Improving dryland cropping system nitrogen balance with no‐tillage and nitrogen fertilization

Studies on N balance due to N inputs and outputs and soil N retention to measure cropping system performance and environmental sustainability are limited due to the complexity of measurements of some parameters. We measured N balance based on N inputs and outputs and soil N retention under dryland agroecosystem affected by cropping system and N fertilization from 2006 to 2011 in the northern Great Plains, USA. Cropping systems were conventional tillage barley (Hordeum vulgaris L.)–fallow (CTB‐F), no‐tillage barley–fallow (NTB‐F), no‐tillage barley–pea (Pisum sativum L.) (NTB‐P), and no‐tillage continuous barley (NTCB). In these cropping systems, N was applied to barley at four rates (0, 40, 80, and 120 kg N ha^?1), but not to pea and fallow. Total N input due to N fertilization, pea N fixation, soil N mineralization, atmospheric N deposition, nonsymbiotic N fixation, and crop seed N and total N output due to grain N removal, denitrification, volatilization, N leaching, gaseous N (NO_x) emissions, surface runoff, and plant senescence were 28–37% greater with NTB‐P and NTCB than CTB‐F and NTB‐F. Total N input and output also increased with increased N rate. Nitrogen accumulation rate at the 0–120 cm soil depth ranged from –32 kg N ha^?1 y^?1 for CTB‐F to 40 kg N ha^?1 y^?1 for NTB‐P and from –22 kg N ha^?1 y^?1 for N rates of 0 kg N ha^?1 to 45 kg N ha^?1 y^?1 for 120 kg N ha^?1. Nitrogen balance ranged from 1 kg N ha^?1 y^?1 for NTB‐P to 74 kg N ha^?1 y^?1 for CTB‐F. Because of increased grain N removal but reduced N loss to the environment and N fertilizer requirement as well as efficient N cycling, NTB‐P with 40 kg N ha^?1 may enhance agronomic performance and environmental sustainability while reducing N inputs compared to other management practices.     

Soil organic carbon and nitrogen in a Minnesota soil as related to tillage, residue and nitrogen management

Soil organic carbon (SOC) and nitrogen (N) are directly influenced by tillage, residue return and N fertilization management practices. Soil samples for SOC and N analyses, obtained from a 23-year field experiment, provided an assessment of near-equilibrium SOC and N conditions. Crops included corn (Zea mays L.) and soybean [Glycine max L. (Merrill)]. Treatments of conventional and conservation tillage, residue stover (returned or harvested) and two N fertilization rates were imposed on a Waukegan silt loam (fine-silty over skeletal, mixed, superactive, mesic Typic Hapludoll) at Rosemount, MN. The surface (0–20 cm) soils with no-tillage (NT) had greater than 30% more SOC and N than moldboard plow (MB) and chisel plow (CH) tillage treatments. The trend was reversed at 20–25 cm soil depths, where significantly more SOC and N were found in MB treatments (26 and 1.5 Mg SOC and N ha⁻¹, respectively) than with NT (13 and 1.2 Mg SOC and N ha⁻¹, respectively), possibly due to residues buried by inversion. The summation of soil SOC over depth to 50 cm did not vary among tillage treatments; N by summation was higher in NT than MB treatments. Returned residue plots generally stored more SOC and N than in plots where residue was harvested. Nitrogen fertilization generally did not influence SOC or N at most soil depths. These results have significant implications on how specific management practices maximize SOC storage and minimize potential N losses. Our results further suggest different sampling protocols may lead to different and confusing conclusions regarding the impact of tillage systems on C sequestration.     

The characteristics of overland flow under varied tillage and cropping systems in Sichuan Basin, China

Data from runoff plots operated over a five year period show that significantly less overland flow is generated with a seasonal no-till ridge system than with contour tillage or straight tillage systems. Seasonal no-till ridge is the optimum system for increasing the availability of water for rainfed agriculture on the dryland soils in the hilly area of Sichuan Province, China.     

