Effects of arbuscular mycorrhizal fungi on the growth and zinc uptake of trifoliate orange (Poncirus trifoliata) seedlings grown in low-zinc soil

The effects of the arbuscular mycorrhizal (AM) fungi, Glomus intraradices and G. versiforme, on growth and zinc (Zn) uptake were investigated in trifoliate orange (Poncirus trifoliata) seedlings exposed to low-Zn soil. Low-Zn decreased growth, levels of leaf chlorophyll, soluble protein and sugar, and soil enzymatic activities, and pH in 0–2 cm rhizosphere soil. Low-Zn soil also decreased mineral nutrients (including Zn) concentrations in the shoots and roots. Glomus intraradices especially, significantly enhanced plant biomass, leaf soluble protein and sugar concentrations, root viability, acid phosphatase, catalase, invertase and urease activities, and easily extractable glomalin content in 0–2 cm and 2–4 cm rhizosphere soil. It also increased concentrations of Zn, phosphorus, potassium and magnesium in the shoots and roots, while decreased the soil pH. Arbuscular mycorrhizal fungi, especially G. intraradices, has the potential to improve growth and Zn uptake of triofoliate orange seedlings grown in low-Zn soil.     

太湖地区水稻土中的β-葡糖苷酶活性

The electrical conductivity （EC） of 1：5 soil-water extract （EC1：5） was studied utilizing path coefficient analysis. The study focused on revealing the main chemical factors contributing to EC of soil extracts and their relative importance. Results showed that the most important factors influencing the EC1：5 of coastal salt-affected soils were the concentration of salt in 1：5 soil-water extract （So）, Cl^-, and the sodium adsorption ratio （SAR）, while effects of pH, CO3^2-, HCO3^, soluble sodium percentage （SSP）, and sodium dianion ratio （SDR） were very weak. Though the direct path coefficients between EC1：5 and SO4^2- , Ca^2＋, Mg^2＋, K^＋, or Na^＋ were not high, influence of other chemical factors caused the coefficients to increase, making the summation of their direct and indirect path coefficients relatively high. Evidences showed that multiple regression relations between EC1：5 and most of the primary factors （So, Cl^-, and SAR） had sound reliability and very good accuracy.     

Methane production and its fate in paddy fields

Abstract

Oxidation of methane and total water soluble organic carbon (TOC) in the subsoil, which percolated from the plow layer, was investigated in a column experiment. The amounts of both methane and TOC in the leachate decreased by percolation in the subsoil.

Fe²⁺ percolated from the plow layer was nearly completely retained in the subsoil. The decomposition of methane and TOC in the subsoil was considered to result in the coupling with the formation of Fe²⁺. Methane was estimated to contribute ca. 19–21% to the total amount of Fe²⁺ formed in the subsoil by the organic materials in the leachate.     

小麦矮化腥黑穗病菌侵染能力的研究

中美专家合作在美国犹他州对小麦矮化腥黑穗病菌的侵染能力进行了研究。试验采用不含抗病基因的小麦品种Cheyanne,播种前用溴甲烷对试验小区进行了熏蒸。接种物为含有多种致病型的冬孢子悬浮液,采用土壤表面喷洒冬孢子悬浮液的方法进行接种,接种密度为每cm20、0.88、8.84、88.45、884.49、8844.89、88449个孢子。结果表明,接种密度为每cm20.88个孢子时即可产生0.21％的穗发病率。对试验数据进行分析后表明,小麦矮化腥黑穗病菌的侵染规律符合侵染概率理论,在本试验条件下,单个孢子的侵染概率为0.0002。     

Effect of increasing levels of nitrogen on yield of tea in different agro-ecological conditions of Pakistan

Field experiment was conducted on mature tea bushes of Qi-Men variety at two different altitudes from sea level i.e. at National Tea Research Institute Shinkiari （1000 m） and on farmer＇s field in Konsh valley at village Battal （1500 m）. Different levels of nitrogen with constant dose of phosphorus and potassium were applied to observe the optimal dose of nutrients for highest yield under local edaphic conditions. The experiment was repeated for three consecutive years. The highest yield of fresh tea leaves were obtained by the application of 420 kg ha^-1 N followed by the application of 360 kg ha^-1 N at 1000 masl. The highest dose of nitrogen also reduced significantly the soil pH in the upper （0-15cm） layer depth during 1998 and 1999. During the year 2000, the reduction in soil pH was observed by the application of highest dose of nitrogen but was non-significant at 5% level. The lower soil depth （15-30 cm） showed the reduction in pH with the highest dose of nitrogen during the experimental year but was statistically non significant. At the higher altitude of 1500 masl the highest yield of fresh tea leaves was obtained by the application of 420 kg ha^-1 during the experimental years but the increase was significant during the year 1999 and 2000. The yield of the fresh tea leaves was positively correlated with the amount of nitrogen application at both the altitudes. The increasing amount of nitrogen decreased the soil pH at both the depths of 0-15cm and 15-30cm. Unlike the lower altitude （1000 m） there was no any significant reduction in the soil pH during 1998 and 1999. A significant reduction in soil pH was found in the year 2000.     

