Soil residual nitrogen under various crop rotations and cultural practices

Crop rotation and cultural practice may influence soil residual N available for environmental loss due to crop N uptake and N immobilization. We evaluated the effects of stacked vs . alternate‐year crop rotations and cultural practices on soil residual N (NH₄‐N and NO₃‐N contents) at the 0–125 cm depth, annualized crop N uptake, and N balance from 2005 to 2011 in the northern Great Plains, USA. Stacked rotations were durum (Triticum turgidum L.)–durum–canola (Brassica napus L.)–pea (Pisum sativum L.) (DDCP) and durum–durum–flax (Linum usitatissimum L.)–pea (DDFP). Alternate‐year rotations were durum–canola–durum–pea (DCDP) and durum–flax–durum–pea (DFDP). Both of these are legume‐based rotations because they contain legume (pea) in the crop rotation. A continuous durum (CD) was also included for comparison. Cultural practices were traditional (conventional tillage, recommended seeding rate, broadcast N fertilization, and reduced stubble height) and improved (no‐tillage, increased seeding rate, banded N fertilization, and increased stubble height) systems. The amount of N fertilizer applied to each crop in the rotation was adjusted to soil NO₃‐N content to a depth of 60 cm observed in the autumn of the previous year. Compared with other crop rotations, annualized crop biomass N was greater with DCDP and DDCP in 2007 and 2009, but was greater with DDFP than DCDP in 2011. Annualized grain N was greater with DCDP than CD, DFDP, and DDFP and greater in the improved than the traditional practice in 2010 and 2011. Soil NH₄‐N content was greater with CD than other crop rotations in the traditional practice at 0–5 cm, but was greater with DDCP than CD and DDFP in the improved practice at 50–88 cm. Soil NO₃‐N content was greater with CD than other crop rotations at 5–10 cm, but was greater with CD and DFDP than DCDP and DDCP at 10–20, 88–125, and 0–125 cm. Nitrate‐N content at 88–125 and 0–125 cm was also greater in the traditional than the improved practice. Nitrogen balance based on the difference between N inputs and outputs was greater with crop rotations than CD. Increased N fertilization rate increased soil residual N with CD, but legume N fixation increased N balance with crop rotations. Legume‐based crop rotations (all rotations except CD) reduced N input and soil residual N available for environmental loss, especially in the improved practice, by increasing crop N uptake and N immobilization compared with non‐legume monocrop.     

综合农艺管理促进夏玉米氮素吸收、籽粒灌浆和品质提高

  【目的】  夏玉米生产中存在种植密度偏低、施肥不合理、玉米收获时间早等问题,造成产量和品质难以提高,经济效益偏低。研究适合黄淮海地区的综合农艺管理措施,以期改善夏玉米籽粒灌浆特性,提高籽粒品质和氮肥利用效率。  【方法】  本试验以郑单958为试材,在山东农业大学连续进行了两年田间试验,综合考虑施肥量、施肥时期、耕作方式、种植密度、收获时间等措施,设置4个处理:传统种植管理措施（对照,T1);高产高效措施 (T2,降低施肥量,优化施肥时期和种植密度,延迟收获);超高产管理措施 (T3,在T2的基础上增加施肥量和种植密度) ;高产高效优化措施 (T4,在T3的基础上适当降低种植密度和施肥量)。T1处理播前小麦秸秆覆盖和免耕,其他处理均为小麦秸秆还田和旋耕。从抽雄期至成熟期,每5天取一次样,测定籽粒干物质量和水分含量,计算灌浆和脱水速率,收获期测产。  【结果】  与T1处理相比,3个综合农艺管理措施均能提高夏玉米后期籽粒灌浆速率,延长籽粒灌浆期,增加粒重,提高产量和经济效益,同时改善籽粒品质。其中,两年产量均以T3处理最高,较T1处理显著增加46.0%～47.8%,其次是T2和T4,较T1处理分别显著增加14.9%～31.6%和25.9%～33.6%;氮肥偏生产力 (PFPN) 以T2和T4处理较高,较T1处理分别增加61.1%～84.5%和53.6%～62.9%。同时,T2和T4处理从籽粒最大含水量时到收获时的灌浆速率显著增加,后期籽粒脱水速率增加,收获时籽粒干重显著提高。优化综合农艺管理措施可改善籽粒品质,其中以T4处理籽粒品质最佳,2017年总淀粉含量和支链淀粉含量较T1处理分别显著增加4.5%和10.1%,直链淀粉含量显著下降7.6%,支链淀粉/直链淀粉增加0.4;可溶性糖和粗蛋白含量分别显著增加6.2%和16.3%;粗脂肪含量显著降低8%。综合农艺管理虽然会增加施肥次数,增加一定的人工投入,但玉米籽粒产量增加,最终的经济效益提高。T4处理经济效益最高,较T2和T3处理两年平均增加613和1084元/hm2。  【结论】  高产高效优化管理措施 (T4) 在超高产管理措施 (T3) 基础上,适当降低种植密度,减少化肥用量,能更有效促进夏玉米籽粒的后期灌浆,增加灌浆时间,促进植株干物质向籽粒的转运。虽然高产高效优化管理措施 (T4) 下产量比超高产管理 (T3)有所降低,但显著高于常规高产高效管理 (T2),且可明显提高玉米品质和肥料利用率,增加净收益。     

