Soil macropore characteristics and aggregate stability with poly-γ-glutamic acid amendment under wetting–drying cycles

Soils are typically subjected to multiple wetting–drying (WD) cycles due to irrigation and seasonal climate cycles, which directly impact soil pore structure and soil aggregate stability. Poly-γ-glutamic acid (γ-PGA) is a polymer used to improve soil water holding capacity and plant growth. However, the impact of γ-PGA on soil pore structure requires further research, particularly under WD cycles. Therefore, we investigated the different amounts of γ-PGA on soil structure, including soil aggregate stability, macropore (>100 μm) structure characteristics and the relationship between macropore characteristics (equivalent pore diameter, pore shape factor, soil porosity, fractal dimension (FD), soil connectivity and the percentage of aggregate content with particle size larger than 0.25 mm) and soil aggregate stability by structural equation modelling (SEM) under WD cycles. A sandy soil and a loam soil were studied, and amended with γ-PGA at three different concentrations: 0 (P0), 0.4% (P4) and 0.8% (P8) (w/w, %). Results showed that γ-PGA amendment increased the mean weight diameter (MWD) and the percentage of aggregate content with particle size larger than 0.25 mm (R_0.25) under WD cycles in both sandy and loam soils, while the MWD between P4 and P8 did not differ significantly. As the number of WD cycles increased, soil porosity (TP) increased due to an increase in pores of 100–500 μm. With γ-PGA added to soil, large microporosity (>1000 μm) increased in sandy soil, but decreased in loam soil. In addition, 8WD cycles also increased the FD (2.6%–4.2%) and pore connectivity (Con) compared with 4WD. Structural equation modelling (SEM) revealed that soil pore characteristics accounted for 74% and 98% of the variation in sandy and loam soils, respectively. TP, FD, Con and R_0.25 directly contributed to MWD, according to the SEM. These findings improve our understanding of pore characteristics and aggregate stability, which are key factors influencing soil quality when amended with γ-PGA during the seasonal WD period.     

氨化秸秆还田对土壤孔隙结构的影响

【目的】土壤孔隙性质是土壤结构性的反映,直接影响着土壤的肥力和水分有效性。定量研究氨化秸秆还田对土壤不同大小等级孔隙数量和孔隙分布的影响,可以为土壤培肥提供科学依据。【方法】采用室内试验方法,设置氨化秸秆加入量为土壤总质量的 0(CK)、 0.384%(S1)、 0.575%(S2)、 0.767%(S3)4个处理,室内培养。在培养0、60、120和180 d,取样测定土壤水分特征曲线(SWRC)数据,利用双指数土壤水分特征曲线模型(DE模型,Double-exponential water retention equation),分析氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙的影响; 基于DE模型的微分函数,探究不同氨化秸秆处理对土壤孔隙分布的影响。【结果】不同处理的土壤水分特征曲线SWRC实测值和DE模型模拟值之间的均方根误差介于0.0036和0.0041 cm3/cm3之间,R2介于0.998和0.999之间,土壤含水量模拟值和实测值非常接近1 ∶1,表明DE模型可以准确反映添加氨化秸秆后土壤含水量随吸力的变化规律,较准确地估算土壤不同大小等级孔隙数量变化。培养120 d内,氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙影响不显著; 培养180 d时,各处理土壤结构孔隙度表现出随着氨化秸秆添加量的增加而增加的趋势; 此时S3对土壤剩余孔隙影响不显著,显著减小了土壤的基质孔隙度(P0.05),极显著地增加了土壤的结构孔隙度(P 0.01)。在孔隙分布中,氨化秸秆促进了土壤已有孔隙向较大孔隙的发育,显著增加了土壤结构孔隙分布数量; 随着氨化秸秆添加量的增加,土壤结构孔隙的分布数量越大,且峰值出现的越早。氨化秸秆增加了土壤中有机质含量; 土壤结构孔隙和总孔隙均与有机质含量呈显著的正相关关系(P 0.05); 有机质可以黏结团聚土壤的矿物颗粒,有效地促进了土壤结构孔隙的发育; 氨化秸秆对土壤孔隙的影响随着时间的进行越来越明显。【结论】氨化秸秆增加了土壤中有机质含量,促进了土壤孔隙结构的发育,增加了土壤的结构孔隙度和总孔隙度,这对改良和培肥土壤、改善土壤耕性具有重要意义。     