Tillage and residue management effects on β-glucosaminidase activity in soils

There is an increasing interest in assessing the effects of tillage systems and residue management on biochemical processes, especially enzyme activities, of soils. This study was carried out to investigate the effects of three tillage systems (no-till, chisel plow and moldboard plow) and four residue placements (bare, normal, mulch and double mulch) on the activity of N-acetyl-β-glucosaminidase (NAGase, EC 3.2.1.30) involved in C and N cycling in soils. The activity values were significantly affected by tillage and residue management practices, being greatest in soils with no-till/double mulch and least with no-till/bare and moldboard/normal. Also, they were the highest under no-till/ double mulch-treated soils. Linear regression analyses showed that the activity of NAGase was significantly correlated with organic C in the surface soils (r=0.89***) and with organic C content at different depths (r=0.97***). The NAGase activity values were significantly correlated with the arylamidase activity values of the soils (r=0.63**), suggesting that tillage and residue management practices have similar impacts on the activities of these enzymes. The activity of this enzyme decreased markedly with increasing depth of the surface soil (0-15 cm) of the no-till/ double mulch-treated plots.     

Soil microbial biomass and mineralization of carbon and nitrogen in ecological, integrated and conventional forage and arable cropping systems

 In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage (FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring grain plots and incubated for 449 days at controlled temperature (15  °C) and moisture content (50% water-holding capacity). There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of microbial biomass C and N, microbial quotient (C_mic/C_org), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient (qCO₂) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized that the lower qCO₂ values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations, but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced tillage intensity in the ECO-ARABLE rotation. Received: 28 October 1998     

Tillage effect on partial budget analysis of cropping intensification under dryland farming in Punjab,Pakistan

A 2-year research experiment was laid out in a split-plot design with moldboard ploughing (MP, control) and minimum tillage (MT) as main plots and crop sequences as sub-plots. Summer-winter cropping sequences were fallow-wheat (Triticum aestivum L.) (FW, control), mungbean (Vigna radiata L.)-wheat (MW), sorghum (Sorghum bicolor L.)-wheat (SW), green manure-wheat (GW) and mungbean-chickpea (MC) (Cicer arietinum L.). During 2010–2011, in summer, mungbean crop produced the highest above ground biomass in mungbean-chickpea sequence under MP tillage (4.24 Mg ha^–1 mungbean) and in mungbean-wheat sequence under MT tillage (4.11 Mg ha^–1 mungbean). In winter, chickpea gave the highest biomass in mungbean-chickpea sequence under both tillage systems. During 2011–2012, mungbean produced the highest above ground biomass in mungbean-wheat sequence under MT tillage (4.43 Mg ha^–1 mungbean) and in both the mungbean-chickpea and mungbean-wheat sequences under MP tillage (4.24 and 4.17 Mg ha^–1 mungbean, respectively). In winter, fallow-wheat sequence gave the highest biomass in both tillage systems. The differences in grain yields were statistically non-significant in both the years. The gross marginal benefit ranged between ?190 and 548$ ha^–1 in the first year and ?165 and 1124$ ha^–1 in the second year. The net benefit values were the highest in mung-chickpea sequence under both tillage systems (1008 and 596$ ha^–1 under MP and MT, respectively), which gave cost–benefit ratios of 5.45 and 3.68, respectively. Use of legume-based cropping sequences is a sustainable and cost-effective practice in drylands of northern Punjab, Pakistan.     

Free amino sugar reactions in soil in relation to soil carbon and nitrogen cycling

Amino sugars represent a major constituent of microbial cell walls and hydrolyzed soil organic matter. Despite their potential importance in soil nitrogen cycling, comparatively little is known about their dynamics in soil. The aim of this study was therefore to quantify the behaviour of glucosamine in two contrasting grassland soil profiles. Our results show that both free amino sugars and amino acids represented only a small proportion of dissolved organic N and C pool in soil. Based upon our findings we hypothesize that the low concentrations of free amino sugars found in soils is due to rapid removal from the soil solution rather than slow rates of production. Further, we showed that glucosamine removal from solution was a predominantly biotic process and that its half-life in soil solution ranged from 1 to 3 h. The rates of turnover were similar to those of glucose at low substrate concentrations, however, at higher glucosamine concentrations its microbial use was much less than for glucose. We hypothesized that this was due to the lack of expression of a low affinity transport systems in the microbial community. Glucosamine was only weakly sorbed to the soil's solid phase (K_d=6.4±1.0) and our results suggest that this did not limit its bioavailability in soil. Here we showed that glucosamine addition to soil resulted in rapid N mineralization and subsequent NO₃⁻ production. In contrast to some previous reports, our results suggest that free amino sugars turn over rapidly in soil and provide a suitable substrate for both microbial respiration and new biomass formation.     

