Nitrogen mineralization from an organically managed soil and nitrogen accumulation in lettuce

The potential of an organically managed Cambic Arenosol to supply nitrogen (N) from either an applied commercial organic fertilizer (granulated hen manure), a compost produced on‐farm, or four different mixtures of both fertilizers was studied in a laboratory incubation and a pot experiment with lettuce. In the incubation experiment, a significant higher apparent N mineralization occurred after hen‐manure application (53.4% of the organic N applied) compared to compost (4.5%) or mixed‐fertilizer application (8.7% to 16.7%). The apparent N mineralization in a mixed treatment consisting of compost and half rate of hen manure (15.4% of the organic N applied) was significantly higher than that estimated based on the N mineralization for compost and hen‐manure treatments (7.6%), proving that a combined application of both fertilizers enhanced organic‐N mineralization when compared to separate fertilizer supply. In the pot experiment, a higher lettuce fresh‐matter yield was obtained with hen manure (1.9 kg m^–2) than with compost (1.7 kg m^–2) or unfertilized control treatment (1.3 kg m^–2). Combined application of compost with only a half rate of hen manure led to yields (2.0 kg m^–2) equal to those obtained with only hen manure. A good correlation was observed between the N‐mineralization incubation data and the N accumulated by lettuce plants in the pot experiment (r = 0.983). Hence, in the organic production of baby‐leaf lettuce, a mixture of compost and hen manure appears to be a good fertilization alternative, since it allows a reduction by half of the typical amount of commercial fertilizer usually applied (granulated hen manure), cutting fertilization costs, and providing an amount of available N that allows maintaining lettuce yields.     

丹江口水库库滨带典型植物群落氮矿化特征

为明确库滨带典型植物群落矿化特征,探究植物化学性质与土壤氮矿化的关系,选取丹江口水库库滨带的苘麻和蛇床群丛.试验采取单一叶处理、单一根处理和根+叶混合等9种处理,分别测定第1、3、7、14、21、31、41、51和61 d的土壤氮矿化量,系统分析添加植物后土壤氮矿化特征.结果表明:1)添加植物后,土壤氮矿化可分为3个阶段,即前期(1 ～7d)各处理矿化量均减小,中期(7 ～41 d)各处理矿化量都有所增加,幅度变化较大,后期(41 ～61d)基本保持平衡,所有处理的土壤矿化量均小于对照(CK)的79.53 mg/kg,单一处理中,苘麻叶(QL)矿化量最高,达到71.62 mg/kg,混合处理最高为苘麻叶+蛇床根(QL+ SR) 26.43 mg/kg;2)添加植物后,土壤微生物的质量分数显著增加(P＜0.05),QL＞4个混合处理＞另外3个单一处理;3)整个试验期间,土壤氮矿化量与植物全碳和全氮质量分数显著相关(P＜0.05),主成分分析(PCA)结果显示全氮质量分数对土壤有机氮矿化影响最明显,重要程度为全氮＞C∶N＞纤维素＞L∶N＞多元酚;4)所有混合处理中,实测氮素矿化量均显著小于预测值(P＜0.01).说明添加苘麻和蛇床后,土壤氮矿化表现为抑制作用,根茎混合处理没有激发效应.该研究为区域植被生态恢复、水土保持与非点源污染治理提供参考依据.     

上海地区水稻土氮素矿化模拟

Six paddy soils of Shanghai, China, were studied after 120 days of anaerobic incubation at 25 ℃ and 35 ℃. Four models, the effective accumulated temperature model, the one-component first-order exponential model (the one-pool model), the two-component first-order exponential model (the two-pool model), and the two-component first-order plus zero-order exponential model including a constant term (the special model), were fitted to the data of observed mineral-N during incubation using non-linear regression procedures. The two-pool model and the special model gave the best fits amongst the four models, and parameters in the special model were more reasonable than those in the other three. Results showed that the special model gave a better prediction of nitrogen mineralization under flooded conditions than the other three models.     

