Relationship between soil test values and analysis of pecan leaves taken at three dates

Abstract

Leaf samples were collected from 24 pecan trees on three dates 1 month apart in June, July, and August. Soil samples were collected in June from each site at three depths: 0–6, 6–12, and 12–18 inches. Correlations between leaf analyses and soil test values were significant for Zn, Ca, Mg, and P. Values were not correlated for K. There was a high negative correlation for leaf Mn and soil pH. Means of leaf analysis values for the three sampling dates were not statistically different for any element. The data indicate that soil sampling should be a satisfactory means of determining fertility needs of pecan orchards, except for N.     

Sampling depth effects on sodium bicarbonate (NaHCO3)‐extractable phosphorus and potassium and fertilizer recommendations

Abstract

Soil test nutrient concentrations vary with depth, especially in perennial cropping systems where fertilizer is broadcast on the soil surface without incorporation. The objective of this study was to determine the effect of fertilizer rate and sampling depth on soil test phosphorus (P) and potassium (K), and P and K fertilizer recommendations for alfalfa (Medicago sativa L.). Five rates of P and K (0, 56, 112, 224, and 336 kg ha^‐1 P₂O₅ and K₂O) were broadcast on established alfalfa stands at three sites with different soil properties and tillage and fertilization histories. In separate plots at one site the same rates of P and K were also incorporated to a depth of 15 cm prior to seeding alfalfa. Soil samples were collected at depths of 0 to 10, 0 to 15, and 0 to 30 cm during the growing season. Fertilizer rates and soil sample depth affected soil test P and K at all sites. Relative to the 30‐cm sample depth, soil test values were higher in fertilized treatments with 10 and 15 cm sample depths due to the concentration of immobile P and K near the soil surface. Sample depths of 10 and 15 cm frequently resulted in lower P and K fertilizer recommendations than those of the 30‐cm depth. Sample depth is an important consideration in routine soil sampling for the purpose of making fertilizer recommendations. If research data used for developing soil test‐based fertilizer recommendation are obtained using a standard sampling depth, routine sampling must also be to the same depth.     

Optimum Soil Acidity Indices for Dry Bean Production on an Oxisol in No‐Tillage System

Abstract

Soil acidity is one of the major yield constraints to crop production in various parts of the world. Quantifying optimum soil acidity indices is an important strategy for achieving maximum economic crop yields on acid soils. Five field experiments were conducted for three consecutive years using dry bean as a test crop on an Oxisol. The lime rates used were 0, 12, and 24 Mg ha^?1 for creating a wide range of soil acidity indices in a no‐tillage cropping system. Grain yield of dry bean was significantly increased by improving soil pH, base saturation, calcium (Ca), magnesium (Mg), and potassium (K) saturation and reducing aluminum (Al) saturation. These soil acidity indices were higher in the 0‐ to 10‐cm soil layer than the 10‐ to 20‐cm soil layer for maximum grain yield. Across two soil depths, optimum values for maximum bean yield were pH 6.5, base saturation 67%, Ca saturation 48%, and Mg saturation 19%. Bean yield linearly increased with increasing K saturation in the range of 1.5 to 3% across two soil depths. There was a significant linear decrease in grain yield with increasing Al saturation in the range of 0 to 8% across two soil depths. Optimal values of soil indices for maximum bean yield can be used as a reference for liming and improving yield of bean crop on Oxisols in a no‐tillage cropping system. Yield components, such as pod number, grain per pod, and 100‐grain weight were significantly improved with liming, and bean yield was significantly associated with these yield components.     

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Abstract

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (D_m) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in D_m of soil aggregate size distribution among tillage treatments, which suggested that D_m could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.     

保护性耕作对旱作农田耕层土壤肥力及酶活性的影响

通过田间定位试验,研究了不同耕作方式对黄土高原西部旱农区耕层土壤肥力和酶活性的影响。结果表明,秸秆还田可以显著提高 0—5和5—10 cm土层有机质、全氮、全磷、全钾、铵态氮、速效磷、速效钾和3种水解酶活性; 10—30 cm 土层仅提高了有机质、全钾和速效钾含量,对其余各养分含量和水解酶活性并无明显影响。免耕降低了0—5、5—10和10—30 cm土层硝态氮含量,但对过氧化氢酶活性有明显促进作用。相关分析表明,土壤有机质、养分和碱性磷酸酶、蔗糖酶活性之间呈极显著相关关系。进一步应用主成分分析表明,土壤有机质、养分和水解酶活性共同反映着黄土高原雨养农区土壤肥力水平的高低。     

