一种新的提高树苗盐容量的移植方法

The influence of quinclorac (3,7-dichloroquinoline-8-carboxylic acid) on enzyme activities in flooded paddy soils was assessed under laboratory conditions. The enzymes differed markedly in their response to quinclorac. Quinclorac inhibited proteinase, hydrogen peroxidase, phosphorylase, and urease activities. The higher the concentration of quinclorac applied, the more significant the inhibition to these observed activities with a longer time required to recover to the level of the control. However, soils supplemented with quinclorac were nonpersistent for proteinase~ phosphorylase and urease as opposed to soils without quinclorac. Dehydrogenase activity was also sensitive to quinclorac. Three soil samples with concentrations of quinclorac higher than 1 μg g^-1 soil declined to less than 20% of that in the control. However, the highest dehydrogenase activity (up to 3.28-fold) was detected in soils with 2 μg g^-1 soil quinclorac on the 25th day after treatment. Quinclorac had a relatively mild effect on saccharase activity at the concentrations used in this experiment and a stimulatory one on soil respiration when added to soil at normal field concentrations. Nonetheless it was inhibited at higher concentrations in paddy soils. Quinclorac is still relatively safe to the soil ecosystem when applied at a normal concentration (0.67 μg g^-1 dried soil) but may have some effects on soil enzymes at higher concentrations.     

Driving factors of soluble organic nitrogen dynamics in paddy soils: Structure equation modeling analysis

Soil soluble organic nitrogen (SON) is one of the most active components in soil nitrogen pools; however, limited information is available with regard to its driving factors, as well as their pathways and degrees of influence. In this study, structural equation modeling was used to analyze the driving factors, their significance, and pathways that affected SON dynamics in a waterlogged experiment of two typical paddy soils incubated for 80 d after green manure application. Soil pH, Eh, microbial biomass, enzyme activity, and SON dynamics were used to construct the structural equation model. Results showed that soil microbial biomass carbon (MBC), protease, glutamine, and initial organic matter (OM) directly and significantly affected soil SON with path coefficients corresponding to 0.405, 0.547, 0.523, and -0.623 (P < 0.01), respectively. Soil microbial biomass carbon and initial OM affected the SON dynamics indirectly through protease and glutamine activity. In addition, pH indirectly affected SON dynamics by glutamine activity. It is implied that soil MBC, protease, glutamine, and initial OM are the key factors affecting SON dynamics in the waterlogged paddy soils after green manure application. Our research indicated that structural equation modeling could provide an effective method to clearly recognize the impact, significance, and pathways of multiple factors on SON dynamics in paddy soils.     

Impact of integrated application of biochar and nitrogen fertilizers on maize growth and nitrogen recovery in alkaline calcareous soil

Biochar application has been considered as a rich source of carbon which helps to improve the physico-chemical properties and fertility of the soil. In Pakistan, excessive use of nitrogen fertilizer is considered a serious problem, so it is of vital importance to examine the effect of biochar on soil with varying doses of nitrogen fertilizer. We hypothesized that addition of biochar to an alkaline calcareous soil could improve not only soil quality and crop yield but also nitrogen use efficiency (NUE), reducing the loss of nitrogen (N) in the form of denitrification, ammonia volatilization, and nitrate leaching. A pot experiment was conducted under 2-factorial completely randomized design having three replications to evaluate the NUE in biochar amended calcareous soil. Biochar was applied at the rate of 0%, 1% and 2% (w/w) in pots filled with 17 kg of soil using various levels of N (0%, 50% and 100% of recommended dose) on maize (Zea mays L.). Several soil quality indicators, uptake, and yield of maize were monitored. Biochar application significantly decreased soil pH, increased water-holding capacity, total organic carbon, maize yield, stomatal conductance, and nitrogen uptake in plant. The results of the study indicated that addition of biochar could not only decrease the use of inorganic fertilizers by improving its quality and yield as in our case biochar at the rate of 1% and N at the rate of 50% provided optimum output minimizing the economic cost eventually.     