利用计算机断层扫描技术研究土壤改良措施下土壤孔隙

为探明不同土壤结构改良措施（秸秆覆盖、免耕、有机肥、保水剂）对土壤孔隙特征及分布的影响,采用计算机断层（computed tomography,CT）扫描法定量分析了土壤孔隙的数目、孔隙度及孔隙在土壤剖面上的分布特征。结果表明：不同措施均提高了土壤总孔隙数、大孔隙数及0.13～1.0 mm孔隙数,且其孔隙度也相应提高。同时孔隙成圆率也得到了改善。各处理中以有机肥和免耕处理效果较佳,其次为保水剂和秸秆覆盖,对照最低。此外,不同措施显著提高了土壤的田间持水量和＞0.25 mm 水稳性团聚体含量,降低了土壤容重,且各处理中,仍以有机肥和免耕处理效果最佳,其田间持水量分别较对照提高了15.9%和16.4%,而土壤容重较对照降低了6.8%和8.8%。相关分析表明：田间持水量、容重和＞0.25 mm水稳性团聚体含量与土壤总孔隙度和大孔隙度呈显著或极显著正相关;而土壤容重对于总孔隙度和大孔隙度及孔隙成圆率呈显著负相关。     

使用自由软件和便携式光学显微镜研究土壤孔隙特征

Total porosity (TP), determined by image analysis, pore type and pore size distribution were evaluated on impregnated soil blocks from an undisturbed Brazilian sandy loam soil using a digital portable optical microscope. The free software Image J (version 1.40g) was used for image analysis. Procedures for soil image collection and analysis were presented. The image analysis allowed the evaluation of pore sizes with diameters ranging from 20 to >1 000 μm. The following types of pores were also obtained: rounded, elongated and intermediate. The results allowed the characterization of the soil as moderately porous (TP=21.6%). Rounded, intermediate and elongated pores were responsible for 11.6%, 31.7% and 56.7% of TP. In relation to pore size 51.1% of TP was in the 100-500 μm size class and a third of TP came from the pores larger than 500 μm.     

土壤调理剂对日光温室土壤理化性质和蔬菜产量、品质的影响

试验研究了土壤调理剂对日光温室土壤理化性质和蔬菜产量、品质的影响。结果表明,施用土壤调理剂能够明显改善土壤结构,增强土壤保水能力,与对照相比,施用2次调理剂后土壤容重降低6.36%,土壤总孔隙度增加4.97%,田间持水量增加6.75%,渗透系数提高46.28%;调理剂还能增加土壤养分含量,提高土壤保肥能力;调理剂能够提高蔬菜的产量和品质,对番茄品质的改善效果尤为明显;调理剂与秸秆配合施用效果更佳。     

2种典型耕作方式影响下的蔗田土壤孔隙结构及其水分运动特性

为了明确农业生产过程中耕作方式对田间土壤孔隙结构及土壤水分运动特性的影响,以广西农地蔗田为研究对象,基于土壤切片技术分析研究免耕和垄耕2种典型耕作方式蔗田的田间土壤孔隙结构特征,并结合土柱模拟入渗试验,探究土壤孔隙结构对土壤水分运动的影响,进一步揭示孔隙结构与土壤水分运动特性之间的相互作用关系。结果表明：随着土层深度的增加,免耕蔗田孔隙形态以聚集的团块状分布为主,垄耕蔗田孔隙形态以条状分布为主。与免耕蔗田相比,垄耕蔗田的土壤总孔隙度和>2.5 mm孔径的孔隙度分别增加32.5%和21.9%。垄耕蔗田在局部土层深度范围内显著增加上下土层孔隙的变异度(p<0.05),显著降低土壤孔隙的连通性(平均邻近指数为0.448)(p<0.05),土壤孔隙形态相对规则(平均成圆率为0.335)。对于土壤水分运动特性,免耕蔗田总体的土壤饱和导水率和质量流率显著高于垄耕蔗田(p<0.05),初始含水率显著低于垄耕蔗田(p<0.05),质量流率随时间变化强度相对较大,提高水流入渗能力。垄耕降低土壤孔隙结构连通性,使水分蓄存在表层土壤中,一定程度上可降低土壤水分的入渗现象,改变蔗...     