Seasonal variation of microbial biomass, activity, and community structure in soil under different tillage and phosphorus management practices

No-tillage systems contribute to physical, chemical and biological changes in the soil. The effects of different tillage practices and phosphorus (P) fertilization on soil microbial biomass, activity, and community structure were studied during the maize growing season in a maize–soybean rotation established for 18 years in eastern Canada. Soil samples were collected at two depths (0–10 and 10–20 cm) under mouldboard plow (MP) and no-till (NT) management and fertilized with 0, 17.5, and 35 kg P ha^?1. Results show that the duration of the growing season had a greater effect on soil microbiota properties than soil tillage or P fertilization at both soil depths. Seasonal fluctuations in soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), in dehydrogenase and alkaline phosphomonoesterase activities, and in total phospholipids fatty acid (PLFA) level, were greater under NT than MP management. The PLFA biomarkers separated treatments primarily by sampling date and secondly by tillage management, but were not significantly affected by P fertilization. The abundance of arbuscular mycorrhizal fungi (AMF; C16:1ω5) and fungi (C18:2ω6,9) was lower under NT than MP at the 10–20-cm soil depth in July. Phosphorus fertilization increased soil microbial biomass phosphorus (SMB-P) and Mehlich-3 extractable P, but had a limited impact on the other soil properties. In conclusion, soil environmental factors and tillage had a greater effect on microorganisms (biomass and activity) and community structure than P fertilization.     

Land management effects on nitrogen and carbon cycling in an Ultisol

Abstract

Soil carbon (C) content in agro‐ecosystems is important in a global context because of the potential for soil to act as a sink for atmospheric CO₂. However, soil C storage in agro‐ecosystems can be sensitive to land management practices. The objective of this study was to examine the impact of land management systems on C and nitrogen (N) cycling in an Ultisol in Alabama. Soil samples (0–10, 10–20, and 20–30 cm depths) were collected from a Marvyn sandy loam soil (fine‐loamy, siliceous, thermic Typic Hapludults) under five different farm scale management systems for at least 5 years. The five systems were cotton (Gossypium hirsutum L.) production managed with 1) conventional tillage only, 2) conventional tillage with a grazed winter cover crop (wheat, Triticum aestivum L.), 3) conservation tillage with a winter cover crop grown for cover only with strip tillage; or taken out of cotton production with either 4) long‐term fallow (mowed), or 5) Conservation Reserve Program with loblolly pine (Pinus taeda L.) (CRP‐pine). Total N, total organic C (TOC), total P, and soil C:N ratios were determined. Potential C mineralization, N mineralization, C turnover and C:N mineralization ratios were determined on samples during a 30‐day laboratory incubation study. The fallow system had significantly higher TOC concentration (7.7 g kg^‐1 C) while the CRP‐pine system had lower TOC concentration (3.1 g kg^‐1 C) compared with the farmed management systems (=4.7 g kg^‐1 C). The fallow system had a significantly lower C turnover at all three soil depths compared with the other management systems. At the 0–10 cm depth, the highest C:N mineralization ratio levels were observed in management systems receiving the most tillage. Our results indicate that for Ultisols in the Southeast the use of surface tillage in land management systems is a controlling factor which may limit soil C sequestration.     

Spatial and temporal variability of soil physical properties of norfolk loamy sand as affected by tillage

Physical properties of field soil vary both spatially and temporally. Because so little information is available concerning the changes in magnitude of soil physical properties as functions of soil depth, distance normal to a crop row, and time, they have largely been ignored in model development. The purpose of this study was to evaluate quantitatively the spatial and temporal variability imposed by several tillage operations on several soil physical properties. Three tillage treatments, replicated 4 times in a randomized complete block design, were (1) conventionally-disked 3 times before planting, (2) full width strip chisel plowed to a 27-cm depth, and (3) in-row-subsoiled plus bedding. Soil physical properties measured were cone index (CI), weight percentage water (Pw), bulk density (Db), soil water characteristic curve, saturated hydraulic conductivity (Ksat) and soil settling. These properties were measured 3 times: immediately after planting soybeans (Glycine max (L.) Merr.) on 16 May; on 3 June; on 8 July 1977. Soil properties were measured at the 0–14, 14–28, and 28–41-cm soil depths at 3 positions relative to the row i.e., in the row, in the trafficked interrow, and in the non-trafficked interrow. Significant differences due to tillage treatment were found for Db, CI, and the soil water characteristic. The greatest spatial variation occurred in the 0–14-cm depth and decreased with depth. Significant differences for most variables were also found for the tillage by depth and tillage by position interactions. All properties exhibited significant temporal variation.     

