Long-Term Effects of Nitrogen Management Practices on Grain Yield,Nitrogen Uptake,and Efficiency in Irrigated Corn

ABSTRACT

Crop management strategies that improve Nitrogen Use Efficiency (NUE) increase profits while reducing the detrimental effects on the environment associated with fertilizer nitrogen (N) loss. Effective N management should include several critical factors that are very interrelated. A study was conducted at the Panhandle Research and Extension Center, Goodwell, OK to evaluate the effects of multiple nitrogen management practices including N rate, source, time of application, methods of fertilizer and residue incorporation over a long period of time on grain yield, N uptake and NUE in irrigated corn. Fourteen treatments were evaluated in a randomized complete block design with three replicates. Results of data analyzed on the individual year and averages of all years showed that grain yield and N uptake were improved with N rates and N management practices compared to checks. Both N recovery and efficiency of use were high for the 118 kg N ha^{? 1} rate.     

Reducing Bioavailability and Leachability of Copper in Soils using Coal Fly Ash,Apatite, and Bentonite

Soils treated with two concentrations of copper (Cu; 200 and 400 mg kg^?1) were amended with three amendments (coal fly ash, apatite, and bentonite) at the rates of 1.5% and 2.5%, respectively. The effects of amendment application on the bioavailability and leachability of Cu in the soil were evaluated using the wheat uptake, single extraction, and sequential extraction tests. The addition of coal fly ash, apatite, and bentonite at the rate of 2.5% increased wheat biomass by 50.5%, 41.1%, and 61.7%, respectively. The application of amendments significantly (P < 0.01) reduced the Cu contents extract that will buy DW (deionized water), TCLP (toxicity characteristics leaching procedure), and DTPA (diethylenetriaminepentaacetic acid) in the soil. The amendments also reduced the water-soluble/exchangeable, carbonate, iron (Fe)–manganese (Mn) oxide, and organically bound fraction contents of Cu but increased the amounts of residual Cu in soil. Our results demonstrated that these amendments were effective in reducing the bioavailability and leachability of Cu in soil.     

黑曲霉对潮褐土镉、锌污染的原位固定修复潜力研究

采用温室盆栽试验,研究了在黑曲霉(30582)作用下油菜对潮褐土Cd、Zn复合污染胁迫的耐性及富集特征。结果表明:接入黑曲霉菌液对油菜地上部干重总体上无明显影响,且降低了油菜对土壤Cd、Zn的吸收量。加入黑曲霉菌液后,油菜地上部和地下部Cd含量较对照最高分别降低了31.60%,37.82%;地上部和地下部Zn含量较对照处理最高分别降低了35.12%,35.74%;土壤有效态Cd、Zn含量显著减少,较对照最高分别降低了30.51%,39.64%。综上,黑曲霉有效地降低了污染土壤中Cd、Zn的生物有效性,对土壤中低浓度重金属污染的原位固定表现出较佳的效果,具备应用于修复Cd、Zn污染土壤的潜力。     

Subcellular distribution and chemical forms of chromium in rice plants suffering from different levels of chromium toxicity

The subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio‐toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes (Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low‐bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low‐bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.     

不同洗涤蜂窝煤灰渣对污染土壤中铅的稳定作用研究

蜂窝煤灰渣具有稳定污染土壤中铅的作用,但可增大土壤pH和电导率(EC)。将蜂窝煤灰渣经过水洗和稀盐酸酸洗后加入铅污染土壤(1000mg·kg-1Pb),研究了不同处理灰渣对铅有效性和土壤性质的影响。结果表明,灰渣经水洗和酸洗后,其pH(分别下降1.94、3.70)和电导率(0.785、0.890mS·cm-1)明显下降,重金属有效性和全量也有一定程度的下降。水洗和酸洗灰渣加入土壤后,土壤磷有效性有一定的上升。污染土壤在未加磷条件下加入原灰渣、水洗灰渣和酸洗灰渣后,DTPA-Pb含量分别下降67.2、195、117mg·kg-1,加磷情况下加入这3种灰渣土壤DTPA-Pb含量分别降低102、91.8、86.8mg·kg-1,各处理与对照的差异均达到0.05的显著水平。连续提取的结果表明,不同处理对土壤铅形态的影响不明显。     

Tree girdling provides insight on the role of labile carbon in nitrogen partitioning between soil microorganisms and adult European beech

Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitrifiers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined.Surprisingly plants preferred organic N over inorganic N and nitrate (NO₃⁻) over ammonium (NH₄⁺) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi Cenococcum geophilum was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of C. geophilum remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms.     