Tillage and crop residue management effects on losses of chemicals from soils

Tillage and crop residue management both influence the losses of nutrients and crop-protection chemicals from the soil to the aqueous environment. Tillage is performed to control weeds, to modify the soil structure and often to incorporate straw, which can no longer be burnt in European Community countries. The resulting changes in the soil alter both the pathways for water flow and the activities of microbes. This paper reviews their effects on water movement and the microbial and physico-chemical processes that influence the vulnerabilities of nutrients and crop-protection chemicals to leaching. It also suggests some possible options for limiting losses of these substances from the soil. There remains considerable scope for cooperation between tillage specialists and those with an interest in the management of nutrients and crop-protection chemicals.     

Predicting crop growth under different cropping and fertilizing management practices

Simulation models are widely used to make predictions of crop growth and yield, and soil carbon and nutrient dynamics under various agricultural practices and soil-climatic conditions. An analytical model of soil carbon and nutrient dynamics, K-model, was expanded to include a plant sub-model (K-Model-P). This allows for the prediction of short- and long-term crop growth, and soil carbon and nitrogen dynamics. The simulations for a short-term experiment (2 growing seasons) with three nitrogen application rates showed that K-Model-P correctly predicted the growth processes of above-ground plant biomass and grain yields. Predicted and measured daily accumulative biomass were significantly correlated, and differences were statistically insignificant. The simulation results for long-term experiments (70 years) of two crop rotations with three soil amendments showed that predicted and measured annual straw and grain yields were significantly correlated, with the differences of less than 13%. Annual crop straw and grain yields can be estimated by the model without significant errors. The agreement between the predicted daily growth and annual yields and experimental data illustrated that the K-Model-P can be used to produce reliable predictions for daily and annual crop growth.     

Dicyandiamide application improved nitrogen use efficiency and decreased nitrogen losses in wheat-maize crop rotation in Loess Plateau

Inhibition of nitrification as a mitigation tool to abate nitrogen (N) losses and improve N use efficiency (NUE) is a promising technology. Nitrification inhibitor (dicyandiamide, DCD) was evaluated in two consecutive wheat-maize rotations (2015–2017), with two different N fertilizer levels applied in wheat (160, 220 kg N ha^?1) and maize (180, 280 kg N ha^?1). More NH₄⁺-N contents (101% and 102% in wheat and 74% and 73% in maize) and less NO₃^–-N contents (37% and 43% in wheat and 46% and 57% in maize) were observed at both N levels treated with DCD compared to without DCD. Higher pH, lower EC and reduced NO₃^–-N accumulation were the other benefits of DCD. The NO₃^–-N accumulation within the 0–200 cm soil profile was significantly less at both N levels with DCD (66 mg kg^?1 and 121 mg kg^?1) compared to without DCD (96 mg kg^?1 and 169 mg kg^?1). Application of DCD also improved the growth and yield in both crops. Increase in NUE from 38% to 49% in wheat and 27% to 33% in maize with DCD at higher N level was also observed. Overall, the effectiveness of DCD in retarding the nitrification process was higher in wheat than maize.     