Combined nitrogen input from legume residues and fertilizer improves early nitrogen supply and uptake by wheat

Soil nitrogen (N) supply for wheat N uptake can be manipulated through legume and fertilizer N inputs to achieve yield potential in low‐rainfall sandy soil environments. Field experiments over 2 years (2015–2016) were conducted at 2 different sites in a low‐rainfall sandy soil to determine the soil N supply capacity relative to wheat N uptake at key growth stages, after a combination of crop residue (removed, wheat or lupin) and fertilizer N (nil, low or high N) treatments were manipulated to improve wheat yield. We measured the temporal patterns of the soil profile mineral N and PAW to 100 cm depth, wheat aerial biomass and N uptake in both years. In 2016 we also measured the disease incidence as a key environmental variable. There was 35 kg ha^?1 more soil mineral N to 100 cm depth following lupin than wheat residues at the end of the fallow on average in both years. In a below average rainfall season, wheat biomass produced on lupin residues was responsive to N input with soil profile mineral N depleted by increased crop N uptake early in the season. In an above average rainfall season, a higher soil mineral N supply increased actual and potential grain yield, total biomass, N uptake, harvest index and water use efficiency of wheat, regardless of the source of N. Our study showed that the combination of lupin residues with high N rate increased soil profile mineral N at early growth stages, providing a greater soil N supply at the time of high wheat N demand, and the inclusion of a legume in the rotation is critical for improving the N supply to wheat, with added disease break benefits in a low‐rainfall sandy soil environment.     

施氮量对夏玉米碳氮代谢和氮利用效率的影响

本试验研究了施氮量（0、90、180、270 kg/hm2）对夏播玉米CF008、金海5号和郑单958碳氮积累、运转及氮肥利用的影响。结果表明,3个品种的茎叶碳氮积累量、成熟期地上部总氮量均为在施氮量180 kg/hm2或270 kg/hm2下较高,但是最终碳氮运转率、氮素吸收效率、氮素利用效率和氮肥利用率均在施氮量90 kg/hm2下较高。本试验中,碳运转率与产量呈正相关,氮运转率与氮肥利用率呈正相关,表明较高的碳氮运转率可以促进产量和氮肥利用率的提高。本研究在施氮量90 kg/hm2下,CF008和金海5号茎鞘的C/N值在吐丝期和成熟期分别为22.11～22.91、35.66～54.23,叶片的C/N值分别为4.32～5.11、9.06～10.57;在施氮量90～180 kg/hm2下,3个品种夏玉米产量达到了10688～11461 kg/hm2;CF008和金海5号的氮肥利用率达到了31.55%～49.33%,而郑单958的氮肥利用率仅为15.11%～19.20%。     

土壤微生物生物氮与植物氮吸收的关系

The contents of the soil microbial biomass nitrogen (SMBN) in the soils sampled from the Loess Plateau of China were determined using chloroform fumigation aerobic incubation method (CFAIM),chloroform fumigation anaerobic incubation method (CFANIM) and chloroform fumigation-extraction method (CFEM). The N taken up by ryegrass on the soils was determined after a galsshouse pot experiment. The flushes of nitrogen (FN) of the soils obtained by the CFAIM and CFANIM were higher than that by the CFEM, and there were significantly positive correlations between the FN obtained by the 3 methods. The N extracted from the fumigated soils by the CFAIM,CFANIM and CFEM were significantly positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the plant N uptake. The contributions of the SMBN and mineral N and mineralized N during the incubation period to plant N uptake were evaluated with the multiple regression method. The results showed that the N contained in the soil microbial biomass might play a noticeable role in the N supply of the soils to the plant.     

