Effects of Various Salt–Alkaline Mixed Stresses on the State of Mineral Elements in Nutrient Solutions and the Growth of Alkali Resistant Halophyte Chloris Virgata

Chloris virgata, a naturally alkali-resistant halophyte, was studied. Various salt–alkali conditions with different salinities and pHs were established by mixing sodium chloride (NaCl), sodium bicarbonate (NaHCO₃), sodium sulfate (Na₂SO₄), and sodium carbonate (Na₂CO₃), in various proportions. The effects of these salt–alkali conditions on the state of mineral elements in nutrient solutions were analyzed using the GEOCHEM-PC program. The relative growth rate (RGR) and tillering rate of stressed C. virgata were determined. The activities of metal ions in nutrient solutions, apart from potassium (K⁺), decreased with both increased salinity and pH, and high pH resulted in precipitation of metal ions and phosphate. Consequently, the high pH of salt–alkaline mixed stress could cause severe nutrient stress in plants. However, when pH was 6.40–8.74, the effects of pH on RGR and tillering rate were not significant, and the high pH surrounding roots might be resisted by the root cells and prevented from invading the intracellular environment. Only when pH > 8.74 did the harmful action of high pH emerge, and the increased pH induced the severe decreases of RGR and tillering rate at the same salinity. The results indicated that pH adjustment outside the roots might be a key physiological mechanism for C. virgata resisting alkali stress.     

Ameliorative Effects of Potassium Phosphate on Salt‐Stressed Pepper and Cucumber

Abstract

Bell pepper (Capsicum annuum cv. Urfa Isoto) and cucumber (Cucumis sativus cv. Beith Alpha F1) were grown in pots containing field soil to investigate the effects of supplementary potassium phosphate applied to the root zone of salt‐stressed plants. Treatments were (1) control: soil alone (C); (2) salt treatment: C plus 3.5 g NaCl kg^?1 soil (C + S); and (3) supplementary potassium phosphate: C + S plus supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil (C + S + KP). Plants grown in saline treatment produced less dry matter, fruit yield, and chlorophyll than those in the control. Supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil resulted in increases in dry matter, fruit yield, and chlorophyll concentrations compared to salt‐stressed (C + S) treatment. Membrane permeability in leaf cells (as assessed by electrolyte leakage from leaves) was impaired by NaCl application. Supplementary KH₂PO₄ reduced electrolyte leakage especially at the higher rate. Sodium (Na) concentration in plant tissues increased in leaves and roots in the NaCl treatment. Concentrations of potassium (K) and Phosphorus (P) in leaves were lowered in salt treatment and almost fully restored by supplementary KH₂PO₄ at 272 mg kg^?1 soil. These results clearly show that supplementary KH₂PO₄ can partly mitigate the adverse effects of high salinity on both fruit yield and whole plant biomass in pepper and cucumber plants.     

Effects of Rice Husk Ash and Bagasse Ash on Phosphorus Adsorption and Desorption in an Alkaline Soil under Wheat–Rice System

Rice husk ash (RHA) and bagasse ash (BA) are available in large quantities in South Asian countries growing rice and sugarcane. Land application of RHA and BA is likely to influence chemistry of soil phosphorus (P) and thereby P adsorption and desorption. Laboratory studies were carried out to investigate the short-term and long-term effects of RHA and BA application on P adsorption and desorption in an alkaline soil under a wheat–rice system. Addition of RHA or BA (10 Mg ha^?1) resulted in a significant decrease in P adsorption compared to the control. The decrease in P adsorption was lower when RHA and BA were applied to either rice or wheat as compared with when applied to both the crops. The BA was more effective in reducing P adsorption than RHA because of its greater P concentration. Fresh addition of RHA and BA at 1% (dry-weight basis) showed a small effect on P adsorption as compared to their long-term application. The Frendulich isotherm equation gave better fit with the experimental data than the Langmuir equation and is reliable to describe the P quantity/intensity relationships of this soil as affected by the additions of RHA and BA. The P-adsorption capacities (revealed from the Langmuir isotherms) of the unamended control, RHA, and BA (applied to both wheat and rice) were 256, 313, and 385 mg kg^?1, respectively; the corresponding bonding energies for the three treatments are 0.0085, 0.0041, and 0.0026 L kg^?1, respectively. Desorption of P was minimum in the control plots and maximum with BA followed by RHA, especially when applied to both the crops.     