Potential of sawdust and corn cobs derived biochar to improve soil aggregate stability,water retention,and crop yield of degraded sandy loam soil

Abstract

Poor soil structure is the main cause of soil degradation; however, biochar the solid carbon-rich production of pyrolysis biomass could improve the soil structure. Biochar from the feed stock sawdust (SD) and corn cobs (CC) was pyrolyzed at 450?°C. Wheat was grown as a test crop and treatments were control, NPK, SDB1% (sawdust biochar), CCB1% (corn cobs biochar), SDB0.5%+CCB0.5%, SDB1%?+?½ NPK, CCB1%?+?½ NPK. The higher growth, higher grain and dry matter yield were displayed by biochar?+?NPK. The lowest pH, the higher organic matter, available P and available K were observed in SDB0.5%+CCB0.5%. However, the highest total N (1.43?g kg^?1) was by NPK treatment. The biochar increased plant available water contents, water contents at field capacity and permanent wilting point, soil porosity and decreased bulk density. The highest stable aggregates were in SDB0.5%+CCB0.5%. Biochar application was found as a useful practice for soil sustainability     

喷灌和畦灌对冬小麦农田表层土壤结构的影响

A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size distribution, pore shape distribution, soil cracks and soil compaction were measured. The sprinkler irrigation brought significant changes to the total soil porosity, capillary porosity, air-filled porosity and pore shape of topsoil layers in comparison with the border irrigation. The total porosity and air-filled porosity of the topsoil in the sprinkler irrigation were higher than those in the border irrigation. The changes in the air-filled and elongated pores were the main reasons for the changes in total porosity. The porosities of round and irregular pores in topsoil under sprinkler irrigation were lower than those under border irrigation. Sprinkler irrigation produced smaller soil cracks than border irrigation did, so sprinkler irrigation may restrain the development of macropore flow in comparison with border irrigation. The topsoil was looser under sprinkler irrigation than under border irrigation. According to the conditions of topsoil structure, it is preferable for crops to grow under sprinkler irrigation than under border irrigation.     

我国主要菜区土壤盐分、酸碱性和肥力状况

从全国主要菜区采取1201个典型菜田耕层土壤样品,对主要菜区土壤盐分、酸碱性和肥力（OM、NO3--N及速效P和K）状况进行了研究。结果表明,（1）全国温室和大棚菜田土壤次生盐渍化严重,土壤硝酸根的积累是引起土壤次生盐化的重要原因之一,而土壤硝酸盐积累是氮肥过量施用所致。全国主要菜区温室和大棚土壤电导率高于蔬菜正常生长土壤电导率临界值（600 ?s/cm）的土样数分别占其总土样数的28.1%和29.3%,居于超高盐度水平（≧1000 ?s/cm）的土样数分别占9.5%和14.9%。温室和大棚土壤电导率与土壤硝态氮含量之间均呈极显著的正相关（温室:n = 285, r = 0.76**;大棚:n = 348, r = 0.86**）。（2）全国主要菜区土壤有机质含量普遍处于中低水平,土壤有机质含量低于其临界值（20 g/kg）的土样数占总土样数的36.9%,处于高含量水平（≧40 g/kg）的仅为10.0%。（3）温室和大棚土壤硝态氮和速效磷大量积累,对生态环境构成了严重威胁。全国主要菜区温室和大棚土壤硝态氮含量居于高含量水平（≧150 mg/kg）的土样数分别占其总土样数的33.0%和30.7%,土壤速效P含量居于高含量水平（≧150 mg/kg）的土样数分别占其总土样数的59.3%和35.3%。（4）北方温室和大棚菜田土壤酸碱度中性化明显,北方主要菜区温室和大棚土壤pH值（分别平均为7.2和7.3;温室:n = 270,大棚:n = 143）显著低于露地土壤（平均7.7,n = 155）。     

Effects of biochar amendment on greenhouse gas emissions,net ecosystem carbon budget and properties of an acidic soil under intensive vegetable production

Biochar addition to soils has been frequently proposed as a means to increase soil fertility and carbon (C) sequestration. However, the effect of biochar addition on greenhouse gas emissions from intensively managed soils under vegetable production at the field scale is poorly understood. The effects of wheat straw biochar amendment with mineral fertilizer or an enhanced‐efficiency fertilizer (mixture of urea and nitrapyrin) on N₂O efflux and the net ecosystem C budget were investigated for an acidic soil in southeast China over a 1‐yr period. Biochar addition did not affect the annual N₂O emissions (26–28 kg N/ha), but reduced seasonal N₂O emissions during the cold period. Biochar increased soil organic C and CO₂ efflux on average by 61 and 19%, respectively. Biochar addition greatly increased C gain in the acidic soil (average 11.1 Mg C/ha) compared with treatments without biochar addition (average ?2.2 Mg C/ha). Biochar amendment did not increase yield‐scaled N₂O emissions after application of mineral fertilizer, but it decreased yield‐scaled N₂O by 15% after nitrapyrin addition. Our results suggest that biochar amendment of acidic soil under intensive vegetable cultivation contributes to soil C sequestration, but has only small effects on both plant growth and greenhouse gas emissions.     

