氮肥施用对冬小麦籽粒产量和氮素表观损失的影响

Excessive nitrogen （N） fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content （Nmin） in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels （average 212 kg N ha^-1）. The average optimum N rate was 96 kg N ha^-1 for the five sites with low initial soil Nmin （average 155 kg N ha^-1） before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha^-1, whereas the farmers＇ conventional N application rate resulted in losses of more than 100 kg N ha^-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields.     

潮土CaCl2-P含量对磷肥施用的响应及其淋失风险分析

【目的】 土壤有效磷 (Olsen-P) 与可溶性磷 (CaCl₂-P) 含量之间存在着平衡,研究磷肥施用量对潮土CaCl₂-P和Olsen-P及其比值的影响,评价磷素的淋失风险,可为潮土区合理利用养分资源、减少磷肥投入和流失提供理论依据。 【方法】 选择长期定位监测基地的5个处理 (对照、NPK、预备处理、NPKM和1.5NPKM处理,简称OP1、OP2、OP3、OP4、OP5),5个处理的土壤Olsen-P含量存在显著差异 (0.8、12.5、25.7、44.7、56.4 mg/kg),据此在每个处理上再设置5个施磷量水平 (F0、F1、F2、F3、F4),试验采取微区形式,随机区组设计,种植作物为夏玉米–冬小麦双季轮作。作物收获后,采集土壤样品,测定土壤Olsen-P和CaCl₂-P含量,建立Olsen-P和CaCl₂-P之间的定量关系。 【结果】 土壤CaCl₂-P含量为0.07～2.68 mg/kg,约为Olsen-P含量的0.5%～5.6%。短期高量磷肥施用可以显著提高土壤Olsen-P和CaCl₂-P含量,但土壤Olsen-P和CaCl₂-P的增加不同步。当土壤Olsen-P低于28.0 mg/kg时,CaCl₂-P/Olsen-P比值随着Olsen-P的增加而降低,当Olsen-P增加至28.0 mg/kg后,CaCl₂-P/Olsen-P比值随着Olsen-P的增加迅速增加,这表明磷肥施用首先提高土壤Olsen-P含量,Olsen-P增长到一定程度后CaCl₂-P才迅速增加。土壤CaCl₂-P和Olsen-P的关系符合双直线模型,突变点时土壤Olsen-P含量为30.2 mg/kg,对应的CaCl₂-P含量为0.3 mg/kg。当土壤Olsen-P含量超过30.2 mg/kg时,土壤磷素淋失风险增加。 【结论】 高量磷肥施用可以提高土壤CaCl₂-P含量,促进作物对磷的吸收,但同时增加了土壤磷素的淋失风险。研究区土壤磷素淋失临界值为30.2 mg/kg,微区试验中超过50%的小区土壤Olsen-P含量已经超过磷素淋失临界值,存在磷素淋失风险,应加强农田磷肥的科学施用和管理。      

Erosion rates evaluated by the Cs technique and direct measurements on long-term runoff plots under tropical conditions

Measured ¹³⁷Cs losses (Bq m⁻²) from long-term runoff plots under tropical conditions and correspondent estimated soil erosion rates (Mg ha⁻¹ year⁻¹) were significantly correlated to directly measured soil losses of the same plots, during the same period (1963–2002). A tendency of higher ¹³⁷Cs activities was observed in soil profiles of the bottom third part of runoff slopes that could be explained by the restricting effect of the collector system on the runoff flow or by tillage translocation. Despite of the very low ¹³⁷Cs activity found in the soil of the plots, the isotopic technique yielded confident results, comparable to those obtained by the traditional direct measurements.     

Soil physical fertility and crop performance as affected by long term application of FYM and inorganic fertilizers in rice–wheat system

Soil fertility, one of the important determinants of agricultural productivity, is generally thought to be supplemented through the application of nutrients mainly through inorganic fertilizers. The physical fertility of the soil, which creates suitable environment for the availability and uptake of these nutrients, is generally ignored. The present study aims to characterize the soil physical environment in relation to the long term application of farm yard manure (FYM) and inorganic fertilizers in rice–wheat. The treatments during both rice and wheat crops were (i) farm yard manure @ 20 t ha⁻¹ (FYM); (ii) nitrogen @ 120 kg ha⁻¹ (N₁₂₀); (iii) nitrogen and phosphorus @ 120 and 30 kg ha⁻¹ (N₁₂₀P₃₀) and (iv) nitrogen, phosphorus and potassium @ 120, 30 and 30 kg ha⁻¹ (N₁₂₀P₃₀K₃₀) in addition to (iv) control treatment, i.e. without any fertilizer and/or FYM addition. The treatments were replicated four times in randomized block design in a sandy loam (typic Ustipsament, non-saline, slightly alkaline). Bulk density, structural stability of soil aggregates and water holding capacity of 0–60 cm soil layer were measured.

