中国亚热带地区酸性土壤上部分酸化的磷矿石的农学潜力

A glasshouse experiment was conducted to evaluate the agronomic potential of four partially acidulated rock phosphates(PARP) in three representative solis sampled from subtripical China.The PARPs were manufactured by attacking a moderately reactive phosphate rock either with sulfuric acid alone or with combination of sulfuric and phosphoric acids at 30 or 60 percent of acidulation.Shoot dry weight and P accumulation of six successive cuttings of ryegrass were used to compare the agronomic potential of these fertilizers with that of the raw rock phosphate(RP) and monocalcium phosphate (MCP).Results indicated that the effectiveness of various phosphates was determined both by the solubility of the phosphates and by the acidity and P-fixing capacity of the soils.The higher the watersoluble P contained,the better the effectiveness of the fertilizer was.Although plant P accumulation of PARP treatments was constantly lower than that of MCP treatment,some PARPs could still get a dry matter production similar to that of MCP treatment.PARP SP60,which was acidulated with a mixture of sulfuric acid and phosphoric acid at 60 percent of acidulation and contained the highest soluble,P,was as effective as MCP in terms of dry matter production on all the soils.S60 and C1 which were both acidulated with sulfuric acid with the former at 60 percent of acidulation and the latter at 30 percent but with a further addition of monoammonium phosphate,were more than 80 percent as efective as MCP,Raw RP also showed a reasonable effectiveness which increased with soil acidity.It was suggested from the study that some of these APRPs could be expected to have a comparable field performance as soluble P fertilizers in the acid soil regions.     

用最小可检测差异技术评估耕作方式对土壤C固定的影响

Three long-term field trials in humid regions of Canada and the USA were used to evaluate the influence of soil depth and sample numbers on soil organic carbon （SOC） sequestration in no-tillage （NT） and moldboard plow （MP） corn （Zea mays L.） and soybean （Glycine max L.） production systems. The first trial was conducted on a Maryhill silt loam （Typic Hapludalf） at Elora, Ontario, Canada, the second on a Brookston clay loam （Typic Argiaquoll） at Woodslee, Ontario, Canada, and the third on a Thorp silt loam （Argiaquic Argialboll） at Urbana, Illinois, USA. No-tillage led to significantly higher SOC concentrations in the top 5 cm compared to MP at all 3 sites. However, NT resulted in significantly lower SOC in sub-surface soils as compared to MP at Woodslee （10-20 cm, P =0.01） and Urbana （20-30 cm, P 〈 0.10）. No-tillage had significantly more SOC storage than MP at the Elora site （3.3 Mg C ha^-1） and at the Woodslee site （6.2 Mg C ha^-1） on an equivalent mass basis （1 350 Mg ha^-1 soil equivalent mass）. Similarly, NT had greater SOC storage than MP at the Urbana site （2.7 Mg C ha^-1） on an equivalent mass basis of 675 Mg ha^-1 soil. However, these differences disappeared when the entire plow layer was evaluated for both the Woodslee and Urbana sites as a result of the higher SOC concentrations in MP than in NT at depth. Using the minimum detectable difference technique, we observed that up to 1 500 soil sample per tillage treatment comparison will have to be collected and analyzed for the Elora and Woodslee sites and over 40 soil samples per tillage treatment comparison for the Urbana to statistically separate significant differences in the SOC contents of sub-plow depth soils. Therefore, it is impracticable, and at the least prohibitively expensive, to detect tillage-induced differences in soil C beyond the plow layer in various soils.     

不同耕作方式对中国东北黑土有机碳的短期影响

A tillage experiment, consisting of moldboard plow （MP）, ridge tillage （RT）, and no-tillage （NT）, was performed in a randomized complete block design with four replicates to study the effect of 3-year tillage management on SOC content and its distribution in surface layer （30 cm） of a clay loam soil in northeast China. NT did not lead to significant increase of SOC in topsoil （0-5 cm） compared with MP and RT; however, the SOC content in NT soil was remarkably reduced at a depth of 5-20 cm. Accordingly, short-term （3-year） NT management tended to stratify SOC concentration, but not necessarily increase its storage in the plow layer for the soil.     