水稻秸秆序批式干发酵产沼气中试及其动力学研究

干发酵处理有机废弃物或生物质废弃物等具有处理量大,用水量少,处理周期短等优势。该试验以水稻秸秆为原料(269 kg,TS为89.19%±0.24%),用沼液(500 kg)调节水稻秸秆含水率至67.58%,覆膜堆沤3 d,并以运行良好沼气池污泥为接种物(300 kg,接种量为28.06%,TS为1.88±0.07%),室温(30~35℃)条件下进行周期为55 d的干发酵中试试验。试验结果表明:反应55 d后,秸秆累积产气量为308.20 m3/t,累积产甲烷量为167.44 m3/t,最高甲烷体积分数达57.88%,最大日产气量为2.33 m3。通过Gompertz模型对水稻秸秆产甲烷曲线进行拟合,拟合出的产甲烷潜力值和实际的产甲烷潜力值很接近,R2为0.990 7,显示出较高的准确性。该研究可为序批式干发酵法处理水稻秸秆提供理论依据和指导。     

Relationship between mineralization and immobilization of nitrogen influenced by various conditions of submerged soils

The relationship between mineralization of soil nitrogen and immobilization of added nitrogen in submerged soils were studied under various soil conditions in a laboratory experiment. Selected factors which constituted soil conditions were content of soil organic nitrogen, quantity of nitrogen addition, temperature, soil drying, puddling, and period of incubation. Each factor contained some treatments in it.

The ratio of mineralization to immobilization, M/I, was relatively constant under various soil conditions. The values of M/I were around 2 except the soil drying treatments, indicating that the amount equivalent to about half of mineralized nitrogen is immobilized simultaneously under nitrogen added condition. Even so, if considered in detail, treatments that stimulate the microbial activities were observed to have increasing effect on M/I.

The ratio of additional mineralization caused by nitrogen addition to immobilization, ΔM/I, is considered to be an index to know the influence of nitrogen addition on the quantitative change of soil nitrogen level. This value was around 1 in the soil without any application of organic matters, and around 0.6 in the soil receiving straw compost for 10 years. Factors that have close relations with the value of ΔM/I were soil organic nitrogen level, temperature, soil drying, and period of incubation.     

Interactive effects of plant growth regulators and nitrogen on corn growth and nitrogen use efficiency

Our objective was to determine the combined effect of some plant growth regulators and nitrogen (N) on corn growth, yield and nitrogen use efficiency. A potted experiment was conducted with two levels of growth regulators [i.e. with or without treatment with Seed king (Kinetine), Root king (Indole-butyric acid) and More king (Chitosan)], two maize cultivars (Calabar White and Obatanpa-98 and three nitrogen rates (0, 90 and 180 kg/ha in the form of urea). The measured parameters were growth attributes, nitrogen uptake, dry matter yield, harvest-index, shoot to root ratio, yield attributes and agronomic and physiological nitrogen use efficiency. Calabar White had taller plants (154.53 cm) more leaves (12.00) and larger leaf area (466.98 cm²) than obatanpa-98 at 6 weeks after sowing. The dry matter yield of both leaf and stem increased significantly (P ≤ 0.05) with increasing N rates but the growth regulators significantly (P ≤ 0.05) increased only the leaf dry matter. The interaction between growth regulators and nitrogen significantly affected the leaf dry matter but not the stem dry matter. There was a considerable (P ≤ 0.05) increase in harvest-index (HI) at the 90 kg/ha N rate with growth regulators and Obatanpa-98 had better HI (30.81%) than Calabar White (27.41%). Obatanpa 98 also had much (P ≤ 0.05) higher grain yield (87.42 g/plant) than Calabar White (65.40 g/plant) but for both cultivars, the grain yield increased progressively with increasing N rate. The uptake of N differed significantly (P ≤ 0.05) among the different partitions of maize (leaves, stems and grains) at various growth stages. Calabar White had the highest N uptake in the leaves and stem whether at silking or at harvest. Obatanpa-98 partitioned more N to the grains than Calabar White. Agronomic nitrogen use efficiency (ANUE) was highest (21.31 gg^?1) at the 90 kg/ha N rate with Obatanpa-98 having a superior (20.26 gg^?1) ANUE to Calabar White (15.94 gg^?1). The physiological nitrogen use efficiency (PNUE) was also highest (8.14 g/kg) at the 90 kg/ha N rate with Obatanpa-98 being more efficient (8.08 gkg) than Calabar White (6.26 g/kg). Thus, both cultivars treated with 90 kgN/ha with or without growth regulators would best optimize nitrogen fertilizer use. However, the growth regulators increased the yield of Calabar White significantly only when no N was applied. In contrast, they increased the yield of the hybrid Obatanpa-98 at all N rates especially at the 180 kgN/ha rate. Thus, under the low input cropping common with Calabar White, treatment with the growth regulators would boost yield. A combined treatment of 180 kg N/ha with the growth regulators would ensure the best yield of Obatanpa-98.     

