Distribution of actinomycetes in oil contaminated ultisols of the Niger Delta(Nigeria)

The distribution of actinomycetes in oil contaminated sandy loam ultisols of the Niger Delta region of Nigeria was studied to aid in understanding the effect of hydrocarbons on indigenous microbial population in tropical soils. The average total counts of actinomycetes in all the oil samples analysed was 10 3 cfu/g. Higher counts of actinomycetes were observed during the dry season than during the wet season. The counts of hydrocarbonoclastic actinomycetes correlated positively with the total count of actinomycetes. The actinomycetes were generally restricted to the top soil(0—10 cm soil depth) although a seemingly deeper(down to 40 cm soil depth) distribution was noticed in the dry season. The isolates included oil degrading species of Actinoplanes, Norcadia, Streptomyces and Streptosporangium. Their high oil utilization ability indicates their positive potential and role in the bioremediation of oil spilled soils.

The Fluxes of Organic C and N, and Microbial Biomass and Maize Yield in an Organically Manured Ultisol of the Guinea Savanna Agroecological Zone of Nigeria

Field experiments were conducted to evaluate the effects of integrated use of agricultural wastes and a compound mineral fertilizer on the fluxes of soil nutrients. Agricultural wastes applied were: livestock manure (cow dung and poultry litter), shoots of Chromolaena odorata and Parkia biglosa (locust bean), Neem (Azadiracta inidca) seed powder/cake and melon shell. These materials were applied at zero (control), 100% (i.e. organic wastes applied at the recommended rates of 10 t/ha) and 70% of their recommended rates plus 30% of the recommended rate of the mineral fertilizer (NPK: 400 Kg/ha). Average values of soil organic carbon (SOC) were 1.94, 1.68, 1.36 and 1.38 for organic wastes alone, organic waste plus mineral fertilizer (NPK) and unamended control. Mineral N ( N plus N) pools were relatively high at 30 and 60 days after planting, and were significantly higher for organically amended soils (550) and wastes applied at reduced rates combined with 120 kg/ha mineral NPK (470) than the unamended control (277). Across sampling dates, SOC values were the highest in poultry manure and neem seed cake. The values of N plus exchangeable N which constitutes plant available nitrogen (PAN) were significantly higher for organically amended soils and wastes applied at reduced rates combined with 120 kg/ha mineral NPK than the unamended control. The % C microbial to C organic ratio was higher in organically amended soils. The temporal profile of SOC, NH4-N and NO3-N showed declines with time, the relationship was linear for SOC (Y = 0.18x + 1.07;R2 = 0.34), by a power function for N (Y = 48.084x-1.79;R2 = 0.91) and a polynomial function for NH4-N (Y = -28.75x + 130.65x - 57.25;R2 = 0.61). The time dynamics of microbial population (cfu) followed trends obtained for SOC.

SOC Turnover and Lime-CO₂Evolution during Liming of an Acid Andisol and Ultisol

Agricultural liming contributes significantly to atmospheric CO2 emission from soils but data on magnitude of lime- contributed CO2 in a wide range of acid soils are still few. Data on lime-contributed CO2 and SOC turnover for global acid soils are needed to estimate the potential contribution of agricultural liming to atmospheric CO2. Using Ca13CO3 (13C 99%) as lime and tracer, here we separated lime-contributed and SOC-originated CO2 evolution in an acidic Kuroboku Andisol from Tanashi, Tokyo Prefecture (35°44′ N, 139°32′ E) and Kunigami Mahji Ultisol of Nakijin, Okinawa Prefecture, Japan (26°38′ N, 127°58′ E). On the average, lime-CO2 was 76.84% (Kuroboku Andisol) and 66.36% (Kunigami Mahji Ultisol) of overall CO2 emission after 36 days. There was increased SOC turnover in all limed soils, confirming priming effect (PE) of liming. The calculated PE of lime (Kuroboku Andisol, 51.97% - 114.95%;Kunigami Mahji Ultisol, 10.13% - 35.61%) was entirely 12C turnover of stable soil organic carbon (SOC) since SMBC, a labile SOC pool, was suppressed by liming in our experiment. Our results confirmed that mineralization of lime-carbonates is the major source of CO2 emission from acid soils during agricultural liming. Liming can influence the size of CO2 evolution from agricultural ecosystems considering global extent of acid soils and current volume of lime utilization. We propose the inclusion of liming in simulating carbon dynamics in agricultural ecosystems.