Developing disease-suppressive soils through crop rotation and tillage management practices

A field laboratory was established in Prince Edward Island, Canada, to determine the effects of 2- and 3-year crop rotations, with conventional and minimum tillage treatments, on the severity of soilborne diseases of potato. The 2-year rotation consisted of spring barley and potato (cv. ‘Russet Burbank’), and the 3-year rotation was barley (undersown with red clover), red clover and potato. Examination of potato stem, stolon, and tuber tissues revealed significantly (P=0.05) lower levels of canker and black scurf caused by Rhizoctonia solani, in plants grown in 3-year vs. 2-year rotations. The severity of dry rot (Fusarium spp.) and silver scurf (Helminthosporium solani) was significantly (P=0.05) lower in tubers from plots managed with 3-year rotations and minimum tillage practices. Potato tubers harvested from 3-year rotational soils were significantly (P=0.05) less diseased than those from 2-year rotational soils following inoculation with Phytophthora erythroseptica, causal agent of pink rot. In greenhouse experiments using field soils from 2- and 3-year rotations, we found that potato plants growing in 3-year rotational soils were significantly (P=0.05) less diseased than those growing in 2-year rotational soils following inoculation with P. erythroseptica. Analysis of root zone bacteria recovered from the rhizosphere (exoroot) and potato root tissues (endoroot) showed that the greatest antibiosis activity inhibiting the growth of soilborne pathogens in vitro occurred in bacterial isolates recovered from the endoroot tissues of 3-year rotation crops under minimum tillage management. Our evidence supports the view that soil agroecosystems can be modified through rotation and conservation tillage practices to improve disease suppression by enhancing the antibiosis abilities of endophytic and root zone bacteria (endo- and exoroot).     

Effects of repeated straw incorporation on crop fertilizer nitrogen requirements, soil mineral nitrogen and nitrate leaching losses

Abstract. The effects of straw disposal by burning and incorporation on soil and crop nitrogen (N) supply, were investigated on two light textured soils in central (ADAS Gleadthorpe) and eastern England (Morley Research Centre) over the period 1984 to 1995. Nitrogen balance calculations showed that after 11 years of contrasting straw incorporation versus burn treatments, the cumulative N returns in straw were c . 570kg/ha at Gleadthorpe and c . 330 kg/ha at Morley However, these N returns via straw incorporation were not reflected in increased total soil N levels in autumn 1994. There were no differences ( P > 0.05) between straw disposal treatments in autumn soil mineral N supply, readily mineralizable N or organic carbon. Similarly, there were no consistent differences between the treatments in terms of crop yield, crop N uptake or optimum fertilizer N rates. Fertilizer N applications of 200 kg N/ha/y increased topsoil organic carbon from 1.18 to 1.28% and total N content from 0.091 to 0.102% on the loamy sand textured soil at ADAS Gleadthorpe, but not at Morley. Previous fertilizer N applications increased the quantity of nitrate-N leached in drainage water by c . 20 kg/ha at Gleadthorpe and c . 60 kg/ha at Morley overwinter 1994/95, and by 10–20 kg/ha at both sites overwinter 1995/96. There was some indication overwinter 1994/95 that straw incorporation reduced nitrate-N leaching by 10–25 kg/ha, but there were no differences between treatments overwinter 1995/96.     