长期施肥下土壤性质变化及其对微生物生物量的影响

在对长期施用化肥以及与有机肥配施处理的红壤稻田土壤水分特征曲线研究的基础上,考察了土壤性质变化及各种孔隙分布特征,探讨了不同大小孔隙分布和有机碳含量以及微生物生物量的关系。结果表明：长期施用有机肥增加了土壤有机碳含量,提高了土壤保持水分的能力。相比于不施肥处理(通气孔隙度0.121 m3/m3),施用有机肥增加了土壤的通气孔隙(通气孔隙度0.156 m3/m3),施用化肥减少了土壤的通气孔隙(通气孔隙度分别为NK 0.11 m3/m3,NP 0.115 m3/m3,NPK 0.082 m3/m3,2NPK 0.113 m3/m3),长期施用有机肥的土壤中大孔隙度和中孔隙度分别是施用化肥和不施肥处理的 1.45 ~ 1.68倍和1.22 ~ 1.43倍,小孔隙度在0.39 ~ 0.41 m3/m3之间,且所有施肥处理之间无显著差异。通过相关分析表明,土壤有机碳含量与土壤总孔隙度和中孔隙度均极显著相关(P<0.01),与土壤大孔隙度显著相关(P<0.05),土壤微生物生物量碳和呼吸强度与大孔隙度显著相关(P<0.05),说明长期施用有机肥是通过提高土壤有机碳来改善土壤中、大孔隙比例,最终提高土壤总孔隙度,增加土壤大孔隙的数量,有利于土壤微生物的活动的。     

大豆秸秆基保水剂对南阳烟田土壤物理性状及烟叶生长的影响

为了促进大豆秸秆基保水剂在农业生产中的应用和推广,作者在河南南阳旱区利用田间试验考察了保水剂用量对烟田土壤物理性状和烟叶生长的影响。结果表明,烟田施用大豆秸秆基保水剂可以显著抑制土壤水分的流失,并且抑制作用随保水剂用量的增加而增强;同时保水剂改善了土壤物理性状,降低土壤体积质量,使土壤孔隙数量增加,提高了土壤总孔隙度,尤其增加了非毛管孔隙度,增强了土壤通气性能。但施用过量容易降低土壤非毛管孔隙度,造成土壤板结;保水剂还可以降低烟叶的蒸腾速率,改善其光合特性,提高水分利用效率,增强烟叶抗旱性,从而提高烟叶株高、茎围和最大叶面积等农艺性状,改善烟叶化学成分。保水剂用量为240 kg/hm2时,土壤平均含水率较对照提高3.1%,总孔隙度提高6.8%,烟叶增产18.4%,上等烟比例提高6.8%。     

Rice straw biochar affects water retention and air movement in a sand-textured tropical soil

Despite the current global attention on biochar (BC) as a soil amendment, knowledge is limited on how BC impacts the physical properties of coarse-textured soils (sand > 95%), particularly in tropical regions. A two-season field-study was conducted to investigate the effect of rice straw BC (3% w/w) on water retention, gas transport and structure of a sand-textured tropical soil. We sampled 3 months and 15 months after BC application and measured wet- and dry-region soil water retention, air permeability and gas diffusivity at selected matric potentials. At all measured potentials and for both sampling times, soil water retention was significantly higher (20–150%) for the BC treatment due to increased fraction of smaller pores (< 30 µm) at the expense of macropores (< 100 µm). Although there was no consistent effect of BC on air-filled porosity, BC significantly reduced air permeability and gas diffusivity (~20%) at ?30 kPa matric potential. After 15-months, air permeability decreased by ~15% after BC amendment, but analyses of the pore structure revealed a more tortuous and complex soil structure. Thus, application of rice straw BC to similar coarse-textured soils will improve soil-water relations and over time provide better structure for agricultural purposes.     

