Influence of Iron Application Methods on Seasonal Variations in Antioxidant Activity of Peanut

The influence of foliar and soil applications of iron (Fe) on variations in antioxidant activity of peanut was investigated in a field experiment. For each method, five levels of Fe–ethylenediamine-N,N'-bis (EDDHA) (in the soil application, 0, 5, 10, 15 and 20 kg ha^?1, and in the foliar application, 0, 1, 2, 3 or 4 gL^?1) were applied. The results revealed that the Fe content of leaves increased significantly by both application methods. In addition, immediately after every spraying of Fe on the leaves, the activities changed significantly: Catalase and peroxidase increased but superoxide dismutase decreased during the growing season. By soil applications, the enzyme activities increased gradually and yet continuously decreased at the last period of the plant growth. For both applications, greater levels of Fe (4 gL^?1 and 20 kg Fe-EDDHA ha^?1 for sprayed and soil applications, respectively) had more positive effects on the activities of peroxidase and catalase than on superoxide dismutase.     

Effects of exogenous SA supplied with different approaches on growth,chlorophyll content and antioxidant enzymes of peanut growing on calcareous soil

To assess the role of salicylic acid (SA) supplied with 5 approaches in alleviating chlorosis induced by iron (Fe) deficiency in peanut plants growing on calcareous soil, SA was supplied as soil incorporation, making slow-release particles, seed soaking, irrigation and foliar application. SA application, particularly, SA supplied by slow release particles, dramatically increased growth parameters, yield and quality of peanut, and increased Fe concentration in peanut grain. Meanwhile, SA application increased the H⁺-ATPase activity, reduced pH of soil, increased Fe³⁺-Chelate Reductase (FCR) activity in roots, and increased Fe concentration in roots. Furthermore, SA increased active Fe content and increased chlorophyll content. In addition, SA improved enzymes activities containing superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and protected Fe deficiency induced oxidative stress. Therefore, SA has a good effect on alleviating chlorosis induced by Fe deficiency on calcareous soil. However, in the 5 SA supplied approaches, foliar application and making slow release particles were more effective.     

Interaction effects of nitrogen and phosphorus fertilizer on nitrogen mineralization of wheat residues in a calcareous soil

Abstract

Because of the high pH of the soil in semiarid regions, phosphorus adsorption is unfavorable. So, considerable amounts of phosphorus fertilizers are used annually, where this fertilizer may affect the plant residues' decomposition. To examine the interaction effects of nitrogen and phosphorus on nitrogen mineralization in calcareous soil, a factorial experiment was performed in a completely randomized design with three replications. The first factor consisted of various C:N ratios (20, 40, and 60 or three levels of nitrogen N₁:0, N₂:11, and N₃:43?kg N ha^?1, respectively) and the second factor consisted of various C:P ratios (87, 174, and 260 or three levels of phosphorus P₁:0, P₂:12, and P₃:45?kg P ha^?1, respectively), under incubation conditions. The results indicated that the cumulative mineral nitrogen content in all treatments, except for N1P2 and N1P3 treatments, started from a positive amount and remained positive until the end of the incubation period. The highest amount of cumulative mineral nitrogen among treatments was related to N3P1 treatment, while the lowest was associated with N2P3 treatment. Mineralization of nitrogen during 60?d of incubation was the dominant phenomenon, except for the N1P2 and N1P3 treatments which remained in the organic phase. The effect of phosphorus on the cumulative mineralization of nitrogen was significant. With increasing the amount of phosphorus, the total inorganic nitrogen diminished. Nitrogen release begins earlier with lower C:N ratios, and therefore the available nitrogen can be released more quickly to the plant. It is generally concluded that, in calcareous soil, the use of nitrogen fertilizer to adjust C:N ratio and to improve the mineralization of wheat residues will be a suitable option.     