Nitrogen and phosphorus transformations as affected by crop residue management practices and their influence on crop yield

Abstract. A 15-year field experiment investigated crop residue management practices, with crop residue removal, burning and incorporation as the main treatments and nitrogen levels as subtreatments. The effects of crop residue management practices on rice and wheat yield were measured for 11 years. Surface soil samples were taken to study nitrogen and phosphorus immobilization/adsorption and their release under laboratory conditions. The field experiment indicated that residue burning and residue removal resulted in greater grain yields of rice (5.57 and 5.53 t/ha, respectively) and wheat (4.12 and 4.02 t/ha, respectively) than residue incorporation (4.51 t/ha rice and 3.72 t/ha wheat). Laboratory experiments indicated that by the addition of crop residues nitrogen and phosphorus were converted to unavailable forms through immobilization and adsorption, respectively.
Crop residue management practices were discontinued after 13 years and wheat and maize crops were grown in sequence. There were significantly greater yields of wheat (3.57 t/ha in 1992–93 and 3.6 t/ha in 1993–94) and of maize (2.1 t/ha in 1993) in plots where the residues had previously been incorporated than where the residues were previously either removed or burned. This is attributed to release of nitrogen and phosphorus from the incorporated residues.     

Integrated soil management in eroded land augments the crop yield and water-use efficiency

Abstract

Cultivated lands in erosion prone agro-ecologies incessantly experience a substantial loss of productive soil and organic matter. Currently, the fertility-management and rainwater-conservation practices are given emphasis separately. This study appraised collectively both the water-conservation and fertility-management practices for the restoration of soil productivity in eroded farmlands. Field experiments were carried out on wheat (Triticum aestivum L.) and maize (Zea mays L.) in eight farmer fields. Four fields of Missa soil series (Typic Ustochrept) and four of Rajar soil series (Typic Ustorthent) were selected. Treatments in each field were: farmers' practice as control without soil-water conservation, and with farmers' rate of fertilizer (per hectare 40 kg N + 30 kg P₂O₅); improved fertilization (per hectare 100 kg N, 60 kg P₂O_5, 2 kg Zn, and 1 kg B) without soil-water-conservation practices; soil-water-conservation practices (deep plowing, bund improvement, ploughing across the contour) + farmers' rate of fertilizers; and soil-water conservation + improved fertilization. Crop grain yields were at the highest with soil-water conservation + improved fertilization (per hectare wheat 3.31 Mg and 1.65 Mg in 2004–2005 and 2005–2006; and maize 4.55 Mg and 4.19 Mg in 2005 and 2006, respectively). The lowest yields were recorded under farmers' practice for both crops. Similar was the response for water-use efficiency and plant uptake of nitrogen, phosphorus, zinc, and boron. Missa soil series was more responsive than was Rajar to integrated soil-management practices. Synergistic application of soil-water conservation and improved fertilization practices significantly improved the crop yields, nutrient uptake, and water-use efficiency.     

Fertilizer value of nitrogen in hen and broiler manure after application to spring barley using different application timing

The nitrogen (N) fertilizer effect of layer hen and broiler manure applied at different times on spring barley yield was studied in seven Swedish field experiments during 2005–2008. Two experiments had parallel field incubations to study N release after fertilizer application. The effect of total N in manure on N offtake was 30–40% that of mineral N, except in a dry year, when the effect was very low. Although the relative proportions of ammonium N, uric acid N and other N differed between the hen and broiler manure, the effect of total N was similar for both. In field incubations, mineral N decreased from 75 to 60% of total N applied in hen manure, whereas it increased from 20 to 50% in broiler manure, because of net immobilization and release, respectively. The limited fertilizer nitrogen replacement value, corresponding to only 30–40% of total N, could be as a result of ammonia volatilization after rather shallow incorporation with harrow. Net N release from broiler manure lasted for 6–8 weeks after application, after which it generally ceased. In some cases, manure application in early spring gave better yield effects than application at sowing, probably because of better synchronization of the N release with crop N requirements. The residual N effect on the N offtake in crop in the year after manure application was on average 3% of the total N applied, equivalent to a fertilizer replacement value of about 6%.     