盐碱地咸水灌溉枸杞种植条件下土壤盐分变化

In order to utilize the wasted saline-sodic soils under shallow groundwater condition,a 3-year field study was carried in a field cropped with Lycium barbarum L.and irrigated by drip irrigation with saline groundwater under the water table depth of 30-40 cm in the northern Yinchuan Plain,China.Effects of cropping duration (one,two,and three years) on soil salinity,soil solution composition,and pH in three adjacent plots were investigated in 2008.Results showed that a high irrigation frequency maintained high soil water potential and subsequently facilitated infiltration and downward movement of water and salt in the crop root zone.Salt accumulated on the edges of the ridges,and soil saturated-paste electrical conductivity (ECe) was higher in the edge.Concentrations of Na+,Ca2+,Mg2+,Cl-,and SO42- in the soil increased with the soil depth as did the ECe,while HCO3- and pH had a relative uniform distribution in soil profile.As planting year increased,the ECe and soil salts in the field had a decreasing tendency,while in the root zone they decreased immediately after irrigation and then remained relatively stable in the following growing seasons.HCO3- and pH had little change with the planting year.Results suggested that the application of drip irrigation with saline water could ameliorate saline-sodic soil and provide a relatively feasible soil environment for the growth of salt-tolerant plant Lycium barbarum L.under the saline-sodic soils with shallow groundwater.     

三种耕作制度下密西西比州两种加入家禽垫料的土壤上磷动态研究

An experiment arranged in a randomized complete block design with three replications was conducted on a Lexington soil (fine-silty, mixed, active, thermic, Ultic Hapludalfs) and a Loring soil (fine-silty, mixed, active, thermic, Oxyaquic Fragiudalfs) in Mississippi from September 1997 to September 2000 on 18 runoff plots under natural rainfall condition to study the phosphorus (P) dynamics in poultry litter amended soils under three management systems combining tillage and planting date treatments to identify effective management practices in southern U. S. A. The management systems in the study were:1) tillage in the fall prior to litter application followed by a delayed planting of fall forages (CT-DP); 2) tillage followed by immediate planting of the fall forage with subsequent litter application (CT-IP); and 3) no-till with planting prior to litter application (NT-IP). The results indicated that there was significant increase in soil P after 3 years of poultry litter application for both Lexington and Loring soils (P <0.05). Based on P budget analysis, the majority of P from poultry litter application (> 90%), was accumulated in both soils. In Loring soil, soluble P mass in the runoff was significantly higher from NT-IP than from CT-DP and CT-IP over the entire study period (P <0.01). For both soils, there were no significant differences in sediment P mass between management systems. For Loring soil, CT-DP and CT-IP were effective management practices to mitigate negative effects due to poultry litter application.     

长期施肥对中国亚热带水稻土土壤稳定性和机械属性的影响

Wet stability, penetration resistance （PR）, and tensile strength （TS） of paddy soils under a fertilization experiment for 22 years were determined to elucidate the function of soil organic matter in paddy soil stabilization. The treatments included no fertilization （CK）, normal chemical fertilization （NPK）, double the NPK application rates （2NPK）, and NPK mixed with organic manure （NPK＋OM）. Compared with CK, Fertilization increased soil organic carbon （SOC） and soil porosity. The results of soil aggregate fragmentation degree （SAFD） showed that fast wetting by water was the key fragmentation mechanism. Among the treatments, the NPK＋OM treatment had the largest size of water-stable aggregates and greatest normal mean weight diameter （NMWD） （P ≤ 0.05）, but the lowest PR and TS in both cultivated horizon （Ap） and plow pan. The CK and 2NPK treatments were measured with PR 〉 2.0 MPa and friability index 〈 0.20, respectively, in the Ap horizon, suggesting that the soils was mechanically unfavourable to root growth and tillage. In the plow pan, the fertilization treatments had greater TS and PR than in CK. TS and PR of the tested soil aggregates were negatively correlated to SOC content and soil porosity. This study suggested that chemical fertilization could cause deterioration of mechanical properties while application of organic manure could improve soil stability and mechanical properties.     

