THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT II. CROP EVAPORATION : SEASONAL AND SOIL FACTORS

Rates of evaporation, soil water deficits and extraction depths for spring cereals and grass were estimated from soil water measurements for a four year period. Estimates of evaporation were also compared with evaporation formulae and evaporimeter values. Evaporation and soil water deficit were highly dependent upon weather, particularly rainfall. Evaporation from grass was noticeably restricted whenever deficits exceed 50 millimeters. Cereals extracted water from a slightly greater depth of soil but developed deficits, up to harvest, very similar to those under grass. Deficits developed in sand and clay soils were also very similar, because water held in large dense clay aggregates is not readily accessible to roots. Although soil type had only minor influence on rates of evaporation, deficits and depths of drying, because of movement of water through fissures, slow drainage and delayed swelling effects soil type has a strong influence on stream behaviour.     

SIMULATION OF THE WATER BALANCE OF SOIL COLUMNS AND FALLOW SOILS

A model is described that predicts the evaporation of water from, and the distribution of water in, a soil column evaporating into a constant environment. It is based on a numerical solution of the flow equation and requires only the initial water distribution in the column, the equilibrium (air-dry) water content at the soil surface and the relationship between volumetric water content and diffusivity. The model predictions show good agreement with a published analytical solution and with experimental results. Modifications to the model that allow for rewetting of the sod by rainfall, and changes in atmospheric conditions above the soil, enable predictions to be made of the water balance of a fallow field. In general, good agreement was obtained with the measured distribution of water deficits in the soil profile, although the predicted water content of the surface 2.5 cm of soil showed systematic differences from the measured values. The reasons for this are discussed.     

农业生产中的铁锰平衡问题

本文根据对菠萝和水稻的研究,论述了土壤和植物体内铁与锰的关系,认为在植物体内铁与锰的比例应保持一个平衡的关系。如果锰多铁少、比例失调,作物的正常生长将受到危害。     

A COMPARISON OF THE POLYCARBOXYLIC ACIDS EXTRACTED BY WATER FROM AN AGRICULTURAL TOP SOIL WITH THOSE EXTRACTED BY ALKALI

Humic and fulvic acids were isolated from an agricultural soil by conventional means. The same soil was extracted with water and the organic matter freed of inorganic and low molecular weight substances. The usual chemical differences between humic acid and fulvic acid were confirmed and the water extract was shown to resemble fulvic acid quite closely. Further fractionation of the fulvic acid and water extract showed that the elemental composition, carboxyl and acidic hydroxyl contents, molecular weights, and infrared spectra of the purified polycarboxylic acids were virtually identical. Both promoted the same growth response in cultured isolated tomato roots. It is suggested that the qualitative similarity of fulvic acid to the polycarboxylic acid extracted by water justifies the use of the more easily isolated fulvic acid in physiological experiments on the direct effects on plants of soil organic matter.     

立体种养结构是提高农业生产率的有效途径

随着人民生活水平的提高和发展国民经济的需要,宜改变现有传统的种植结构,即改平面结构为立面结构,以增加生物的利用层,在时间和空间上充分利用各类资源,提高能量和物质的转化效率,这是提高农业生产率的有效途径。     

THE SURFACE TENSION OF SOIL WATER

Because of their organic matter content, the surface tension of water of soils is about 8 to 9 erg cm ^-2 (8 to 9 × 10 ^-7 J cm ^-2) less than that of pure water. It is estimated that the surface tension of soil solution is 63–64 erg cm ^-2 in the surface soils studied.     

Fuzzy综合评判在农业经营决策中的应用

应用Fuzzy综合评判进行农业经营方案的决策,经与现有的方法进行比较,表明Fuzzy综合评判对决策方案的评价选择更具有精确性。     

中国农业科学院农业资源与农业区划研究所

研究所现有1个国家工程实验室（土壤肥料资源高效利用国家工程实验室）、2个农业部重点开放实验室（“作物营养与施肥”和“资源遥感与数字农业”重点开放实验室）,设有“国家化肥质量监督检验中心”、“农业部微生物肥料和食用菌菌种质量监督检验测试中心”和“中国农业微生物菌种保藏管理中心”.     