Effects of cropping systems on nitrogen,phosphorus and potassium forms and soil organic carbon in a Gray Luvisol

The effects of up to 23 years of agricultural cropping of a boreal forest soil on soil organic carbon (SOC) and N, P, and K pools were studied. The cropping systems studied were: (a) continuous barley, (b) continuous forage bromegrass, (c) continuous forage legume, and (d) barley/grass-legume forage rotation. Continuous bromegrass increased while other cropping systems decreased SOC in the surface soil. Kjeldahl N in soil approximately followed the trend in SOC. The net gain in N under continuous grass was attributed mostly to nonsymbiotic N fixation. Changes in SOC content appeared to be also influenced by cropping and tillage frequencies. Changes in fixed (intercalary) ammonium were small. There was no measurable change in total P, in part, because input was only slightly higher than crop offtake. Organic P increased under continuous bromegrass, and tended to decrease under continuous legume. The C/N and C/P ratios of soil organic matter decreased slightly with cropping. Exchangeable K (K_ex) was decreased by cropping systems containing a legume crop to a greater extent than those without a legume crop. Most of the decrease occurred in the 0–15 cm depth. Nitric acid extractable K was not affected by cropping. Since net loss of K_ex to 30 cm depth was substantially less than crop offtake, it is suggested that subsoil K reserves and matrix K were supplying a major portion of the crops' K requirement. It is concluded that the effects of cropping systems on SOC, N, P and K are influenced by crop type, and cropping and tillage frequencies.     

华北平原不同种植制度对粮食作物氮素利用和土壤氮库的影响

冬小麦-夏玉米一年两熟是华北平原粮食作物的主要种植制度,存在氮肥利用率低、土壤氮素过量累积问题。为探索华北平原氮素高效利用的适宜种植制度,采用15N示踪技术,基于3 a田间定位试验,对一年两熟冬小麦-夏玉米的常规水氮和优化水氮、两年三熟冬小麦-夏玉米-春玉米与冬小麦-夏大豆-春玉米及一年一熟春玉米3种种植制度的作物产量、15N利用率、氮素去向和土壤氮库表观平衡进行研究。结果表明,两年三熟的冬小麦-夏玉米-春玉米产量为32 248.52 kg/hm2,分别比一年两熟和一年一熟提高22.16%和52.88%;15N利用率为33.36%,比一年一熟提高26.12%。3种种植制度的氮肥去向最高为土壤残留,其次为作物吸收和损失,两年三熟冬小麦-夏玉米-春玉米的作物吸氮量最高为151.82 kg/hm2,土壤氮库表观盈余量为21.22 kg/hm2,显著低于其他种植制度。综合分析,冬小麦-夏玉米-春玉米两年三熟在稳产高产和提高氮素利用率上具有可持续的潜力,是华北平原未来较为理想的种植制度。     

Soil carbon, nitrogen, pH, and earthworm density as influenced by cropping practices in the Inland Pacific Northwest