Impact of Crude Oil on Soil Nitrogen Dynamics and Uptake by Legumes Grown in Wetland Ultisol of the Niger Delta, Nigeria

The effects of crude oil on soil nitrogen dynamics and cycling in plant-soil ecosystems and its effect on the growth of legumes (Calopogonium mucunoides, Centrosema pubescens and Pueraria phaseolodes) grown in wetland ultisols were investigated. The test plants species were grown on wetland soil simulated with 0.35, 10.8, 20.5, and 50 g.kg-1levels of crude oil contamination. The results showed time and species dependent variation in mineral N content of the treated soils. The variation is indicative of significant interaction between the hydrocarbon content and plant species. Variations in microbial N and microbial C were similar and correlation between the microbial N and the total C (Organic matter (C) + hydrocarbon content (C)) in soil was highly significant (r = 0.96, n = 12, P ≤ 0.01). The presence of hydrocarbon contaminant widens the C:N ratio in soil and leads to more available N being immobilized by soil microorganisms, which reduces available N for plant uptake. This result implies that crude oil contamination significantly reduces N uptake by plants but increases N accumulation in soil microbial biomass. The findings show that N dynamics, transformation and cycling in soil are influenced by hydrocarbons and that the interactions between hydrocarbon content and plant species in contaminated soil are remarkable. The use of plant Centrosema pubescens with poultry manure or NPK fertilizer for bioremediation is more effective than that of Calopogonium mucunoides and Pueraria phaseoloides. However, the selective attributes of the various treatment approaches adopted here may be exploited for enhanced remediation of contaminated wetlands in the Niger Delta region of Nigeria.

Application of Cow Manure Combined with Rice Husk Ash to Increase Soybean (Glycine max (L.) Merr) Production in Indonesia Ultisol

This study aims to determine the ability of CM(Cow Manure)combined with RHA(Rice Husk Ash)to provide a significant effect on the growth and production of soybean planted in an ultisol.It was conducted in a pot experiment at the Experimental Site of the Faculty of Agriculture,Sriwijaya University,Indralaya,Indonesia between September 2019 and February 2020 using completely randomized design factorial with two factors which were two rate levels of RHA at 3.75 and 7.5 tons·ha^(-1) and three rate levels of CM at 0,10,and 20 tons·ha^(-1).It is important to note that each combination was repeated three times,thereby,leading to a total of 18 pots.The variables studied were plant growth and yield which are represented by plant height,the total number of pods,number of filled pods,seed weight per plant,and soybean produced.The results showed that CM combined with RHA was effective in increasing nutrient availability and reducing soil acidity.It was discovered that CM had a significant effect on soil pH,plant height,the total number of pods,number of filled pods,seed weight per plant,and soybean produced while RHA did not have any significant difference on all the variables observed.However,the combination of 10 tons·ha-1 CM with 3.75 tons·ha-1 RHA was observed to be the best combination treatment to increase the growth and production of soybean in ultisol as indicated by its ability to produce 2.58 tons·ha^(-1) soybean.

Effects of Phosphate Adsorption on Adsorption-Desorption and Availability of Cu and Zn Ions in Ultisols and Alfisols

Surface charge, secondary adsorption- desorption and form distribution of Cu2+ and Zn2+ in Ultisols and Alfisols having adsorbed phosphate were studied by potentiometric titration, adsorption equilibrium and sequential extraction method, respectively. The soil surface negative charges increased whereas the amount of positive charges decreased with increase of P adsorbed. The soil secondary adsorption capacity for Cu2+ and Zn2+ was positively significantly correlated with the amount of P adsorbed by the soils, which could be described by the Langmuir equation. The amounts of Cu2+ and Zn2+ desorption from soils were decreased after P adsorption by the soils and the relationship between them was linear. After the soils adsorbed P, form distribution of Cu2+ and Zn2+ in soils changed remarforbly.

