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.     

Heavy‐Metal Contamination of Soil and Vegetables in Wastewater‐Irrigated Agricultural Soil in a Suburban Area of Hanoi,Vietnam

The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serve as sources of water for irrigating vegetable farms. The purposes of this study were to identify the impact of wastewater irrigation on the level of heavy metals in the soils and vegetables and to predict their potential mobility and bioavailability. Soil samples were collected from different distances from the canal. The average concentrations of the heavy metals in the soil were in the order zinc (Zn; 204 mg kg^?1) > copper (Cu; 196 mg kg^?1) > chromium (Cr; 175 mg kg^?1) > lead (Pb; 131 mg kg^?1) > nickel (Ni; 60 mg kg^?1) > cadmium (Cd; 4 mg kg^?1). The concentrations of all heavy metals in the study site were much greater than the background level in that area and exceeded the permissible levels of the Vietnamese standards for Cd, Cu, and Pb. The concentrations of Zn, Ni, and Pb in the surface soil decreased with distance from the canal. The results of selective sequential extraction indicated that dominant fractions were oxide, organic, and residual for Ni, Pb, and Zn; organic and oxide for Cr; oxide for Cd; and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order of Cd > Ni > Cr > Pb > Cu > Zn and in the order of Cd > Ni > Cr > Zn > Cu > Pb for the ethylenediaminetetraaceitc acid (EDTA) treatment. The EDTA treatment gave greater leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were fully released from the exchangeable fraction, and some heavy metals were fully released from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the vegetables exceeded the Vietnamese standards. The transfer coefficients for the metals were in the order of Zn > Ni > Cu > Cd = Cr > Pb.     

Influence of pH on Productivity,Nutrient Use Efficiency by Dry Bean,and Soil Phosphorus Availability in a No‐Tillage System

Abstract

Low pH is one of the most yield‐limiting factors for crop production in Cerrado soils. The objective of this study was to determine influence of soil pH on grain yield and its components, and use of nutrients by dry bean in a no‐tillage system in an Oxisol (Typic Haplorthox) of the Cerrado region of Brazil. Five field experiments were conducted for three consecutive years. The pH levels were low (5.3), medium (6.4), and high (6.8), created by applying lime at the rates of 0, 12, and 24 Mg ha^?1. Grain yield and its components were significantly influenced by soil pH. Adequate pH for grain yield and its components was 6.4. Maximum variation in grain yield was measured by shoot dry weight, and minimum variation was due to 100‐grain weight. Nutrient utilization efficiency was in the order of magnesium (Mg) > phosphorus (P) > calcium (Ca) > potassium (K) > nitrogen (N) > copper (Cu) > manganese (Mn) > zinc (Zn) > iron (Fe). Soil extractable P increased linearly with increasing pH in the range of 5.3 to 7.3. These results show that adequate soil pH is an important soil acidity index in improving bean yield in Brazilian Oxisols.     

Loss‐on‐Ignition Method to Assess Soil Organic Carbon in Calcareous Everglades Wetlands

Measurement of soil carbon (C) is important for determining the effects of Everglades restoration projects on C cycling and transformations. Accurate measurement of soil organic C by automated carbon–nitrogen–sulfur (CNS) analysis may be confounded by the presence of calcium carbonate (CaCO₃) in Everglades wetlands. The objectives of this study were to compare a loss‐on‐ignition (LOI) method with CNS analysis for assessment of soil C across a diverse group of calcareous Everglades wetlands. More than 3168 samples were taken from three soil depths (floc, 0–10, 10–30 cm) in 14 wetlands and analyzed for LOI, total C, and total calcium (Ca). The LOI method compared favorably to CNS analysis for LOI contents ranging from 0 to 1000 g kg^?1 and for soil total Ca levels from 0 to 500 g Ca kg^?1. For all wetlands and soil depths, LOI was significantly related to total C (r² = 0.957). However, LOI was a better predictor of total C when LOI exceeded 400 g kg^?1 because of less interference by CaCO₃. Total C measurement by CNS analysis was problematic in soils with high total Ca and low LOI, as the presence of CaCO₃ confounded C analysis for LOI less than 400 g kg^?1. Inclusion of total Ca in regression models with LOI significantly improved the prediction of total C. Estimates of total organic C by CNS analysis were obtained by accounting for C associated with CaCO₃ by calculation, with results being similar to total organic C values obtained from LOI analysis. The proportion of C in organic matter measured by the LOI method (51%) was accurate and applicable across wetlands, soil depths, and total Ca levels; thus LOI was a suitable indicator of total organic C in Everglades wetlands.     