Farmers within the Inland Pacific Northwest are gradually transitioning to direct seed (DS) practices that reduce soil disturbance and increase surface residue compared to conventional tillage (CT). Despite this transition the impacts of DS practices on soil properties and fauna in commercial fields has been little studied in the region. During the spring and summer of 2002 and 2003 we compared soil organic carbon (SOC), total nitrogen (TN), pH, and earthworm and cocoon densities in CT and DS fields planted to either spring wheat or pea in the Palouse region of northern Idaho. In 2002 mean SOC within the 0–10-cm depth was greater in DS fields (2.05%) than at the same depth in CT fields (1.79%), however SOC within the 30–40-cm depth was lower under DS compared to CT. Mean soil pH within the 0–10-cm depth was 5.35 under DS and 5.61 under CT indicating that pH stratification can occur when tillage is reduced. Tillage effects on SOC, TN, and pH were not found in 2003. Tillage also did not significantly influence earthworm densities, which averaged 39 individuals m⁻² in 2002 and 57 individuals m⁻² in 2003. Correlations were detected in 2003 DS fields between soil properties (SOC and TN) and earthworm and cocoon densities at depths above 30 cm while in 2002 correlations in DS fields occurred with cocoon density, but not with earthworm density. Direct seed management can increase near-surface SOC and TN concentrations compared to CT practices, however, SOC concentrations deeper in the soil appear to remain the same or possibly decrease. Higher SOC and TN near the soil surface, as found in DS fields, appear to promote greater earthworm densities, which may improve long-term soil productivity.     

不同蔬菜种植模式对土壤淋溶水总氮、总磷和COD的影响

以中国农业大学曲周实验站始于2002年的日光温室有机蔬菜长期定位试验为基础,采用渗漏计装置收集地下1 m深淋溶水,通过测定2014年春茬茄子与秋茬芹菜土壤淋溶水总氮、总磷和化学需氧量(COD),研究不同蔬菜种植模式(有机、综合、常规)下土壤养分淋失情况。结果表明:有机模式总氮淋失量两茬蔬菜之和为137.02 kg·hm~(-2),分别比综合和常规模式减少12.0%和25.9%;总磷淋失量两茬蔬菜之和为18.23 kg·hm~(-2),分别比综合和常规模式高51.2%和119.9%;淋溶水COD两茬蔬菜之和为856.99 kg·hm~(-2),分别比综合和常规模式高32.4%和3.1%。3种模式下不同时期淋溶水总氮、总磷与COD变化趋势差异显著。春茬茄子总氮淋失量前期维持在较高水平,追肥后出现峰值,之后迅速降低,进入6月份后一直在较低水平波动;总磷淋失量变化相对平缓,呈先增加后减小的变化趋势,6—7月间达到峰值;淋溶水COD前期稍有降低,追肥前达到最低值,进入5月份后到茄子季结束呈现逐渐上升的趋势。综上,有机种植模式在减少氮素淋失方面较综合和常规模式表现出优势,但会显著增加磷素淋失风险,并在一定程度上提高淋溶水COD。     

Effects of 5 years of corn residue grazing and baling on nitrogen cycling,soil compaction,and wind erosion potential

Abstract

Corn residue grazing can provide a valuable and cost effective means of feeding cattle and is a common practice in most corn producing states. Mechanical means of residue removal (baling) is also often practiced as a means of harvesting cattle feed. However, there are concerns about the effects of management practices that remove crop residue on soil processes such as compaction, aggregation, and N cycling. To study these concerns, an experiment with four treatments including control, light grazing, heavy grazing, and baling was carried out for 5?years at the University of Nebraska-Lincoln Water Resources Field Laboratory near Brule, NE. Soil penetration resistance was measured after 3, 4, and 5?years of residue removal. Wind erodible fraction, mean weight diameter of dry aggregates, and soil total N were measured after 5?years. Corn yields were determined throughout the study. Results indicate that light grazing showed little or no difference from the no residue removal treatment, but heavy grazing and baled treatments often had higher penetration resistance, indicating that high rates of residue removal may increase risks of soil compaction. However, compaction did not appear to be cumulative over time. No significant differences were observed in wind erodible fraction and dry aggregate mean weight diameter. However, there were trends that suggest heavy grazing and baling may, in the long term, reduce dry aggregate stability, increasing wind erosion potential. Results also show that in the surface 0–2.5?cm grazing animals may increase soil total N and that baling residue may decrease soil N content. There was no impact on corn yields throughout the study. Overall, corn residue grazing and baling appear to have little or no adverse effects on soil compaction, aggregation, or nitrogen cycling after 5?years.     