Exogenous Nitric Oxide Effects on Physiological Characteristics of a Peanut Cultivar Growing on Calcareous Soil

This study examined the effects of exogenous nitric oxide (NO) on physiological characteristics of peanut (Arachis hypogaea L.) growing on calcareous soil. Sodium nitroprusside (SNP) was added into slow-release fertilizer (SRF) or sprayed on leaves to supply NO for iron-deficient peanut. The results showed that root application of SNP at 5.63 mg/g and foliar spray of SNP at 1.0 mmol L^?1 significantly enhanced the peanut growth, pod yield, and quality. The soil pH was reduced, and available iron content and iron (Fe³⁺) reductase activity in root were increased, indicating NO application improved the availability of iron in the soil. Additionally, NO increased the chlorophyll and active iron content in young leaves, implying NO enhanced the availability of iron within the plant. Nitric oxide also inhibited the malondialdehyde (MDA) accumulation in leaves and increased the activity of antioxidant enzymes, which protected peanut against iron-deficiency-induced oxidative stress. It was concluded that NO might be employed for ameliorating iron-deficient chlorosis of peanut on calcareous soil when added into SRF or sprayed on leaves.     

Mutual Effects of Boron and Zinc on Peanut (Arachis hypogaea L.) Growth and Mineral Nutrition

The mutual effects of boron (B) and zinc (Zn) on growth, total chlorophyll (Chl), membrane permeability (MP), and nutrient content were investigated in peanut (Arachis hypogaea L.). The soil was treated with five levels of B (0, 4, 8, 16, 32 mg kg^?1) and three levels of Zn (0, 10, 20 mg kg^?1). Plant growth was progressively depressed with increasing of B. However, Zn addition had an inhibitory effect on B toxicity and decreased growth reduction caused by excess B. In Zn-untreated plants, B and Zn contents were enhanced by increasing of B; moreover, both Zn and B addition enhanced Zn content. The Chl content decreased and MP increased, resulting from B toxicity; however, Zn addition partially ameliorated the adverse effects of B toxicity on Chl and MP. Increasing B enhanced phosphorus (P), potassium (K), calcium (Ca), iron (Fe), Zn, copper (Cu), and sodium (Na) contents in peanut shoots.     

Effects of Nitric Oxide on Iron-Deficiency Stress Alleviation of Peanut

The aim of this research was to study the role of nitric oxide (NO) in alleviating iron deficiency induced chlorosis of peanut (Arachis hypogaea L.). For this study, sodium nitroprusside (SNP) was used to supply NO for hydroponic peanut plants. After 18 days, the peanut seedlings growing without iron exhibited significant leaf interveinal chlorosis, and this iron-deficiency induced symptom was completely prevented by NO. An increased content of chlorophyll and active iron was observed in NO-treated young leaves, suggesting an improvement of iron availability in plants. In addition, the improved rhizosphere acidification and increased secretion of organic acids by root in NO-treated plants suggesting that NO is effective in modulating iron uptake and transport inside the peanut plants. Furthermore, NO treatment alleviated the increased accumulation of superoxide anion (O₂^??) and malondialdehyde (MDA), and modulated the antioxidant enzymes. However, the SNP with a prior sunlight treatment that does not release NO had no significant effect on the chlorophyll levels in iron-deficient plants. Therefore, these results support a physiological action of NO on the availability, uptake and transport of iron in the plant.     

Growth and phosphorus uptake of maize cultivated alone,in mixed culture with other crops or after incorporation of their residues

Intercropping or rotating of P‐efficient crop species which mobilize sparingly soluble P by their root exudates can have beneficial effects on growth and P uptake of P‐inefficient species. We aimed at studying the effect of intercropping or incorporating of crop residues of P‐efficient crops on the components of maize P‐uptake, i.e. the root‐system size and P influx (P‐uptake rate per unit root length). This was studied in 3 pot experiments in a low‐P sandy soil. In the first experiment, maize was intercropped with white lupine, sugar beet or oilseed rape, and with groundnut in the second experiment. In the third experiment, maize was grown after incorporating the crop residues of white lupine, sugar beet or oilseed rape. Maize growth and yield was strongly inhibited when intercropped with white lupine, sugar beet or oilseed rape, probably because of competition for nutrients. But with groundnut as the accompanying species, maize yield was increased by a factor of 3, mainly because of an enhanced P influx. Crop residues of oilseed rape and sugar beet increased the yield of maize by factors 2 and 1.6, respectively, because of a 3 and 2 times higher P uptake as compared to maize grown after maize without incorporation of crop residue. The reason for the higher maize P‐uptake after oilseed rape was an 11 times higher P influx as compared to maize without crop residues, and after sugar beet residues because of an enhanced root growth and a 4 times higher P influx. Lupine residues did not improve maize growth, mainly because of a low P influx, which was even less than that of maize grown without crop residues. The soil solution P concentration and calcium acetate lactate‐extractable P (CAL P) measured in this study did not reflect the P availability as indicated by the plants (P uptake, P influx). This indicates that other mechanisms such as P mobilization in the rhizosphere by root exudates or cell‐wall components were responsible for the increased P availability. These mechanisms need further investigation.     