有机配体、竞争阳离子和pH对土壤中Zn分解的影响

A series of experiments were conducted to examine the interactive effects of an organic ligand, a competing cation, and pH on the dissolution of zinc （Zn） from three California soils, Maymen sandy loam, Merced clay, and Yolo clay loam. The concentrations of soluble Zn of the three soils were low in a background solution of Ca（NO3）2. Citric acid, a common organic ligand found in the rhizosphere, was effective in mobilizing Zn in these soils; its presence enhanced the concentration of Zn in soil solution by citrate forming a complex with Zn. The ability of Zn to form a complex with citric acid in the soil solution was dependent on the concentration of citric acid, pH, and the concentration of the competing cation Ca^2＋. The pH of the soil solution determined the extent of desorption of Zn in solid phase in the presence of citric acid. The amounts of Zn released from the solid phase were proportional to the concentration of citric acid and inversely proportional to the concentration of Ca（NO3）2 background solution, which supplied the competing cation Ca^2＋ for the formation of a complex with citrate. When the soil suspension was spiked with Zn, the adsorption of Zn by the soils was retarded by citric acid via the formation of the soluble Zn-citrate complex. The dissolution of Zn in the presence of citric acid was pH dependent in both adsorption and desorption processes.     

氮施用水平和方式对高粱作物产量和质量的影响

A field study was conducted for two years at the Arid Zone Research Institute, Dera Ismail Khan, Pakistan, to determine the optimum level of nitrogen and efficient application method in the production of sorghum （Sorghum bicolor L.）. Using four levels of nitrogen, i.e., 0, 60, 90, and 120 kg ha^-1, and two different application methods （soil application and foliar spray）, the experiment was laid out in a split-plot design, where the main plots were used to determine the effective method of application and the subplots were used to detect the influence of N levels on the grain yield. The average data obtained after two years of study indicated an increase in the grain yields with an increase in N levels irrespective of the method used of N application. The grain yield increased from 2.92 to 5.61 t ha^-1 in the plots that were treated with 90 kg N ha^-1 compared with the control plots. Quadratic regression analysis showed that the increase in the yield was higher at the lower levels of N compared with the succeeding higher levels. The soil application method, producing an average grain yield of 4.79 t ha^-1, was found to be superior to the foliar spray method with an average grain yield of 4.56 t ha^-1. The protein content of the grain showed a linear increase with N application, attaining the maximum at 120 kg N ha^-1 in both the methods of N application. In addition, compared with the method of soil application, higher crude protein contents were observed using the method of foliar spray at all N levels.     

盆栽研究钢渣用作铁肥对玉米生长和土壤改良的作用

The feasibility of steel slag used as an iron fertilizer was studied in a pot experiment with corn. Slag alone or acidified slag was added to two Fe-deficient calcareous soils at different rates. Results showed that moderate rates （10 and 20 g kg^-1） of slag or acidified slag substantially increased corn dry matter yield and Fe uptake. Application of steel slag increased the residual concentration of ammonium bicarbonate-diethylenetriamine pentaacetic acid （AB-DTPA） extractable Fe in the soils. The increase of extractable Fe was usually proportional to the application rate, and enhanced by the acidification of slag. Steel slag appeared to be a promising and inexpensive source of Fe to alleviate crop Fe chlorosis in Fe-deficient calcareous soils.     