从沉积物中分离重金属不同提取方法的比较

Three extraction methods, ultrasonic assisted extraction (USE), microwave assisted extraction (MSE), and conventional single extraction (CSE), in conjunction with the modified three-stage BCR sequential extraction procedure (SEP) were applied to examine the contents of Cd, Cu, Cr, Ni, Pb and Zn from lake sediment samples, to know whether these techniques can reduce extraction time and improve reproducibility. The SEP and developed alternative single extraction methods were validated by the analysis of certified reference material BCR 601. By the use of optimized sonication and microwave conditions, steps 1, 2 and 3 of the BCR sequential extraction methods (excluding the hydrogen peroxide digestion in step 3, which was not performed with sonication and microwave) could be completed in 15-30 min and 60- 150 s, respectively. The recoveries of total extractable metal contents in BCR 601, obtained by three single extractions ranged from 93.3%-102%, 88.9%-104% and 81.2%-96.2% for CSE, USE and MSE, respectively. The precision of the single extraction methods was found in the range of 3.7%-9.4% for all metals (n = 6).     

Metal Contamination in Nullah Dek Water and Accumulation in Rice

A research study was carried out to determine the electrical conductivity （EC）, residual sodium carbonate （RSC）, sodium adsorption ratio （SAR）, pH and metals in metal-polluted irrigation water from a nullah and those in soils over a period of time, and the effect of metals on rice yield and metal concentrations in rice grain and straw. Two sites （I and If） were selected on the bank of Nullah Dek at Thatta Wasiran in Sheikhupura District （Pakistan）, with two rice varieties, Super Basmati and Basmati 385, at both sites. Water samples were collected during rice crop growth at 15-day intervals from August 3 to November 1, 2002. The results showed that Nullah Dek water had an EC 〉1.0 dS m^-1 and RSC of 2.78-4.11 mmolc L^-1, which was hazardous for crops, but the SAR was within the safe limit. Cu, Mn Cd and Sr were also within safe limits. The soil analysis showed that Site Ⅱ was free from salinity/sodicity, whereas Site Ⅰ was saline sodic. Among metals, Zn was sometimes deficient, Cu, Mn and Fe were adequate, and St, Ni and Cd were within safe limits in the soil at both the sites. After the rice crop harvest, concentrations of all metals tested were usually slightly increased, being higher in the upper soil layer than the lower. In addition, Basmati 385 produced higher rice grain and straw yield than Super Basmati. Chemical analysis of rice grain indicated the presence of Zn, Cu, Fe, Mn, Pb and Sr, whereas rice straw contained Zn, Cu, Fe, Mn and Sr, with Cd and Ni both being found in minute quantities.     

Metal contamination in Nullah Dek water and accumulation in rice

Corn field experiments with two treatments, NP and NPK, where N in the form of urea, P in the form of calcium phosphate, and K in the form of KCl were applied at rates of 187.5, 33.3, and 125 kg ha^-1, respectively, on soils derived from Quaternary red clay were conducted in the hilly red soil region of Zhejiang Province, China. Plant grains and stalks were collected for determination of K content. Seven equations were used to describe the kinetics of K release from surface soil samples taken before the corn experiments under electric field strengths of 44.4 and 88.8 V cm^-1 by means of electro-ultrafiltration （EUF） and to determine if their parameters had a practical application. The second-order and Elovich equations excellently described K release; the first-order, power function, and parabolic diffusion equations also described K release well; but the zero-order and exponential equations were not so good at reflecting K release. Five reference standards from the field experiments, including relative grain yield （yield of the NP treatment/yield of the NPK treatment）, relative dry matter yield （dry matter of the NP treatment/dry matter of the NPK treatment）, quantity of K uptake in the NP treatment （no K application）, soil exchangeable K, and soil HNO3-soluble K, were used to test the effectiveness of equation parameters obtained from the slope or intercept of these equations. Correlations of the ymax （the maximum desorbable quantity of K） in the second-order equation and the constant b in the first-order and Elovich equations to all five reference standards were highly significant （P ≤ 0.01）. The constant a in the power function equation was highly significant （P 〈 0.01） for four of the five reference standards with the fifth being significant （P ≤ 0.05）. The constant b in the parabolic equation was also significantly correlated （P ≤ 0.05） to the relative grain yield and soil HNO3-soluble K. These suggested that all of these parameters could be used to estimate the soil K supplying capacity and the crop response to K fertilizer.