Decomposition of barley straw in a subarctic soil in the field

Summary The mass loss and N dynamics of barley stems and leaves, placed on the soil surface or buried, were examined over two summers. There was little difference in mass loss or N dynamics in straw placed 7.5 or 15 cm deep. However, the surface straw lost mass much more slowly and immobilized more N for a longer time than the buried straw. Filter paper had a slow rate of mass loss initially, but once started, lost mass much more rapidly than either the barley stems or leaves. Loss of mass was closely correlated with the cellulose loss in straw, whether buried or placed on the soil surface. The sustained rate of mass loss was 6.3 and 7.0% month^-1, respectively, for surface and incorporated leaves compared with 3.5 and 4.3% month^-1, for surface and incorporated stems. The greater loss sustained by the leaves was attributed to a lower lignin content rather than a higher N content, because the addition of N to the straw after 30 days in the field failed to increase CO₂ evolution. Maximum net N immobilization occurred within 30 days for all the barley straw, except for the stems placed on the ground surface, which did not reach maximum N immobilization until the second summer. Immobilization and mineralization of N were estimated for a 3000 kg ha^-1 grain crop. Surface straw immobilized 3.8 kg N ha^-1 in the 1st year and 9 kg N ha^-1 in the 2nd year, whereas incorporated straw immobilixed 3.5 kg N hs^-1 in the 1st year and mineralized 4.5 kg N ha^-1 in the 2nd year. Thus, in Alaska, residue management does not affect N fertilizer requirements in the 1st year, but an additional 13.5 kg N ha^-1 is required for surface residues in the 2nd year.     

Nutrition Management and Farm’s Age Affect Saffron Daughter Corms Behavior,Nutrients Uptake and Economic Water and Fertilizer Use Efficiency: A Large Scale On-farm Experiment in Torbat Heydarieh,Iran

ABSTRACT

Evaluation of the relationships between nutritional patterns and farms’ age with the behavior of saffron (Crocus sativus L.) daughter corms based on farmers’ management (on-farm) can be crucial in improving saffron sustainable yield. Furthermore, in commercial saffron production, especially in small farms, the purchased water and fertilizers are the basis of sustainable saffron profitability, hence, recognizing the relationships between economic water use efficiency (EWUE) and economic fertilizer use efficiency (EFUE) can be important. An on-farm experiment was conducted on a large scale based on farmers’ management in Torbat Heydarieh, Iran. The farms’ age (1–6 years old) and fertilizers management approaches (organic, mineral and integrated) were considered as the first and second factors, respectively. Large-sized daughter corms number and weight and corms N and P content increased with increasing farms’ age from 1 to 4 years old. However, these parameters decreased with increasing farms’ age from 4 to 6 years old. Irrespective of saffron farms’ age, the minimum large-sized daughter corms number and weight were observed when mineral fertilizer management was practiced. By contrast, the maximum values were related to integrated fertilizer management. In each type of fertilizer management, EWUE and EFUE (based on large-sized daughter corms monetary value) increased with increasing farms age from 1 to 4 years. However, increase in farms age from 4 to 6 years caused a significant reduction in mentioned indices. Overall, if high-quality saffron corm production is needed, corms should be harvested in the fourth year to gain the maximum yield and profit.     

生物炭和堆肥提高西澳大利亚沙质平原土壤上的作物产量但这种效应是短期的

Sandplain soils on the south coast of Western Australia have low inherent fertility, which is mainly due to poor nutrient retention caused by insufficient clay and organic colloidal material. Previous research has shown the benefits in nutrient levels and retention from adding clay to sandplain soils; however, there is almost no information on the addition of organic amendments. A field experiment was established at the Esperance Downs Research Station, Western Australian, in May 2010, to assess the effects of wheat straw (WS) and chicken manure (CM) biochars and compost with and without phosphorus (P) addition on soil properties and crop production over five growing seasons. The five seasons alternated between winter and summer crops.~The CM and WS biochar and compost treatments significantly increased crop yields and P uptake in 3, 2 and 1 of the five seasons, respectively. The yield increases $(P<0.05)$ were no more than 8\%. By the end of the third season, no differences in crop yields were found that could be attributed to the organic amendments. The addition of P increased crop yields in each winter cropping season. Phosphorus addition explained more than 30\% of the variation in crop yields. Despite marginal P levels and summer drought conditions, arbuscular mycorrhizal root colonisation was not affected by the organic amendments. There were no significant interactions between the organic amendments and P addition in terms of crop yields, P uptake or P uptake efficiency. We conclude that much of the effect of the organic amendments was due to direct nutrient addition which dissipated over time.     