Effect of Calcareous Soil on Photosynthesis Rate,Mineral Nutrition,and Source‐Sink Ratio of Table Grape

Abstract

Vitis vinifera L. cv Aurora grafted on S.O.4 (medium lime‐tolerance) rootstock was grown in pot with a high‐carbonate‐soil and a low‐carbonate‐soil. The aim of the trial was to check soil effect on some physiological features such as leaf chlorophyll (Chl) concentration and gas exchange, whole‐canopy gas exchange, mineral nutrition, dry matter partitioning, and technological grape parameters. Measurements for whole‐canopy gas exchange were taken using a custom‐built, flow‐through whole‐canopy gas exchange system set up to run continuous, automated, and simultaneous net carbon exchange rate (NCER) readings of four canopies. The most significant findings were: (a) high‐carbonate‐soil decreased leaf and whole canopy photosynthesis, grape yield, and total dry matter production; (b) high‐carbonate‐soil increased the distribution share of dry matter in the trunk and roots, as compared to the low‐carbonate‐soil, and decreased the share of dry matter in the clusters; and (c) lime‐stress conditions affected mineral nutrition, especially P and K concentrations, which were depressed in most of the organs.     

Previous Corn Row Effects on Potassium Nutrition and Yield of Subsequent No‐Till Soybeans

Abstract

Narrow‐row soybean [Glycine max (L.) Merr.] production in corn [Zea mays L.]–soybean rotations results in various distances of soybean rows from previous corn rows, yet little is known about soybean responses to proximity to prior corn rows in no‐till systems. The objective of this study was to evaluate the impacts of preceding corn rows on potassium (K) nutrition and yield of subsequent no‐till soybeans. Four field experiments involving a corn–soybean rotation were conducted on long‐term no‐till fields with low to medium K levels from 1998 to 2000 near Paris and Kirkton, Ontario, Canada. In the corn year, treatments included K application rate and placement in conjunction with tillage systems or corn hybrids. Before soybean flowering, soil exchangeable K concentrations (0–20 cm depth) in previous corn rows were significantly higher than those between corn rows. At the initial flowering stage, trifoliate leaf K concentrations of soybeans in preceding corn rows were 2.0 to 5.3 g kg^?1 higher than those from corresponding plants between corn rows. Yield of no‐till soybeans in previous corn rows increased 10 to 44% compared to those between previous corn rows. Positive impacts of prior corn rows on soil K fertility, soybean leaf K, and soybean yield occurred even when K fertilizer was not applied in the prior corn season. Deep banding of K fertilizer tended to accentuate row vs. between‐row effects on soybean leaf K concentrations in low‐testing soils. Corn row effects on soybeans were generally not affected by either tillage system or corn hybrid employed in the prior corn crop. Potassium management strategies for narrow‐row no‐till soybeans should take the potential preceding corn row impacts on soil K distribution into account; adjustments to current soil sampling protocols may be warranted when narrow‐row no‐till soybeans follow corn on soils with low to medium levels of exchangeable K.     

Comparison of preplant and fertigated micronutrients on the growth of the Hebe ’inspiration’

Abstract

Micronutrients may be provided to plants in containers either via pre‐plant inclusion in the growing medium or via fertigation, or both. For Hebe ’Inspiration’ plants growing in a soilless potting medium, micronutrients applied as a single pre‐plant application or via weekly liquid fertilizer applications were equally effective in producing optimum growth over a 12‐month period. Under the conditions of this experiment, the liquid fertilizer did not need to contain more than (in mg/L) 0.5 = iron (Fe), 0.1 = copper (Cu), 0.1 = zinc (Zn), 0.8 = manganese (Mn), and 0.1 = boron (B). Growth was excellent for the full 12 months, without supplementation via the liquid fertilizer, when there were micronutrient concentrations of (in mg/L extract) 29 = Fe, 0.5 = Cu, 3 = Mn, 0.6 = Zn, and 0.14 = B in a 1:1.5 volume in a 2mM DTPA extract of the medium at potting.     