The average mean weight diameter (MWD) was highest in FYM-plots both in rice (0.237 mm) and wheat (0.249 mm) closely followed by that in N₁₂₀P₃₀K₃₀ plots. The effect of FYM in increasing the MWD decreased with soil depth. The addition of both FYM and N₁₂₀P₃₀K₃₀ increased the organic carbon by 44 and 37%, respectively in rice. The total porosity of soil increased with the application of both FYM and N₁₂₀P₃₀K₃₀ from that in control plots. In 0–15 cm soil layer, the total porosity increased by 25% with FYM from that in control plots. This difference decreased to 13% in 15–30 cm soil layer. The average water holding capacity (WHC) was 16 and 11% higher with FYM and N₁₂₀P₃₀K₃₀ application from that in control plots. The MWD, total porosity and WHC improved with the application of balanced application of fertilizers. The grain yield and uptake of N, P and K by both rice and wheat were higher with the application of FYM and inorganic fertilizers than in control plots. The carbon sequestration rate after 32 years was maximum (0.31 t ha⁻¹ year⁻¹) in FYM-plots, followed by 0.26 t ha⁻¹ year⁻¹ in N₁₂₀P₃₀K₃₀-plots, 0.19 t ha⁻¹ year⁻¹ in N₁₂₀P₃₀ and minimum (0.13 t ha⁻¹ year⁻¹) in N₁₂₀-plots.     

Influence of method of land preparation on weed regeneration in cowpea (Vigna unguiculata L. Walp.)

The influence of four methods of land preparation on weed regeneration and the efficacy of imazaquin (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidasol-2yl]-3-quinolinecarboxylic acid) applied singly at 0.18 kg a.i. ha⁻¹, and in tank mixture with either 2.0 kg a.i. ha⁻¹ of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamine) or 0.64 kg a.i. ha⁻¹ of diuron (N′-(3,4-dichlorophenyl)-N, N-dimethylurea) in cowpea (Vigna unguiculata L. Walp.) was studied in the late season of 1989 at the University of Benin and in the early season of 1990 at the Nigerian Institute for Oil Palm Research (NIFOR), Benin City, Nigeria. The methods of land preparation were: no-tillage (NT-B with all the stubble mulch packed and burnt in situ); no-tillage (NT-Pa, the existing vegetation was killed with paraquat and the sod left in situ); ploughing (P); ploughing and harrowing (P+H). The number of regenerating weeds was significantly greater were the land was prepared by no-till and the stubble mulch left in situ compared with all other methods of land preparation. There were no significant differences in number of regenerating weeds and the weed biomass between NT-B, P and P+H. Herbicide treatments significantly reduced both the number of regenerating weeds and weed biomass irrespective of the method of land preparation. Herbicides generally performed better in NT-B, P, P+H than in NT-Pa plots. Cowpea pod or grain yield was not significantly influenced by the method of land preparation. However, it was significantly depressed where the plots were left unweeded for all methods of land preparation, especially so in the NT-Pa treatment. These observations suggest that where a good degree of burn or stubble mulch removal is achieved, further soil tillage may not necessarily enhance the efficacy of imazaquin and its tank-mixtures with diuron or metolachlor.     

Leaching of N,P and glyphosate from two soils after herbicide treatment and incorporation of a ryegrass catch crop