Effects of Exogenous Salicylic Acid on Physiological Characteristics of Peanut Seedlings under Iron-Deficiency Stress

The effects of salicylic acid (SA) on iron (Fe) deficiency in peanut (Arachis hypogaea L.) were studied by adopting the hydroponic experiment. Iron deficiency caused serious chlorosis, inhibited plant growth and dramatically decreased the concentration of Fe in the roots. Furthermore, it decreased the active Fe content and chlorophyll content, and disturbed ionic homeostasis. In addition, Fe deficiency significantly increased the content of malondialdehyde (MDA) and the superoxide anion (O₂^??) generation rate. Addition of SA increased Fe concentration in the shoots and roots, active Fe content, chlorophyll content, the net photosynthetic rate, and transpiration rate. Moreover, SA supplementation alleviated the excess absorption of manganese (Mn), copper (Cu) and zinc (Zn) induced by Fe deficiency. In addition, the chlorosis symptom was alleviated and the plant growth was improved. Meanwhile, addition of SA increased the activities of catalase (CAT) and peroxidase (POD), and decreased the content of MDA and the O₂^?? generation rate. These results suggest that exogenous SA can alleviate Fe-deficiency induced chlorosis by promoting the plant growth, improving the efficiency of Fe uptake, translocation and utilization, protecting antioxidant enzymes system, and stimulating mineral element maintenance.     

Tillage and amendment effects on soil carbon and nitrogen mineralization and phosphorus release

The influence of tillage and nutrient amendment management on nutrient cycling processes in soil have substantial implications for environmentally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organic matter variables (carbon (C), nitrogen (N) and phosphorus (P)) and C and N mineralization and P release were determined for a Dothan fine-sandy loam soil in southeastern Alabama. Tillage systems investigated were strip (or conservation) and conventional tillage with various soil nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0–10 cm depth increment) organic matter variables were determined for all tillage/amendment combinations. Carbon and N mineralization and P release were determined on surface soils for each field treatment combination in a long-term laboratory incubation. Soil organic P concentration was 60% greater in soils that had been conventionally tilled, as compared with strip-tilled, both prior to and following laboratory incubation. Carbon and N mineralization results reflected the effects of prior tillage amendment regime, where soils maintained under strip-till/broiler litter mineralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readily mineralizable pool of N (6.1%) than with conventional till (4.2%); broiler litter amendments had a larger labile N fraction (6.7%) than was found in soils receiving either mineral fertilizer (4.1%) or no amendment (4.7%). Tillage also affected P release measured during the incubation study, where approximately 20% more inorganic P was released from strip-tilled soils than from those maintained under conventional tillage. Greater P release was observed for amended soils as compared with soils where no amendment was applied. Results from this study indicate that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern US soil.     

Effects of Exogenous Salicylic Acid and Nitric Oxide on Peanut Seedlings Growth under Iron Deficiency

Salicylic acid (SA) and nitric oxide (NO), which are known as important signaling molecules in plants, could be promising compounds for the reduction in stress sensitivity. The aim of the present work was to study the physiological changes in peanut (Arachis hypogaea L.) seedlings grown in growth medium that contained 0.1 mM SA, 0.25 mM sodium nitroprusside (SNP, a NO donor), or in full (SA+SNP) or half [1/2 (SA+SNP)] combined strengths under iron (Fe) deficiency. After 21 days of treatment, Fe deficiency significantly inhibited peanut plant growth, destroyed photosynthetic system, and caused oxidative damages. Addition of SA, SNP, and 1/2 (SA+SNP), especially SA+SNP, alleviated the stress, increased the contents of chlorophylls, and promoted plant growth. They improved Fe uptake, transport, and availability in peanut plants by increasing the activities of H⁺-ATPase and ferric chelate reductase (FCR), and promoting Fe translocation from cell wall to cell organelle and soluble fraction in leaves. Furthermore, they also effectively mitigated oxidative damages by increasing the activities of antioxidant enzymes in peanut leaves and roots. The results from the present study indicate that application of SA, SNP, or 1/2 (SA+SNP) can overcome the adverse effect of Fe deficiency, but the combined application of SA+SNP is more effective in alleviating Fe deficiency stress.     

