长期施氮、磷、钾化肥对玉米产量及土壤肥力的影响

以1990年建立的国家褐潮土土壤肥力与肥料效益长期监测基地(北京昌平站)的长期肥料定位试验为研究平台,研究了不同施肥制度对玉米产量和土壤肥力的影响。结果表明,长期均衡地施NPK肥或NPK与有机肥配施,可以显著提高玉米产量和土壤有机质、全氮、全磷、速效氮、速效磷、速效钾等肥力指标,并能提高土壤微量元素的含量;而不均衡施肥(N、NK、NP、PK)导致相应的营养元素的耗竭。相关分析表明,在褐潮土上增施磷肥和有机肥对提高玉米产量具有重要的作用。     

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.     

Endomycorrhizae in a newly cultivated acidic meadow: Effects of three years of barley cropping,tillage, lime,and phosphorus on root colonization and soil infectivity

The dynamics of mycorrhizae under disturbance created by crop production is not well understood. A 3-year experiment was undertaken on a nutrient-poor and acidic land that had last been cultivated in the early 1970s. We observed the effects of cropping spring barley (Hordeum vulgare L.) under four P-fertilizer levels and four levels of lime, in a minimum (rototillage), a reduced (chisel), or a conventional tillage system, on the mycorrhizal receptiveness of the host (maximum level of mycorrhizal colonization, as measured at harvest) and soil infectivity most probable number method. The host receptiveness decreased with time, while crop yields and soil infectivity increased simultaneously with time. Liming increased mycorrhizal colonization of barley roots and soil infectivity. P additions decreased root colonization but did not significantly affect the most probable number valuse. Slightly higher soil infectivity estimates were found under reduced tillage.     

Influence of subsoil amelioration with lime,phosphorus and potassium on the yield of soybeans and barley

Abstract

The effects of mixing lime and large quantities of phosphorus and potassium fertilizers with the subsoil were studied on 16 Maryland subsoils. These subsoils were covered with 10. cm of a fertile surface soil so the subsoils’ effect would be the major variable. Soybeans were grown on these soils in the greenhouse. These subsoils received 65.2 and 83.0 ug/g of phosphorus and potassium respectively. Two treated subsoils were also studied in the field. Simulated subsoiling in the field was accomplished by digging to a depth of 50.8 cm. Lime, 148 or 440 Kg P/ha, and 186 or 558 Kg K/ha were mixed with each 15 cm depth of subsoil. Soybeans and/or barley were planted on the field plots.

In general, the subsoils studied in the greenhouse indicated that the combined amendments of lime, phosphorus and potassium to the subsoils increased root production in the subsoil, nitrogen content in the soybean shoots, and yield.

First year field results on the Othello (Typic Ochraquult) soil indicated that soybean yields on treated subsoil plots were not significantly different from soil receiving the same surface applications of fertilizer. However the second year after treatment, the yields of double cropped soybeans and barley were increased by 706 Kg/ha (10.5 bu/acre) and 710 Kg/ha (14.4 bu/acre) respectively when compared to similar quantities of phosphorus and potassium applied to the surface soil of nonsubsoiled plots.

On the Monaouth (Typic Hapludult) soil, the first year yields of subsoil plots treated with lime, phosphorus, and potassium also failed to improve yields compared to surface application of the fertilizer. Lime, 440 Kg P/ha, and 558 Kg K/ha applied to the subsoil did significantly improve yields of full season soybeans over the untreated soil by 720 Kg/ha (10.7 bu/acre).     

