. The C/N ratio of the native silt organic matter was higher and that of clay organic matter lower than whole soil C/N ratios. Differences between the C/N ratio distributions of native and labelled organic matter were small. The relative distribution of labelled N and C was very similar confirming that the turnover of C and N in soil organic matter is closely interrelated.     

Land-use effects on the composition of organic matter in particle-size separates of soil: I. Lignin and carbohydrate signature

Soil from Eutrochrept A horizons under long-term spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp) and arable rotation (Ar) was fractionated according to particle size and analysed for contents of C, N, lignin-derived phenols and carbohydrates. Whole soil from Sf, Df, Gp and Ar contained 84, 59, 73 and 25 g C kg^?1 soil, respectively. For all sites, the C content declined and C/N ratio increased in the order: clay (<2 μm), silt (2–20 μm), sand (20–2000 μm). Clay and silt were significantly lower in C in Ar than in Sf, Df and Gp, C associated with sand being substantially lower under arable rotation. The yield of lignin-derived phenols decreased and carboxyl functionality and methoxyl demethylation of lignin derivatives increased with decreasing particle size, indicating a progressive lignin alteration. Whole soil from Sf and Gp was substantially higher in vanillyl (V), syringyl (S) and cinnamyl (C) units (VSC) than soil from Df and Ar. Compared to whole soil, clay was depleted and sand enriched in VSC. Only sand appeared to be affected significantly by land use. Sand from Ar and Df was more enriched in VSC than sand from Gp and Sf. Whole soil carbohydrates decreased in the order: Gp>Ar>Df>Sf. Sand- and clay-sized separates were enriched in carbohydrates compared to silt. Carbohydrates in sand were mainly of plant origin whereas microbially-derived sugars accounted for a larger proportion in the clay. Compared to Sf, Df and Gp, clay from Ar was enriched and sand depleted in microbial sugars. Lignin and carbohydrate distribution patterns indicate that organic matter was in a more advanced stage of decomposition in the sand separates from forest than from agricultural A horizons. The forest soils also show a higher degree of oxidative changes in lignin associated with clay. In contrast, differences between silt from the four A horizons were small.     

Exploitation of potassium by various crop species from primary minerals in soils rich in micas

We investigated the question of whether exchangeable K⁺ is a reliable factor for K⁺ availability to plants on representative arable soils (Aridisols) rich in K⁺-bearing minerals. Five soils with different textures were collected from different locations in Pakistan and used for pot experiments. The soils were separated into sand, silt, and clay fractions and quartz sand was added to each fraction to bring it to 1 kg per kg whole soil, i.e., for each fraction the quartz sand replaced the weight of the two excluded fractions. On these soil fraction-quartz mixtures wheat, elephant grass, maize, and barley were cultivated in a rotational sequence. Growth on the sand mixture was very poor and except for the elephant grass all species showed severe K⁺-deficiency symptoms. Growth on the mixture with silt and clay fractions was much better than on the sand fraction; there was no major difference in growth and K⁺ supply to plants whether grown on silt or clay, although the clay fraction was rich and the silt fraction poor in exchangeable K⁺. On both these fractions the plant-available K⁺ supply was suboptimal and the plants showed deficiency symptoms except for the elephant grass. This plant species had a relatively low growth rate but it grew similarly on sand, silt, and clay and did not show any K⁺ deficiency symptoms, with the K⁺ concentration in the plant tops indicating a sufficient K⁺ supply regardless of which soil fraction the plants were grown in. The reason for this finding is not yet understood and needs further investigation. It is concluded that on soils rich in mica, exchangeable K⁺ alone is a poor indicator of K⁺ availability to plants and that mica concentrations in the silt and clay fraction are of greater importance in supplying crops with K⁺ than exchangeable K⁺.     

Evaluation of Soil Degradation Impact on Wheat Yield by Geographical Information System

Soil degradation and its relation to wheat yield were analyzed in a 1041.2-ha catchment in Ustic soil moisture regime in north-central Anatolia, Turkey. The soils in the study area were sampled based on a randomized sampling scheme, using 142 samples from topsoil and 115 samples from subsoil. All the soil samples were analyzed for sand, silt, clay, coarse material (material with a diameter of >2 mm), soil organic matter, phosphorous, nitrogen, boron, zinc, iron, electrical conductivity, pH, hydraulic conductivity, and cation exchange capacity. Wheat yield was measured at 115 sampling locations. Data were evaluated by global information system (GIS) will and variable reduction (factor analysis) techniques. The majority of the soil properties exhibited high variation with a skewed distribution. Low organic-matter content, high penetration resistance, low water-holding capacity, and deficiency in some macro- and microelements were the most important factors limiting wheat yield.     

Spatial variability of soil properties and wheat yields in an irrigated field

Abstract

An irrigated farmer's field at Hafizabad village in Dera Ismail Khan District of Northwest Frontier Province of Pakistan was sampled at a regular grid spacing of 50x15 m from surface (15 cm) to study the spatial variability of soil properties and wheat yield. The farm measured 250x75 m. Soil samples collected were analyzed for soil pH, lime content, organic matter, mineral nitrogen (N), ammonium bicarbonate (AB)‐DTPA‐extractable phosphorus (P) and potassium (K), and soil texture. A uniformly trial on wheat with a uniform rate of 120 kg N ha^‐1, 90 kg P₂O₅ ha^‐1, and 60 kg K₂O ha^‐1 was laid out. The results showed that the soil P had the highest coefficient of variation (CV 46%) followed by organic matter (36.20%) and clay content (33.81%). Grain yield had also a considerable variation in the field (CV=31.84%). Geostatistical technique of semivariogram analysis showed that mineral N, AB‐DTPA‐extractable K, sand, silt, and clay content had the strong spatial structure. Maps of soil fertility and crop productivity of the farm was prepared using modern geostatistical technique of kriging. The farm was divided into different management zones based on these maps for fertility management.