The residual phosphorus,potassium, chlorides and other salts in soils following five years of fertility studies

Abstract

Soil samples were taken from six experimental sites (3 in phosphorus and 3 in the potassium rate studies) to depths of 60 or 90 cm. Phosphorus from the various rates of applied P was found to have accumulated in the surface soil except where mechanical mixing was suspected. Potassium from the various rates of applied K was found accumulated in soil depths of 0 to 20 cm. However, the accumulated amounts of P and K were small in comparison to the rates applied. In the potassium studies, chlorides accumulated in the subsoils of the two sites that had restricted soil layers.     

Long-term straw mulch effects on crop yields and soil organic carbon fractions at different depths under a no-till system on the Chengdu Plain,China

Proposal

A 12-year field experiment was conducted to assess straw mulch effects on soil organic carbon fractions, the carbon pool management index (CPMI) at different depths, and crop yield under a no-till rice-wheat rotation system on the Chengdu Plain, southwestern China.

Materials and methods

There were two treatments in the experiment: no-till without straw mulch (CK) and no-till with straw mulch (SM). The soil was sampled at 0–5, 5–10, 10–20, and 20–30-cm depths. Soil total organic carbon (TOC), the labile organic carbon fractions, including particulate organic carbon (POC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and permanganate-oxidizable carbon (KMnO₄-C), and the CPMI were analyzed. The crop grains were measured between September 2013 and May 2018.

Results and discussion

Between 2013 and 2018, rice and wheat grain yields under SM were comparable to CK, except there were higher rice yields in 2016 and higher wheat yields in 2017 under SM. The soil organic carbon decreased as soil depth increased in both treatments. Soil TOC, POC, and KMnO₄-C concentrations at 0–5 and 5–10 cm, CPMI at 0–5 and 5–10 cm, and DOC at 0–5, 5–10, and 10–20-cm soil depths were significantly greater under SM than under CK, whereas the MBC at 0–5 and 5–10 cm under SM was lower than CK. The POC/TOC, KMnO₄-C/TOC, and DOC/TOC ratios were greater under SM in the 0–5 and 5–10 cm, 0–5 cm, and 5–10 and 10–20-cm layers than CK, respectively, whereas the MBC/TOC ratio decreased under SM at 0–5, 5–10, and 10–20-cm depths.

Conclusions

The results showed that straw mulching should be adopted when a no-till rice-wheat cropping system is used in southwestern China because it leads to effective improvements in SOC sequestration while still maintaining normal crop yields.

     

Response of the soil macrofauna abundance and community structure to drought stress under agroforestry system in southeastern Qinghai-Tibet Plateau

ABSTRACT

Soil macrofauna is vital for soil functions and soil-mediated processes in all ecosystems. However, environmental perturbations, such as drought, that threaten both the abundance and function of soil macrofauna remain mostly unexplored, particularly in an agroforestry system. We investigated the effects of drought on soil macrofauna abundance and vertical distribution under three different planting systems including two intercropping systems, comprising Chinese prickly ash (Zanthoxylum bungeanum) intercropped with soybean (Glycine max) (Z-G) or bell pepper (Capsicum annuum) (Z-C), and one monoculture system, comprising only Z. bungeanum (Z). Soil samples were collected at depths of 0–10, 10–20, and 20–30 cm, and soil macrofauna and chemical properties were analyzed. Soil dryness negatively affected soil macrofauna in all planting systems. Drought reduced the total macrofauna density, biomass, genera richness, and Pielou’s evenness. Additionally, drought significantly decreased density and biomass of Drawida and Eisenia but had no effect on Carabid beetles. Soil macrofauna density was highest in the Z-G intercropping system and higher at 0–10 cm than at other soil depths. These results indicate that intercropping soybean rather than bell pepper increases the abundance and biomass of soil macrofauna, and drought remarkably impacts the response of soil macrofauna to planting systems.     