Effects of permafrost thawing on vegetation and soil carbon pool losses on the Qinghai–Tibet Plateau,China

Bearing a total organic carbon (TOC) content of 9.3–10.7 kg C/m², alpine grassland soils of the Qinghai–Tibet plateau's permafrost region bear a greater organic carbon pool than do grassland soils in other regions of China or than tropical savannah soils. The easily released light fraction organic carbon (LFOC) accounts for 34–54% of the TOC and is particularly enriched in the topsoil (0–0.10 m). The LFOC in the organic carbon pool of alpine cold meadow and alpine cold steppe soils decreased at exponential and quadratic rates, respectively, as the vegetative cover decreased. When the vegetative cover of alpine cold meadows decreased from > 80 dm²/m² to 60 dm²/m², the topsoil TOC and LFOC dropped by 20.4% and 38.4%, respectively. Similarly, when the vegetative cover of alpine cold meadow decreased from 50 dm²/m² to 30 dm²/m² and < 15 dm²/m², the topsoil LFOC content dropped by 60% and 86.7%, respectively. Under climatic warming, the degradation of permafrost and vegetation have resulted in serious soil organic carbon (SOC) loss from the carbon pool. Land cover changes that occurred between 1986 and 2000 are estimated to have resulted in a 1.8 Gg C (120 Mg C/yr) loss in SOC, and a concomitant 65% decrease in the LFOC, in the 0–0.30 m soil layer in the Qinghai–Tibet plateau's permafrost regions. Since the region's ecosystems are quite sensitive to global climate changes, if global warming persists, alpine cold grassland ecosystems are expected to further degrade. Hence, the influence of global climatic change on soil carbon emissions from alpine grasslands should receive more attention.     

Effect of the Concentration of Phosphorus on Growth and Nutrition of Leucospermum cordifolium ‘Flame Spike’

The aim of this study was to determine how phosphorus (P) concentration affects growth, concentration and distribution of nutrients in Leucospermum cordifolium ‘Flame Spike’ (Proteaceae). The trials were performed at the School of Agriculture (ETSIA) of the University of La Laguna (28° 28′ 43′′ N, 16° 19′ 7′′ W) with 64 plants (1-year-old) grown for 12 months in silica sand, fed with nutrient solutions containing different levels of P_i (5, 10, 15 and 20 mg L^?1). At 6, 9, and 12 months, whole plants were taken from each experimental unit and divided into root, stem (main, first, second, and third growth) and leaves (adult, first, second, and third growth), which were measured, weighed, and analyzed. The data enabled a nutritional diagnosis, including the limiting P concentrations and nutrient interactions. P concentrations above 5 mg L^?1 caused a reduction in growth, which in the third samples was significant (P < 0.05). Plants treated with 15 and 20 mg L^?1 P attained similar dry weights (P > 0.05). Some young leaves showed a certain degree of chlorosis, probably due to iron (Fe) deficiency. Fully developed young leaves (YFEL) were suitable for nutritional diagnosis of P, and the P concentration of the nutrient solution affected the foliar manganese (Mn) concentration. This latter factor was related to the zinc (Zn) concentration in the roots.     

Effects of Continuous Use of Chemical Fertilizers and Manure on Soil Fertility and Productivity of Maize–Wheat under Rainfed Conditions of the Western Himalayas

Long-term effects of continuous use of chemical fertilizers and manure on soil fertility and productivity of a maize–wheat system were investigated in the ongoing long-term fertilizer experiment, during rabi (2007–2008) and kharif (2008) seasons at the research farm of Chaudhary Sarwan Kumar Himachal Pradesh Agricultural University–Hill Agricultural Research and Extension Centre, Dhaulakuan. After 16 cropping cycles, bulk density decreased in plots where farmyard manure (FYM) was applied, whereas pH decreased in all the treatments. The organic carbon content of the soil increased in all the treatments except 100% nitrogen (N). Cation exchange capacity (CEC) increased in all the treatments over the initial status of the soil. Available N showed buildup over the initial status in most of the treatments. Available phosphorus (P) declined from initial status in treatments where only N was applied alone or with FYM. There was reduction in available potassium (K) status in all the treatments except 100% NPK. Continuous addition of FYM with balanced application of inorganic fertilizers improved content of exchangeable calcium (Ca) and magnesium (Mg) over initial status compared to imbalanced application of fertilizers. Continuous use of imbalanced inorganic fertilizers resulted in lesser crop yields and nutrient uptake compared to that with the application of balanced dose of inorganic fertilizers with FYM.     