农业生物技术学报

研究了生物频谱辐射对小鼠桑椹胚玻璃化冷冻后体内外发育的影响,并采用荧光染色法对经生物频谱辐射前后的胚胎进行囊胚细胞计数,以评估生物频谱对冷冻损伤的恢复程度。结果表明在EFS40玻璃化溶液中处理1min一步法冷冻保存的胚胎,解冻后经生物频谱辐射,其发育率由对照组的54％提高到98％,差异极显著（P<0.01）。冷冻胚胎辐射后移植于同期化处理的受体子宫中,妊娠率和产仔率与对照组相比差异均不显著（40％∶56％;50％∶42％）（P>0.05）。将新鲜胚、经辐射的新鲜胚、冷冻胚、冷冻后经生物频谱照射共四组胚胎,用H33342染色,证实冷冻后胚胎的囊胚细胞数与对照组（新鲜胚）相比显著减少（24±3.4∶52±5.4）（P< 0.01）。解冻后的胚胎经生物频谱辐射后,其囊胚细胞数显著高于不加辐射组（35±5.624±3.4）（P<0.01）。另外,新鲜胚胎用生物频谱辐射后,其囊胚细胞数（49±3.1）与对照组相比无显著差异（P> 0.05）。     

THE CONTENTS AND SORPTION OF CADMIUM IN SOME AGRICULTURAL SOILS OF ENGLAND AND WALES

Cadmium sorption was measured in 10 agricultural soils with pH ranging from 4.5 to 7.9, and total Cd content from 0.27 to 1.04 μg g^?1 dry soil. With initial Cd concentrations of 0.5 to 100.0 μM, sorption from 0.002 M CaCl₂ was described by the Freundlich adsorption equation but the gradients of the isotherms increased when the initial concentrations were below 0.5 μm. This indicates that there are specific sites of differing sorption energy; differences between soils in the gradients of the isotherms at low initial concentration could largely be accounted for by their contents of ‘free’ Fe₂O₃. When initial concentrations were below 0.5 μm there was a linear relationship between the quantity of Cd sorbed and the final concentration in solution. This relationship held with all soils except that of lowest pH from which there was a net loss of Cd to the solutions. Desorption was measured from three soils with contrasting pH. With the soil of lowest pH, over 80 per cent of sorbed Cd was desorbed to 0.002 m CaCl₂ and up to 30 per cent to 100 or 500 μm solutions of heavy metal chlorides. In contrast, only very small proportions (<1.25 per cent) were desorbed from the other soils with pH 6.7 and 7.8. The results indicate that Cd is strongly sorbed by soils of pH of above 6.0 when added in amounts comparable to additions in sewage sludges or phosphatic fertilizers, and illustrate the importance of liming as a means of reducing the mobility of this metal in soils.     

THE EFFECT OF DENSITY ON WATER RETENTION PROPERTIES OF FIELD SOILS

The bulk density, available water (A_ν), air capacity (C_α), and retained water capacity (θ_ν) were determined for 158 A, B, and C horizons of field soils. Clay (< 2 μm) and silt (2=60 μm) were also determined. Statistical analysis of the results demonstrated that bulk density exerts a profound influence on A_ν, C_α, and θ_ν, but the effect varies between texture groups and horizons. Significant negative correlations were obtained between bulk density and C_α for most texture and horizon groups. In B and C horizons A_ν and θ_ν also decrease with increasing density, whereas in A horizons A_ν and θ_ν tend to increase with bulk density except in silty soils. Within a limited range it is feasible to control these parameters by using field techniques to achieve optimum bulk density for particular soils.     

大气中二氧化碳增加对气候及农业的影响

本文综述人类活动对大气中二氧化碳的影响,回顾了温室气体与近百年来气候的变化。在综合国内外一些近期研究成果基础上,初步估计了温室效应引起的未来气候变化趋势——地面平均气温将可能在不断升降波动过程中趋于变暖。同时论述了二氧化碳增加及气候变暖对农业可能造成的重要影响。     

COMPARISON OF THE CERAMIC PLATE AND THE PRESSURE MEMBRANE TO DETERMINE THE 15 BAR WATER CONTENT OF SOILS

Volumetric water contents of 17 mineral and 3 peat soils were measured at 15 bar pressure using the ceramic plate and the pressure membrane apparatus. There was no overall significant difference between the results from the two types of apparatus and both ranked the soils in essentially the same order. Although soils of high clay or organic matter content retained up to 13.5% more water on the ceramic plate than on the pressure membrane, available water capacity (AWC) of a clay soil would be decreased by only 1–2%, and that of a peat soil by 3–4%. Due to its greater reliability, the ceramic plate is an acceptable alternative to the pressure membrane when used to determine the 15 bar water content.