The N2O product ratio of nitrification and its dependence on long-term changes in soil pH

The contribution of nitrification to the emission of nitrous oxide (N₂O) from soils may be large, but its regulation is not well understood. The soil pH appears to play a central role for controlling N₂O emissions from soil, partly by affecting the N₂O product ratios of both denitrification (N₂O/(N₂+N₂O)) and nitrification (N₂O/(NO₂⁻+NO₃⁻). Mechanisms responsible for apparently high N₂O product ratios of nitrification in acid soils are uncertain. We have investigated the pH regulation of the N₂O product ratio of nitrification in a series of experiments with slurries of soils from long-term liming experiments, spanning a pH range from 4.1 to 7.8. ¹⁵N labelled nitrate (NO₃⁻) was added to assess nitrification rates by pool dilution and to distinguish between N₂O from NO₃⁻ reduction and NH₃ oxidation. Sterilized soil slurries were used to determine the rates of chemodenitrification (i.e. the production of nitric oxide (NO) and N₂O from the chemical decomposition of nitrite (NO₂⁻)) as a function of NO₂⁻ concentrations. Additions of NO₂⁻ to aerobic soil slurries (with ¹⁵N labelled NO₃⁻ added) were used to assess its potential for inducing denitrification at aerobic conditions. For soils with pH?5, we found that the N₂O product ratios for nitrification were low (0.2-0.9‰) and comparable to values found in pure cultures of ammonia-oxidizing bacteria. In mineral soils we found only a minor increase in the N₂O product ratio with increasing soil pH, but the effect was so weak that it justifies a constant N₂O product ratio of nitrification for N₂O emission models. For the soils with pH 4.1 and 4.2, the apparent N₂O product ratio of nitrification was 2 orders of magnitude higher than above pH 5 (76‰ and 14‰). This could partly be accounted for by the rates of chemodenitrification of NO₂⁻. We further found convincing evidence for NO₂⁻-induction of aerobic denitrification in acid soils. The study underlines the role of NO₂⁻, both for regulating denitrification and for the apparent nitrifier-derived N₂O emission.     

Depletion of non‐exchangeable NH$ _4^+ $ at the root–soil and hyphae–soil interface of VA mycorrhizal maize (Zea mays) and parsley (Petroselinum sativum)

Mobilization of non‐exchangeable ammonium (NH ) by hyphae of the vesicular‐arbuscular mycorrhizal (VAM) fungus Glumus mosseae was studied under controlled experimental conditions. Maize (Zea mays) and parsley (Petroselinum sativum) were grown either alone or in symbiosis with Glomus mosseae in containers with separated compartments for roots and hyphal growth. In one experiment, ¹⁵NH was added to the soil to differentiate between the native non‐exchangeable NH and the non‐exchangeable NH derived from N fertilization. Non‐exchangeable NH was mobilized by plant growth. Plant dry weight and N uptake, however, were not significantly influenced by mycorrhizal colonization of the roots. The influence of root infection with mycorrhizal fungus on the mobilization of non‐exchangeable NH was negligible. In the hyphal compartment, hyphal uptake of N resulted in a decrease of NH in the soil solution and of exchangeable NH . However, the NH concentration was still too high to permit the release of non‐exchangeable NH . The results demonstrate that, in contrast to roots, hyphae of VAM fungi are not able to form a non‐exchangeable‐NH depletion zone in the adjacent soil. However, under conditions of a more substantial depletion of the exchangeable NH in the mycorrhizal sphere (e.g., with longer growth), an effect of mycorrhiza on the non‐exchangeable NH might be found.     