Correlation and path coefficient analyses of yield and yield components of eggplant (Solanum melongena) in a coarse-textured Ultisol

Assessment of variability and understanding of traits relationship in eggplant species are vital pre-requisite for formulating an effective breeding programme.We studied 23 genotypes of eggplants in a coarse-textured Ultisol using a randomized complete block design experiment with three replications.Data were collected on number of branches,number of leaves,number of nodes and internodes,stem diameter,plant height,floral and yield traits.Results revealed significant(p=0.05)variation in the flowering and fruiting pattern of the genotypes.‘Yalo x K3BC2P10 gave the highest individual fruit weight of 80.8 g.Individual fruit weight contributed the highest direct positive effect on the fruit yield.It acted majorly through plant height,number of branches,number of leaves and number of days to first fruit set as revealed in the path coefficient result.Individual fruit weight,number of fruits per plant,plant height,number of days to 50%flowering,number of branches,numbers of days to first flowering and 50%fruit set had positive direct effect on yield.These traits should be considered in developing high yielding eggplant breeding programme.

温度和氮添加对旱地红壤反硝化功能基因丰度的影响

研究旱地红壤反硝化微生物功能基因nirS、nirK、nosZⅠ和nosZⅡ的丰度对温度和氮添加的响应,可为农田红壤养分管理和生态环境保护提供指导和建议。本研究以长期常规氮磷钾施肥的旱地红壤为研究对象,设置3个氮添加(N0、25、50mg/kg)处理和3个温度处理(15、25、35℃)进行微宇宙培养试验,在培养的7和30d后破坏性采集土样,进行土壤DNA提取,测定反硝化微生物功能基因丰度。结果表明:培养7d后,nirS、nirK、nosZⅠ和nosZⅡ基因丰度均在25℃时最高;培养30d后,nirS、nirK、nosZⅠ和nosZⅡ基因丰度在15℃时最高,且随着温度升高而下降。氮添加对反硝化微生物功能基因丰度无显著影响。3因素方差分析表明,温度、氮添加和培养时间的交互作用显著影响反硝化微生物功能基因丰度。综上,旱地农田反硝化功能基因丰度受氮添加影响较小,但受温度显著影响,其丰度可能会呈现出日变化和季节变化,在土壤采样和氧化亚氮动态监测时应特别注意。

长期施用猪粪对红壤完全氨氧化菌基因丰度的影响

完全氨氧化菌(comammox Nitrospira)的发现对硝化微生物的研究提出了新的挑战。大量研究表明完全氨氧化菌在陆地生态系统中广泛分布,但其在农田土壤中的分布规律及其对长期施用粪肥的响应尚不清楚。研究了长期施用猪粪对农田红壤完全氨氧化菌、氨氧化古菌(AOA)和氨氧化细菌(AOB)功能基因(amoA)丰度的影响,及其与土壤净硝化速率的关系。结果表明:与不施肥的对照处理相比,猪粪施用显著提高土壤有机质和养分含量,且随着猪粪的施用量增加而增加。同时,施用中量和高量猪粪显著提升土壤净硝化速率,增幅分别达到317%和416%。所有处理中,完全氨氧化菌丰度以进化枝A为主,进化枝B丰度极低,大多为非特异性扩增产物,但进化枝A的amoA丰度均低于氨氧化古菌和氨氧化细菌。长期施用高量猪粪显著提升进化枝A的amoA基因丰度,表明存在喜好富营养环境的完全氨氧化菌,而有效磷是最主要的影响因子。相关性分析表明,进化枝A的amoA丰度与净硝化速率呈显著正相关(P<0.01),而氨氧化古菌和氨氧化细菌则没有,表明进化枝A可能在长期施用粪肥的农田红壤硝化过程中发挥重要功能。综上所述,长期施用粪肥显著提高农田红壤养分含量和完全氨氧化菌进化枝A的amoA丰度,进化枝A可能在农田红壤硝化过程中扮演重要角色。

侵蚀程度对不同粒径团聚体中养分含量和红壤有机质稳定性的影响

以三种侵蚀程度的红壤(轻度、中度、严重)为供试材料,研究其>0.25 mm水稳性团聚体中的养分(全氮、全磷、全钾、有机质)和不同形态有机碳(易氧化态和难氧化态)的含量状况和分布特点。结果表明:随着红壤由轻度、中度到严重侵蚀的变化,>0.25 mm水稳性团聚体中有机质、全氮和全磷含量逐渐降低;>0.25 mm水稳性团聚体中的养分对土壤养分的贡献率为[>4 mm]>[0.5～1 mm]>[1～2 mm]>[2～4 mm]>[0.25～0.5 mm];侵蚀红壤的全氮、全磷和有机质均与>0.25 mm水稳性团聚体含量显著正相关。土壤有机碳、易氧化碳和难氧化碳的含量随着红壤侵蚀程度的增强逐渐降低,并且均与>0.25 mm水稳性团聚体、有机质、全氮、全磷呈极显著正相关。有机质氧化稳定性系数与不同粒径水稳性团聚体、土壤有机质、全氮和全磷均呈负相关。