Tillage Effects on Particulate and Mineral‐Associated Organic Matter in Two Tropical Brazilian Soils

Abstract

Two Ferralsols (350 and 600 g kg^?1 clay) from the Brazilian Cerrado Region were evaluated for long‐term effects (5 and 8 years) of no tillage on carbon (C) stocks in particulate (>53 µm) and mineral‐associated (<53 µm) soil organic matter (SOM) fractions. Carbon stocks in particulate SOM increased under no tillage compared with conventional tillage, and the rate was higher in the clayey soil (0.62 Mg C ha^?1 yr^?1) than in the sandy clay loam soil (0.31 Mg C ha^?1 yr^?1). In contrast, the mineral‐associated SOM in the top soil layer (0–20 cm) was not affected by tillage system. Sequestration of atmospheric C in tropical no‐tillage soils seems to be due to accumulation of C in labile SOM fractions, with highest rates in clayey soils probably due to physical protection.     

Comparison of thermal and chemical stability of Cu–humic complexes

Purpose

The purpose of this study was to investigate relationships between chemical and thermal stabilities of Cu–humic complexes. The study of the chemical stability was based on pedological methods used for the determination of the bond strength of metal ions in soils by chemical leaching agents. The samples with various contents of the Cu(II) ions and their bond strength were put to the thermal analysis in order to correlate their thermo-oxidative behavior with their stability determined by leaching.

Materials and methods

The humic acid was extracted from the South-Moravian lignite by standard alkaline extraction. The humic sample was used in two different forms: as the solid powder and as the hydrogel prepared by the acidic precipitation of humate. Six various concentrations of copper(II) solutions were used for the complexation of the humic powder and the hydrogel, in order to study the influence of their initial concentration on both the determined stabilities of the prepared complexes. Their chemical stability was assessed in terms of the Cu(II) ions release from the humic acid structure into two different extraction agents (MgCl₂ and HCl solutions). Their thermo-oxidative behavior was investigated employing the thermogravimetry.

Results and discussion

The complexation capacity of the humic hydrogel was higher in comparison with the humic powder. The amounts extractable from the Cu–humic complexes by the used leaching agents are higher for the humic powder, which shows on the lower chemical stability. The thermal degradation of the prepared complexes proceeds in several steps and this character remains also after the removal of the mobile and the ion-exchangeable fractions by the MgCl₂. The elimination of these fractions as well as the extraction of the strongly bound Cu(II) ions shift the thermal degradation to higher temperatures. The incombustible residue increases with the Cu(II) content in the complexes except for the samples extracted by the HCl.

Conclusions

The form of humic sample used for the preparation of the Cu–humic complexes influences both the chemical stability and the thermal one. The main reason is probably a better accessibility of the functional groups in the humic gel, which enables forming stronger binding copper(II) ions. The results showed that the thermal and chemical stabilities are closely related, which corresponds with the shift of the thermal degradation to higher temperatures after removing the less stable fractions from the humic complexes.     

Effects of the 1982–1983 El Nino on Humboldt penguin colonies in Peru

The Humboldt penguin Spheniscus humboldti is endemic to the Peruvian Current which flows northward along the coast of Chile and Peru. This species has greatly diminished from its former abundance.The coast of Peru is characterised by high biological productivity which concentrates fish such as the anchovy Engraulis ringens, the main prey item of marine predators including seabirds. In years of the abnormal oceanographic conditions of El Nino, the schools of anchovies become unavailable to the seabirds and they disperse in search of food. Massive mortality, especially of juveniles, results and there is nest desertation and lack of reproduction.This paper describes the effects of the 1982–1983 El Nino on Humboldt penguin colonies in Peru. There has been an overall population decline of 65% and the surviving population in 1984 was estimated to be between 2100 and 3000 adults. Although El Nino is a periodic event and the Humboldt penguin has evolved to adapt to such unpredictable changes, the environment has now been altered by man. Under these circumstances, the 1982–1983 El Nino has contributed to placing this species in a critical position.     

Effects of climate factors and soil properties on soil nutrients and elemental stoichiometry across the Huang–Huai–Hai River Basin,China

Purpose

Soil nutrients, elemental stoichiometry, and their associated environmental control play important roles in nutrient cycling. The objectives of this study were (1) to investigate soil nutrients and elemental stoichiometry, especially potassium and its associative elemental stoichiometry with other nutrients under different land uses in terrestrial ecosystems; (2) to discuss the impacts of climate factors, soil texture, and soil physicochemical properties; and (3) to identify the key factors on soil nutrient levels and elemental stoichiometry.