磷肥减施对玉米根系生长及根际土壤磷组分的影响

【目的】 我国农业过量和不合理施用磷肥现象普遍存在,导致磷资源的浪费,对环境也造成潜在威胁。研究减少磷肥用量对玉米产量、根系形态及根际中磷转化特征的影响,为集约化农业生产体系中磷肥合理施用提供技术基础。 【方法】 在河北省衡水小麦玉米轮作体系下连续三年进行了田间试验,在冬小麦季设置4个P₂O₅用量处理:0、112.5、150.0、187.5 kg/hm2,收获后在原处理小区免耕播种夏玉米。利用WinRHIZO根系分析系统分析获取根长、直径等数据,测定玉米籽粒产量、生物量和地上部磷含量及根际土壤中磷形态等指标。 【结果】 与农民习惯磷肥用量(P₂O₅187.5 kg/hm2)相比,3年磷肥用量减施20%~40%处理(P₂O₅150和112.5 kg/hm2),玉米籽粒产量、根系长度与直径和土壤有效磷含量尚未发生明显变化。但3年不施磷处理,根际土壤有效形态磷含量和玉米籽粒产量开始出现下降趋势。2009年和2010年玉米收获期,不施磷肥处理根际土壤有机磷含量低于非根际土壤。2008年玉米苗期和收获期土壤有机磷分组中,中等活性有机磷含量最高;磷肥减施20%~40%处理苗期根际中中等活性有机磷含量显著低于非根际土壤。土壤无机磷形态分组研究发现:从玉米苗期到收获期,各磷肥处理根际和非根际土壤中Ca₂-P下降明显;而不同磷肥处理间土壤中Ca₁₀-P、Ca₈-P、O-P (闭蓄态磷)、Al-P和Fe-P含量差异不显著。减施磷肥处理2008年玉米苗期根际土壤微生物量P含量较非根际土壤高;与习惯施肥量相比,磷肥减施未明显降低根际土壤微生物量磷。 【结论】 在华北小麦玉米轮作种植体系下,在土壤肥力水平较高地区,连续3年将小麦季磷肥的习惯用量减少20%~40%,对夏玉米产量、根系形态以及根际土壤无机磷、有机磷、微生物量磷含量影响尚不明显,因此,该地区磷肥施用量可从习惯用量的P₂O₅180 kg/hm2减至112.5 kg/hm2。     

Effect of long-term organic and mineral fertilizer on physical properties in root zone of a clayey Ultisol

To explore the effects of long-term organic and mineral fertilization practices on the physical properties in Ultisol of south China, a study was conducted since 1998 to investigate the effects of a control (CK), application of chemical fertilizers (NPK), application of organic manure (OM), and NPK fertilizer plus straw returning (NPK + straw). Results showed that OM significantly increased soil water retention capacity at all tensions but with larger increment in low tension at depths of 0–10 cm and 10–20 cm (p < 0.05) when compared with the CK. On the contrary, NPK and NPK + straw led to a decrease in soil water retention capacity under chemical treatments. In the field both in wet and dry periods, soil water content was significantly higher in OM than in NPK + straw and NPK (p < 0.05) since soil hydraulic conductivity (saturated and unsaturated) are lower in OM than in other treatments (p < 0.05). OM was also found to have the lowest soil bulk density and penetration resistance of the four treatments. A high negative correlation was observed between the soil organic carbon and the bulk density and the penetration resistance (p < 0.01). In this way, the application of OM improved the clayey soil physical properties.     

Effects of lime and sewage sludge on soil,pasture production,and tree growth in a six‐year‐old Populus canadensis Moench silvopastoral system

In many regions worldwide, silvopastoral systems are implemented to enable sustainable land use allowing short, medium, and long‐term economic returns. However, the short‐term production in silvopastoral systems is often limited due to nonappropriate soil‐fertility management. This study evaluated the effects of two doses of lime (0 and 2.5 t CaCO₃ ha^–1) and three sewage‐sludge treatments (0, 200, and 400 kg total N ha^–1 y^–1 applied in 2 consecutive years) on soil characteristics (soil pH, soil organic matter [SOM], soil nitrogen, cation‐exchange capacity [CEC]), pasture production, and tree growth in a silvopastoral system of Populus × canadensis Moench in Galicia, northern Spain during 6 years after establishment. Soil pH increased during the experimental period for all treatments, although this effect was more pronounced after lime application. Changes in SOM and soil nitrogen content were not consistent over time, but sewage‐sludge application seemed to result in higher values. Higher CEC was found for treatments with lime and sewage‐sludge application. Following incorporation of lime and sewage sludge, pasture production was significantly enhanced (cumulative pasture production 51.9 t DM ha^–1 for Lime/N400 compared to 39.0 t DM ha^–1 for No lime/N0). This higher pasture production also affected tree growth due to more severe competition between pasture and tree resulting in slower tree growth. Liming and application of sewage sludge are relevant measures to improve soil fertility and thereby optimizing the overall production of silvopastoral systems. However, it is important not to overintensify pasture production to ensure adequate tree growth.     