Effect of different soil cultivation systems,including no-tillage,on electro-ultrafiltration extractable organic nitrogen

The effect of different long-term soil-cultivation systems (ploughing, two types of cultivator, notillage) on organic N, extracted with the electroultrafiltration (EUF) technique, was studied in two arable soils, a Luvic Phaeozem derived from loess and a Eutric Cambisol. A modified EUF extraction procedure (the 80°C fraction extended from 5 to 90 min) was used to investigate the release of organic N from the ploughing and no-tillage treatment, and the content of hydrolysable N was measured in the combined filtrates. No-tillage and the two non-turning cultivation systems led to an accumulation of EUF organic N in the 0- to 10-cm depth compared to the ploughing treatment. In the lower horizon (15–25 cm) the reverse pattern was found in the loamy soil, with higher concentrations after ploughing than after reduced tillage. However, in the sandy soil all four cultivation treatments showed similar values in the 15- to 25-cm depth. During the time of investigation (May 1987 to February 1989) an EUF organic N accumulation occurred, which was about twice as high in the loamy as in the sandy soil. Therefore we conclude that in the sandy soil the mineralization of organic N was faster, and that reduced tillage retarded its degradation. In the total 0- to 25-cm depth, this delay was not observed in the loamy soil. The N release rates were much lower in the sandy than in the loamy soil and they were higher for the notillage than for the ploughing treatment. Only 30–40% of the total organic N desorbed was hydrolysable and the amino acid composition indicates that part of it originated from microbial Cells. The overall evaluation showed clearly that EUF-extractable organic N is a sitespecific factor.     

过量施氮对旱地土壤碳、氮及供氮能力的影响

【目的】过量施氮会影响土壤有机碳、氮的组成与数量,进而改变土壤供氮能力,但关于西北旱地长期过量施用氮肥后土壤有机碳、氮及土壤供氮能力变化的研究尚缺乏。本文在长期定位试验的基础上,通过分析不同氮肥水平特别是过量施氮条件下土壤硝态氮,有机碳、氮和微生物量碳、氮的变化,探讨长期过量施氮对土壤有机碳、氮及供氮能力的影响。【方法】长期定位试验位于陕西杨凌西北农林科技大学农作一站。在施磷(P2O5)100kg/hm2的基础上,设5个氮水平,施氮量分别为N 0、80、160、240、320 kg/hm2。重复4次,小区面积40 m2,完全随机区组排列。种植冬小麦品种为小堰22。本文选取其中3处理,以不施氮为对照(N0)、施氮量N 160 kg/hm2为正常施氮(N160),施氮量N 320 kg/hm2为过量施氮(N320),分别于2012年6月小麦收获后和10月下季小麦播前采集土壤样品,进行测定分析。【结果】过量施氮导致下季小麦播前0—300 cm各土层硝态氮含量显著增加,平均由对照的2.8 mg/kg增加到15.5 mg/kg;同时,0—60 cm和0—300 cm土层的硝态氮累积量分别由对照的47.2和108.9 kg/hm2增加到76.5和727.7 kg/hm2。过量施氮也增加了夏闲期间0—300 cm土层土壤有机氮矿化量,由对照的72.4 kg/hm2增加到130.7 kg/hm2。但过量施氮未显著增加土壤的有机碳含量,却显著增加了土壤有机氮含量,过量施氮0—20、20—40 cm土层土壤有机碳分别为9.24和5.39 g/kg,有机氮分别为1.05和0.71 g/kg,较对照增加52.2%和54.3%。同样,过量施氮未显著影响0—20、20—40 cm土层土壤微生物量碳含量,其平均含量分别为253和205 mg/kg,却显著提高了0—20、20—40 cm土层土壤微生物量氮含量,由对照的24.1和7.5 mg/kg提高到43.6和16.1 mg/kg。【结论】过量施氮可以显著增加旱地土壤剖面中的硝态氮累积量、夏闲期氮素矿化量、小麦播前土壤氮素供应量和土壤微生物量氮含量,但对土壤有机碳和微生物量碳没有显著性影响,同时过量施氮增加了土壤硝态氮淋溶风险,故在有机质含量低的黄土高原南部旱地冬小麦种植中不宜施用高量氮肥,以减少土壤氮素残留和农业投入,达到保护环境和培肥土壤的目的。     