Cropping sequence and nitrogen fertilizer effects on the productivity and quality of malting barley and soil fertility in the Ethiopian highlands

The productivity and quality of malting barley were evaluated using factorial combinations of four preceding crops (faba bean, field pea, rapeseed, and barley) as main plots and four nitrogen fertilizer rates (0, 18, 36, and 54 kg N ha^?1) as sub-plots with three replications at two sites on Nitisols of the Ethiopian highlands in 2010 and 2011 cropping seasons. Preceding crops other than barley and N fertilizer significantly improved yield and quality of malting barley. The highest grain yield, kernel plumpness, protein content, and sieve test were obtained for malting barley grown after faba bean, followed by rapeseed and field pea. Nitrogen fertilizer significantly increased yield, protein content, and sieve test of malting barley. All protein contents were within the acceptable range for malting quality. Inclusion of legumes in the rotation also improved soil fertility through increases in soil carbon and nitrogen content. We conclude that to maximize yield and quality of malting barley, it is critical to consider the preceding crop and soil nitrogen status. Use of appropriate break crops may substitute or reduce the amount of mineral N fertilizer required for the production of malting barley at least for one season without affecting its quality.     

玉米—花生混作体系中不同施氮水平对花生铁营养及固氮的影响

盆栽试验结果表明,不同氮水平条件下玉米—花生混作可明显改善花生铁营养。与单作相比,混作花生新叶叶绿素SPAD值明显提高,新叶活性铁浓度提高12.4%～27.1%,同时花生根瘤数和固氮酶活性显著增加。在本试验种植密度下,施氮水平和种植方式对单株花生生物量无显著影响,而施氮对玉米根际土壤活性铁浓度的提高有一定的促进作用,并且花生根瘤数和固氮酶活性受施氮水平影响较大。说明石灰性土壤上玉米—花生混作对花生铁营养改善及提高花生的固氮能力具有重要作用;施氮水平对花生铁营养影响不大,但随施氮量增加对花生共生固氮有抑制作用。     

冬季作物-双季稻轮作种植模式氮、磷、钾养分循环与产量可持续性特征

研究分析农业生态系统NPK养分循环和产量的可持续性,对实现养分资源优化管理和农业可持续发展具有重要意义。基于长期冬季作物-双季稻轮作种植定位试验,分析了2004—2017年冬闲-双季稻、马铃薯-双季稻、紫云英-双季稻、黑麦草-双季稻、油菜-双季稻等轮作种植模式早、晚稻产量的可持续性与稳定性;采用投入产出法（Input-Output Analysis）分析不同轮作种植模式NPK养分循环与平衡状况。结果表明：1）黑麦草-双季稻模式早稻产量变异系数与可持续性指数分别为0.09和0.81,说明稻田冬种黑麦草有利于促进早稻产量稳定性和可持续性的提高;油菜-双季稻模式晚稻产量变异系数与可持续性指数分别为0.07和0.82,说明稻田冬种油菜有益于晚稻产量稳定性和可持续性的提高;2）长期冬季作物-双季稻轮作种植未影响水稻产量和糙米NPK养分含量（P>0.05）;3）在稻田轮作种植周年内目前的NPK投入水平下,黑麦草-双季稻、紫云英-双季稻、油菜-双季稻、马铃薯-双季稻等模式均存在严重的K亏缺现象,K亏缺量分别为375.70 kg（K）·hm^-2、279.98 kg（K）·hm^-2、363.71 kg（K）·hm^-2、93.74 kg（K）·hm^-2;黑麦草-双季稻、紫云英-双季稻、油菜-双季稻等模式均在冬季作物种植季存在严重的K亏缺现象,K亏缺量分别为240.07 kg（K）·hm^-2、89.57 kg（K）·hm^-2、140.08 kg（K）·hm^-2,但马铃薯-双季稻模式在马铃薯种植季K盈余为255.21 kg（K）·hm^-2;同时黑麦草-双季稻模式和紫云英-双季稻模式均存在冬季作物种植季存在N亏缺,N亏缺量分别为59.47 kg（N）·hm^-2和89.17 kg（N）·hm^-2;油菜-双季稻模式和马铃薯-双季稻模式在晚稻种植季均存在严重的K亏缺现象,K亏缺量分别为45.93 kg（K）·hm^-2、124.33 kg（K）·hm^-2。冬季作物-双季稻轮作种植模式的养分循环是冬季作物和外部投入的NPK肥料共同驱动的养分循环,建议科学管理冬季作物和3季的NPK养分投入。     