Effects of Arsenic‐Contaminated Irrigation Water on Growth,Yield, and Nutrient Concentration in Rice

Abstract

A study was undertaken to determine the effects of different concentrations of arsenic (As) in irrigation water on Boro (dry‐season) rice (Oryza sativa) and their residual effects on the following Aman (wet‐season) rice. There were six treatments, with 0, 0.1, 0.25, 0.5, 1, and 2 mg As L^?1 applied as disodium hydrogen arsenate. All the growth and yield parameters of Boro rice responded positively at lower concentrations of up to 0.25 mg As L^?1 in irrigation water but decreased sharply at concentrations more than 0.5 mg As L^?1. Arsenic concentrations in grain and straw of Boro rice increased significantly with increasing concentration of As in irrigation water. The grain As concentration was in the range of 0.25 to 0.97 µg g^?1 and its concentration in rice straw varied from 2.4 to 9.6 µg g^?1 over the treatments. Residual As from previous Boro rice showed a very similar pattern in the following Aman rice, although As concentration in Aman rice grain and straw over the treatments was almost half of the As levels in Boro rice grain. Arsenic concentrations in both grain and straw of Boro and Aman rice were found to correlate with iron and be antagonistic with phosphorus.     

Long‐Term Integrated Nutrient Management for Rice‐Based Cropping Pattern: Effect on Growth,Yield, Nutrient Uptake,Nutrient Balance Sheet,and Soil Fertility

Abstract

A 7‐year‐long field trial was conducted on integrated nutrient management for a dry season rice (Boro)–green manure (GM)–wet season rice (T. Aman) cropping system at the Bangladesh Rice Research Institute Farm, Gazipur during 1993–1999. Five packages of inorganic fertilizers, cow dung (CD), and GM dhaincha (Sesbania aculeata) were evaluated for immediate and residual effect on crop productivity, nutrient uptake, soil‐nutrient balance sheet, and soil‐fertility status. Plant height, active tiller production, and grain and straw yields were significantly increased as a result of the application of inorganic fertilizer and organic manure. Usually, the soil‐test‐based (STB) fertilizer doses for a high‐yield goal produced the highest grain yield of 6.39 t ha^?1 (average of 7 years) in Boro rice. Application of CD at the rate of 5 t ha^?1 (oven‐dry basis) once a year at the time of Boro transplanting supplemented 50% of the fertilizer nutrients other than nitrogen (N) in the subsequent crop of the cropping pattern. A positive effect of GM on the yield of T. Aman rice was observed. Following GM, the application of reduced doses of phosphorus (P), potassium (K), sulfur (S), and zinc (Zn) to the second crop (T. Aman) did not reduce yield, indicating the beneficial residual effect of fertilizer applied to the first crop (Boro rice) of the cropping pattern. The comparable yield of T. Aman was also observed with reduced fertilizer dose in CD‐treated plots. The total P, K, and S uptake (kg/ha/yr) in the unfertilized plot under an irrigated rice system gradually decreased over the years. The partial nutrient balance in the unfertilized plot (T₁) was negative for all the nutrients. In the fertilized plots, there was an apparent positive balance of P, S, and Zn but a negative balance of N and K. This study showed that the addition of organic manure (CD, dhaincha) gave more positive balances. In the T_4c treatment at 0–15 cm, the application of chemical fertilizers along with the organic manures increased soil organic carbon by (C) 0.71%. The highest concentration of total N was observed with T_4c followed by T_4d and T_4b, where CD was applied in Boro season and dhaincha GM was incorporated in T. Aman season. The sixfold increase in soil‐available P in T_4b‐, T_4c‐, T_4a‐treated plots was due to the addition of CD. Dhaincha GM with the combination of chemical fertilizer helps to mobilize soil‐available P by 3 to 6 ppm. The highest amount of soil‐available S was found in T_4c‐ and T_4a‐treated plots. It was 2.5 times higher than that of the initial soil. The application of CD and dhaincha GM along with chemical fertilizers not only increased organic C, total N, available P, and available S but also increased exchangeable K, available Zn, available iron (Fe), and available manganese (Mn) in soil.     