Comparison of the difference method and 15N technique for studying the fate of nitrogen from plant residues in soil

We compared the dynamics of net mineralization of nitrogen (N) derived from white clover material (Ndfc) as measured by the difference and the ¹⁵N methods in a pot experiment with a sandy loam (15°C and pF 2.4) planted with Italian ryegrass. On day 22, mineralized Ndfc (soil mineral N plus plant N uptake) was 5.8% and 1.3% of added N for the ¹⁵N and the difference methods, respectively. The discrepancy was reduced on day 43. On day 64, the relationship was reversed, and on day 98 the values given by the two methods were 22.8% and 29.5%, respectively. The results obtained by the two methods were linearly correlated (r = 0.987) and, on average, did not differ significantly. Nevertheless, the different temporal patterns led to appreciably different parameter values as estimated by fitting of a reparameterized Richards model. On day 22, clover amendment reduced mineralized N derived from soil (Ndfs) by 3.4 mg N pot^–1. The reason for this was that the clover amendment led to a reduction in plant growth and uptake of Ndfs, most likely because of allelopathy, while mineral Ndfs did not increase correspondingly. Clover-induced Ndfs in the microbial biomass of 5.1 mg N pot^–1 suggested that the mineral Ndfs not taken up by plants had been reimmobilized. Towards the end of the experiment, clover-induced Ndfs in the biomass declined to 1.5 mg N pot^–1, while mineralized Ndfs due to clover amendment increased to 5.1 mg N pot^–1. The results strongly suggested that this increase was caused by a real stimulation of humus N mineralization by clover amendment rather than by isotope displacement or pool substitution. Received: 5 May 1997     

Nitrogen release from air‐dried biosolids for fertilizer value

Mineral‐N production by air‐dried biosolids was measured in an Australian tenosol type soil with two moisture conditions over 70 days, using a controlled laboratory incubation procedure. The biosolids were from both air‐drying pans and stockpiles. Inorganic‐N components (NH₄‐N, NO₃‐N and NO₂‐N) were present in all biosolids, with higher concentrations in samples from air‐drying pans compared with stockpiles of 1 yr age. Nevertheless, significant production of NO₃‐N occurred in moist soil amended with all air‐dried biosolids. In contrast, saturated soil amended with air‐dried biosolids generally showed a net loss of inorganic‐N compounds during incubation, presumably owing to denitrification. In the saturated soil, only biosolids from air‐drying pans provided NO₃‐N production from existing NH₄‐N. The results indicated that biosolids from air‐drying pans provided the most robust production of NO₃‐N, compared with aged material from the stockpiles, owing to the reduced N content and increased stability of the organic fraction in stored biosolids. However, the rates of N‐mineralization in the tenosol soil were substantially lower than reported for more fertile soil types and most of the organic‐N content of the biosolids remained undegraded by day 70. The biosolids thus may substantially remain to provide improved properties of soil, such as structure and water‐holding capacity. The results suggest that anaerobically digested biosolids from air‐drying pans are potentially highly consistent products that could be effective replacements for inorganic‐N fertilizer in agricultural production.     