Effects of vertical distribution of soil inorganic nitrogen on root growth and subsequent nitrogen uptake by field vegetable crops

Information is needed about root growth and N uptake of crops under different soil conditions to increase nitrogen use efficiency in horticultural production. The purpose of this study was to investigate if differences in vertical distribution of soil nitrogen (N_inorg) affected root growth and N uptake of a variety of horticultural crops. Two field experiments were performed each over 2 years with shallow or deep placement of soil N_inorg obtained by management of cover crops. Vegetable crops of leek, potato, Chinese cabbage, beetroot, summer squash and white cabbage reached root depths of 0.5, 0.7, 1.3, 1.9, 1.9 and more than 2.4 m, respectively, at harvest, and showed rates of root depth penetration from 0.2 to 1.5 mm day^?1 °C^?1. Shallow placement of soil N_inorg resulted in greater N uptake in the shallow‐rooted leek and potato. Deep placement of soil N_inorg resulted in greater rates of root depth penetration in the deep‐rooted Chinese cabbage, summer squash and white cabbage, which increased their depth by 0.2–0.4 m. The root frequency was decreased in shallow soil layers (white cabbage) and increased in deep soil layers (Chinese cabbage, summer squash and white cabbage). The influence of vertical distribution of soil N_inorg on root distribution and capacity for depletion of soil N_inorg was much less than the effect of inherent differences between species. Thus, knowledge about differences in root growth between species should be used when designing crop rotations with high N use efficiency.     

Effect of long-term beef manure application on soil test phosphorus,organic carbon,and winter wheat yield

In this study, 24 years (1990–2013) of data from a long-term experiment, in Stillwater, Oklahoma (OK), were used to determine the effect of beef manure on soil test phosphorus (STP), soil organic carbon (SOC), and winter wheat (Triticum aestivum L.) yield. Beef manure was applied every 4 years at a rate of 269 kg nitrogen (N) ha^?1, while inorganic fertilizers were applied annually at 67 kg N ha^?1, 14.6 kg phosphorus (P) ha^?1, and 27.8 kg potassium (K) ha^?1 for N, P, and K, respectively. Averaged across years, application of beef manure, and inorganic P maintained STP above 38 mg kg^?1 of Mehlich-3 extractable P, a level that is far beyond crop requirements. A more rapid decline in SOC was observed in the check plot compared to the manure-treated plot. This study shows that the application of animal manure is a viable option to maintaining SOC levels, while also optimizing grain yield.     

有机复混磷肥对石灰性土壤无机磷形态组成及其变化的影响

实验室培养条件下,研究了有机复混磷肥对石灰性土壤无机磷组成变化的影响。结果表明: 1）单独施用有机物料对提高土壤速效磷含量的影响不大,但施用磷肥,无论是磷酸一铵化肥还是有机复混磷肥,均显著提高了土壤速效磷含量;施用有机复混磷肥提高土壤速效磷的幅度（67.5mg/kg～80.4mg/kg）高于施用磷酸一铵化肥处理（62.3mg/kg）;有机复混磷肥中有机物料的含量高低对土壤速效磷含量的影响不大。2）单独施用有机物料具有提高土壤Ca2-P含量的作用,且明显提高了Ca8-P含量,但对Al-P、Fe-P、O-P、Ca10-P含量影响不大;施用无机磷肥和有机复混磷肥,显著提高了土壤Ca2-P、Ca8-P、Al-P含量,而对Fe-P、O-P、Ca10-P含量的影响很小;与磷酸一铵化学磷肥处理相比,施用有机复混磷肥对Ca2-P含量影响较小,但明显提高了Ca8-P含量,Fe-P含量也表现增加的趋势,而Al-P含量明显降低,O-P和Ca10-P含量的变化则没有明显规律;有机复混磷肥中有机物料的比例高低对土壤无机磷组成变化的影响没有表现出明显的规律性。3）施用磷肥引起速效态Ca2-P和缓效态Ca8-P的变化最大,其它形态无机磷的变化相对较小。与磷酸一铵化肥处理相比,有机复混磷肥处理Ca8-P的变异提高幅度增加,而Al-P的变异提高幅度减小,其它指标库容的变异幅度与之相近。4）施磷处理土壤速效磷含量与土壤Ca2-P、Ca8-P含量呈线性正相关,相关系数分别达到0.9888、0.9867,而Al-P、 Fe-P、O-P、Ca10-P与土壤速效磷相关性不显著,磷肥施入土壤后,土壤无机磷库中Ca2-P、Ca8-P的变化对土壤速效磷含量的贡献最大。     

Tillage effects on water storage during fallow, and on barley root growth and yield in two contrasting soils of the semi-arid Segarra region in Spain