During 2005–2007, studies were carried out in two field experiments in southwest Sweden with separately tile‐drained plots on a sandy soil (three replicates) and on a clay soil (two replicates). The overall aim was to determine the effects of different cropping systems with catch crops on losses of N, P and glyphosate. Different times of glyphosate treatment of undersown ryegrass catch crops were examined in combination with soil tillage in November or spring. Drainage water was sampled continuously in proportion to water flow and analysed for N, P and glyphosate. Catch crops were sampled in late autumn and spring and soil was analysed for mineral N content. The yields of following cereal crops were determined. The importance of keeping the catch crop growing as long as possible in the autumn is demonstrated to decrease the risk of N leaching. During a year with high drainage on the sandy soil, annual N leaching was 26 kg/ha higher for plots with a catch crop killed with glyphosate in late September than for plots with a catch crop, while the difference was very small during 1 yr with less drainage. Having the catch crop in place during October was the most important factor, whereas the time of incorporation of a dead catch crop did not influence N leaching from either of the two soils. However, incorporation of a growing catch crop in spring resulted in decreased crop yields, especially on the clay soil. Soil type affected glyphosate leaching to a larger extent than the experimental treatments. Glyphosate was not leached from the sand at all, while it was found at average concentrations of 0.25 μg/L in drainage water from the clay soil on all sampling occasions. Phosphorus leaching also varied (on average 0.2 and 0.5 kg/ha/yr from the sand and clay, respectively), but was not significantly affected by the different catch crop treatments.     

Wind erosion and airborne dust deposition in farmland during spring in the Horqin Sandy Land of eastern Inner Mongolia, China

In the Horqin Sandy Land of eastern Inner Mongolia in northern China, wind erosion in farmland is very common in a period from thawing of frozen surface soil in mid-March to sowing of crops in the end of April, largely because of dry and windy weather. However, little is known about the magnitude of wind erosion and associated nutrient losses due to erosion and the addition of nutrients by airborne dust deposition to farmlands during this period. A field experiment was conducted in an Entisol with sand origin under corn (Zea mays L.) production to investigate daily changes in wind speed and wind erosion intensity (as measured by soil transport rate) over a period from 20 March to 30 April 2001. We also measured daily rates of airborne dust deposition during the spring seasons with the high frequency of dust storm occurrence. The rates of soil transport by wind varied greatly from 13.2 to 1254.1 kg ha⁻¹ per day, averaging 232.1 kg ha⁻¹ per day, largely attributable to great variation between days in wind speed within the study period. The potential losses of nutrients through wind erosion were 0.26–24.95 kg ha⁻¹ per day (averaging 4.62 kg ha⁻¹ per day) in organic matter, 0.02–1.64 kg ha⁻¹ per day (averaging 0.31 kg ha⁻¹ per day) in nitrogen and 0.01–0.7 kg ha⁻¹ per day (averaging 0.13 kg ha⁻¹ per day) in phosphorus. The mean rates of airborne dust deposition ranged from 4.0 to 48.9 kg ha⁻¹ per day, averaging 19.9 kg ha⁻¹ per day, during the spring seasons. The potential addition of organic matter, nitrogen and phosphorus by dust input to the experimental field was, on average, 0.54, 0.04 and 0.02 kg ha⁻¹ per day, respectively. Although the addition was a fraction of the losses due to erosion, nevertheless, dust input in the spring seasons is one of the major suppliers of soil nutrition. The fact that the addition of nutrients by dust is about 1/10 of the losses of soil nutrients through wind erosion suggests that developing and adopting more effective management practices to reduce soil erosion losses and to improve soil fertility are crucial to achieve a sustainable agricultural system in a fragile, semiarid sandy land environment.     

Soil biotic and biochemical factors in a long-term tillage and stubble management experiment on a vertisol. 2. Nitrogen deficiency with zero tillage and stubble retention

The aim of this investigation was to find the cause of poor growth of barley that occurred with zero tillage and stubble retention in a long-term fallow management experiment on a vertisol in southern Queensland. The experiment compares 12 treatments comprising three factors of tillage (zero, mechanical), stubble (burnt, retained) and nitrogen fertilizer (0, 23 and 46 kg ha⁻¹ year⁻¹) in four randomised blocks. Dry matter yield of barley at anthesis showed a highly significant Mitscherlich relationship with tissue nitrogen (N) concentration. Cate-Nelson analysis indicated a critical N concentration of 1.58%N. The barley responded to fertilizer N although 9 of 12 zero-till, stubble-retained plots and 5 of 12 mechanical-till, stubble-retained plots still lay below the critical N concentration. Zero-till, stubble-retained treatment had least nitrate-N in the soil profile to 120 cm indicating a problem in N supply rather than in N recovery by the roots.

The effects of the long-term treatments on properties related to the N supplying capacity of the soil were investigated by determinations on topsoil samples from which undecomposed stubble was removed. Soil from zero-till, stubble-retained treatment had more organic carbon (C) and Kjeldahl N than mechanical-till, stubble-retained treatment which had more than stubble-burnt treatments. The C:N ratio of the soil was lower in stubble retained treatments. Kjeldahl N was higher with annual N fertilization only where stubble was retained. Organic C increased and Kjeldahl N decreased over a 3 year period in all treatments. Respiration of CO₂, mineralizable N, and microbial biomass C and N in the soil were all greater with long-term stubble retention than with stubble burning irrespective of tillage treatment.