氮水平对水稻植株氮素损失的影响

利用15N差值法,在溶液培养条件下研究了不同氮肥水平对水稻植株氮损失的影响,并就影响水稻氮损失的因素进行了分析。结果表明,对前期正常供氮的水稻幼苗做为期10 d的不同氮(N 04、0、801、60 mg/L)处理,水稻植株生物量未受显著影响,表明前期吸收氮可维持水稻生长。但是,随着供氮水平的提高,叶片及根的含氮量显著增加,而15N的丰度却显著下降,叶片15N的丰度显著高于根。说明高氮处理增加了水稻植株吸氮量并稀释了前期吸收的15N,而且根系累积的氮向地上部转移。缺氮(N 0 mg/L)与过量供氮(N 160 mg/L)均显著增加植株氮的损失率,而适量供氮(N 80 mg/L)则氮肥利用率显著提高。水稻的生长期显著影响植物氮的损失率,在N 80 mg/L的条件下,随着水稻生长期的延长,植株氮损失从11.6%增加到22.3%。同时,随着供氮水平的增加,叶片中NH4+-N含量和谷草转氨酶(GOT)活性均显著增加,叶片组织pH也随之增加。表明植物体内铵浓度增加而引起的氨挥发是导致植物氮损失增加的原因之一。     

Root growth and N‐uptake activity of oilseed rape (Brassica napus L.) cultivars differing in nitrogen efficiency

Nitrate‐N uptake from soil depends on root growth and uptake activity. However, under field conditions N‐uptake activity is difficult to estimate from soil‐N depletion due to different loss pathways. We modified the current mesh‐bag method to estimate nitrate‐N‐uptake activity and root growth of two oilseed‐rape cultivars differing in N‐uptake efficiency. N‐efficient cultivar (cv.) ‘Apex' and N‐inefficient cv. ‘Capitol' were grown in a field experiment on a silty clayey gleyic fluvisol near Göttingen, northern Germany, and fertilized with 0 (N₀) and 227 (N₂₂₇) kg N ha^–1. In February 2002, PVC tubes with a diameter of 50 mm were installed between plant rows at 0–0.3 and 0–0.6 m soil depth with an angle of 45°. At the beginning of shooting, beginning of flowering, and at seed filling, the PVC tubes were substituted by PVC tubes (compartments) of the same diameter, but with an open window at the upper side either at a soil depth of 0–0.3 or 0.3–0.6 m allowing roots to grow into the tubes. Anion‐exchange resin at the bottom of the compartment allowed estimation of nitrate leaching. The compartments were then filled with root‐free soil which was amended with or without 90 mg N (kg soil)^–1. The newly developed roots and nitrate‐N depletion were estimated in the compartments after the installing period (21 d at shooting stage and 16 d both at flowering and grain‐filling stages). Nitrate‐N depletion was estimated from the difference between NO ‐N contents of compartments containing roots and control compartments (windows closed with a membrane) containing no roots. The amount of nitrate leached from the compartments was quantified from the resin and has been taken into consideration in the calculation of the N depletion. The amount of N depleted from the compartments significantly correlated with root‐length density. Suboptimal N application to the crop reduced total biomass and seed‐yield formation substantially (24% and 38% for ‘Apex’ and ‘Capitol’, respectively). At the shooting stage, there were no differences in root production and N depletion from the compartments by the two cultivars between N₀ and N₂₂₇. But at flowering and seed‐filling stages, higher root production and accordingly higher N depletion was observed at N₀ compared to N₂₂₇. Towards later growth stages, the newly developed roots were characterized by a reduction of root diameter and a shift towards the deeper soil layer (0.3–0.6m). At low but not at high N supply, the N‐efficient cv. ‘Apex’ exhibited higher root growth and accordingly depleted nitrate‐N more effectively than the N‐inefficient cv. ‘Capitol’, especially during the reproductive growth phase. The calculated nitrate‐N‐uptake rate per unit root length was maximal at flowering (for the low N supply) but showed no difference between the two cultivars. This indicated that the higher N‐uptake efficiency of cv. ‘Apex’ was due to higher root growth rather than higher uptake per unit of root length.     