In semi-arid areas under rainfed agriculture water is the most limiting factor of crop production. To investigate the best way to perform fallow and its effect on soil water content (SWC) and root growth in a barley (Hordeum vulgare L.) crop after fallow, an experiment was conducted on two soils in La Segarra, a semi-arid area in the Ebro Valley (Spain). Fallow was a traditional system used in these areas to capture out-of-season rainfall to supplement that of the growing period, usually lasting 16 months, from July to October of the next year. Soil A was a loamy fine Fluventic Xerochrept (Haplic Calcisol, FAO) of 120 cm depth and Soil B was a loamy Lithic Xeric Torriorthent (Calcaric Regosol, FAO) of only 30 cm depth. The experiment was continued for four fallow-crop cycles in Soil A and for two in Soil B. In Soil A, three tillage systems were compared: subsoil tillage (ST), minimum tillage (MT) and no-tillage (NT). In Soil B, only MT and NT were compared. In the fields cropped to barley, SWC and root length density (LV) were measured at important developmental stages during the season, lasting from October to June. In the fallow fields SWC was also monitored. Here, evaporation (EV), water storage (WS) and water storage efficiency (WSE) were calculated using a simplified balance approach. The fallow period was split in two 8-month sub-periods: July–February (infiltration) and March–October evaporation (EV). In Soil A, values of WSE were in the range 10–18% in 1992–1993, 1993–1994 and 1994–1995 fallow, but fell to 3% in 1995–1996. Among tillage systems, NT showed significantly greater WSE in the July–February sub-period of 1992–1993 and 1993–1994 fallow, but significantly lower WSE in the March–October sub-period, due to greater EV under NT. Consequently, no differences in total WSE were found between tillage systems. In Soil B, WSE was low, about 3–7%, and there were no difference between tillage systems. During the crop period, the differences in SWC and LV between tillage systems were small. Regarding yields, the best tillage system depended on the year. NT is potentially the best system for executing fallow, but residues of the preceding crop must be left spread over the soil.     

Effects of boron and lime on boron concentration and growth of forage legumes under greenhouse conditions

Abstract

Maximum yields of red clover, alfalfa, and birdsfoot trefoil were obtained when 0.25 to 1.0 ppm B was added to the soil. An application of lime to raise the soil pH to 5.8–6.3 improved yields, while at pH 6.8 a decline in yield in the first and second cuts of birdsfoot trefoil was noted. There was a marked B x lime interaction on the yield of all cuts of birdsfoot trefoil and first cut of red clover, with much higher yields with high rates of lime at high rates of added B.

Levels of 4 to 9 ppm B in the leaf tissue of the three crops were in the deficiency range. Boron concentrations of 21 to 45, 39 to 52, and 30 to 45 ppm in the first cuts of red clover, alfalfa, and birdsfoot trefoil were indicative of sufficiency and were associated with maximum yields, while levels of >59, >99, and >68 ppm, respectively, in the three crops were in the toxicity range. Sufficiency levels of soil B for legumes appeared to be related to pH since B deficiency was more severe at higher pH than at lower pH. Liming of soil from pH 5.3 to 6.8 resulted in decreased concentration of B in all the three crops with the smallest decreases in alfalfa. There was a marked B x lime interaction on the B concentrations of the three crops, with much higher B concentrations in high B treatments at low soil pH than at high pH values.     

Reappraisal of methods of application of nitrogen and phosphorus at sowing on the yield,grain protein content and nitrogen economy of malting barley in Sweden

Abstract

To compare the relative efficiency of different fertilisation strategies, malting barley was fertilised with calcium ammonium nitrate (CAN) or compound ammonium nitrate with phosphorus (NP) applied in two ways: broadcast and harrowed into the seedbed before seeding or banded using the Scandinavian combi-drill design, with the fertiliser between every second seed row, and 40 mm below. A fixed nitrogen level (120 kg N ha^?1) was used, giving four fertiliser treatments. Eleven experiments were carried out the years 1992–1994, with latitudes 55° 55′ N as southern and 59° 36′ N as northern limit. Fertiliser-use efficiency, defined as grain yield, or grain nitrogen yield, per unit of applied N, was strongly affected by the treatments: values for combi-drilled were higher than for broadcast fertiliser and higher for NP than for CAN, with the effects being additive. The best treatment, using both banding and NP, resulted, as a mean of all trials, in a grain yield increase of 939 kg ha^?1 at 15% moisture content, or a nitrogen yield increase of 18 kg nitrogen ha^?1 compared with the poorest, using broadcast CAN. The N combi-drill effect was expected to be dependent on water availability, but this could not be confirmed when accumulated rainfall during crop establishment was used as test variable. The combi-drill effect was strongest in places where major extractable cations were abundant, possible explanations for this are discussed. Application of P to the crop and the use of combi-drill are recommended for malting barley fertilisation in Sweden.     

