Nitrate fate in a Mexican Andosol: Is it affected by preferential flow?

Andosols are the dominant soils in the Valle de Bravo basin, the origin of a significant amount of Mexico City's drinking water. The main land use is agriculture and most of the existing surface water bodies are eutrophic. Nitrogen fertilizer is used extensively. There have been very few studies on nitrate (NO₃⁻) fate in this type of soil and region. Comprehensive laboratory studies were conducted to determine the fate of NO₃⁻ in an Andosol profile from Valle de Bravo, in order to assess the risk of water resources contamination. Nitrate retention was analysed statically (using batch experiments) and dynamically (using intact and packed soil columns) at different soil depths and its competition with Cl⁻ was evaluated. Complementary laboratory experiments were conducted to study water transport through the columns and nitrogen transformations in the soil. In batch and columns, NO₃⁻ adsorption was linear in the range of concentrations studied and higher in the deepest soil layer. Preferential flow pathways were found in the unaltered deeper soil layers, while tillage activity in the top layer destroyed the pore continuity. In spite of the deeper soil layer's greater capacity for NO₃⁻ retention, the presence of preferential flow pathways coupled with high rainfall intensities, makes the NO₃⁻ mobile below the root zone at 1 m depth and increases the risk of groundwater contamination. The results illustrate the complexity of nitrate fate in Andosols and can be used to improve agricultural practices in the central Mexico region.     

The effect of organic supplementation of solarized soil on the quality of tomato fruit

Soil solarization, used to control weeds and soil-borne pathogens in hot climates, has not yet been widely adapted as a commercial practice because of its lack of efficacy. Experiments were carried out in southern Italy over two growing seasons to study the effect of three levels (0, 0.35 and 0.7 kg m⁻²) of organic supplementation of the soil prior to solarization on soil mineral availability and fruit quality attributes. Soil temperature and chemical properties were monitored, together with changes in the physical characteristics and chemical composition of tomato fruits grown under commercial greenhouse conditions. Organic supplementation increased the soil temperature achieved through solarization by 3.9 to 5.5 °C. Organic supplementation increased (P ≤ 0.05) the soil concentration of NO₃⁻-N, exchangeable K₂O, Ca²⁺, Na⁺ and Mg²⁺ and the level of electrical conductivity in the soil extract. Physical characteristics of tomato fruits were improved by supplementation, with fresh and dry weight enhanced up to 11 and 21%, respectively, mesocarp thickness up to 19%, firmness up to 36% and skin redness (a^*/b^* ratio) up to 24%. As the supplementation rate was raised from 0 to 0.7 kg m⁻², the fruit content of reducing sugars increased (P ≤ 0.01) from 1.75 to 2.14 g per 100 g f.w., ash from 0.49 to 0.62%, soluble solid from 5.12 to 6.18 °Brix, titratable acidity from 0.16 to 0.19%, and ascorbic acid from 25.1 to 32.5 mg 100 mL⁻¹. We concluded that organic supplementation appears to be a valuable and environmentally friendly way to improve the mineral availability in the soil and improve fruit quality of tomato.     

烤烟油分与烟叶理化特性关系的初步研究

[目的]探讨烟叶油分与烟叶理化特性的关系及其对烟叶品质的影响。[方法]以K326和云烟85品种为供试材料,从烟叶主要化学成分、物理特性和植物生长必需元素3个方面,分析比较了不同油分烟叶之间的差异。[结果]在化学成分方面,油分"多"的烟叶比油分"有"的烟叶总糖和还原糖含量分别高1.43和3.24个百分点,总氮和氯离子含量分别低0.01和0.08个百分点。在物理特性方面,油分"多"的烟叶比油分"有"的烟叶叶质重高1.27 mg/cm2,平衡含水率高0.13%,自由燃烧时间长2.6 s。[结论]烟叶糖分(总糖、还原糖)含量与烟叶油分呈极显著正相关,而总氮含量与烟叶油分呈极显著负相关。Mo含量与油分呈正相关,而Al2O3S、iO2和Cl含量与油分呈负相关。烟叶油分不足会导致烟叶糖碱比不协调,烟叶偏薄,吸湿性和燃烧性变差。     

紫花苜蓿根系与土壤物理性质的关系

紫花苜蓿根系的研究对其生产、引种及种植苜蓿所产生的生态价值都有非常重要的意义,而土壤物理性质对根系的影响是巨大的。同时,根系通过自身的机械穿插、根系代谢、根系分泌物对土壤物理性质有重要的影响。对紫花苜蓿根系与土壤水分、土壤盐分、土壤养分的相互影响进行了总结,阐述了紫花苜蓿根系与土壤物理性质的相互关系。     