榆林沟流域水土资源开发利用研究

研究了黄河中游第 4期试点流域——榆林沟流域水土资源与环境优势、水土资源开发利用所存在的问题 ,提出了该流域水土资源开发利用途径 ,并通过措施的对位配置 ,对水土资源开发利用实际效果进行了分析     

沙土区薄壁连拱护岸墙试验与应用

沙土区薄壁连拱护岸墙为悬臂式支撑、薄壁连拱无底板结构,拱板中间采用无砂砼排水孔的钢筋砼肋形预制板,冲沉法施工,造价低廉;外形美观,抗倾、抗滑性能强。该墙为平原沙土区河道水土保持及修复找到了一条经济合理、施工方便、简便易行的护坡办法,具有较高的实用价值和广阔的推广使用前景。     

Nitrogen pools and turnover in arable soils under different durations of organic farming: II: Source‐and‐sink function of the soil microbial biomass or competition with growing plants?

The following parameters were measured on seven field plots at 3 sites which had been under organic farming for different periods of time: mineral nitrogen (N _min) contents, in situ net nitrogen mineralization (N _net), soil microbial biomass carbon (C _mic), and nitrogen (N _mic) contents, and extractable organic N contents. The measurements were conducted every three weeks from spring 1995/1996 to autumn 1997. The objective was to test whether, under organic farming: 1) temporal fluctuations of N_mic contents over the course of the year are indicative for a source‐and‐sink function for plant‐available N of the soil microbial biomass, and 2) temporal variations in N_mic content can be related with in situ N_net or plant N uptake. N_min contents gradually increased after ploughing in autumn until late winter. During intensive plant growth in spring, values rapidly declined. In situ N_net fluctuated only moderately and reached high values during intensive plant growth (May—July) as well as after soil cultivation in autumn. The C_mic and N_mic contents generally were low in winter, increased in spring and reached maxima in late spring or summer. In spring, the increase in C_mic contents preceded the increase in N_mic contents, resulting in elevated C_mic:N_mic ratios until shooting of winter wheat. This corresponds to an uptake of available soil nitrogen by the plants at the expense of soil micro‐organisms. The subsequent increase in N_mic contents, coinciding with high plant N uptake rates, indicates an enhanced, plant‐induced N mobilization at that time. Possible mobilization mechanisms are discussed. Soil microbial biomass exerted a source‐and‐sink function for extractable organic N on some of the field plots. Estimates of in situ N_net measurements were neither correlated significantly with soil microbial biomass N, N_mic flux, N_mic turnover, nor with plant N uptake. Lower N_mic turnover rates on 41 years versus 3 years organically managed fields indicate a stabilizing effect of organic farming on soil microflora.     

Effects of hydroxy-aluminum on flocculation and permeability of silt and clay fractions separated from paddy soils

Flocculation tests and permeability measurements were carried out for silt and clay fractions separated from surface and subsurface horizons of four paddy soils. There was not much difference in the flocculating power between A1(OH)_2.2C1_0.8 and CaSO₄. Their flocculation value, 0.3 to 3 mM, was attained by adding the reagents at the rate of 0.24 to 2.4 mmol/100 g of the silt and clay. The flocculation with A1(OH)_2.2C1_0.8 or CaSO₄ did not affect the sediment volume of the silt and clay. This sediment volume was smaller for the surface than for the subsurface horizons of each soil, suggesting that soil organic matter and repetition of wetting and drying contribute to the stable aggregation of the silt and clay in the surface horizon. The permeability was higher for the silt and clay fractions separated from the surface horizon than that from the subsurface horizon, and the addition of 2.5 to 4.2 mmol of A1(OH)_2.2C1_0.8 or CaSO₄/100g of the silt and clay increased its permeability by 1.5 to 4 times. The effect of A1(OH)_2.2C1_0.8 was more lasting than that of CaSO₄ and was recognized even after 200 ml of water passed through 1 g of the silt and clay. The effect of the flocculating reagent on the permeability was more or less enhanced by air-drying the treated silt and clay.