Numbers of root-lesion nematodes (Pratylenchus thornei Sher and Allen) and stunt nematode (Merlinius brevidens (Allen) Siddiqi) following a wheat crop were substantially greater with zero-till than with mechanical-till. Root-lesion nematode were increased by N fertilization of previous crops while stunt nematodes were increased by stubble-retention. Earthworm numbers were increased by stubble retention particularly when combined with zero tillage.

Factors responsible for observed differences in soil nitrate and crop response to N in this field experiment appear to be: (a) N immobilization by recently retained stubble, (b) lower rates of mineralization of soil N under surface-retained stubble, and (c) higher rates of leaching in zero-till treatment.     

Yield and N uptake as affected by soil tillage and catch crop

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.     

Potassium balances for arable soils in southern England 1986–1999

Abstract. The behaviour of potassium (K) in a range of arable soils was examined by plotting the change in exchangeable K of the topsoil (Δ K_ex) at the end of a 3–5 year period against the K balance over the same period (fertilizer K applied minus offtake in crops, estimated from farmers' records of yield and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops MAFF 2000) are valid averages, 10–50% of Δ K_ex was explained by the balance, relationships being stronger on shallow/stony soils. Excess fertilizer tended to increase K_ex and reduced fertilization decreased it, requiring between 1.2 and 5.4 kg K ha⁻¹ for each mg L⁻¹Δ K_ex. However, merely to prevent K_ex falling required an extra 20 kg K ha⁻¹ yr⁻¹ fertilizer on Chalk soils and soils formed in the overlying Tertiary and Quaternary deposits, despite clay contents >18%. Whereas, on older geological materials, medium soils needed no extra K and clays gained 17 kg K ha⁻¹ yr⁻¹. It is unlikely that the apparent losses on some soil types are anomalies due to greater crop K contents. Theory and the literature suggest leaching from the topsoil as a major factor; accumulation in the subsoil was not measured. Recommendations for K fertilization of UK soils might be improved by including loss or gain corrections for certain soil types.     

Effects of long-term winter wheat, summer fallow residue and nutrient management on field hydrology for a silt loam in north-central Oregon

In a region where water is the primary limiting factor of crop production, loss of water from fields by overland flow represents an economic loss to producers. Traditional crop management practices in north-central Oregon have led to crop water loss by overland flow. In 1931, a long-term experiment was begun near Pendleton, Oregon, in a Walla Walla silt loam (coarse-silty, mixed, mesic Typic Haploxeroll—US; Kastanozems—FAO), to examine the influence on soil fertility and crop production by nutrient amendments and crop residue management practices. This experiment provided the opportunity to evaluate the influence of a several traditional farming practices on field hydrology. Tillage in all treatments consisted of moldboard plowing and multiple passes with secondary tillage equipment to smooth the surface for planting and for weed control. The treatments were combinations of nutrient amendments (0.90 kg N ha⁻¹ commercial fertilizer, and 145 kg N ha⁻¹ from manure) and residue management (fall-burn, spring-burn, and no-burn), whose soil organic carbon increased with increasing nutrient amendments. These treatments were in a winter wheat–fallow system and represent a set of past and current cultural practices. Overland flow from these treatments was measured. Lister furrows separated the plots of 12 m×40 m (≈0.05 ha) to prevent overland flow from treatment to treatment and were instrumented with weirs to capture and measure overland flow. To determine if hydrologic differences existed between treatments, we tested the overland flow to precipitation (Q/P) ratio. The Q/P ratio (P<0.15) was greatest within crop year/low soil fertility (0 kg N ha⁻¹, burn) whereas the high fertility (145 kg N ha⁻¹, no-burn) treatment crop year plots Q/P ratios were similar to fallow, standing stubble plots. Most notably, the manure amendment plots in crop, produce significantly less overland flow than the other residue and nutrient management practices, and marginally less overland flow than treatments in stubble. This research demonstrates that overland flow was greater from low fertility and stubble burned treatments. Increased overland flow increases the risk of soil erosion and loss of water to overland flow is potentially a loss of needed soil water for crop growth and production.     