Materials and methods

Soil data, including pH, bulk density (BD), cation exchange capacity (CEC), volumetric water content (VMC), clay, silt and sand contents, total carbon (TC), nitrogen (TN), phosphorous (TP) and potassium (TK), available nitrogen (AN), phosphorus (AP), potassium (AK), and soil organic matter (SOM) under different land-use types, were collected, and their elemental stoichiometry ratios were calculated. Climate data including temperature, precipitation, relative humidity, wind speed, and evapotranspiration were collected. The least significant difference test and one-way analysis of variance were applied to investigate the variability of soil nutrients and elemental stoichiometry among land-use types; the ordinary least squares method and the general linear model were used to illustrate the correlations between soil nutrients, elemental stoichiometry, and soil properties or climate factors and to identify the key influencing factors.

Results and discussion

Woodlands had the highest SOM, TN, AN, and AK contents, followed by grasslands, croplands, and shrublands, while the TP and TK contents only varied slightly among land-use types. SOM, TN, AN, N/P, and N/K were strongly negatively correlated to soil pH (p <?0.05) and were strongly positively correlated to soil CEC (p <?0.05). For soil texture, only C/N was moderately negatively correlated to silt content but moderately positively correlated to sand content (p <?0.05). For climate factors, SOM, TN, AN, N/P, and N/K were significantly negatively correlated to evapotranspiration and temperature (p <?0.05), and the correlations were usually moderate. Soil pH explained most of the total variation in soil nutrients, and climate factors explained 5.64–28.16% of soil nutrients and elemental stoichiometry (except for AP (0.0%) and TK (68.35%)).

Conclusions

The results suggest that climate factors and soil properties both affect soil nutrients and elemental stoichiometry, and soil properties generally contribute more than climate factors to soil nutrient levels. The findings will help to improve our knowledge of nutrient flux responses to climate change while also assisting in developing management measures related to soil nutrients under conditions of climate change.

     

Comparison of Shoemaker–McLean–Pratt and Modified Mehlich Buffer Tests for Lime Requirement on Pennsylvania Soils

Abstract

The Shoemaker–McLean–Pratt (SMP) buffer test is commonly used in Pennsylvania and throughout the United States to determine the lime requirement (LR) of acid soils. The buffer contains potassium chromate, a carcinogen, and all waste must be collected for disposal in a hazardous waste facility. An alternative to the SMP buffer is the Mehlich buffer. Although the Mehlich buffer contains barium chloride (BaCl₂), also a hazardous and regulated compound, calcium chloride (CaCl₂) has been shown to be an effective substitute. The goal of this study was to compare the SMP buffer and the modified Mehlich buffer (CaCl₂ substituted for BaCl₂) for estimating LR on PA soils and to determine if the modified Mehlich buffer could provide an effective alternative to the SMP test. Twenty‐two agriculturally important Pennsylvania soils with pH values ranging from 4.5 to 6.4 were collected, and the actual LR of each soil was determined by incubating soils for 3 months with calcium carbonate. The modified Mehlich buffer was a more accurate predictor of the lime required to raise soils to either pH 6.5 (r²=0.92) or 7.0 (r²=0.87) in comparison to the SMP buffer (r²=0.87 and 0.82, respectively). Comparison of calibration equations for Mehlich buffer versus lime requirement derived in this study were similar to those developed on soils from other states and geographic regions.     

Effects of alternative management practices on the economics,energy and GHG emissions of a wheat–pea cropping system in the Canadian prairies