The impact of soil and crop management practices on soil-borne root diseases and wheat yields

Abstract. The most important root diseases of wheat in southern Australia are take-all, rhizoctonia bare patch and cereal cyst nematode. Control of grasses in annual pastures in the year preceding wheat crops decreased take-all on wheat and the amount of the take-all fungus in soil, decreased the damage caused by Rhizoctonia , and gave yield increases. Fumigation of cereal-growing soils gave yield increases in wheat of 0.75 to 2.8 tonnes per hectare, indicating that in southern Australia soil-borne root diseases impose a major constraint on productivity. Residues of the herbicide chlorsulfuron one year after application to an alkaline soil increased root damage by Rhizoctonia in barley and decreased grain yields by 1.5 tonnes per hectare. Root damage by cereal cyst nematode was decreased by direct drilling wheat and also by having a barley cultivar resistant to the pathogen as a preceding crop. The number of cysts of cereal cyst nematode on wheat roots was increased by the application of superphosphate in bands with the seed. These results show that in southern Australia soil management strategies which decrease the levels of root disease greatly increase grain yields.     

氮肥运筹对水稻养分吸收特性及稻米品质的影响

以水稻品种扬两优6号为材料,研究了田间条件氮肥运筹对水稻养分吸收及产量和品质的影响。结果表明,高氮处理(N240)成熟期氮素积累总量、磷素积累总量和钾素积累总量分别比中氮(N150)和低氮处理(N0)增加了21.5%、18.5%1、8.3%和134.6%、127.0%和82.7%;产量增加了10.4%和39.6%。在相同氮素水平下,采用B种施肥比例(基肥∶分蘖肥∶穗粒肥=30%∶20%∶50%),水稻成熟期氮素积累总量比A处理(基肥∶分蘖肥∶穗粒肥=40%∶30%∶30%)增加了15.4%,产量提高了7.3%。在高氮处理(N240)条件下,采用B施肥比例,蛋白质含量显著提高,直链淀粉显著降低,但提高了稻米的垩百度而使稻米外观品质变劣。     

Ten-year comparison of the influence of organic and conventional crop management practices on the content of flavonoids in tomatoes

Understanding how environment, crop management, and other factors, particularly soil fertility, influence the composition and quality of food crops is necessary for the production of high-quality nutritious foods. The flavonoid aglycones quercetin and kaempferol were measured in dried tomato samples (Lycopersicon esculentum L. cv. Halley 3155) that had been archived over the period from 1994 to 2004 from the Long-Term Research on Agricultural Systems project (LTRAS) at the University of California-Davis, which began in 1993. Conventional and organic processing tomato production systems are part of the set of systems compared at LTRAS. Comparisons of analyses of archived samples from conventional and organic production systems demonstrated statistically higher levels (P < 0.05) of quercetin and kaempferol aglycones in organic tomatoes. Ten-year mean levels of quercetin and kaempferol in organic tomatoes [115.5 and 63.3 mg g(-1) of dry matter (DM)] were 79 and 97% higher than those in conventional tomatoes (64.6 and 32.06 mg g(-1) of DM), respectively. The levels of flavonoids increased over time in samples from organic treatments, whereas the levels of flavonoids did not vary significantly in conventional treatments. This increase corresponds not only with increasing amounts of soil organic matter accumulating in organic plots but also with reduced manure application rates once soils in the organic systems had reached equilibrium levels of organic matter. Well-quantified changes in tomato nutrients over years in organic farming systems have not been reported previously.     

Effects of residue management on nitrogen losses in surface and sub-surface water from sugarcane fields

The effect of three sugarcane (Saccharum officinarum L.) residue-management plans on nitrogen losses in surface runoff and sub-surface leachate was studied for 3 years. The three management plans evaluated were conventional burning (CB), compost application with burning (COMB), and remaining green cane trash blanketing (GCTB) treatment. In the CB treatment, sugarcane residue was burned after harvest. The COMB treatment consisted of compost applied at ‘off bar’ with sugarcane residue burned immediately after harvest. Compost was applied in the amount of 13.4 Mg ha^?1 annually. Surface runoff was collected with automatic refrigerated samplers and sub-surface leachate was collected with pan lysimeters over a period of 3 years. Total nitrogen (TN), NO₃/NO₂–N, and NH₄–N were measured. The mean losses of nitrogen (TN, NO₃/NO₂–N, and NH₄–N) from the COMB treatment after the burning procedure (post-harvest, years 2 and 3) were on average 2.7 times higher than those before harvest and burning (pre-harvest, year 1). Mean leaching losses of NO₃/NO₂–N were 0.36, 0.82, and 0.10 kg ha^?1 for the CB, COMB, and GCTB treatment, respectively. The losses of NO₃/NO₂–N from the GCTB treatment in surface runoff and sub-surface leachate were significantly reduced compared to the CB and COMB treatment.     