Soil physical responses to novel rice cultural practices in the rice–wheat system: Comparative evidence from a swelling soil in Nepal

Soil puddling in advance of rice (Oryza sativa L.) transplanting disperses surface aggregates and generates compaction at depth. As a management scheme for rice, puddling is typically considered advantageous for maximizing resource availability and yield. However, some experimental findings suggest a conflict between edaphic conditions created by this establishment technique and the performance of subsequent non-rice crops like wheat (Triticum aestivum L.). At a site in the mid-hills region of Nepal on a silt loam soil with vertic characteristics, we compared the impact of six rice tillage (surface tillage—T₁, shank subsoiler—T₂, shank subsoiler + moldboard plough—T₃) and establishment (soil puddling + transplanting—TPR, direct seeding—DSR) combinations on soil physical properties over two cycles of the rice–wheat rotation. For the rice season, 0–20 cm saturated hydraulic conductivity (K_sat) in the DSR plots was 2.6 and 4.3 times higher than their TPR counterparts in the first (Y₁) and second (Y₂) years, respectively (TPR-Y₁ = 93 mm day⁻¹, DSR-Y₁ = 241 mm day⁻¹, TPR-Y₂ = 133 mm day⁻¹, DSR-Y₂ = 582 mm day⁻¹), whereas tillage method did not significantly influence K_sat in this soil layer. The impact of rice establishment method was reflected in higher TPR bulk densities in the 5–10 (DSR = 1.19 g cm⁻³, TPR = 1.24 g cm⁻³) and 10–15 cm (DSR = 1.24 g cm⁻³, TPR = 1.29 g cm⁻³) depth increments in the wet season. Although none of the treatments significantly influenced the position or thickness of the plough sole, penetration resistance profiles suggest that vertical fractures with reduced soil strength were created within the pan region by deep tillage (T₂ and T₃), although these features were not associated with higher hydraulic conductivities from 20 to 50 cm. As the soils dried at the end of the rice season, crack propagation in the deep tilled plots (T₂ and T₃) was more pervasive. During the wheat season, comparable bulk density profiles and soil moisture retention characteristics across the treatments suggest that many of the edaphic changes induced by contrasting rice tillage and establishment practices did not persist in the self-mulching, vertic soils at our site. Conversely, significant increases in K_sat among the DSR plots from Y₁ to Y₂ (Y₁ = 241 mm day⁻¹, Y₂ = 582 mm day⁻¹) imply a temporal element to soil structural regeneration with adoption of direct seeding.     

Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model

Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO₂) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: dC_sail(t)/dt = −kC_soil(t) and that soil C-CO₂ emission is proportional to the C decay rate in soil, where C_soil(t) is the available labile soil C (g m⁻²) at any time (t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till (F_NT) and tilled (F_T) fluxes, which is: F_T=a₁F_NT e^−a₂t, where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R²), index of agreement and model efficiency, with R² as high as 0.97. The two parameters included in the model are related to the difference between the decay constant (k factor) of tilled and no-till plots (a₂) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage (a₁). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a₁) and −1.52 × 10⁻² and 2.2 × 10⁻² day⁻¹ (a₂). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters.     

Predicting soil erosion in conservation tillage cotton production systems using the revised universal soil loss equation (RUSLE)

Despite being one of the most profitable crops for the southeastern USA, cotton (Gossypium hirsutum L.) is considered to create a greater soil erosion hazard than other annual crops such as corn (Zea mays L.) and soybeans (Glycine max (L.) Merr.). Reduced tillage systems and cover cropping can reduce soil erosion and leaching of nutrients into ground water. The objectives of this study, which was conducted in north Alabama from 1996 to 1998, were to assess the impact of no-till and mulch-till systems with a winter rye (Secale cereale L.) cover crop and poultry litter on soil erosion estimates in cotton plots using the revised universal soil loss equation (RUSLE). Soil erosion estimates in conventional till plots with or without a winter rye cover crop and ammonium nitrate fertilizer were double the 11 t ha⁻¹ yr⁻¹ tolerance level for the Decatur series soils. However, using poultry litter as the N source (100 kg N ha⁻¹) gave soil erosion estimates about 50% below the tolerance level under conventional till. Doubling the N rate through poultry litter to 200 kg N ha⁻¹ under no-till system gave the lowest soil erosion estimate level. No-till and mulch-till gave erosion estimates which were about 50% of the tolerance level with or without cover cropping or N fertilization. This study shows that no-till and mulch-till systems with cover cropping and poultry litter can reduce soil erosion in addition to increasing cotton growth and lint yields, and thus improve sustainability of cotton soils in the southeastern USA.     