Senescence of the flag leaf and grain yield following late foliar and root applications of phosphate on plants of differing phosphorus status

The balance between leaf senescence, induced by phosphorus deficiency, and grain growth was examined in wheat plants grown in sand with high (control) and low phosphorus (low‐P) nutrition. Foliar applications of P were made prior to anthesis and at early and mid grain development. Low‐P plants were also given an additional dose of P via the roots at mid grain development.

Foliar applications of P had no effect on leaf function (net CO₂ exchange rate), or grain development in control plants. However, P applied to the flag leaf of low‐P plants delayed senescence and thus increased leaf area duration, but this did not result in a significant increase in grain yield per ear. Phosphorus applied to the ear surface (the glumes) of low‐P plants increased the concentration of P in the grain, but did not increase the number of cells per grain, or the grain yield per ear. The late application of P via the roots also delayed senescence in low‐P plants, but did not cause an increase in yield.

These experiments indicate that grain growth in low‐P plants is not limited by the level of supply of photosynthate, or the availability of P during the actual period of grain development. Phosphorus translocated to the grain late in plant development is used inefficiently in plants that are adequately supplied with phosphorus and in plants suffering from P deficiency.     

丛枝菌根菌对棉花生长及产量的影响

研究了不施肥与施P肥3种丛植菌根菌C．igaspora(Gi．r) Glomus mosseae(G．m)和Glomus versiforme(G．v)对棉花生长及产量的影响。结果表明,丛技菌根菌可显著提高棉花叶片光合速率,改善水分状况,促进棉花生长发育,提高籽棉产量,尤其是霜前花产量。其中以接种G.v处理对棉花增产效应最大。     

Evaluating the performance of mungbean genotypes for grain yield,phosphorus accumulation and utilization efficiency

Ten mungbean (Vigna radiata R. Wilczek) genotypes were evaluated for grain yield and phosphorus (P) efficiency at adequate and deficient P in soil. Genotypes differed significantly in plant height, grain yield, P accumulation (PA), and other P-efficiency parameters at both P levels. The genotype “AEM-40/30” had maximum plant height, grain yield, and phosphorus physiological efficiency index (PPEI) under P deficiency. The genotypes were distributed into nine groups based on their relationship between total PA and grain yield at deficient P level. Moreover, genotypes were categorized into low, medium, or high efficient for each parameter by allotting index score (1, 2, or 3). Maximum cumulative index score (25) was attained by the genotypes “AEM-40/30 and AEM-20/3/87”, and genotype “AEM-30/5/8/90” scored least total index (14). The significant differences among mungbean genotypes for PA, phosphorus harvest index (PHI), PPEI, and grain yield can be exploited to select or identify P-efficient mungbean genotypes.     

接触施用包膜控释肥对玉米产量、根系分布和土壤残留无机氮的影响

采用田间小区试验,研究了习惯施肥与接触施用包膜控释肥料对夏玉米生长、产量、根系分布和土壤无机氮残留的影响。结果表明,接触施用包膜控释肥料没有抑制玉米的出苗和幼苗生长;减氮1/3的控释肥处理(N 120kg/hm2)与习惯施肥处理(N180 kg/hm2)的玉米产量没有差异。在0—30 cm土层,与对照和习惯施肥处理相比,接触施用控释肥增加了距茎基部0—10 cm区域内玉米根长密度的分布,占总根长的59%~64%;玉米收获后,减量控释肥处理土壤剖面各个土层Nmin含量与对照相比无显著增加,习惯施肥和全量控释肥处理(N 180 kg/hm2)在60—90、90—120 cm土层的Nmin累积显著高于对照。综合考虑玉米生长、产量以及根系分布和氮素淋失风险,本试验条件下,接触施用控释肥N120 kg/hm2是夏玉米季较为理想的选择。     