Effects of cropping systems on soil organic matter in a pair of conventional and biodynamic mixed cropping farms in Canterbury, New Zealand

Effects of cropping systems on soil organic matter (SOM) in a pair of conventional and biodynamic mixed cropping farms were investigated. Soil samples (0–75 and 75–150-mm depths) were analysed for total carbon (TC), total nitrogen (TN), microbial biomass C (BC) and microbial biomass N (BN), and sequentially extracted for labile and stable SOM using cold water, hot water, acid mixtures and alkalis. In the biodynamic farm, TC and TN decreased with increasing period of cropping but the reverse occurred under pastures. These were not shown in soils from the conventional farm, probably due to N fertilizer additions. Under pastures, increases in SOM were attributed to greater biological N₂ fixation and the return of plant residues and excreta from grazing animals. Overall, sensitive SOM quality indicators found for labile SOM were BN, BN:TN and HC:TC, and for stable SOM were HCl/HFC, HCl/HFC:TC, humin C, humin N, humin C:TC and humin N:TN. The BN and BN:TN were better indicators than BC and BC:TC. The humin fraction was strongly related to both labile and stable SOM fractions suggesting that humin contained non-extractable strongly complexed SOM components with mineral matter and also non-extractable plant and microbial residual components. Received: 10 October 1996     

稻麦轮作农田氮素循环的DNDC模型分析

基于长江中下游稻麦轮作体系的氮肥施用田间试验,采用Denitrification- Decomposition model (DNDC) 模型研究了气候条件、土壤属性、农业管理等输入因素的不确定性对子粒产量、作物氮吸收、氨挥发、N2O排放等预测结果的影响。结果显示:采用DNDC模型模拟的土壤氨挥发速率和N2O排放通量与田间实测结果较为吻合,氨挥发通量模拟值与实测值相关系数为0.688,N2O排放通量模拟值与实测值相关系数为0.528,均达极显著水平,表明DNDC模型预测农田土壤氮素具有较高可信度。模拟结果显示,气温和氮肥用量是影响作物产量和吸氮量的关键因素;土壤氨挥发主要受氮肥品种影响,并随氮肥用量增加而增加;土壤N2O排放主要受温度、土壤pH值、土壤有机碳含量的影响。为使DNDC能更有效地估算氨挥发和N2O排放,有必要获取更翔实的资料以减少输入数据的不确定性。     

稻麦轮作区保护性耕作条件下氮肥对水稻生长发育和产量的调控效应

20062~008年在四川省广汉市开展了保护性耕作措施下水稻氮肥调控试验,设置不同秸秆还田量(0、6000、12000 kg/hm2)、施氮量水平(0、1502、10 kg/hm2)以及氮素分配比例(6∶2∶2、6∶3∶1、8∶2)。结果表明,和施N 150 kg/hm2相比,N 210 kg/hm2处理水稻分蘖力、干物质积累量、开花期的植株个体和群体质量均有升高,花后茎鞘贮藏物质的输出及光合物质积累量增加,子粒产量提高7.3%。在施N 150 kg/hm2水平和基肥∶蘖肥∶穗肥=6∶2∶2分配比例下,与旋耕无麦秸还田处理相比,免耕秸秆还田与否对水稻茎蘖消长、干物质积累及子粒产量影响较小,但花后绿叶功能期延长,光合产物积累在产量形成中所占比例增加。在施N 210 kg/hm2水平和基肥∶蘖肥∶穗肥=6∶3∶1分配比例下,免耕还田麦秸量从6000 kg/hm2增加至12000 kg/hm2,水稻分蘖力明显增强,干物质积累量增大,开花期个体和群体质量提高,单位面积穗数和穗实粒数增多,产量增加4.1%;将氮肥分配比例由6∶3∶1变为8∶2,即增加基肥用量,减少中后期的氮素供应会导致分蘖高峰后分蘖大量死亡,有效穗数降低,穗粒数减少,产量下降。以上结果说明,氮素的充分供应是保护性耕作水稻获得高产的重要前提和基础,适当提高麦秸还田量、增加中后期氮素供应,能提高氮素利用率及分蘖成穗率和结实率,利于稳产高产。     