Effect of crop type and crop growth on atmospheric nitrogen deposition

Varying atmospheric nitrogen (N) depositions for different crops were observed at Bad Lauchstädt (Saxony‐Anhalt, Germany) when using the ITNI system (ITNI = Integrated Total Nitrogen Input), which is based on the ¹⁵N isotope dilution method. These differences were only partly explained by climatic influences. The effects of crops on the atmospheric N deposition measured by the ITNI system are discussed. For this purpose, data of six different plant species recorded in 1998 were re‐analyzed. It was found that the airborne N input is closely correlated with the morphology and metabolism of crops. Daily atmospheric N depositions of 129.0–360.8 g per hectare were measured for the plant species used. The nutritional supply of plants, especially with N, is another factor of influence on the N input from the atmosphere which should be considered. To investigate this aspect, a pot experiment was conducted with the grass Lolium perenne at three different N levels. An increase in the airborne N uptake (corresponding to N fertilization) was observed as biomass production rose.     

Overwinter soil denitrification activity and mineral nitrogen pools as affected by management practices

During freeze-thaw events, biophysical changes occurring in soils can affect processes such as mineralization, nitrification and denitrification which control inorganic N balances in agro-ecosystems. To evaluate the impact of these climatic events on soil biochemical properties, a study was conducted comparing soil denitrification enzyme activity (DEA), dissolved organic C (DOC) and inorganic N levels before and after the winter season in plots under: (1) continuous corn (Zea mays L.) (CC) with annual chisel plow and disking, (2) corn-soybean (Glycine max L.) (CS) rotation with chisel plow every other year prior to planting soybean, and (3) corn-soybean-wheat (Triticum aestivum L.)/hairy vetch (Vicia villosa Roth) (CSW-V) with ridge tillage during the corn and soybean crops, and dairy manure application during the corn year. Soil cores were collected in late autumn and immediately after spring thaw at 0-5, 5-10, 10-15, and 15-30 cm depths. Regardless of management practices, freeze-thaw events resulted in significant (2-10 times) increases in NH₄⁺-N, NO₃^--N (P<0.001) and DOC (P<0.01) levels at all soil depths. Following freeze-thaw, DEA remained unchanged in the 5-30 cm depth but dropped significantly (P<0.01) in the 0-5 cm soil layer. In that layer, soils which had been chisel plowed during the previous growing season lost 78-84% of the DEA recorded during the fall, whereas in the plots amended with manure during the previous season, the loss of activity was 40-45%. These data indicate that frequent tillage, compared with manure additions, is more conducive to overwinter loss of DEA in surface layers of soils subject to freeze-thaw cycles.     

Nitrate leaching from a shallow limestone soil growing a five course combinable crop rotation: the effects of crop husbandry and nitrogen fertilizer rate on losses from the second complete rotation

Abstract. The field experiment tested the effects of three management systems on nitrate leaching losses from a five crop rotation on the Lincolnshire Limestone in Eastern England. The Standard system was similar to farming practice in the area. The Protective system integrated individual practices which were expected to decrease nitrate losses (e.g. cover crops, cultivation delay in autumn and reduced intensity, manipulation of drilling dates and, during the first few years of the first rotation, straw incorporation). The Intermediate system was a compromise between the two extremes. All crops were grown at full and half recommended nitrogen rates. This paper reports data from the second full rotation (years 6–10), thus enabling the medium-term effects of continued management practices to be investigated. Average annual nitrogen leaching losses at 49, 35 and 25 kg N ha^–1 for Standard, Intermediate and Protective systems, respectively, were significantly different. The respective flow-weighted average NO₃ concentrations were 167, 131 and 96 mg l^–1. Thus, adopting nitrate retentive practices through the rotation was able to substantially decrease losses. The Protective system was as effective as in the first full rotation, demonstrating that 10 years of such practices had not failed in the medium-term. However, continued minimal cultivation caused serious problems of weed build-up. The cost of weed control and yield loss caused by grass weeds made cereal production uneconomic in some years. Thus, rules for nitrate leaching control need to be tempered with practical and agronomic considerations. Also, few (if any) management techniques tested guaranteed that nitrate losses would be small in all years, as the interaction with winter weather, particularly rainfall, was of vital importance.     