Simple phosphorus saturation index to estimate risk of dissolved P in runoff from arable soils

Abstract. There is increasing evidence that phosphorus has been accumulating in the surface horizons of agricultural soils to the extent that some soils represent a potential diffuse source of pollution to surface waters. The relationships between equilibrium phosphorus concentration at zero sorption (EPC ₀) of soil and a number of soil physicochemical variables were investigated in the surface layers of arable and grassland agricultural soils sampled from the Thame catchment, England. Soil EPC₀ could be predicted from an equation including soil test (Olsen) P, soil phosphate sorption index (PSI) and organic matter content (OM) (R²=0.88; P <0.001) across a range of soil types and land use. The simple index Olsen P/PSI was found to be a good predictor of EPC₀ (R²=0.77; P <0.001) and readily desorbable (0.02 m KCl extractable) P (R²=0.73; P <0.001) across a range of soil types under arable having soil organic matter contents of <10%.     

Soil C, N and crop yields in Alabama's long-term ‘Old Rotation' cotton experiment

The Old Rotation cotton experiment at Auburn, Alabama, is the oldest, continuous cotton experiment in the world (cf. 1896). Long-term cropping systems provide a unique opportunity to observe the effects of 100 years of cropping on soil organic carbon (SOC). The objective of this paper was to summarize limited data on SOC and N cycling in this historic experiment. Soil organic C has been measured on the 13 plots (6 cropping systems) in 1988, 1992 and 1994. Long-term planting of winter legumes with no other source of N applied resulted in higher SOC (9.5 g C kg⁻¹) in the plow layer (0–20 cm depth) compared to continuous cotton with no winter cover crops (4.2 g C kg⁻¹). A 3-year rotation of cotton–winter legumes–corn–small grain–soybean resulted in 12.1 g C kg⁻¹. There was a significant (P<0.05), quadratic cotton yield response (R²=0.54) to increasing SOC. Winter legume cover crops supplied between 90 and 170 kg N ha⁻¹. Where no N has been applied in fertilizer or from a legume crop, annual N removal in the cotton crop is around 13 kg ha⁻¹, about the same as that fixed in precipitation.     

Barley yield and evapotranspiration governed by tillage practices in interior Alaska

Tillage and residue management practices are sought in the subarctic where small grain production is often curtailed by the lack of soil water. Barley (Hordeum vulgare L.) grain yield and evapotranspiration were compared among four tillage and three residue management practices near Delta Junction, Alaska, USA from 1988 through 1991. Barley was hand-harvested in the fall whereas soil water content was determined biweekly during the growing season by neutron attenuation. Grain yield was similar for spring disk, fall chisel, and conventional (fall and spring disk) tillage across years. No tillage, however, resulted in a 260 kg ha⁻¹ greater yield as compared with fall chisel and conventional tillage in 1990 when evaporative demand exceeded that in other years by nearly 10%. In 1990 and 1991, grain yield from plots devoid of stubble and loose straw was at least 200 kg ha⁻¹ greater than from plots with stubble or stubble and loose straw. Barley consumed at least 15 mm more water to achieve the greater yield on no tillage or no stubble and loose straw plots. Water-use efficiency did not vary among tillage treatments, but was greatest in 1990 for plots devoid of stubble and loose straw. This study suggests that, in dry years with high evaporative demand, no tillage or removal of stubble and loose straw from the soil surface will enhance grain production and water-use efficiency of barley in the subarctic.     