Effect of methods of application on the efficiency of urea broadcast onto lowland rice (Oryza sativa L.)

Summary We evaluated the effect of different methods of application on the efficiency of urea broadcast at a rate of 100 kg N ha^-1 onto lowland rice (Oryza sativa L. var. SPR 60) in a field experiment conducted on a Phimai soil (Fluvic Tropaquepts) during the dry season of 1989. Analysis of the floodwater on the first day after the fertilizer application showed a high initial concentration of urea-N. Addition of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT), broadcast with the urea into the floodwater, caused an apparent reduction in the rate of urea disappearance and a subsequent accumulation of NH₃–N in the floodwater; this ureas inhibitor also suppressed the rise in floodwater pH, with a resultant reduction in the partial pressure of ammonia (pNH₃) compared with the unamended urea application. The use of nBTPT did not decrease the N loss from broadcast urea not did it increase the grain yield. Among the different methods of applying broadcast urea that we tested, the broadcast application of granular urea onto drained soil shortly after removing floodwater followed by flooding 2 days later appeared to be a good N management practice, offering considerable potential for improving the efficiency of urea applied to lowland rice crops.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

15N示踪研究烤烟对氮的吸收及分配

采用盆栽试验，利用^15N示踪研究了烤烟对不同形态氮的吸收利用规律。结果表明，烤烟各部位叶片对氮素的积累量表现为中部叶〉上部叶〉下部叶；肥料氮进入的比例具有下部叶〉中部叶〉上部叶的规律。不同生育期肥料氮进入烟叶中的比例，以团棵期最高，之后肥料氮进入的比例减少，统计分析结果表明（5％水平），从现蕾期到成熟期之间差异不大。同位素^15N标记肥料施入土壤后约39％～53％被烟株吸收利用，约22％～41％损失，约20％～37％残留于土壤中。     

宣威市紫色土辣椒氮磷钾肥配比试验研究

对紫色土辣椒氮、磷、钾适宜施用量研究表明，紫色土氮磷钾肥对辣椒产量的影响顺序是磷肥〉氮肥〉钾肥。磷是限制辣椒产量的主导因子。在施用菜籽饼肥600kg／hm^2，折N31．2kg／hm^2、P2O5 11.7kg／hm^2、K2O 8．1kg／hm^2的基础上，辣椒产量≥20400kg／hm^2的氮磷钾优化组合施肥范围：N=113．9～204．6kg／hm^2，P2O5=145．9～177．2kg／hm^2，K2O=49．3～153．8kg／hm^2，N：P2O5：K2O=1：0．87～1．28：0．43～0．75。建议氮、磷、钾肥适宜用量为：N159．2kg／hm^2，P2O5 161．5kg／hm^2，K2O 101．5kg／hm^2，N：P2O5：K2O=1：1．01：0．64，辣椒最高产量预测值为21961．5kg／hm^2，施肥利润5417．7元／hm^2，投产比1：5．00。适量的氮、磷、钾营养使得养分比例平衡，有利于增加辣椒收果数，提高鲜椒产量，从而增加效益。     

用~(15)N标记肥料研究旱地冬小麦氮肥利用率与去向

在黄土旱塬 2年的田间试验表明 ,在特殊干旱年里小麦施氮肥增产仍很显著 ,但氮肥效果受到明显抑制 ,施氮处理间小麦产量差异不显著。播种前土壤水分含量对旱作小麦产量有决定性作用。15N微区试验表明 ,尿素作基肥混施入耕层后 ,小麦当年利用率为 3 6 6%～ 3 8 4% ,土壤残留率为 2 9 2 %～ 3 3 6%。氮肥的后效显示 ,土壤残留的氮素可被第 2茬小麦部分利用 ,占施氮量的 2 1 %～ 2 8% ,相当于 0～ 40cm土壤残留氮的 6 7%～ 8 7%。土壤残留的氮素主要集中在 0～ 40cm土层中 ,土壤剖面中残留氮随土壤深度增加而减少。膜间种植对小麦产量、氮肥利用率在试验年里没有显示作用 ,但大大增加了氮肥在土壤中的残留率。