Effects of Aporrectodea caliginosa (Savigny) on nitrogen mobilization and decomposition of elevated‐CO2 Charlock mustard litter

This study was conducted to improve our understanding of how earthworms and microorganisms interact in the decomposition of litter of low quality (high C : N ratio) grown under elevated atmospheric [CO₂]. A microcosm approach was used to investigate the influence of endogeic earthworm (Aporrectodea caliginosa Savigny) activity on the decomposition of senescent Charlock mustard (Sinapis arvensis L.) litter produced under ambient and elevated [CO₂]. Earthworms and microorganisms were exposed to litter which had changed in quality (C : N ratio) while growing under elevated [CO₂]. After 50 d of incubation in microcosms, C mineralization (CO₂ production) in the treatment with elevated‐[CO₂] litter was significantly lower in comparison to the ambient‐[CO₂] litter treatment. The input of Charlock mustard litter into the soil generally induced N immobilization and reduced N₂O‐emission rates from soil. Earthworm activity enhanced CO₂ production, but there was no relationship to litter quality. Although earthworm biomass was not affected by the lower quality of the elevated‐[CO₂] litter, soil microbial biomass (C_mic, N_mic) was significantly decreased. Earthworms reduced C_mic and fungal biomass, the latter only in treatments without litter. Our study clearly showed that A. caliginosa used the litter grown under different [CO₂] independent of its quality and that their effect on the litter‐decomposition process was also independent of litter quality. Soil microorganisms were shown to negatively react to small changes in Charlock mustard litter quality; therefore we expect that microbially mediated C and N cycling may change under future atmospheric [CO₂].     

根系分泌物对根际土壤关键氮转化过程的影响

根系分泌物是影响土壤氮素转化、N₂O排放和植株氮肥利用率的重要因素之一,也是土壤学、植物营养学、作物生理生态与耕作栽培学、环境科学等学科的重要关注点。为全面认识根系分泌物在土壤氮循环中的作用,综述了根系分泌物的种类和测定方法,介绍了根系分泌物影响土壤关键氮转化过程及N₂O排放的机理,根系分泌物对土壤硝化和反硝化过程及N₂O排放的抑制作用,并对该领域未来的研究方向进行了展望。为土壤氮素转化的土壤–植物–微生物互作机制研究提供一定参考,以进一步提高氮肥利用率,减少氮肥引起的环境污染。     

固定化菌株在土壤中的繁殖释放及性能分析

不同条件下固定化菌株在土壤中的释放情况存在差异,本实验测定固定化枯草芽孢杆菌在不同条件下土壤中的释放及其降解特性。通过设定不同温度、水分、pH值测定固定化枯草芽孢杆菌在灭菌土壤中的释放情况,并分别用碱扩散法、碳酸氢钠抽提-钼锑抗比色法、乙酸铵抽提-火焰光度计法测定菌株的固氮、解磷、解钾性能。结果表明：固定化菌株在温度35℃和40℃、水分为50ml/100g、pH5-8时均能大量繁殖释放,固定化后在不同温度和水分条件下不影响其降解特性。该研究结果为固定化菌株在农业复合微生物肥料上的应用提供理论基础。     

纤维素酶—木聚糖酶—漆酶的共固定化

多酶共固定化能发挥多酶的协同作用,实现底物到产物的一步转化。文章以纤维素酶、木聚糖酶和漆酶分别固定化工艺研究为基础,选择pH敏感型可逆可溶性聚合物Eudragit L-100为载体,应用物理吸附法制备固定化纤维素酶、木聚糖酶和漆酶。采用物理吸附和共价交联相结合的方法进行酶的固定化研究发现,当pH为4.8、反应温度为60℃、反应时间为40 min、载体浓度为1.6%和EDC浓度为0.1%时,纤维素酶、木聚糖酶和漆酶的固定化率分别为50.86%、36.90%及25.93%。