Long-Term Fertilizer Use Altered Soil Microbial Community Structure but Not α-Diversity in Subtropical Southwestern China

Eurasian Soil Science - Despite the general consensus that fertilizer is the most important driver of the evolution of soil microbial communities, the specific effects of long-term fertilizer use...     

Land Use and Soil Organic Carbon in China’s Village Landscapes

Village landscapes, which integrate small-scale agriculture with housing, forestry, and a host of other land use practices, cover more than 2 million square kilometers across China. Village lands tend to be managed at very fine spatial scales (≤ 30 m), with managers both adapting their practices to existing variation in soils and terrain (e.g., fertile plains vs. infertile slopes) and also altering soil fertility and even terrain by terracing, irrigation, fertilizing, and other land use practices. Relationships between fine-scale land management patterns and soil organic carbon (SOC) in the top 30 cm of village soils were studied by sampling soils within fine-scale landscape features using a regionally weighted landscape sampling design across five environmentally distinct sites in China. SOC stocks across China’s village regions (5 Pg C in the top 30 cm of 2 × 10 6 km 2 ) represent roughly 4% of the total SOC stocks in global croplands. Although macroclimate varied from temperate to tropical in this study, SOC density did not vary significantly with climate, though it was negatively correlated with regional mean elevation. The highest SOC densities within landscapes were found in agricultural lands, especially paddy, the lowest SOC densities were found in nonproductive lands, and forest lands tended toward moderate SOC densities. Due to the high SOC densities of agricultural lands and their predominance in village landscapes, most village SOC was found in agricultural land, except in the tropical hilly region, where forestry accounted for about 45% of the SOC stocks. A surprisingly large portion of village SOC was associated with built structures and with the disturbed lands surrounding these structures, ranging from 18% in the North China Plain to about 9% in the tropical hilly region. These results confirmed that local land use practices, combined with local and regional variation in terrain, were associated with most of the SOC variation within and across China’s village landscapes and may be an important cause of regional variation in SOC.     

Tillage Effects on Soil Quality Indicators and Nematode Abundance in Loessial Soil under Long‐Term No‐Till Production

Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha^?1 year^?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha^?1 year^?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.     

Effects of Plant Residue Decomposition on Soil N Availability,Microbial Biomass and β-Glucosidase Activity During Soil Fertility Improvement in Ghana