Tillage intensity and fertility level effects on nitrogen and carbon cycling in a vertisol

Abstract

Because of erosion problems, an effort has been undertaken to evaluate the effect of tillage intensity on carbon (C) and nitrogen (N) cycling on a vertisol. Soil samples at 0–10, 10–20, and 20–30 cm depth were collected from a split plot experiment with five different levels of tillage intensity on Houston Black soil (fine, montmorillonitic, thermic Udic Pellusterts). The experiment was a split plot design with 5 replications. The main plots were chisel tillage, reduced tillage, row tillage, strip tillage, and no tillage. The subplots were soil fertility levels with either high or low fertilizer application rate. Total N, total phosphorus (P), organic C, inorganic N, and C:N ratio were measured on soil samples as well as the potential C mineralization, N mineralization, C turnover, and C:N mineralization ratio during a 30 d incubation. Total P and organic C in soil were increased, with 0.9 and 0.8 kg P ha^‐1 and 20.6 and 20.0 kg C ha^‐1, for high and low soil fertility, respectively. Fertilizer application had no effect on either total N at the 0–10 cm depth, or on soil nutrient status below 10 cm. Potential soil N mineralization was decreased at the 0–10 cm depth and increased at the 20–30 cm depth by the high fertilizer treatment. Chisel tillage decreased total N and P in the 0–10 cm depth, with 1.4 and 1.6 kg N ha^‐1 and 0.8 and 0.9 kg P ha^‐1. However, chisel tillage increased total N and P at the 10–20 cm depth, with 1.3 and 1.2 kg N ha^‐1, and 0.72 and 0.66 kg P ha^‐1 for chisel tillage and no tillage, respectively. Tillage intensity increased C mineralization and C turnover, but reduced N mineralization at the 0–10 cm depth. The results indicate that intensively tilled soil had a greater capacity for C mineralization and for reductions in soil organic C levels compared to less intensively tilled systems.     

Nutrient content of maize and soil organic matter status under various tillage methods and farmyard manure levels

Abstract

A two-year field study was conducted under semi-arid conditions in Pakistan to assess the role of tillage systems and farmyard manure on soil, plant nutrients and organic matter content. Four tillage systems (zero, minimum, conventional and deep tillage) and three farm manure levels were used. Maize crop was grown up to maturity. Uptake of N, P and K in maize shoots improved in tillage systems compared to non-tillage and treatments where farmyard manure was applied. Soil N status decreased in the deep tillage systems, whereas it increased in all other tillage systems and in the farmyard manure amended treatments. Increase in soil P values was observed under minimum and conventional tillage, whereas deep tillage resulted in a decrease. Farmyard manure amendments increased soil P and soil K in all systems. Tillage did not affect soil K levels. Results demonstrate that reduced tillage is practicable in arid and semi-arid regions since it improves soil fertility.     

Influences of nitrogen treatments and irrigation methods on soil chemical properties

Abstract

Changes in soil chemical properties were investigated in conjunction with an ongoing study of fertility and irrigation relationships of cotton. Four irrigation methods and five nitrogen fertilization rates were the primary focus of the study. The four irrigation regimes studied were: high frequency center pivot, low frequency center pivot, furrow irrigated, and unirrigated. Nitrogen rates were 0, 30, 60, 90, and 120 lb N/A. Soil samples were collected from each plot in 6‐in‐ increments to a depth of 24 in. in 1982 and again in 1986 after four years of continuous cotton production. The soil samples were analyzed for pH, organic matter (OM), P, K, electrical conductivity (EC), and NO₃ ^‐‐N. All background soil characteristics were found to vary with depth with the exception of NO₃ ^‐‐N. The follow‐up sampling and testing in 1986 showed significant differences in soil properties as a function of irrigation, N‐fertilization, depth, and their interactions. Nitrates were accumulated in the 18 to 24‐in. depth under high (120 lb N/A) fertilization, and in the 0 to 6‐in. depth under the four lower treatments (0, 30, 60, and 90 lb N/A). Soil pH was highest in the furrow and high frequency center pivot irrigated regimes and lowest in the unirrigated regime. Soil pH also decreased with depth. Electrical conductivity of the soil was highest in the high frequency regime and not significantly different among the other three irrigation methods. The 0M content of the soil was greatest in the high frequency regime but not significantly different in the low frequency, furrow, or unirrigated blocks. Soil 0M was found to decrease with depth through 18 in. in all cases. The P and K status of the soil was not changed as a result of the N fertilization or irrigation treatments.     