灌后通气处理对温室黄瓜生长和品质的影响

Rhizosphere aeration, irrigation with aerated water, and post-irrigation aeration would positively impact crop growth and yield. The objective of this study was to determine the effect of 4 post-irrigation aeration levels on plant growth, yield, irrigation-use efficiency （IUE）, and fruit market and nutritional quality of greenhouse cucumber under subsurface drip irrigation （SDI） and furrow irrigation （FI）. The post-irrigation aeration levels were 0.00, 0.50, 0.75, and 1.00 times half the estimated porosity of the plot rhizosphere. The experimental design was a two-faetor split-plot in randomized complete blocks with irrigation （FI and SDI） as the main treatments and 4 aeration levels as the sub-treatments. Ridge and furrow main plots （2.4 m ~ 2.4 m） with 4 ridges were replicated 5 times. Each of the 4 ridges （1.44 m2 in area） in the main plots was used as a sub-treatment plot. The results showed that post-irrigation aeration enhanced greenhouse cucumber plant growth, yield, IUE, and fruit market and nutritional quality. These parameters generally increased with increasing aeration levels under both FI and SDI. The aeration effect was generally higher under SDI than FI, and the IUE under SDI was almost twice that under FI. Further investigation would be required to elucidate the plant physiological mechanisms and soil processes responsible for the observed effects.     

Fulvic acid displaces manure to improve soil in vegetable greenhouse

Acid soil has led to a significant decrease in vegetable yield in high-yield greenhouse vegetable production system. Chicken manure and fulvic acid (FA) application experiment was conducted to evaluate the effects on chemical properties of soil in vegetable greenhouse so as to confirm whether FA could replace chicken manure in acid soil amelioration under the same addition levels of nutrient, when compared to the effect of chemical fertilizers application alone on acid soil improvement. The results showed that the pH of soil added with chicken manure and FA, respectively, increased from the original value of 5.4 to 5.99 and 6.32 at the end of the experiment, while soil pH applied only with chemical fertilizers decreased to 5.43. Correlation analysis indicated that cation exchange capacity (CEC) of soil was positively correlated with soil pH buffering capacity. The peak values of soil CEC and pH buffering capacity occurred in April each year and subsequently tended to decrease in August and December throughout the experiment. Data demonstrated that chicken manure and FA in combination with soil contributed to soil base saturation that increased from 26.5%, 33.8% to 36.7%, 45.9% in chicken manure and FA treated soil during December 2011 to December 2012, respectively; however, chemical fertilizers displayed an adverse effect on soil base saturation that decreased from 17.1% to 5.6% on the same time period. Exchangeable aluminum (Al) concentration showed a weak but significant increase by 5.2% on August 2012 in comparison to April 2012, as chemical fertilizers were added into soil alone. Unlike to chemical fertilizer, chicken manure and FA significantly decreased soil exchangeable Al concentration from the original value of 5.37 cmol kg^?1 to 4.56 and 4.22 cmol kg^?1 at the end of experiment respectively. Compared to total yield treated solely with chemical fertilizers, chemical fertilizers combination with chicken manure or FA resulted in an increase in total yield in 2011 and 2012. Although chicken manure and FA possessed the same trend of improving acidic soil in vegetable greenhouse, a greater contribution was attributed to FA due to its lower mineralization rate of organic matter. Therefore, it was suggested that FA could completely displace chicken manure in improvement in acidic soil in vegetable greenhouse.     

Excessive application of nitrogen and phosphorus fertilizers induces soil acidification and phosphorus enrichment during vegetable production in Yangtze River Delta,China

Intensive vegetable cultivation has developed very rapidly in China, and investigation of current soil nutrient problems in vegetable fields and their potential environmental risk is important for local soil nutrient management strategies. Three hundred and sixty‐six soil samples were collected from greenhouse vegetable fields, open vegetable fields and rice/wheat rotation fields in southern Jiangsu Province, the most intensive vegetable‐producing areas in Yangtze River Delta, China, for the analysis of their soil fertility status. Soil acidification and P enrichment were the main problems identified in this area of vegetable production, with about 20 and 17% of the open and greenhouse vegetable field soils, respectively, being extremely acid with soil pH values below 5.0. In contrast, no soils under rice/wheat rotation fields were as acidic. Percentages of sites with Olsen‐P concentrations < 90 mg/kg were 61, 85 and 0% for soils growing greenhouse vegetable, field vegetable and rice/wheat, respectively. The nitrogen (N) surplus for vegetable fields exceeded 170 kg/ha/crop, and the phosphorus (P) surplus exceeded 40 kg/ha/crop. Thus, current vegetable production leads to potential environmental risks of N and P pollution of nearby aquatic bodies. Insufficient supplementation with potassium fertilizers was found in some vegetable fields. Several ameliorative measures are proposed.     