物理农业的现状及其发展前景

物理农业是近些年来发展起来的一种新的高科技农业技术。它是利用基本物理学科的知识和相关领域的高新技术相结合,应用于农业科研和生产中,在无污染的条件下达到增产、优质、抗病的目的,并具有广阔的发展前景。     

毕节地区烟叶主要物理特性分析

[目的]为了明确毕节地区各烟区的烟叶物理特性。[方法]通过对2005年毕节地区8县(市)烟叶主要物理性状的测定,分析了不同地点、颜色和等次间烟叶物理性状的差异,并对不同地点间烟叶物理性状进行聚类分析,研究了烟叶物理性状间及其与海拔间的相关性。[结果]毕节地区各区烟叶物理性状均在较适中范围,综合物理性状表现较好;不同县(市)烟叶的物理性状差异达到1%显著水平;桔色烟的物理性状表现均优于柠色烟;不同等次间除含梗率外其余物理性状差异显著;主要物理性状间显著相关,海拔与单位叶面积重显著正相关;对不同区域烟叶综合物理性状聚类分析,可将毕节地区划为3个类型烟区。[结论]该研究为改进毕节地区的烟叶生产技术提供了理论依据。     

Ⅱ.药菊一种病毒分离物理化特性的研究

从安徽省药菊产区显花叶症状的菊花上分离到一株病毒(代号Chm—91),标准紫外吸光度(A_(260)~(0.1%)为4.78,A_(260)/A_(280)比值为1.73;粒子平均分子量为1.835×10~6道尔顿,沉降系数为97.58S;该分离物的外壳蛋白由各含236个氨基酸相同亚基所组成,亚基的分子量25100,等电点5.2。核酸为单链RNA,有四个大小不同组份。整个核酸在粒子中的含量是16.6%,碱基百分比中鸟嘌呤(G)为23.6,腺嘌呤(A)为27.7,胞嘧啶(C)为19.4,尿嘧啶(U)为29.6;也基本相似于国外报道的TAV。据此作者认为Chm—91分离物为TAV或属它的一个株系。这是TAV为害(药)菊花在我国首次详细报道。     

几个理化因子对无籽西瓜无性系增殖的影响

本文研究了不同激素配比、温度、光强、蔗糖浓度对无籽西瓜无性系增殖的影响．研究结果表明：对无籽西瓜无性系增殖的最佳激素配比为ＢＡ（０．５）＋ＩＡＡ１，温度以２５°为好，光强最好在３０００ｌｘ以上，蔗糖浓度以５％为宜．     

物理农业技术在种子选后处理中的应用

物理农业是近年发展起来的一项高科技农业技术,它利用基本物理学科知识和相关领域的高新技术相结合,应用于农业科研和生产.针对种子加工选后处理的传统与常规技术存在的问题与不足,综述采用物理新技术处理种子的特点、意义及应用,重点介绍磁化处理技术,并提出解决问题的对策.     

Heart Rate,Net Cost of Transport,and Metabolic Power in Horse Subjected to Different Physical Exercises

Considering that workload can also be expressed in terms of estimated net transport cost (COT), the metabolic energy needed to transport unit mass of animal unit distance, the aim of our study was to describe the heart rate (HR), COT, and the total metabolic power requirement per kilogram (P) during different exercises (aerobic, anaerobic, and aerobic–anaerobic exercises). On the basis of their attitude, 25 horses, divided into five equal groups, traveled a distance of 6,000 m, walking at 100 m/min in a horse walker (group A); performed 20-minute treadmill walk at 130 m/min, average speed up gradient of 5% (group B); performed a 700-m-long show jumping course with 13 fences (group C); traveled a distance of 2,100 m galloping at a speed of 700 m/min (group D); and traveled a distance of 2,000 m trotting at a speed of 660 m/min (group E). On each horse, HR was continuously recorded by means of an equine HR monitor. COT was calculated with the following formula: (HR − 35) kg⁻¹ m⁻¹ 10³; P was calculated applying the formula: (HR − 35) min⁻¹ kg⁻¹. COT and P values, estimated from the mean HR, measured continuously during each experimental condition showed no linear relationship with HR and speed. The use of combined weight of horse and tack (group C and D) and horse, tack, and sulky (group E) statistically changed the results of formula application. COT and P change in different exercises and provide additional information about performance in athletic horses.