Yield,Nutrient Uptake,and Soil Chemical Properties as Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System

Abstract

In Oxisols, acidity is the principal limiting factor for crop production. In recent years, because of intensive cropping on these soils, deficiency of micronutrients is increasing. A field experiment was conducted on an Oxisol during three consecutive years to assess the response of common bean (Phaseolus vulgaris L.) under a no‐tillage system to varying rates of lime (0, 12, and 24 Mg ha^?1) and boron (0, 2, 4, 8, 12, 16, and 24 kg ha^?1) application. Both time and boron (B) were applied as broadcast and incorporated into the soil at the beginning of the study. Changes in selected soil chemical properties in the soil profile (0- to 10‐ and 10- to 20‐cm depths) with liming were also determined. During all three years, gain yields increased significantly with the application of lime. However, B application significantly increased common bean yield in only the first crop. Only lime application significantly affected the soil chemical properties [pH; calcium (Ca²⁺); magnesium (Mg²⁺); hydrogen (H⁺)+ aluminum (Al³⁺); base saturation; acidity saturation; cation exchange capacity (CEC); percent saturation of Ca²⁺, Mg²⁺, and potassium (K⁺); and ratios of exchangeable Ca/Mg, Ca/K, and Mg/K] at both soil depths (0–10 cm and 10–20 cm). A positive significant association was observed between grain yield and soil chemical properties. Averaged across two depths and three crops, common bean produced maximum grain yield at soil pH_w of 6.7, exchangeable (cmol_c kg^?1) of Ca²⁺ 4.9, Mg²⁺ 2.2, H⁺+Al³⁺ 2.6, acidity saturation of 27.6%, CEC of 4.1 cmol_c kg^?1, base saturation of 72%, Ca saturation of 53.2%, Mg saturation of 17.6%, K saturation of 2.7%, Ca/Mg ratio of 2.8, Ca/K ratio of 25.7, and Mg/K ratio of 8.6. Soil organic matter did not change significantly with addition of lime.     

Effects of 30 years of cropping and tillage systems on surface soil test changes

Abstract

A common belief is that no‐till systems with adequate fertility will improve soil quality over other tillage systems. The objectives of this study were to determine if crop phase, tillage systems, and n rate in a long‐term rotation affected soil chemical analyses in the surface 15 cm of soil and to evaluate the trend in chemical analyses. To test this hypothesis, surface soil samples were taken from a long‐term (30‐year) cropping and tillage study. This study was initiated in 1965 on a Harney silt loam soil in Central Kansas with every phase of the wheat‐sorghum‐fallow (WDF) rotation included each year. Tillage systems included clear‐till (CT), reduced‐till (RT), and no‐till (NT). In 1975, four nitrogen (N) rates (0, 22, 45, 67 kg N ha¹) were incorporated by subdividing the tillage plots. Topdressed N, as ammonium nitrate, was the only fertilizer added throughout the duration of the study. Soil samples were taken at depths of 0 to 7.5 and 7.5 to 15 cm in all plots in 1965 and in 1995. In 1998, soils on 1997 sorghum plots were samples in 2.5‐cm increments to 15 cm. Samples from all dates were analyzed for pH, available phosphorus (AP), and organic matter (OM), and deviations from the controls from 1965 to 1995 were assessed by subtracting 1995 results from 1965 results. The change in soil pH showed a crop phase by sample depth interaction. In the wheat phase, pH in the top 7.5 cm increased by 0.19 and increased by 0.28 in the 7.5–15 cm layer. In the fallow phase, pH increased by 0.04 and 0.35 in the top 7.5 cm and 7.5–15 cm layers, respectively. The pH change for sorghum was intermediate for both depths. The increase in overall pH from 1965 to 1995 was unexpected and contrary to normal expectations of a decrease over time. Soil OM was not changed significantly over the 30 years of the study, suggesting that OM buildup or depletion is very slow under this cropping system on a nearly level soil with minimal soil erosion. Increasing the rate of N application significantly reduced pH in the upper increment samples, but had little effect on pH below 10 cm. The NT system had the lowest surface increment in pH, but differences among tillage systems were minimal below 7.6 cm. The AP was highest for NT in the surface increment, but for CT at deeper depths. Likewise, OM was highest for NT in the 2.5 cm increment and the CT at deeper increments. Under the present N management, pH may reach levels where herbicide effectiveness and phosphorus availability could be affected adversely. Deep tillage by one‐way or mold‐board plowing might be an interim solution to raise the pH before liming is implemented or P fertilizer is added to maintain adequate AP throughout the top 15 cm. Nitrogen management may need to be changed to some form of band‐type placement to reduce the total N applied. Under the conditions of this study (WSF, reduced tillage, and 57 cm annual precipitation), soil OM increased very slowly.     