耕作方式及秸秆还田对华北平原土壤全氮及其组分的影响

为明确耕作方式对农田土壤全氮及其组分的影响,该文于中国农业大学吴桥实验站展开研究。田间试验布置于2008年,设置翻耕秸秆不还田(PT),翻耕秸秆还田(PTS),免耕秸秆还田(NTS)和旋耕秸秆还田(RTS)4个处理。于2015年冬小麦收获后取样,测定分析了土壤全氮、颗粒氮、矿物结合态氮含量以及土壤全氮储量。研究结果表明,0~5和5~10 cm土层的土壤全氮含量NTS和RTS显著高于PTS,但10~20和20~30 cm土层显著降低(P0.05)。0~50 cm土层的土壤全氮储量秸秆还田各处理间差异不显著,但NTS和PTS较PT分别提高了7.78%和11.09%(P0.05)。在土壤全氮及其组分中,土壤颗粒氮对耕作方式表现出最高的敏感性。0~5 cm土层的土壤颗粒氮含量及其在土壤全氮中的占比NTS和RTS均高于PTS,但在20~30 cm土层均低于PTS(P0.05)。与PT相比,PTS仅提高了0~20 cm土层的土壤全氮和颗粒氮含量,而土壤矿物结合态氮含量没有显著差异,NTS和RTS则同步提高了0~10 cm土层的土壤全氮、颗粒氮及矿物结合态氮含量(P0.05)。综上所述,免耕和旋耕提高了土壤全氮及其组分在表层土壤中的分布,翻耕则在较深土层更具优势,但翻耕阻碍了耕层土壤矿物结合态氮的积累,增加了氮素损失风险。     

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     

Effect of nitrogen fertilization on nitrogen dynamics in oilseed rape using 15N‐labeling field experiment

In order to optimize nitrogen (N) fertilization and to reduce the environmental impact of oilseed rape without decreasing yield, a clearer understanding of N dynamics inside the plant is crucial. The present investigation therefore aimed to study the effects of different N‐application rates on the dynamics of N uptake, partitioning, and remobilization. The experiment was conducted on winter oilseed rape (Brassica napus L. cv. Capitol) under three levels of N input (0, 100, and 200 kg N ha^–1) from stem elongation to maturity using ¹⁵N‐labeling technique to distinguish between N uptake and N retranslocation in the plant. Nitrogen fertilization affected the time‐course of N uptake and also the allocation of N taken up from flowering to maturity. Most pod N came from N remobilization, and leaves accounted for the largest source of remobilized N regardless the N‐application rate. However, the contribution of leaves to the remobilized N pool increased with the N dose whereas the one of taproot decreased. Stems were the main sink for remobilized N from stem elongation to flowering. Leaves remained longer on N200 than on N0 and N100 plants, and N concentration in fallen leaves increased with the N treatment and in N100 plants along an axial gradient from the basal to the upper leaves. Overall, these results show that the timing of N supply is more crucial than the N amount to attain a high N efficiency.     

Response of soil microbial communities and the production of plant-available nitrogen to a two-year rainfall manipulation in the New Jersey Pinelands

Projected changes in precipitation patterns in the northeastern U.S. may alter soil moisture dynamics and cause a shift in the structure and function of soil microbial communities. We studied the potential for such changes by manipulating annual precipitation amount in an oak-pine forest of the New Jersey Pinelands. During a two-year field study we tested the effects of a complete rain exclusion, as well as a doubling of rainfall, on soil microbial biomass, community composition (phospholipid fatty acid analysis) and the production of plant-available nitrogen (nitrogen mineralization + amino-acid production). We found that neither microbial biomass nor community composition was affected by the experimental manipulations. Despite having studied the organic horizon, the relatively high sand content appeared to influence this response by limiting the extent to which soil moisture increased in response to elevated rainfall. Furthermore, a strong correlation between soil moisture and the physiological status of Gram-negative bacteria suggested that soil microbes in the New Jersey Pinelands are well adapted to soil drying. We observed a sustained accumulation of ammonium in drought plots that was more than four times the value of all other treatments after one year. The relationship between soil moisture and nitrogen mineralization changed with season, suggesting that the effect of changing rainfall patterns on nitrogen cycling will depend upon microbial physiological demand and substrate diffusion. Based on available estimates of foliar N concentration in the New Jersey Pinelands, we conclude that neither the accumulation of ammonium in drought plots, nor the changes in nitrogen mineralization rates in response to high and low soil moisture will affect plant nitrogen demand. However, if the ammonium pool in dry soil had been mobilized by precipitation, a shift towards a higher bacteria:fungi ratio - and therefore higher nitrogen mineralization rates - may have occurred.     