几种侵蚀红壤中有机质和团聚体的关系

以3种侵蚀红壤（轻度、中度、严重）为供试材料,利用干湿筛法获得其不同粒径的水稳性团聚体（〉4 mm,2～4 mm,1～2 mm,0.5～1 mm,0.25～0.5 mm）,分析团聚体中有机质的分布。结果显示,随着侵蚀程度的增强,〉0.25mm水稳性团聚体的含量逐渐下降,而团聚体的分散度却依次升高;无论何种侵蚀程度,湿筛后团聚体的组成均以小粒径团聚体（〈0.25 mm）占优势。轻度和中度侵蚀的红壤,其有机质含量随着团聚体粒径的增大而增大,严重侵蚀的则相反;侵蚀红壤有机质含量和〉0.25 mm水稳定性团聚体呈显著正相关,3种侵蚀红壤团聚体对土壤有机质的贡献为轻度侵蚀〉中度侵蚀〉严重侵蚀。

几种侵蚀红壤有机无机复合状况及其与土壤养分的关系

用傅积平改进法测定了亚热带3种(轻度、中度和严重)侵蚀红壤的有机无机复合状况,并分析了其与土壤养分的关系。试验得出:随着红壤由轻度、中度到严重侵蚀的变化,土壤养分(有机质、全氮和全磷)含量逐渐减小;供试红壤腐殖质的结合形态主要以紧结合态和松结合态为主,稳结合态腐殖质含量最少;随着红壤侵蚀程度的增强,结合态腐殖质含量和有机无机复合量均减少,土壤有机无机复合度变化不明显。土壤复合量与结合态腐殖质、团聚体水稳性呈极显著正相关,有机无机复合度与它们也正相关。红壤的养分因子中,全氮、全磷和有机质与土壤结合态腐殖质的相关性较好,而全钾和阳离子交换量与土壤结合态腐殖质的相关性不大。3种结合态腐殖质中,紧结合态与红壤养分(全氮、全磷和有机质)的相关性最高。

侵蚀红壤中结合态腐殖质及其与水稳性团聚体的关系

以亚热带地区3种侵蚀程度（依据其植被、坡度以及土层厚度不同分为轻度、中度和严重侵蚀）的红壤为供试材料，利用湿筛法获得粒径〉4、2～4、1～2、0．5～1、0．25～0．5mm的水稳性团聚体，分析侵蚀红壤和团聚体中3种结合态（紧结态、松结态和稳结态）腐殖质含碳量的分布特征，及其对〉0．25mm团聚体稳定性的影响。结果表明：随着红壤侵蚀程度的增强，3种结合态腐殖质的含碳量均逐渐减小。在轻度侵蚀的红壤中，随着团聚体粒径的增大，其紧结态和松结态腐殖质的含碳量逐渐升高，稳结态腐殖质的含碳量逐渐降低；但是在中度和严重侵蚀红壤中，不同粒径团聚体的3种结合态腐殖质的含碳量基本相同。侵蚀红壤的紧结态、松结态腐殖质的含碳量与其〉0．25mm水稳性团聚体的含量均呈极显著正相关（r分别为0．88，0．74），说明土壤中腐殖质与矿物质的结合方式和松紧程度不一样，其对侵蚀红壤的结构具有不同的影响。