Nitrogen mineralization from mature bio‐waste compost in vineyard soils. III Simulation of soil mineral‐nitrogen dynamics

A model for nitrogen (N) dynamics in compost‐amended vineyard soils was tested for its predictive power. A soil–mineral N data set from a 3‐year field study on four different vineyard sites was used for model evaluation. The soils were treated with mature bio‐waste compost (30 and 50 Mg ha^–1 fresh matter, respectively). The model calculated soil mineral‐N contents at all sites with an overall mean bias error of –2.2 kg N ha^–1 for layers of 0.1 m thickness and an overall mean absolute error of 7.4 kg N ha^–1 layer^–1. Modeling efficiencies for the simulations of the respective treatments ranged from –0.05 to 0.41, and Willmott's Index of Agreement showed values of between 0.41 and 0.81. Acceptable model predictions as defined by the observed variability of mineral‐N contents in the respective soils ranged from 40% to 72%. A strong increase in soil mineral‐N concentration following the compost application at all sites could not be reproduced with the model, thereby reducing the prediction accuracy significantly. The model performance confirms that previously derived N‐mineralization parameters are suitable to describe the N release from soil‐applied mature bio‐waste compost under the environmental conditions of vineyards in Germany.     

添加钢渣恢复厌氧消化酸化系统提高沼气产量

针对厌氧消化酸化后传统恢复产气方法成本高,产气率低的问题,该文通过对比研究钢渣和碱对酸化后发酵体系的恢复作用,结果表明酸化体系添加钢渣后累积产气率为285.33 m L/g,较传统法(加碱)提高了25.8%,两组数据差异显著。同时对恢复产气后的p H值,总挥发性脂肪酸(total volatile fatty acid),碱度(alkalinity),挥发性脂肪酸(volatile fatty acids)进行了监测分析,发现两组的上述数据差异并不显著,TVFA/TA和丙酸/乙酸的比值更加有效指示两体系恢复后的稳定性,且添加钢渣体系较加碱体系提前8 d恢复正常。最后分析了恢复产气后消化液中重金属,两体系的重金属含量完全满足NY/T 2065-2011沼肥施用技术规范中的相关要求,此举提供了一种优于传统恢复酸化液渣产气的方式,为解决实际工程易酸化、恢复产气成本高的问题提出了新的解决方法。     

Significance of organic nitrogen uptake from plant residues by soil microorganisms as affected by carbon and nitrogen availability

Soil microorganisms can use a wide range of nitrogen (N) compounds. When organic N sources are degraded, microorganisms can either take up simple organic molecules directly (direct route), or organic N may be mineralized first and taken up in the form of mineral N (mineralization-immobilization-turnover [MIT] route). To determine the importance of the direct route, a microcosm experiment was carried out. Two types of wheat residue were added to soil samples, including younger residue with a carbon (C) to N ratio of 12 and older residue with a C to N ratio of 29. Between days 1 and 4, the gross N mineralization rate reached 8.4 and 4.0 mg N kg⁻¹ dry soil day⁻¹ in the treatment with younger and older residue, respectively. During the same period, there was no difference in protease activity between the two residue amended treatments. The fact that protease activity was not related to gross N mineralization, even though the products of protease activity are the substrates for N mineralization, suggests that not all organic molecules released from residue or soil N passed through the soil mineral N pool. In fact, when leucine and glycine were added, only 10 and 53% of the amino acid-N, respectively, was mineralized. The fraction of N taken up via the direct route was estimated to be 55 and 62% for the young and older residue, respectively. After 28 days of incubation, the proportion of amino acid-N mineralized had increased especially in the soil amended with older residue, suggesting that the MIT route became increasingly important. This result is supported by an increase in the activities of enzymes responsible for the intracellular assimilation of ammonium (NH₄⁺). Our results suggest that in contrast to what is proposed by many models of soil N cycling, both the direct and MIT routes were operative, with the direct route being the preferred route of residue N uptake. The direct route became less important over time and was more important in soil amended with older residue, suggesting that the direct route is favored by lower mineral N availabilities. An important implication of these findings is that when the direct route is dominant, gross N mineralization underestimates the amount of N made available from the residue.     

