A Method for Baiting Corticium rolfsii and of Estimating the Sclerotial Population in Soil

Abstract

The use of tissue blocks of Xanthosoma sagittifolim for baiting Corticium rolfsii from soil is described. The baiting technique has been found efficient for gross estimation of the viable sclerotial content of air-dried soil. The results obtained by this method compare well with those determined by the sieving technique of Rodriguez-Kabana et al.     

Relative Efficiency of Zinc Sulfate and Zinc Oxide–Coated Urea in Rice–Wheat Cropping System

Abstract

Rice–wheat cropping system covers about 24 million hectares in China, India, Pakistan, Nepal, and Bangladesh, and zinc deficiency is widespread in rice–wheat belts of all these five countries. The current practice of applying zinc sulfate heptahydrate (ZnSO₄ · 7H₂O) to soil is problematic because of the poor quality of the nutrients available in the market to the farmers. Zinc (Zn)–coated urea is therefore being manufactured to guarantee a good‐quality Zn source. This article reports the results from a field study conducted to study the relative efficiency of zinc sulfate and zinc oxide (ZnO)–coated ureas in rice–wheat cropping system. The highest grain yield of rice–wheat cropping system was obtained with 2.0% coating of urea. Zinc sulfate was also a better coating material than ZnO. Partial factor productivity, agronomic efficiency, apparent recovery, and physiological efficiency of applied Zn decreased as the level of Zn coating was increased.     

Aspartase Activity of Soils Under Different Management Systems

Abstract

Recent interest in soil tillage, cropping systems, and residue management has focused on low‐input sustainable agriculture. This study was carried out to evaluate the effects of various management systems on aspartase activity in soils. This enzyme [L‐aspartate ammonia‐lyase, EC 4.3.1.1] catalyzes the hydrolysis of L‐aspartate to fumarate and NH₃. It may play a significant role in the mineralization of organic N in soils. The management systems consisted of three cropping systems [continuous corn (Zea mays L.) (CCCC); corn‐soybean [Glycine max (L.) Merr.]‐corn‐soybean (CSCS); and corn‐oat (Avena sativa L.)‐meadow‐meadow (COMM) {meadow was a mixture of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] at three long‐term field experiments initiated in 1954, 1957, and 1978 in Iowa and sampled in June 1987. The plots received 0 or 180 (or 200) kg ha^?1 before corn and an annual application of 20 kg P and 56 kg K ha^?1. The tillage systems (no‐tillage, chisel plow, and moldboard plow) were initiated in 1981 in Wisconsin and sampled in May 1991. The crop residue treatments were: bare, normal, mulch, and double (2×) mulch. The residue in the study was corn stalks. Results showed that, in general, crop rotation in combination with N fertilizer treatments affected aspartase activity in the following order: COMM>CSCS>CCCC. Because of nitrification of the NH₄ ⁺ or NH₄ ⁺‐forming fertilizers, which resulted in decreasing the pH values, N fertilizer application, in general, decreased the aspartase activity in soils in the order: CCCC>CSCS>COMM. The effect of tillage and residue management practices on aspartase activity in soils showed a very wide variation. The trend was as follows: no‐till/2× mulch>chisel plow/mulch>moldboard plow/mulch>no‐till normal>chisel plow/normal>no‐till bare>moldboard plow/normal. Aspartase activity decreased with increasing depth in the plow layer (0–15 cm) of the no‐till/2× mulch. The decreased activity was accompanied by decreasing organic C and pH with depth. Statistical analyses using pooled data (28 samples) showed that aspartase activity was significantly, linearly correlated with organic C (r=0.78^***) and exponentially with soil pH (r=0.53**). The variation in the patterns and magnitudes of activity distribution among the profiles of the four replicated plots was probably due to the spatial variability in soils.     