长期施肥和耕作管理对华北平原土壤肥力的影响

In the North China Plain, fertilizer management and tillage practices have been changing rapidly during the last three decades; however, the influences of long-term fertilizer applications and tillage systems on fertility of salt-affected soils have not been well understood under a winter wheat (Triticum aestivum L.)-maize (Zea mays L.) annual double cropping system. A field experiment was established in 1985 on a Cambosol at the Quzhou Experimental Station, China Agricultural University, to investigate the responses of soil fertility to fertilizer and tillage practices. The experiment was established as an orthogonal design with nine treatments of different tillage methods and/or fertilizer applications. In October 2001, composite soil samples were collected from the 0–20 and 20–40 cm layers and analyzed for soil fertility indices. The results showed that after 17 years of nitrogen (N) and phosphorous (P) fertilizer and straw applications, soil organic matter (SOM) in the top layer was increased significantly from 7.00 to 9.30–13.14 g kg-1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg-1 in the 20–40 cm layer. Soil total N (TN) was increased significantly from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg-1 in the 0–20 and 20–40 cm layers, respectively, with N fertilizer application; however, there was no apparent effect of straw application on TN content. The amounts of soil total P (TP) and rapidly available P (RP) were increased significantly from 0.60 to 0.67–1.31 g kg-1 in the 0–20 cm layer and from 0.52 to 0.60–0.73 g kg-1 in the 20–40 cm layer with P fertilizer application, but were decreased with combined N and P fertilizer applications. The applications of N and P fertilizers significantly increased the crop yields, but decreased the rapidly available potassium (RK) in the soil. Straw return could only meet part of the crop potassium requirements. Our results also suggested that though some soil fertility parameters were maintained or enhanced under the long-term fertilizer and straw applications, careful soil quality monitoring was necessary as other nutrients could be depleted. Spreading straw on soil surface before tillage and leaving straw at soil surface without tillage were two advantageous practices to increase SOM accumulation in the surface layer. Plowing the soil broke aggregates and increased aeration of the soil, which led to enhanced organic matter mineralization.     

Aspartase Activity of Soils Under Different Management Systems

Abstract

Recent interest in soil tillage, cropping systems, and residue management has focused on low‐input sustainable agriculture. This study was carried out to evaluate the effects of various management systems on aspartase activity in soils. This enzyme [L‐aspartate ammonia‐lyase, EC 4.3.1.1] catalyzes the hydrolysis of L‐aspartate to fumarate and NH₃. It may play a significant role in the mineralization of organic N in soils. The management systems consisted of three cropping systems [continuous corn (Zea mays L.) (CCCC); corn‐soybean [Glycine max (L.) Merr.]‐corn‐soybean (CSCS); and corn‐oat (Avena sativa L.)‐meadow‐meadow (COMM) {meadow was a mixture of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] at three long‐term field experiments initiated in 1954, 1957, and 1978 in Iowa and sampled in June 1987. The plots received 0 or 180 (or 200) kg ha^?1 before corn and an annual application of 20 kg P and 56 kg K ha^?1. The tillage systems (no‐tillage, chisel plow, and moldboard plow) were initiated in 1981 in Wisconsin and sampled in May 1991. The crop residue treatments were: bare, normal, mulch, and double (2×) mulch. The residue in the study was corn stalks. Results showed that, in general, crop rotation in combination with N fertilizer treatments affected aspartase activity in the following order: COMM>CSCS>CCCC. Because of nitrification of the NH₄ ⁺ or NH₄ ⁺‐forming fertilizers, which resulted in decreasing the pH values, N fertilizer application, in general, decreased the aspartase activity in soils in the order: CCCC>CSCS>COMM. The effect of tillage and residue management practices on aspartase activity in soils showed a very wide variation. The trend was as follows: no‐till/2× mulch>chisel plow/mulch>moldboard plow/mulch>no‐till normal>chisel plow/normal>no‐till bare>moldboard plow/normal. Aspartase activity decreased with increasing depth in the plow layer (0–15 cm) of the no‐till/2× mulch. The decreased activity was accompanied by decreasing organic C and pH with depth. Statistical analyses using pooled data (28 samples) showed that aspartase activity was significantly, linearly correlated with organic C (r=0.78^***) and exponentially with soil pH (r=0.53**). The variation in the patterns and magnitudes of activity distribution among the profiles of the four replicated plots was probably due to the spatial variability in soils.     