In recent years alternative farming practices have received considerable attention from Canadian producers as a means to improve their net return from grain and oilseed production. Enhancing the efficiency of nitrogen fertilizer use, including a pulse crop in the rotation, reducing tillage and pesticide use are seen as viable options to reduce reliance on fossil fuel, lower input costs and decrease the risk of soil, air and water degradation. The objective of this study was to determine the effects of 16 alternative management practices for a 2-year spring wheat (Triticum aestivum L.)–field pea (Pisum sativum L.) rotation on economic returns, non-renewable energy use efficiency, and greenhouse gas emissions. The alternative management methods for wheat consisted of a factorial combination of high vs. low soil disturbance one pass seeding, four nitrogen (N) fertilizer rates (20 kg N ha^?1, 40 kg N ha^?1, 60 kg N ha^?1 and 80 kg N ha^?1), and recommended vs. reduced rates of in-crop herbicide application. Alternative management practices for field pea were high vs. low soil disturbance one pass seeding. The resulting 16 cropping systems were evaluated at the whole farm level based on 4 years (two rotation cycles) of data from field experiments conducted on two Orthic Black Chernozem soils (clay loam and loam textures) in Manitoba, Canada. The highest net returns on the clay loam soil were for the high disturbance system with 60 kg N ha^?1 applied to wheat and the recommended rates of in-crop herbicides. The lowest application rate of N, together with low disturbance seeding, provided the highest economic returns on the loam soil. Energy use efficiency was highest for the lowest rate of N application for both tillage systems. The highest rate of N fertilizer and recommended rates of in-crop herbicide produced little additional yield response, lower net returns, and higher GHG emissions. An increase in N fertilizer application from 20 kg ha^?1 to 80 kg ha^?1 increased whole farm energy requirements by about 40%, while reducing herbicide rates had negligible effects on grain yields and total energy input. Overall, as N fertilizer rate increased, the associated GHG emissions were not offset by an increase in carbon retained in the above-ground crop biomass. Moderate to high soil test NO₃-N levels at experimental sites reduced the potential for positive yield responses to N fertilizer in this study, thus minimizing the economic benefits derived from N fertilizer application.     

Effects of supplemental‐nitrogen on the quality of rice proteins

A study was conducted on the effect of supplemental nitrogen (N) (20 hg/ha) applied as a foliar spray or to the soil on seed production, protein percentage, and protein fractions of rice. Plants were grown in a greenhouse over two different periods of time, i.e., August 1988 to January 1989 (Period I), and December 1988 to April 1989 (Period II). Nitrogen was applied to the leaves 10 and 20 days after anthesis (DAA), and to the soil at anthesis and at 15 DAA. Average temperature was 28.7°C during Period I and 32°C during Period II, corresponding to 18.7 and 22.0 growing degree‐day/day (GDD/day), respectively. The difference in GDD/day reduced the plant cycle from 130 days during Period I to 109 days during Period II. Plants grown during Period II had larger numbers of spikelets, a higher percentage of “full grown grains”;, and higher grain weight. Although percentage crude protein was about the same for the two periods, prolamin content was increased and the albumin+globulin fraction was decreased during Period II, but with no difference in glutelin content. The increase in number of spikelets, percent full grains, and grain weight appeared to result in a greater energy demand for plants grown during Period II. This may explain the increase in prolamins, since prolamin synthesis requires less energy than globulin or albumin synthesis. There was a simultaneous decrease in albumin and globulin synthesis during Period II. The content of glutelins, which represent the major reserve proteins in rice grains, was constant during both periods.     

A Comparison of Super-Valid Restricted and Row–Column Randomization

In complete block experiments, treatments are often randomized within blocks without any other restrictions. When the blocks are rows of plots and the blocks are laid out in parallel so that also columns of plots are formed, there might be random effects of both rows and columns. In this situation, a row–column design is a natural choice. Super-valid restricted randomization is another option. This article compares these randomization procedures for small complete block experiments (5–10 treatments in 3–6 blocks). Validity of a randomization procedure is defined for mixed-effects models. The two randomization procedures are compared with regard to average variance in pairwise comparisons. Row–column randomization is recommended when either there are at least four replicates, or the number of replicates is three and intercolumn variance is not known to be small. These conclusions assume a model with fixed effects of treatments and random effects of rows and columns, and estimation using the REML method and the Kenward and Roger approximation.     

Landscape and Land‐Use Effects on the Spatial Variation of Soil Chemical Properties

The current study addressed the spatial variation of soil organic matter (SOM), total nitrogen (TN), extractable phosphorus (EP), and extractable potassium (EK) in agricultural soils of a representative region, northeast China. Soil cation exchange capacity (CEC) and the effects of landscape attributes and land use were also investigated. The techniques used included conventional statistics, geostatistics, and geographic information systems (GIS). Our study demonstrated that EP had the greatest coefficient of variation (CV), and CEC had the least CV. The experimental semivariograms of the five soil chemical properties included in this study were all fitted with exponential models. The five soil variables all showed moderate spatial dependence. The SOM, EK, and CEC decreased with increasing altitude. Significant negative relationships were found between the slope gradient and EP, EK, and CEC. Relatively steeper slopes might result in greater soil erosion, which leads to a decline in soil nutrients. Soil types had significant impacts on all soil chemical properties, which reflect the effect of the parent soil material. In general, the mean values of soil variables for vegetable land were statistically greater than those for upland and paddy fields. After being divided into two parts along the Yinma River, soil samples of the western part have statistically greater SOM, EP, EK, and CEC values than those collected from the eastern part.     