Potassium Fixation and Release Characteristics of Some Benchmark Soil Series under Rice–Wheat Cropping System in the Indo‐Gangetic Plains of Northwestern India

Abstract

Potassium (K) fixation and release in soil are important issues in long‐term sustainability of a cropping system. Fixation and release behavior of potassium were studied in the surface and subsurface horizons in five benchmark soil series, viz. Dhar, Gurdaspur, Naura, Ladowal, and Nabha, under rice–wheat cropping system in the Indo‐Gangetic plains of India. Potassium fixation was noted by adding six rates of K varying from 0 to 500 mg kg^?1 soil in plastic beakers while K release characteristics were studied by repeated extractions with 1 M HNO₃ and 1 M NH₄OAc extractants. The initial status of K was satisfactory to adequate. Potassium fixation of added K increased with the rate of added K irrespective of soil mineralogy and soil depth. Soils rich in K (Ladowal and Nabha) fixed lower amounts (18–42%) of added K as compared to Gurdaspur, Dhar, and Naura (44.6–86.4%) soils low in K. The unit fertilizer requirement for unit increase in available K was more in low‐K soils. The study highlights the need for more studies on K fixation in relation to the associated minerals in a particular soil. Potassium‐release parameters such as total extractable K, total step K, and CR‐K varied widely in different soil series, indicating wide variation in the K‐supplying capacity of these soils. K released with 1 M NH₄OAc extractant was 20–33% of that obtained with 1 M HNO₃. Total extractable K using 1 M HNO₃ varied from 213 to 528 mg kg^?1 and NH₄OAc‐extractable K ranged from 71 to 312 mg kg^?1 soil in surface and subsurface layers of different soil series. The Ladowal and Nabha series showed higher rates of K release than Gurdaspur, Dhar, and Naura series, indicating their greater K‐supplying capacity.     

Estimating Drainage under Cotton with Chloride Mass Balance and an EM38

Methodologies that use electromagnetic induction and resistivity in soil profiles to estimate drainage across whole fields and catchments require complex models or measurement systems that are not easily available or difficult to apply at the farm level. The objective of the present study was to define a methodology that could use information easily available to agronomists and commercial cotton consultants to estimate drainage in irrigated Vertisols using a chloride (Cl^?) mass balance approach. A secondary objective of this study was to eliminate or minimize the expensive and tedious laboratory analyses for determining Cl^? concentration in soils. A model was developed using electromagnetic induction measurements taken with an EM38 instrument in the horizontal mode (EM_H) to estimate the chloride concentration in a saturated soil extract in the 0- to 1.2-m depth of irrigated Vertisols. A stepwise linear regression model where the independent variables were soil water storage, exchangeable sodium percentage, and EM_H predicted chloride concentration the best. The chloride concentrations thus estimated were similar to measured values only when measured chloride concentrations in the saturated extract were ≤10 meq L^?1 (355 mg L^?1 = 240 mg kg^?1). These values of chloride were then inserted into a chloride mass balance model to estimate deep drainage. In more saline soils, large differences occurred between measured and estimated chloride. Values of drainage based on estimated chloride concentrations in the range of 0–10 meq L^?1 were very similar to those based on measured chloride concentrations. There is potential to use an EM38 for quick assessment of deep drainage under irrigated conditions in the field.     

Comparison of Soil Organic‐Matter Characteristics under the Energy Crop Giant Reed,Cropping Sequence and Natural Grass

The objective of this study was to determine, on the same pedological, topographic, and climatic conditions, the effects of a continuous giant reed cropping (GR), a cropping sequence (CS), and untilled natural grass (NG) on some soil characteristics. Selected characteristics included total soil organic carbon (TOC), light fraction carbon (LFC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC). The various humic fractions and their ratios, humification ratio (HR), humification degree (HD), and humification index (HI) were also evaluated. Results indicate that GR, characterized by low tillage intensity, showed greater values than tilled management system (CS) for all the previously mentioned properties, with the exception of the humification parameters, which were not statistically different between the two systems. Regarding the difference between GR and NG (the latter usually considered as a reference or baseline for evaluating attributes of soil quality), GR generally showed greater values for all organic parameters, with the exception of MBC and humus characteristics.     