土壤碳氮对多年生能源草、覆盖作物和氮施肥的响应

Cover crop and nitrogen(N) fertilization may maintain soil organic matter under bioenergy perennial grass where removal of aboveground biomass for feedstock to produce cellulosic ethanol can reduce soil quality. We evaluated the effects of cover crops and N fertilization rates on soil organic carbon(C)(SOC), total N(STN), ammonium N(NH_4-N), and nitrate N(NO_3-N) contents at the0–5, 5–15, and 15–30 cm depths under perennial bioenergy grass from 2010 to 2014 in the southeastern USA. Treatments included unbalanced combinations of perennial bioenergy grass, energy cane(Saccharum spontaneum L.) or elephant grass(Pennisetum purpureum Schumach.), cover crop, crimson clover(Trifolium incarnatum L.), and N fertilization rates(0, 100, and 200 kg N ha~(-1)). Cover crop biomass and C and N contents were greater in the treatment of energy cane with cover crop and 100 kg N ha~(-1) than in the treatment of energy cane and elephant grass. The SOC and STN contents at 0–5 and 5–15 cm were 9%–20% greater in the treatments of elephant grass with cover crop and with or without 100 kg N ha~(-1)than in most of the other treatments. The soil NO_3-N content at 0–5 cm was 31%–45% greater in the treatment of energy cane with cover crop and 100 kg N ha~(-1)than in most of the other treatments.The SOC sequestration increased from 0.1 to 1.0 Mg C ha~(-1)year~(-1)and the STN sequestration from 0.03 to 0.11 Mg N ha~(-1)year~(-1)from 2010 to 2014 for various treatments and depths. In contrast, the soil NH_4-N and NO_3-N contents varied among treatments,depths, and years. Soil C and N storages can be enriched and residual NO_3-N content can be reduced by using elephant grass with cover crop and with or without N fertilization at a moderate rate.     

褐土区农田土壤氮磷淋溶特征及其管理措施

自20世纪90年代以来,持续过量氮磷化肥投入导致农业面源污染日益严重,了解农田土壤氮磷淋溶特征是降低地下水污染的基础。基于田间调查、长期定位肥料试验和田间试验,分析褐土区氮磷的盈余状况,阐明该区农田土壤氮磷的盈余变化、淋溶特征;评价田间管理措施对农田土壤氮磷淋溶的影响。结果表明,典型褐土区关中平原过量施氮的土壤达到83%以上,大量土壤硝态氮已经迁移到100cm土层以下,15%的水井地下水的硝态氮含量超过10 mg·L~(-1)(WHO饮用水标准);80%耕层土壤有效磷(Olsen-P)含量已超过20mg·kg-1,富磷土壤已出现可溶性磷素向耕层以下迁移的现象。氮肥和磷肥的投入量、氮磷吸收量和土壤氮磷残留量之间存在着3个发展阶段:环境友好-资源高效阶段、环境低风险-资源低效阶段和环境有害-资源无效阶段。与当地常规水肥投入量相比,在保证产量的前提下,化肥减量、降低灌溉量、施用生物炭或秸秆还田都可以降低氮磷淋失量;其中化肥减量、降低灌溉可显著降低氮磷的淋失,其次是施用生物炭和秸秆。施用秸秆条件下,阻控硝态氮淋失与微生物生物量碳氮的提高、土壤硝化势降低或反硝化势升高有关。此外,需要关注褐土区粮果复合系统中土壤氮磷淋溶的环境效应、地下水硝酸盐污染的溯源等问题。