Long-term effect on soil biochemical status of a Vertisol under conservation tillage system in semi-arid Mediterranean conditions

Long-term field experiments are expected to provide important information regarding soil properties affected by conservation management practices. Several studies have shown that soil enzyme activities are sensitive in discriminating among soil management effects. In this study we evaluated the long-term effect of direct drilling (DD) under a crop rotation system (cereals–sunflower–legumes), on the stratification of soil organic matter content and on biochemical properties in a dryland in southwest Spain. The results were compared to those obtained under conventional tillage (CT). Soil biochemical status was evaluated by measuring the enzymatic activities (dehydrogenase, β-glucosidase, alkaline phosphatase and arylsulphatase) during the flowering period of a pea crop. Soil samples were collected in May 2007 at three depths (0–5, 5–10 and 10–20 cm).Total organic carbon (TOC) contents and values of soil enzyme activities were higher in soils subjected to DD than to CT, specifically at 0–5 cm depth. Although a slight decrease of TOC and enzymatic activities with increasing soil depth was observed, no significant differences were found among different depths of the same treatment. This could be related to the high clay content of the soil, a Vertisol. Enzyme activities values showed high correlation coefficients (from r = 0.799 to r = 0.870, p < 0.01) with TOC. Values of activity of the different enzymes were also correlated (p < 0.01).Values of stratification ratios did not show significant differences between tillage practices. The high clay content of the soil is responsible for this lack of differences because of the protection by clay mineral of TOC and soil enzymes activities.Long-term soil conservation management by direct drilling in a dryland farming system improved the quality of a clay soil, especially at the surface, by enhancing its organic matter content and its biological status.     

不同灌溉方式对保护地土壤酸化特征的影响

自连续13a在同一地块以不同灌溉方式进行灌溉试验的保护地,分层采集沟灌、滴灌、渗灌3个处理0～60cm土层土壤样品,研究灌溉方式对土壤酸化特征的影响。结果表明,3种灌溉处理土壤活性酸度和交换性酸含量均随着土层加深而降低,各处理间土壤活性酸度在0～40cm土层差异明显,总体为沟灌>渗灌>滴灌;土壤交换性酸差异出现在0～30cm土层,为渗灌>沟灌>滴灌;土壤交换性Al3+随土层加深呈先增加后降低的变化趋势,且以滴灌含量最低。各处理土壤盐基饱和度(BS)随土层加深而增加,在0～30cm土层为滴灌>渗灌>沟灌。土壤pH与交换性酸、硝态氮含量呈极显著负相关,与盐基饱和度、特别是Ca2+饱和度呈极显著正相关;Al3+占交换性酸比例与有机质含量呈极显著负相关。总之,保护地土壤酸化与硝态氮含量、盐基饱和度、有机质含量关系密切;与沟灌和渗灌相比,滴灌更利于抑制土壤酸化。     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.     

保护性耕作对土壤养分分布及冬小麦吸收与分配的影响

通过田间试验研究了华北平原山前平原区不同耕作方式下土壤氮、磷、钾等养分分布及冬小麦吸收与分配变化和对产量的影响。试验设深翻耕秸秆还田(MC)、秸秆还田旋耕(X)、秸秆粉碎免耕(NC)和整秸覆盖免耕(NW) 4 种冬小麦播前土壤耕作方式。试验结果表明, 6 年的不同耕作处理对土壤养分分布及冬小麦吸收与分配有显著影响。秸秆还田旋耕可显著提高土壤表层(0~5 cm)有机质、全氮以及碱解氮、速效磷、速效钾含量,但随土壤深度增加, 提高效果呈逐渐下降趋势; 20~30 cm 土层土壤有机质、全氮和速效氮含量显著低于秸秆粉碎免耕处理。两种免耕模式(NC、NW)植株的全氮、全磷、全钾含量在苗期明显低于翻耕(MC)和旋耕(X)模式,在返青期差异最为显著。到拔节和扬花期, 免耕(NC、NW)植株的全氮、全磷、全钾含量与翻耕(MC)和旋耕(X)之间的差异逐渐减少, 并最终影响到籽粒养分的积累。