施用微生物有机肥对连作条件下西瓜的生物效应及土壤生物性状的影响

为探讨施用微生物有机肥对连作条件下西瓜生长、土壤微生物的影响,在西瓜连作3年的土壤上采用小区试验方法分析施用微生物有机肥对西瓜的生物学效应及对土壤微生物群落结构的影响。试验设置4个处理,依次为健康菜园土育苗(CK)、健康菜园土育苗+定植期增施微生物有机肥(施肥量为每株25 g)、健康菜园土+微生物有机肥育苗(微生物有机肥︰健康菜园土=1︰49)、健康菜园土+微生物有机肥育苗+定植期增施微生物有机肥(施肥量为每株25 g)。结果显示:在育苗及定植期均施用微生物有机肥使西瓜的生物学性状得到显著改善。与对照相比,施用微生物有机肥使西瓜株高、叶片数、叶绿素含量、植株氮、磷、钾吸收总量以及西瓜品质、产量显著增加(P<0.05);同时,微生物有机肥富含优质碳源和微生物,健康菜园土育苗+定植时增施微生物有机肥和健康菜园土+微生物有机肥育苗+定植期增施微生物有机肥处理土壤中细菌总量与对照相比分别增加24.9%~51.0%和35.7%~55.8%,放线菌数量分别增加18%~41%和15%~35%,真菌数量分别增加7.4%~21.9%和4.9%~31.9%;土壤中有益菌数量和放线菌与真菌的比例增加可有效抑制尖孢镰刀菌活性,对枯萎病的防治率高达83%以上。微生物有机肥能激发连作土壤有益微生物活性,显著改善和调节连作西瓜生长,对西瓜的连作障碍有明显缓解作用。     

高山峡谷区移民安置耕地产值测算

通过野外调查和发放表格填报的方式收集大岗山水电站库区耕地产值测算相关资料,针对高山峡谷区耕地质量随地形分布的差异,引入河谷系数,构建耕地产值的测算模型,对高山峡谷区移民安置耕地产值测算方法进行了探讨。结果表明,大岗山水电站石棉县库区耕地综合产值为23 593.05元/hm2,泸定县库区耕地综合产值为17 429.40元/hm2,大岗山库区耕地综合产值为20 974.27元/hm2。通过适宜于高山峡谷区移民安置耕地产值测算模型的构建,可为高山峡谷区移民安置补偿提供科学依据。     

北疆滴灌复播青贮玉米耗水规律初步研究

通过2011年滴灌复播青贮玉米小区试验,试验设置了165、210、255、300、345mm 5个水分处理,研究了不同灌溉定额下滴灌复播青贮玉米耗水规律及生长特性。试验结果表明:整个生育期内耗水强度呈现由低到高再到低的变化趋势,拔节期和抽雄吐絮期的耗水强度分别达到7.00～16.99mm/d和4.37～7.81mm/d,拔节期和抽雄吐絮期为需水关键期;通过试验数据拟合认为滴灌复播青贮玉米灌水定额在313.6～417.61mm较为适宜。     

马铃薯连作地健康株与病株根区土壤微生态特性比较

为探索甘肃省连作马铃薯健康生长的微生态机制,采用常规养分分析法测定了健康株与病株根区土壤中速效氮磷钾含量,稀释平皿涂抹法测定土壤放线菌数量,琼脂块法筛选拮抗放线菌;16S rRNA序列分析法鉴定优势放线菌,发酵液抑菌试验检测优势放线菌灭癌素链霉菌(S. gancidicus)对马铃薯病原真菌的抑菌作用。结果表明,在连作4年的田中：马铃薯病株根区土壤的速效P、K含量分别较健株低29.9%、12.5%,铵态氮含量较健株高24.1%。在高氏1号培养基上,病株根区土壤中放线菌总数、小单孢菌及未鉴定放线菌数量较健株分别减少51.1%、83.0%及53.9%;腐植酸琼脂培养基上,病株根区土壤中放线菌总数、链霉菌数量较健株分别减少46.0%、46.7%。在病、健株根区土壤中,对4株靶标真菌的拮抗潜势SAAP值均病株小于健株。健株根区土壤中的优势放线菌为灭癌素链霉菌(S. gancidicus),该菌对4株马铃薯常见土传病原真菌立枯丝核菌(R. solani)、茄病镰刀菌(F. solani)、硫色镰刀菌(F. sulphureum)及大丽轮枝菌(V. dahliae)均有抑制作用;病株根区土壤中的优势放线菌为加利利链霉菌(S. galilaeus),该菌为马铃薯疮痂病致病菌。由此可知,保持连作马铃薯健康生长的根区土壤微生态特征是,高量磷钾及低量氮的速效养分组合,较多放线菌且拮抗放线菌的拮抗潜势较大,优势放线菌为有益菌。