科尔沁沙地旱作农田土壤退化的过程和特征

在一个较小的时空尺度上对科尔沁沙地典型旱作农田土壤物理和化学特性在风蚀沙化过程中的演变特征及其退化过程进行了的探讨。结果表明 :旱作农田由于周边沙质草地的开垦而发生风蚀沙化 ,3～ 5年的时间就会使 5 %～ 15 %的细粒物质吹蚀 ,表土粗化 ,向风沙沉积特征发展 ,土体结构破坏 ,容重增加 0 .0 5～ 0 .15 g/ cm3,总孔隙度降低 3%～ 5 % ,持水性能变劣 ,养分也随之丧失 ;<0 .0 5 mm的粘粉粒吹蚀 1% ,土壤有机质和全氮含量下降 0 .2 5 9g/ kg和 0 .0 16 4 g/ kg;土壤退化的演变 ,既有系统本身的自然属性决定的内在原因 ,更重要的是人为的外部干扰体系的驱动 ;退化的过程既有渐变型 ,又有跃变型     

溶质类型与矿化度对半干旱盐渍化地区果园土壤水分有效性的影响

盐渍化土壤水分有效性是制约土地生产能力的关键因素之一。研究不同盐分类型及矿化度的盐溶液对土壤水分有效性的影响, 可为微咸水合理灌溉以及促进土壤生产潜力的发挥提供科学依据。本研究采用离心法在室内研究了脱水过程中灌溉水的溶质类型(NaCl和Na₂SO₄)与矿化度(0、1 g·L^-1、3 g·L^-1、5 g·L^-1、10 g·L^-1)对半干旱盐渍化地区果园土壤水分有效性的影响。结果表明: 不同矿化度的NaCl和Na2SO4处理均可使田间持水量、暂时萎蔫系数、永久萎蔫系数、迟效水和无效水较对照有所降低。不同矿化度的NaCl处理以及1 g·L^-1的Na₂SO₄处理土壤全有效水和速效水都较对照增加, 3 g·L^-1、5 g·L^-1和10 g·L^-1的Na₂SO₄处理土壤全有效水和速效水都较对照减小。不同矿化度的NaCl和Na₂SO₄处理均可使土壤通气孔隙和毛管孔隙相对减少, 非活性孔隙增大, 其中矿化度为5 g·L^-1的NaCl和Na₂SO₄处理对其影响最为明显, 通气孔隙分别较对照减小16.8%和14.8%, 毛管孔隙分别较对照减小5.2%和6.5%, 非活性孔隙分别较对照增加15.7%和14.4%。NaCl对于土壤比水容量和毛管断裂的延迟效果比NaSO₄明显。且土壤溶液盐分含量增加, 土壤持水能力下降、供水性能增加而土壤抗旱性降低。     

城市土壤压实对土壤水分特征的影响——以南京市为例

通过对南京市不同土地利用下的土壤容重、孔隙度和土壤水分特征曲线的测定，研究了压实对土壤水分特征参数的影响。结果表明城市土壤存在严重的压实退化现象，土壤容重和孔隙度能够很好地反映土壤的压实程度。随着压实程度的增加，土壤的田间持水量增加，萎蔫点含水量增加，而土壤的最大有效水含量却明显减少。所以，压实土壤对水分的调节能力下降，使其上生长的植物更不容易获得水分供应。     

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus and cadmium and planted to spinach

The objective of the investigation was to evaluate the effect of applied phosphorus (P) and cadmium (Cd) on Cd chemical forms determined by sequential extraction and the relationship between these forms and plant responses, i.e., dry weights, concentration, and total uptake of Cd and P in a greenhouse experiment. Treatments consisted of five levels of Cd (5, 10, 20, 40 and 80 mg kg^?1 soil as cadmium sulfate) and four levels of P (0, 15, 30 and 60 mg kg^?1 soil as monocalcium phosphate), which were added to the soil and left to equilibrate for 1 month under greenhouse conditions. Spinach seeds (Spinacea oleracea L., cv Viroflay) were sown and then grown for 8 weeks. The chemical composition in the aerial part of the pant and soil was determined. Application of Cd decreased plant dry matter and increased Cd concentration in the plant, whereas at each level of applied Cd, P increased plant dry matter and decreased plant Cd concentration. All chemical forms of Cd in soil, as determined by a fractionation method, were increased following Cd application, the highest being the carbonatic form. Phosphorous application decreased exchangeable and carbonatic forms of Cd, whereas it increased other forms.