添加葡萄糖对红壤农田肥料氮转化及其酸化的影响

采用室内培养实验,初步研究了外加葡萄糖对红壤肥料氮素转化及其酸化作用的影响,其中葡萄糖添加量充足,为8 g·kg^(–1)干土,氮肥以(NH4)_(2)SO_(4)和KNO_(3)为例。结果表明,在对照、单施(NH4)_(2)SO_(4)或KNO3处理中,土壤中氮转化过程主要以有机氮净矿化和铵态氮净硝化为主,这主要是由于红壤可利用碳源较少。而外加足够葡萄糖碳源可快速(2 d内)促进土壤及其100 mg·kg^(–1)氮肥中的NH_(4)^(+)-N和NO_(3)^(-)-N几乎全部被微生物同化,30 d培养期间微生物同化促进28%~50%的肥料氮迅速转化为固相有机态氮。单施(NH4)_(2)SO_(4)或KNO_(3)主要通过硝化作用和盐效应降低土壤pH,但微生物对NH_(4)^(+)-N的生物固定可抑制其硝化导致的酸化作用,而微生物对NO_(3)^(-)-N的生物固定可提高土壤pH高达0.78个单位。因此,添加葡萄糖等碳源可促进农田土壤中NH_(4)^(+)-N和NO_(3)^(-)-N的微生物同化,缓解氮肥引起的土壤酸化作用。研究结果对提高农田土壤的保氮能力和氮肥利用率、抑制土壤酸化等具有重要意义。

柠檬酸、葡萄糖和有机质对植物磷素吸收和土壤磷素形态的影响

研究了柠檬酸、葡萄糖和有机质（栎树类凋落物和三叶草茎叶）对几种栽培和野生植物磷素吸收以及高度风化老成土中磷素形态的影响。在未加入无机磷的情况下，连续加入柠檬酸溶液增加了温室盆栽大豆（Ｇｌｙｃｉｎｅｍａｘ（Ｌ．）Ｍｅｒｒ．）和高粱（Ｓｏｒｐｈｕｍｂｉｃｏｌｏｒ）对磷素的吸收。这表明，柠檬酸可以溶解土壤中被铁、铝氧化物固定的磷。当无机磷和柠檬酸溶液同时加入后。由于有机配位体能够阻止土壤对磷素的吸附和固定，植物对磷的吸收总量明显高于仅仅加入无机磷的对照。不论是否加入无机磷，葡萄糖均没有增加植物对磷素的吸收，但却改变了土壤中磷素的形态。该试验的结果还表明，Ｈｅｄｌｄｙ等人提出的土壤磷素分级方法不适于有机质含量很低的酸性土壤。在另一种性质极为相似的酸性土壤中施入粉碎的栎树（Ｑｕｅｒｃｕｓｓｐｐ．）凋落物和三叶草（ＴｒｉｆｏｌｉｕｍＰｒａｔｅｎｓｅ）后，野生商陆（Ｐｈｙｔｏｌａｃｃａａｍｅｒｉｃａｎａ）吸收磷素的能力增强。通过进一步对土壤中的磷素进行化学分级，结果表明，这些有机物质可以改变土壤中磷素存在的形态。本文还就有机质分解过程中的中间产物对土壤磷素有效性的影响机理进行了探讨。

Why Were the Soil Tunnels of Cu Chi and Iron Triangle in Vietnam So Resilient?

At the peak of the Vietnam War, the network of tunnels in the Iron Triangle and Cu Chi linked Viet Cong (VC) support bases over a distance of some 250 km, from the Ho Chi Minh Trail and Cambodian border to the outskirts Saigon. In the early 1960s, the United States escalated its military presence in Vietnam in support of a non-Communist regime in South Vietnam. The North Vietnamese and VC troops gradually expanded the tunnels. Tunnels frequently were dug by hand in Old Alluvium terraces, and only a short distance at a time. Four major efforts were made by the US Military to locate and destroy these tunnels. These included Operation Crimp, a search and destroy mission which began in 1966 and a geological and soil survey approach was used to detect VC tunnels. Later in 1967, General William Westmoreland tried launching a larger assault on Cu Chi and the Iron Triangle areas. The operation called Operation Cedar Falls was an expanded version of Operation Crimp. Finally in 1969, B-52s started carpet bombing the Cu Chi and Iron Triangle areas and destroyed many of the tunnels. However, not before the tunnels had proven very effective in 1960s at hiding and protecting the VC during US occupation of the area. The nature and properties of the Old Alluvium soils were key to the soil tunnels being so resilient. Soils located in Old Alluvium terraces had high levels of clay and iron. Iron (Fe) leached from the upper soil layers (0 to 1.5 m) and accumulated in the lower layers (1.5 to 20 m) and became a cement-like binding agent. When dried the soil layers took on properties close to concrete, and were resistant to ever becoming soft and moist again especially around the aerated tunnel walls. The tunnels were dug in the monsoon season when the upper layers of soil were soft and moist but not in dry season. The soils were highly stable without any lining or support. After drying out, the soil materials surrounding the tunnel turned into concrete like material that could withstand adjacent explosive blasts.