With limited use of inorganic fertilizers on smallholder farms,plant residues could be viable alternatives for soil fertility improvement.This study was conducted to determine how residue quality and decomposition of nine plant species influence soil N availability,microbial biomass,andβ-glucosidase activity during soil fertility improvement.Significant differences in N concentration were found among the species,ranging from 12.2 g kg-1 in Zea mays to 39.2 g kg-1 in Baphia nitida.The C/N ratio was the highest in Z.mays(34.4),whereas lignin and polyphenol concentrations were the greatest in Acacia auriculiformis.The highest decomposition rate(0.251%per day)occurred in Tithonia diversifolia,and the lowest in A.auriculiformis,Albizia zygia,B.nitida,and Z.mays,with the half-lives of 28-56 d.Between 80%and 89%of N,P,K,Ca,and Mg were released from T.diversifolia in 7 d,compared with over 70%retention in A.auriculiformis,B.nitida,and Z.mays.The decomposition and nutrient release half-lives of Gliricidia sepium,Leucaena leucocephala,Azadirachta indica,and Senna spectabilis were less than 14 d.Soil mineral N,microbial biomass,andβ-glucosidase activity increased under all treatments,with T.diversifolia having the greatest effect.While N mineralization occurred in all of the species throughout the experiment,an initial N immobilization was recorded in the A.zy.gia,B.nitida,A.auriculiformis,and Z.mays treatments for up to 14 d.Decomposition and nutrient release rates,mineral N,soil microbial biomass,andβ-glucosidase activity were dependent on residue quality,and P and lignin levels,the lignin/N ratio,and the(lignin+polyphenol)/N ratio had the most significant effects(P≤0.05).     

Cultivation‐Induced Effects on the Soil Organomineral Matrix and Their Bearing on Crust Development on Two Soil Formations from Tanzania

Abstract

Land degradation as a result of land‐use practices is a major environmental concern to sustainable agricultural production in Tanzania. The effect of clearing and long‐term cultivation on physical, chemical, and biological characteristics is described in two representative soil formations from eastern Tanzania: Mkindo (Eutric Fluvisol) in the Mvomero district and Mafiga (Ferric Lixisol) in the Morogoro district. The results have shown that in the Mkindo site, 10 years of continuous rice cultivation has led to severe changes in most characteristics of the soil. Significant effects of cultivation coincide with those considered to favor clay dispersion and crusting phenomena, including changes in soil reaction, clay content, and mineralogy as well as generalized desaturation of the exchange complex, increasing sodicity, and severe losses of soil organic matter (SOM). In contrast, at the Mafiga site, 30 years of a less disturbing cultivation system, including periodic fallows, have also modified some soil characteristics but to a lower extent than at Mkindo. Decreased soil colloidal properties at the Mkindo site and lower stability against biological degradation, reflected by carbon (C)–release curves, than the Mafiga site could be causally connected to clay illuviation processes leading to accumulation of calcium (Ca) and magnesium (Mg) but mainly caused by changes in SOM characteristics such as losses of humic (HA) and fulvic acid (FA) and accumulation of humin.     

Bioresource Nutrient Recycling and Its Relationship with Biofertility Indicators of Soil Health and Nutrient Dynamics in Rice–Wheat Cropping System

A field experiment was conducted for 3 years during 2006–2009 in India to study the effects of plant nutrient recycling through crop residue management, green manuring, and fertility levels on yield attributes, crop productivity, nutrient uptake, and biofertility indicators of soil health in a rice–wheat cropping system. The study revealed that soil microbial biomass carbon (SMBC) and carbon dioxide (CO₂) evolution were significantly greatest under crop residue incorporation (CRI) + Sesbania green manuring (SGM) treatment and were found at levels of 364 μg g^?1 soil and 1.75 μg g^?1 soil h^?1, respectively; these were increased significantly by recycling of organic residues. Activities of dehydrogenase and phosphatase enzymes increased significantly after 3 years, with maximum activity under CRI + SGM treatment. The CRI with or without SGM significantly influenced the plant height, number of tillers m^?2, number of grains panicle^?1 or ear^?1, and 1000-grain weight. Mean yield data of rice and wheat revealed that CRI or crop residue burning (CRB) resulted in slightly greater yield over crop residue removal (CRR) treatment. The CRI + SGM treatment again observed significantly greatest grain yields of 7.54 and 5.84 t ha^?1 and straw yields of 8.42 and 6.36 t ha^?1 in rice and wheat, respectively, over other crop residue management treatments. Total nitrogen (N), phosphorus (P) and potassium (K) uptake in rice–wheat system was greatest with amounts of 206.7, 37.2, and 205.6 kg ha^?1, respectively, in CRI + SGM treatment. Fertility levels significantly influenced the rice and wheat yield with greatest grain yields of 6.66 and 5.68 t ha^?1 and straw yields of 7.94 and 5.89 t ha^?1 in rice and wheat, respectively, with the application of 150% of recommended NPK. Total NPK uptake in rice–wheat system also increased significantly with increase in fertility levels with greatest magnitude by supplying 150% of recommended NPK. Overall, nutrient recycling through incorporation of crop residues and Sesbania green manuring along with inorganics greatly improved the crop productivity, nutrient uptake, and biofertility indicators of soil health with substantial influence on SMBC, CO₂ evolution, and dehydrogenase and phosphatase enzyme activities. This indicates that crop residue management along with Sesbania green manuring practice could be a better option for nutrient recycling to sustain the crop productivity and soil health in intensive rice–wheat cropping system in India as well as in similar global agroecological situations, especially in China, Pakistan, and Bangladesh.     