长期施肥对小麦-玉米作物系统土壤腐殖质组分碳和氮的影响

通过对华北平原小麦–玉米轮作农田生态系统18年田间施肥试验,研究了长期不同施肥处理对耕层（0—20 cm）土壤腐殖质及活性腐殖质组分碳和氮的影响。试验设化肥NPK不同组合（NPK、NP、NK、PK）,全部施用有机肥（OM）,一半有机肥+化肥NPK（1/2OMN）及不施肥（CK）共7个处理。结果表明,各施肥处理均能在不同程度上增加土壤腐殖质（胡敏酸、富里酸和胡敏素）及活性腐殖质（活性胡敏酸和活性富里酸）组分碳和氮含量,提高可浸提腐殖质（胡敏酸和富里酸）及活性腐殖质组分碳和氮分配比例;但施肥对土壤活性腐殖质组分碳和氮含量的增加率均分别高于腐殖质组分碳和氮。各处理土壤腐殖质及活性腐殖质组分碳和氮含量均为OM处理最高,且有机肥与化肥NPK配施高于单施化肥各处理;而化肥处理中NPK均衡施用效果最好。说明施用有机肥、有机肥与化肥NPK配施及化肥NPK均衡施用是增加土壤腐殖质及活性腐殖质组分碳和氮的关键;活性腐殖质组分碳和氮较腐殖质组分碳和氮对施肥措施的响应更灵敏。     

Biological and physical effects of non-native earthworms on nitrogen cycling in riparian soils

Global nitrogen cycling is being altered by anthropogenic disturbances including invasion by non-native species. European and Asian earthworms have invaded northern temperate forests in North America with dramatic consequences for litter thickness, forest floor plant diversity, and soil nitrogen cycling. Invasive earthworms present at the boundary of terrestrial and aquatic ecosystems (i.e., riparian zones) may alter the flux of nitrogen into adjacent aquatic ecosystems. We examined how nitrogen cycling in riparian soil responds to amendments of invasive earthworms or artificial earthworm burrows. In earthworm-free riparian plots (0.25 m²), we established treatments of invasive earthworms (60 g fresh mass·m⁻²), artificial burrows (120 m⁻²), or control plots and sampled the plots after 30 days. Before and after treatment application we measured major soil characteristics (water-filled pore space, organic matter, and pH), nitrogen pools (exchangeable NH₄⁺ and NO₃⁻), and nitrogen transformation rates (net N-mineralization, net nitrification, and denitrification). Exchangeable NH₄⁺ and NO₃⁻ changed through time but did not differ among treatments. Net N-mineralization and net nitrification rates did not change through time and were similar across all treatments. However, denitrification rates in plots with added earthworms were 4 times greater than rates in control and burrow-only plots, which represents a large rapid increase in gaseous nitrogen flux out of these riparian soils. For all response variables, artificial burrows responded similarly to control plots, suggesting that earthworm biological activity (i.e., feeding, excretion, and mucus production) rather than physical effects (i.e., burrowing and soil aeration) drove the changes in nitrogen cycling. Examination of soil nitrogen pool and flux measurements suggest that this increase in denitrification was coupled with NH₄⁺ consumption by nitrifying bacteria, but future studies are needed to confirm this hypothesis. We conclude that the activity of invasive earthworms in riparian zones can increase the flux of N out of riparian zones, but the hydrologic context of the riparian zone (e.g., pore-water residence time) ultimately controls whether denitrification or nitrate leaching is the dominant flux of N.