茶多酚和铜对可变电荷土壤钙镁释放的影响

通过批平衡试验,研究茶多酚、铜和体系pH对可变电荷土壤释放钙镁离子的影响。研究发现,铜离子初始浓度为2.0 mmol/L,最终体系pH为5.0时,随着茶多酚添加量的增加,可变电荷土壤表面的负电荷增加,土壤表面释放的钙镁离子量减少。茶多酚初始添加量为20 g/kg,最终体系pH为5.0时,随着铜离子初始浓度的升高,可变电荷土壤对铜离子的吸附量增加,铜离子通过与钙镁离子发生离子交换,形成对吸附位点的竞争,从而增加钙镁离子的释放。茶多酚初始添加量为20 g/kg,铜离子浓度为2.0mmol/L,随着pH的升高,可变电荷土壤钙镁离子释放量下降。在相同pH条件下,茶多酚可以通过自身的吸附增加可变电荷土壤表面负电荷,减少可变电荷土壤钙镁离子的释放量。研究结果可为茶园土壤酸化和污染控制提供参考。

Effects of Organic Anions on Phosphate Adsorption and Desorption from Variable-Charge Clay Minerals and Soil

Effects of citrate and tartrate on phosphate adsorption and desorption from kaolinite,goethite,amorphous Al-oxide and Ultisol were studied.P adsorption was significantly decreased as the concentration of the organic anions increased from 10^-5 to 10^-1 M.At 0.1 M and pH 7.0,tartrate decreased P adsorption by 27.6%-50.6% and citrate by 37.9-80.4%,depending on the kinds of adsorbent.Little Al and/or Fe were detected in the equilibrium solutions,even at the highest concentration of the organic anions.Effects of the organic anions on phosphate adsorption follow essentially the competitive adsorption mechanism.The selectivity coefficients for competitive adsorption can be used to compare the effectiveness of different organic anions in reducing P adsorption under given gonditions. Phosphate desorption was increased by 3 to 100 times in the presence of 0.001 M citrate or tartrate compared to that in 0.02 M KCl solution alone.However,for all the soil and clay minerals studied the amount of P desorbed by citrate or tartrate was generally lower than or close to that of isotopically exchangeable P.The effect of organic anions on phosphate desorption arises primarily from ligand exchange.

生物质炭对重金属污染红壤中蚯蚓活性的影响

生物质炭改良剂在钝化污染土壤中重金属的同时,显著改善土壤物理、化学和生物性质。该文通过添加2%400℃下制备的玉米、水稻、小麦、大豆、豌豆等秸秆生物质炭到Cd和Pb染毒红壤中,研究蚯蚓(赤子爱胜蚓)暴露30 d后的体重损失率、死亡率和体内抗氧化酶活性等指标的影响。结果表明,施加生物质炭显著降低Cd、Pb染毒土壤中可交换态重金属含量。另外,蚯蚓体重损失率分别从改良前的37.16%和38.81%降低至改良后的(31.92%±2.54%)和(28.02%±1.46%),同时死亡率从46.67%分别降低至(40.00%±2.98%)和(32.00%±6.29%),但都未达显著水平(P>0.05)。相比于染毒土壤,施加生物质炭处理土壤中蚯蚓体内过氧化氢酶(CAT)、过氧化物酶(POD)活性和丙二醛(MDA)含量在Cd污染土壤中分别显著降低15.19%~44.89%、12.09%~56.57%、32.52%~59.13%;在Pb污染土壤中分别显著降低1.54%~20.70%、18.44%~48.94%、44.65%~58.46%。相关性分析结果表明,Cd和Pb污染土壤中蚯蚓的CAT、POD活性和MDA含量与Cd和Pb的可交换态、可交换态+碳酸盐结合态均存在显著负相关关系。因此,施加秸秆生物质炭不仅可以钝化污染土壤中的重金属Cd和Pb,也有利于改善赤子爱胜蚓的生存环境;而蚯蚓体内抗氧化酶活性相比于个体指标可以更灵敏地反映土壤质量变化。