Effects of freeze–thaw cycles and the soil water content on carbon and nitrogen changes in different soil types of Heilongjiang Province,China

To reveal the influence of freeze–thaw cycles (FTCs) on soil carbon and nitrogen changes, six typical soils in Northeast China were selected as the research objects to conduct a FTC simulation test in an artificial climate chamber. Three soil volumetric water contents (10%, 20%, 30%) and eight FTCs (0, 2, 4, 6, 8, 10, 15, 20) were set. The results showed that the soil organic carbon (SOC) and microbial biomass carbon (MBC) contents of different soil types under the FTCs initially exhibited a downward and then an upward trend, while the dissolved organic carbon (DOC) content exhibited an upward and then a downward trend. Otherwise, the fourth and sixth FTCs were the key points of change. The SOC, MBC and DOC contents in paddy fields were higher than those in dry fields, showing upward and then downward trends spatially from northeast to southwest. The SOC and MBC contents in each soil type were the highest at the 20% water content, and the DOC content gradually increased with increasing water content. The ammonium nitrogen (NH₄⁺-N) content in different soil types at different water contents under the FTCs showed an upward trend first, then a downward trend and finally an upward trend. The NH₄⁺-N content in paddy fields was higher than that in dry fields. The nitrate nitrogen (NO₃^‒-N) content showed a downward trend first, then an upward trend and finally a downward trend. The NO₃^‒-N content in dry fields was higher than that in paddy fields. The NH₄⁺-N contents in the three soil types on the Sanjiang Plain were significantly higher than those on the Songnen Plain. The NH₄⁺-N and NO₃^‒-N contents showed upward trends with increasing water content, but the differences were not significant. The results have implications for the study of different types of soils and provide references for research on the mechanism of soil carbon and nitrogen transformation in typical farming areas in Northeast China.     

Effects of Organic Amendments on Productivity and Profitability of Bell Pepper–French Bean–Garden Pea System and on Soil Properties during Transition to Organic Production

A transition period of at least 2 years is required for annual crops before the produce may be certified as organically grown. There is a need to better understand the various management options for a smooth transition from conventional to organic production. The purpose of this study was to evaluate the effects of different organic amendments and biofertilizers (BFs) on productivity and profitability of a bell pepper–french bean–garden pea system as well as soil fertility and enzymatic activities during conversion to organic production. For this, the following six treatments were established in fixed plots: composted farmyard manure (FYMC, T₁); vermicompost (VC, T₂); poultry manure (PM, T₃) along with biofertilizers (BF) [Rhizobium/Azotobacter + phosphorus solubilizing bacteria (Pseudomonas striata)]; mix of three amendments (FYMC + PM + VC + BF, T₄); integrated nutrient management (FYMC + NPK, T₅); and unamended control (T₆). The yields of bell pepper and french bean under organic nutrient management were markedly lower (25.2–45.9% and 29.5–46.2%, respectively) than with the integrated nutrient management (INM). Among the organic treatments, T₄ and T₁ produced greater yields of both bell pepper (27.96 Mg ha^?1) and french bean (3.87 Mg ha^?1) compared with other treatments. In garden pea, however, T₄ gave the greatest pod yield (7.27 Mg ha^?1) and was significantly superior to other treatments except T₅ and T₁. The latter treatment resulted in the lowest soil bulk density (1.19 Mg m^?3) compared with other treatments. Similarly, soil organic C was significantly greater in all the treatments (1.21–1.30%) except T₂ compared to T₆ (1.06%). Plots under INM, however, had greater levels of available nitrogen–phosphorus–potassium (NPK) than those under organic amendments. T₁ plots showed greater dehydrogenase and acid phosphatase activities compared with other treatments. However, T₄ and T₅ plots had greater activities of β-glucosidase and urease activities, respectively. The cost of cultivation was greater under organic nutrient management (except T₂) compared with INM. The latter treatment gave greater gross margin and benefit/cost (B/C) ratio for all vegetables, except that T₂ gave greater B/C ratio in garden pea compared with other treatments. We conclude that T₁ and T₄ were more suitable for enhancing the productivity of bell pepper–french bean–garden pea system, through improved soil properties, during transition to organic production.