长期不施磷肥对旱地红壤养分比例与玉米产量的影响

在湖南祁阳国家红壤肥力与肥料效益长期监测基地,于2008年对已有18年旱地红壤肥料试验历史的不施肥、NK、NP、PK、NPK处理下玉米产量、pH以及养分状况等指标进行了研究.结果表明,长期不施磷肥、只施氮钾肥导致玉米绝产.施用磷肥有极显著的增产作用,其中NP、PK与NPK处理分别比不施肥处理玉米增产33.2%、66.39%与151.45%.施磷的增产作用主要体现在玉米穗粒数、百粒重以及公顷穗数的增加.长期施用氮肥造成了土壤酸化,尤以NK处理酸化严重(pH值降至4.1),导致玉米产量连年下降.长期不施磷肥、只施氮钾肥,导致土壤全磷量和有效磷量降低,而全氮、全钾、碱解氮、有效钾量增加,表现为土壤氮磷钾养分比例严重失衡.NK处理的土壤氮磷钾全量比例为2.8:1:44.5,其它施磷处理的为1.09～1.32:1:17.96～19.36;NK处理的土壤氮磷钾速效量为31:1:57,其它施磷处理的为0.7～1.16:1:1.07～4.6.     

Influence of long-term tillage, straw and N fertilizer on barley yield, plant-N uptake and soil-N balance

Long-term influence of N fertilizer, tillage and straw on crop production and soil properties are not well known in central Alberta. Field experiments were established in autumn 1979, on a Black Chernozemic soil and on a Gray Luvisolic soil in north-central Alberta to determine the long-term effect of tillage, straw and N fertilizer on yield and N uptake of barley (Hordeum vulgare L.). Fertilizer N was applied annually at 56 kg ha⁻¹. The 11 year averages of barley yields and N uptake under zero tillage were lower than under conventional tillage. Retention rather than removal of straw tended to reduce barley yield for the initial 6 years and 2 year at Site 1 and Site 2, respectively. A simple mathematical model of average annual plant N uptake and grain yield could account for most of the variation in the data observed at both sites (R² = 0.907; P < 0.01). Final values of soil N, calculated using a mass balance approach, agree closely with values measured at the end of the eleventh year. Conventional tillage and zero tillage, with addition of fertilizer N and retention of straw, were the only treatments with apparent but small net addition of N to soil at Site 1 (40 kg ha⁻¹ and 117 kg ha⁻¹, respectively). At Site 2, only the zero tillage treatment with addition of fertilizer and retention of straw gained soil N (29 kg ha⁻¹). In conclusion, soil ecosystems functioning in subhumid environments with slight to moderate heat limitations such as those in central Alberta can adapt, within a few years, to zero tillage practices with full retention of straw.     

不同水分条件下分层施磷对冬小麦根系分布及产量的影响

研究不同水分条件下分层施磷对冬小麦根长分布、水分利用效率(water use efficiency,WUE)及产量的影响,旨在找出旱地农业最佳水肥处理方式。试验设不施磷(CK)、表施磷(surface P,SP)、深施磷(deep P,DP)和侧深施磷(deep-band P,DBP)4种处理,每个施磷水平下设补充灌溉(W1)和干旱(整个生育期无补充灌溉)(W2)2种水分处理。结果表明,施磷位置及补充灌溉显著(P0.05)影响冬小麦孕穗期根长分布、WUE及产量,同时会改变根系空间分布。干旱胁迫使冬小麦0~30 cm土层根长密度下降,降低17.5%,却促进了30 cm以下土层根长发育,增加13.3%,促进对土壤水分和磷素的吸收,从而提高产量。无论灌溉与否,施磷处理0~30 cm土层根长密度、吸磷量、WUE及产量均显著高于CK(P0.05)。施磷位置对冬小麦WUE和产量的影响随土壤水分而异,无补充灌溉时,与磷肥表施相比,磷肥深施显著增加WUE和产量(P0.05),分别平均增加28.5%和16.0%,且深层根长(30~100 cm)与吸磷量、WUE和产量的变化趋势一致;而在补充灌溉时,与磷肥表施相比,磷肥深施却显著降低WUE(P0.05),平均降低13.3%,且深层根长与WUE、产量的关系缺乏规律性。该试验结果表明,土壤水分供应不足时,磷肥深施有利于促进冬小麦深层土壤根系生长发育,提高对土壤水分吸收利用能力,从而利于形成高产。该研究可为理解作物生长及产量对水分养分空间耦合的响应提供理论依据。