Effect of plant age on in-soil decomposition and nitrogen content of sunn hemp tissue

ABSTRACT

The effects of plant age at the time of mowing on sunn hemp (Crotalaria juncea L.) tissue decomposition, nitrogen (N) release, and fiber content in Krome very gravelly loam were assessed. Combined leaf and stem tissue from 42-, 77- or 112-day-old sunn hemp plants was placed in mesh bags and buried below the soil surface in the field. Bags were removed bi-weekly and dry weights, N concentration, acid detergent fiber (ADF) and neutral detergent fiber (NDF) concentrations in buried sunn hemp tissues were determined. There was a rapid decrease plant tissue dry weight during the first 14 days after tissue was buried, followed by a slow gradual decrease. The amount N per hectare was much lower for 42-day-old than 112-day-old sunn hemp. Tissue of the youngest plants decomposed the quickest. Forty two-day-old tissue had a higher N concentration, N mineralization rate, and lower NDF and ADF than 77- or 112-day-old tissue. Mowing and soil incorporation of a 42-day-old instead of a 77- to 112-day-old sunn hemp cover crop prior to planting a cash crop can be beneficial for a fast-growing cash crop planted soon after soil incorporation of the cover crop.     

保护性耕作对土壤微团聚体碳、氮分布的影响

以7年不同耕作的定位试验为研究对象,研究了深松、旋耕、免耕等保护性耕作对关中土小麦-玉米轮作条件下微团聚体分布以及微团聚体中有机碳和全氮含量的影响。结果表明,秸秆粉碎旋耕、秸秆覆盖深松处理提高了特征微团聚体的组成比例,而秸秆还田+传统耕作和免耕处理对特征微团聚组成比例的影响较小。与传统耕作比较,旋耕、深松处理均能提高较大粒级微团聚体中(0.050~.25 mm和0.010~.05 mm)有机碳及全氮含量,而免耕使0.010~.05 mm微团聚体中的有机碳和全氮含量有所降低;旋耕、深松和免耕对小粒级微团聚体(0.01 mm)中的有机碳和全氮含量影响较小。相关分析表明,土壤有机碳与0.050~.25 mm和0.010~.05 mm粒级微团聚体中的有机碳、全氮之间均显著正相关,而与0.01 mm粒级微团聚体的有机碳、全氮含量不相关;土壤全氮与0.05~0.25 mm粒级的全氮、有机碳显著相关。0.010~.05 mm粒级微团聚体的碳、氮与0.050~.25 mm粒级微团聚体的碳、氮间显著正相关,而0.01 mm粒级微团聚体的碳、氮与其它粒级的碳、氮间不相关。从土壤微团聚体中碳、氮的分布考虑,旋耕、深松是当地较理想的耕作方式。     

Effect of nitrogen fertilization and irrigation on soil microbial activities and population dynamics — a field study

In a field experiment, net nitrogen (N) mineralization and immobilization were studied in relation to: 1) population dynamics and activities of N-metabolizing soil microbial communities, 2) changes in substrate-induced respiration (SIR) and 3) potential urease acitvity. Nitrogen fertilization (80 kg NO₃-N ha^-1) without irrigation induced additional N mineralization up to 280 kg N ha^-1. Net N-mineralization was weakly correlated to cell numbers of ammonifying and NH₄⁺-oxidizing microorganisms. Potential urease activity, respiration activity, and substrate-induced respiration activity were not correlated with the amount of mineralized nitrogen. Irrigation significantly increased potential urease activity of the soil microflora. Substrate induced respiration activity and basal respiration activity of the soil microflora were highest in the unfertilized and non irrigated treatment. But greatest differences were detected between the two sampling dates. NO₂^--oxidizing and ammonifying microbial populations increased, while populations of NH₄⁺-oxidizing and denitrifying microorganisms decreased with time. The results of this study demonstrate the interaction of nitrogen fertilizer application and irrigation on population dynamics of N-transforming soil microorganisms and microbial activities under field conditions. Detailed microbiological investigations of this type improve our understanding of nitrogen transformations in soil and suggest possible reasons of nitrogen losses, so that N fertilizer can be used more effectively and N losses be reduced.