Soil macroporosity,hydraulic conductivity and air permeability of silty soils under long-term conservation tillage in Indiana

With the increasing use of conservation tillage, many questions about the long-term effects of tillage system on soil physical properties have been raised. Studies were conducted to evaluate saturated hydraulic conductivity (K_SAT), macropore characteristics and air permeability of two silty soils as affected by long-term conservation tillage systems in the state of Indiana. Measurements were taken during the tenth year of a tillage study on a Chalmers silty clay loam (Typic Haplaquoll) and the fifth year of a study on a Clermont silt loam (Typic Ochraqualf). Tillage systems were moldboard plow, chisel, ridge till-plant, and no-till in a rotation of corn (Zea mays L.) and soya beans (Glycine max L.). Saturated hydraulic conductivity was measured on large soil columns (25 × 25 × 40 cm) before spring tillage, and macropore size and continuity were assessed with staining techniques. Intact soil cores (8 cm diam × 10 cm) were collected in early July in the row and non-trafficked interrow at three depths (10–20, 20–30, and 30–40 cm) and were analyzed for air permeability (K_air), air-filled porosity and bulk density. Saturated hydraulic conductivity values were in the order plow > chisel > ridge till > no-till for the Chalmers soil and were significantly greater in the plow treatment than in the other 3 tillage systems on the Clermont soil. Differences in K_SAT between the 2 soils were generally greater than differences among tillage systems, and coefficients of variation were lower for treatments that did not include may fall tillage operations. At the 10-cm depth on the Chalmers soil, the chisel treatment had the greatest number of stained cylindrical channels, whereas for the Clermont soil the ridge till had the greatest number at this depth. Although the no-till treatment had similar or fewer total channels, it had the most continuous channels from the 10-cm depth to the 20- and 30-cm depths on both soils. Tillage system, row position and depth all affected K_air. On the Chalmers soil, plow, chisel and ridge systems had lower K_air between rows than in the row at the 10–20-cm depth, whereas no-till had constant K_air in the row and between the row. On the Clermont soil, ridge till had the highest K_air of all treatments at the 10–20-cm depth, and no-till had the highest K_air of all treatments at the 20–30-cm depth.     

Effect of nitrogen levels and Rhizobium strains on symbiotic N2 fixation and grain yield of Phaseolus vulgaris L. genotypes in normal and saline-sodic soils

Summary Following screening, selection, characterization, and symbiotic N₂ fixation with 12,5, 25.0, and 40.0 mg N kg^–1 in normal and saline-sodic soils, only two Phaseolus vulgaris genotypes (HUR 137 and VL 63) and two Rhizobium spp. strains (ND 1 and ND 2) produced maximum nodulation, nitrogenase activity, plant N contents, and grain yields in saline-sodic soil, with 12.5 mg N kg^–1, compared with the other strains. However, interactions between strains (USDA 2689, USDA 2674, and ND 5) and genotypes (PDR 14, HUR 15, and HUR 138) were significant and resulted in more nodulation, and greater plant N contents, nitrogenase activity, and grain yields in normal soils with 12.5 mg N kg^–1 compared with salt-tolerant strains. Higher levels of N inhibited nodulation and nitrogenase activity without affecting grain yields. To achieve high crop yields from saline-sodic and normal soils in the plains area, simultaneous selection of favourably interacting symbionts is necessary for N economy, so that bean yields can be increased by the application of an active symbiotic system.     

Tillage and residue management effects on arylamidase activity in soils

Recent interest in soil tillage and residue management has focused on low-input sustainable agriculture. This study was conducted to investigate the effect of three tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch) on a most recently detected enzyme in soils, arylamidase activity. This enzyme catalyzes the hydrolysis of an N-terminal amino acid from peptides, amides, or arylamides. Results showed that arylamidase activity is greatly affected by tillage and crop residue placement. The greatest activity was found with chisel/mulch, moldboard plow/mulch, and no-till/double mulch, and the lowest with moldboard plow/normal and no-till/bare. Arylamidase activity was significantly correlated with organic C (r=0.59**) and soil pH _CaCl2 (r=0.55**)_, and decreased with soil depth. Results of this work suggest that the activity of this enzyme is affected by soil management, and indicate its potential ecological significance because of its role in the N cycle.     