氨基酸对三种石灰性土壤磷素有效性的影响及其作用差异机制

磷是农作物生长发育的必需元素,为了保证我国粮食安全,提高农作物的产量,提高磷肥有效性十分重要。本试验选取三种石灰性土壤（郑州潮土、周口褐土和昌图风沙土）为研究对象,通过90天的室内埋土试验,在三种土壤中研究氨基酸与磷酸一铵配施对提高土壤中磷肥有效性的影响。研究结果表明:（1）氨基酸在三种石灰性土壤中均能够提高磷酸一铵的有效性,郑州潮土、周口褐土和昌图风沙土的磷肥有效性与单施磷酸一铵相比分别提高了21.16%、10.87%和4.06%;（2）氨基酸的加入降低了土壤中Ca₂-P向Ca₈-P或其他难溶形态磷的转化,通过对三种土壤进行相关性和通径分析的得出在郑州潮土、周口褐土和昌图风沙土中主要决策因子是Ca₂-P,决策系数分别到达了0.836、0.946和0.712（P < 0.05）,郑州潮土、周口褐土主要限制因子是Ca₈-P,决策系数分别为?0.066、?0.401（P < 0.05）,昌图风沙土主要限制因子是Ca₈-P和Fe-P,决策系数分别为?0.080和?0.105（P < 0.05）;（3）氨基酸的加入能够降低三种石灰性土壤的pH和CaCO₃含量,有利于提高磷肥有效性;（4）通过对三种土壤的有效磷含量与土壤理化性质进行冗余分析,得出有机质（SOM）和碳酸钙 （CaCO₃）是影响磷肥在三种土壤中固定速率差异的主要原因,SOM和CaCO₃分别解释了有效磷含量全部变异的36.5%和25.6% （P < 0.05）。氨基酸在三种石灰性土壤中均能够提高磷肥有效性,主要途径是降低土壤的pH和CaCO₃含量,抑制Ca₂-P的快速转化。在三种石灰性土壤中,氨基酸作用有差异的主要原因是三种土壤中SOM和CaCO₃含量的差异,提高SOM,降低土壤中CaCO₃能够降低土壤对磷的固定,提高磷肥有效性。     

Increased predicted losses of phosphorus to surface waters from soils with high Olsen-P concentrations

Abstract. Diffuse soluble reactive P (SRP) & total P (TP) loads from over 50 major river catchments in Northern Ireland were predicted using an export coefficient modelling approach. Phosphorus export coefficients for each CORINE land cover class, derived from satellite imagery, allowed the prediction of P loads from a breakdown of the CORINE land cover classes by catchment using a GIS. This approach was validated using observed P loads calculated from flow and concentration data. Mean measured Olsen-P concentrations in the soil A-horizon were also determined on a catchment basis. Plots of P loads to the watercourse versus Olsen-P concentrations in the soil showed a breakpoint around 22 mg Olsen- P l⁻¹ for both SRP & TP data. Below Olsen-P concentrations of 22 mg l⁻¹, SRP & TP losses were essentially independent of Olsen-P at 0.28 and 0.63 kg P ha⁻¹ yr⁻¹, respectively. Above Olsen-P concentrations of 22 mg l⁻¹, there was considerable spread in the P loss data. Nevertheless, significant upward trends in SRP and TP losses to watercourses were detected with increasing Olsen-P at a rate of approximately 0.5 and 1.0 kg P ha⁻¹ yr⁻¹, for SRP and TP respectively, for each 10 mg l⁻¹ increase in Olsen-P.     

Soil erosion estimation in conservation tillage systems with poultry litter application using RUSLE 2.0 model

Soil erosion is a major threat to global economic and environmental sustainability. This study evaluated long-term effects of conservation tillage with poultry litter application on soil erosion estimates in cotton (Gossypium hirsutum L.) plots using RUSLE 2.0 computer model. Treatments consisting of no-till, mulch-till, and conventional tillage systems, winter rye (Secale cereale L.) cover cropping and poultry litter, and ammonium nitrate sources of nitrogen were established at the Alabama Agricultural Experiment Station, Belle Mina, AL (34°41′N, 86°52′W), beginning fall 1996. Soil erosion estimates in cotton plots under conventional tillage system with winter rye cover cropping declined by 36% from 8.0 Mg ha⁻¹ year⁻¹ in 1997 to 5.1 Mg ha⁻¹ year⁻¹ in 2004. This result was largely attributed to cumulative effect of surface residue cover which increased by 17%, from 20% in 1997 to 37% in 2004. In conventional tillage without winter rye cover cropping, soil erosion estimates were 11.0 Mg ha⁻¹ year⁻¹ in 1997 and increased to 12.0 Mg ha⁻¹ year⁻¹ in 2004. In no-till system, soil erosion estimates generally remained stable over the study period, averaging 0.5 and 1.3 Mg ha⁻¹ year⁻¹with and without winter rye cover cropping, respectively. This study shows that cover cropping is critical to reduce soil erosion and to increase the sustainability of cotton production in the southeast U.S. Application of N in the form of ammonium nitrate or poultry litter significantly increased cotton canopy cover and surface root biomass, which are desirable attributes for soil erosion reduction in cotton plots.