畜禽有机肥氮、磷在红壤中的矿化特征研究

选用腐熟的猪粪、鸡粪和第四纪红土发育的典型红壤为试验材料,通过室内培养试验,研究了土壤中矿质氮(NO-3-N和NH4+-N)及Olsen-p的动态变化.结果表明,有机肥中氮和磷的矿化具有不同特征.氮在红壤中的矿化阶段为:前4周缓慢释放,矿化速率为N 0.29～0.46mg/(kg·d);4～10周快速释放,矿化速率为N...     

长期定位试验中氮肥与磷肥有机肥联合施用通过刺激根的生长增加玉米产量和养分吸收

Imbalanced application of nitrogen (N) and phosphorus (P) fertilizers can result in reduced crop yield, low nutrient use efficiency, and high loss of nutrients and soil nitrate nitrogen (NO₃^--N) accumulation decreases when N is applied with P and/or manure; however, the effect of applications of N with P and/or manure on root growth and distribution in the soil profile is not fully understood. The aim of this study was to investigate the combined effects of different N and P fertilizer application rates with or without manure on maize (Zea mays L.) yield, N uptake, root growth, apparent N surplus, Olsen-P concentration, and mineral N (Nmin) accumulation in a fluvo-aquic calcareous soil from a long-term (28-year) experiment. The experiment comprised twelve combinations of chemical N and P fertilizers, either with or without chicken manure, as treatments in four replicates. The yield of maize grain was 82% higher, the N uptake 100% higher, and the Nmin accumulation 39% lower in the treatments with combined N and P in comparison to N fertilizer only. The maize root length density in the 30--60 cm layer was three times greater in the treatments with N and P fertilizers than with N fertilizer only. Manure addition increased maize yield by 50% and N uptake by 43%, and reduced Nmin (mostly NO₃^--N) accumulation in the soil by 46%. The long-term application of manure and P fertilizer resulted in significant increases in soil Olsen-P concentration when no N fertilizer was applied. Manure application reduced the apparent N surplus for all treatments. These results suggest that combined N and P fertilizer applications could enhance maize grain yield and nutrient uptake via stimulating root growth, leading to reduced accumulation of potentially leachable NO₃^--N in soil, and manure application was a practical way to improve degraded soils in China and the rest of the world.     

Leaching Methods Can Underestimate Mineralization Potential of Soils

Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl₂), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH₄⁺)-N and nitrate + nitrite (NO₃^?+ NO₂^–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH₄⁺-N (1 g kg^?1) and NO₃^–-N (0.6 g kg^?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH₄⁺-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH₄⁺.     

应用几种植物物质及化合物抑制土壤脲酶活性和提高植物尿素氮的回收率

Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodora Hook., P1), robust eucalyptus (E. robusta Smith, P2), Nepal camphortree (Cinnamomum glanduliferum (Wall.) Nees, P3), tea (Camellia sinensis (Linn.) O. Ktze. f., P4), oleander (Nerium indicum Mill, P5), rape (Brassica campestris L., P6),Chinese tallow tree (Sapium sebiferum L., P7), tung (Vernicia fordii (Hemsl.), P8), and croton (Croton tiglium L., P9), 7 chemicals, boric acid (C1), borax (C2), oxalic acid (C3), sodium oxalite (C4), sodium dihydrogen phosphate (C6), sodium silicate (C7) and sodium citrate (C8), and a natural organic substance,humic acid (C5), on urease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied through incubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. After incubation at 37 ℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity were selected and then incubated for 14 days at 25 ℃. Results of the incubation experiments showed that soil urease activity was greatly inhibited by them, and the inhibition effect followed an order of P2＞P4＞C3＞C2＞P3＞C1＞HQ＞P1.The 7 selected materials reduced the accumulative amounts of N released from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively, and postponed the N release peak by 2～4 days in the incubation period of 14 days under constant temperature, as compared to the control (no inhibitor).In the pot experiment with the 7 materials at two levels of addition, low (L) and high (H), the C1 (H), C3(H), C1 (L), P4 (L) and C2 (L) treatments could significantly increase the dry weights of the aboveground parts and the total biomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% as compared to the control (no hibitor).