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.     

不同耕法及秸秆还田对土壤水分运移变化的影响

[目的]探讨不同耕法与秸秆还田方式下,旱地草甸土土壤水分随深度运移的变化,为今后生产中因地制宜制定科学合理的耕作与培肥技术提供理论依据。[方法]采用田间定位试验,研究3种耕法免耕、浅翻、深翻与3种秸秆还田方式覆盖还田、浅翻还田、深翻还田条件下,作物生长不同时期、不同深度土层土壤含水量、田间持水量和容重的变化。[结果]土壤水分的年际间变化与降水量和降水变率有一定的关系。秸秆不还田条件下,连续2 a免耕,年际间土壤含水量随深度变化的特征曲线基本一致,0—20 cm耕层田间持水量降低13.62%,而浅翻与深翻分别增加11.32%和27.98%;耕翻深度对20—30 cm土层水分的影响较大,随作物生长和地表覆盖度增加,40 cm以下土层含水量的变化减弱。秸秆还田条件下,0—20 cm耕层浅翻还田与深翻还田田间持水量分别增加16.24%,5.08%,而土壤容重降低0.12,0.09 g/cm~3。[结论]同一耕法有秸秆还田处理土壤水分含量高于无秸秆还田,降水量越少,差异越明显。与免耕和免耕覆盖比较,翻耕与翻耕还田均增加了作物生长期间土壤含水量,提高了作物抗旱能力,产量有增加趋势。     

Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

CQESTR simulates the effect of management practices on soil organic carbon (SOC) stocks. The beta version of the model had been calibrated and validated for temperate regions. Our objective was to evaluate the CQESTR model performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W), tillage systems consisted of no tillage (NT); reduced tillage (RT) (one disc plow and one harrow leveling [RT1] or one heavy disc harrow and one harrow leveling [RT2]); and conventional tillage (CT) (two heavy disc harrows followed by one disc plow and two harrow levelings). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling), and CT (one disk plow, two heavy disk harrowings, and two harrow levelings). CQESTR underestimated SOC at both sites, especially under NT systems, indicating that adjustments (e.g., the inclusion of clay mineralogy factor) are necessary for more accurate simulation of SOC in the tropics. In spite of this, measured and simulated values of SOC in the 0–20 cm depth were well correlated (southeast, R² = 0.94, p < 0.01; northeast, R² = 0.88, p < 0.05). With respect to initial conditions (native forest), CQESTR estimated a decrease in SOC stocks in plowed and no-tillage systems. In 2006, in the southeast, SOC stocks were 28.8, 23.7, 23.2, and 22.0 Mg ha^?1 under NT, RT2, RT1, and CT, respectively; in the northeast, stocks were 36.0, 33.8, and 32.5 Mg ha^?1 under NT, RT, and CT, respectively. The model estimated carbon emissions varying from 0.36 (NT) to 1.05 Mg ha^?1 year^?1 (CT) in the southeast and from 0.30 (NT) to 0.82 (CT) Mg ha^?1 year^?1 in the northeast. CQESTR prediction of SOC dynamics illustrates acceptable performance for the two tropical soils of Brazil.     

Peanut macronutrient absorptions characteristics in response to soil compaction stress in typical brown soils under various tillage systems

Soil tillage, a major agricultural management, could effectively alter soil structure and plant growth, particularly under groundnut plantations. To understand effects of different tillage measures on nitrogen(N), phosphorus(P) and potassium(K) absorptions and use efficiencies for peanut (Arachis hypogaea L.), four tillage treatments: no tillage (NT), deep loosing (DL), deep plow (DP), and shallow plow (SP), were examined for two growing years at three typical peanut-producing sites of Qishan, Wangcheng, and Xiadian in Shandong, China. Results showed that average soil bulk density under DL, DP, and SP at the three sites was decreased by 7.1–19.5% compared with NT treatment for the 2 years. Significantly higher average total N accumulations in underground peanut part patterned as DP (163 kg/ha) > SP (149 kg/ha) > DL (144 kg/ha) > NT (117 kg/ha), while total N in aboveground peanut part was 8.7–22.1% higher under DP than other treatments. Absorptions of N, P, and K in underground parts were extremely significantly contributed to high peanut yields (P < 0.01), whereas increase of N and P absorptions in aboveground parts did not promote peanut yields. Soil bulk density was significantly negatively correlated with plant macronutrient amounts in underground peanut parts and peanut yields (P < 0.01). Moreover, N:P, N:K, and P:K ratios were similar between NT and noncompaction stress treatments of DL, DP, and SP. These results indicate that DP is a rational tillage practice for promoting nutrient uptake amount, efficiency, and peanut yields by alleviating soil compaction stress in peanut-producing fields.     

Earthworm populations and growth rates related to long-term crop residue and tillage management

Conventional tillage creates soil physical conditions that may restrict earthworm movement and accelerate crop residue decomposition, thus reducing the food supply for earthworms. These negative impacts may be alleviated by retaining crop residues in agroecosystems. The objective of this study was to determine the effects of various tillage and crop residue management practices on earthworm populations in the field and earthworm growth under controlled conditions. Population assessments were conducted at two long-term (15+ years) experimental sites in Québec, Canada with three tillage systems: moldboard plow/disk harrow (CT), chisel plow or disk harrow (RT) and no tillage (NT), as well as two levels of crop residue inputs (high and low). Earthworm growth was assessed in intact soil cores from both sites. In the field, earthworm populations and biomass were greater with long-term NT than CT and RT practices, but not affected by crop residue management. Laboratory growth rates of Aporrectodea turgida (Eisen) in intact soil cores were affected by tillage and residue inputs, and were positively correlated with the soil organic C pool, suggesting that tillage and residue management practices that increase the soil organic C pool provide more organic substrates for earthworm growth. The highest earthworm growth rates were in soils from RT plots with high residue input, which differed from the response of earthworm populations to tillage and residue management treatments in the field. Our results suggest that tillage-induced disturbance probably has a greater impact than food availability on earthworm populations in cool, humid agroecosystems.     

Long-term cultivation effects on hydraulic properties of a Walla Walla silt loam

Hydraulic properties of a Walla Walla silt loam were significantly changed by 50 years or more of cultivation under either a wheat-peas rotation (tillage depth 30 cm) or a wheat-summerfallow rotation (tillage depth 15 cm) as compared with no cultivation. Soil pH was reduced to depths as great as 60 cm in the cultivated sites; dry bulk density was increased to depths as great as 40 cm. Expressions of these changes were greater in the wheat-peas rotation because tillage was deeper than in the wheat-summerfallow rotation. Small reductions in soil organic matter were also noted in the cultivated sites. In the 60- to 90-cm depth, all three sites had similar bulk density, pH, cation exchange capacity, soil texture, desorption water characteristic, and hydraulic conductivity. In the upper 40-cm layer the desorption water characteristic showed that cultivation produced more smaller pores at the expense of large pores; in the upper 30-cm layer of the cultivated soils hydraulic conductivity was reduced at least 10-fold for water potentials > −100 cm of H₂O. Steady-state drainage profiles and associated assumptions suggest that long-term cultivation increased the hydraulic gradient in the upper 35 cm, and that the low saturated conductivity of the 0- to 15-cm layer had an overall drying effect on the 15- to 35-cm layer. In the cultivated soils increased runoff and denitrification in the plow layer should both be expected and water relations in the 15- to 35-cm layer should favor microorganisms sensitive to high water potentials. Simulations suggested that long-term cultivation decreased evaporation rates an estimated 40% and in wet soil, increased the drying time needed to attain optimum moisture for tillage.