Carbon Dioxide Emission from Black Soil as Influenced by Land‐Use Change and Long‐Term Fertilization

Land‐use change and soil management play a vital role in influencing losses of soil carbon (C) by respiration. The aim of this experiment was to examine the impact of natural vegetation restoration and long‐term fertilization on the seasonal pattern of soil respiration and cumulative carbon dioxide (CO₂) emission from a black soil of northeast China. Soil respiration rate fluctuated greatly during the growing season in grassland (GL), ranging from 278 to 1030 mg CO₂ m^?2 h^?1 with an average of 606 mg CO₂ m^?2 h^?1. By contrast, soil CO₂ emission did not change in bareland (BL) as much as in GL. For cropland (CL), including three treatments [CK (no fertilizer application), nitrogen, phosphorus and potassium application (NPK), and NPK together with organic manure (OM)], soil CO₂ emission gradually increased with the growth of maize after seedling with an increasing order of CK < NPM < OM, reaching a maximum on 17 August and declining thereafter. A highly significant exponential correlation was observed between soil temperature and soil CO₂ emission for GL during the late growing season (from 3 August to 28 September) with Q₁₀ = 2.46, which accounted for approximately 75% of emission variability. However, no correlation was found between the two parameters for BL and CL. Seasonal CO₂ emission from rhizosphere soil changed in line with the overall soil respiration, which averaged 184, 407, and 584 mg CO₂ m^?2 h^?1, with peaks at 614, 1260, and 1770 mg CO₂ m^?2 h^?1 for CK, NPK, and OM, respectively. SOM‐derived CO₂ emission of root free‐soil, including basal soil respiration and plant residue–derived microbial decomposition, averaged 132, 132, and 136 mg CO₂ m^?2 h^?1, respectively, showing no difference for the three CL treatments. Cumulative soil CO₂ emissions decreased in the order OM > GL > NPK > CK > BL. The cumulative rhizosphere‐derived CO₂ emissions during the growing season of maize in cropland accounted for about 67, 74, and 80% of the overall CO₂ emissions for CK, NPK, and OM, respectively. Cumulative CO₂ emissions were found to significantly correlate with SOC stocks (r = 0.92, n = 5, P < 0.05) as well as with SOC concentration (r = 0.97, n = 5, P < 0.01). We concluded that natural vegetation restoration and long‐term application of organic manure substantially increased C sequestration into soil rather than C losses for the black soil. These results are of great significance to properly manage black soil as a large C pool in northeast China.     

Grapevine Rootstock Effects on Lime‐Induced Chlorosis,Nutrient Uptake,and Source–Sink Relationships

Abstract

The experiment considered Vitis vinifera L. cv. “Pinot blanc” clone VCR5 grafted on a lime‐susceptible (3309 C) and a lime‐tolerant (41 B) hybrid rootstock and grown in 45 L pots of a calcareous and a non‐calcareous soil. Each treatment included plants bearing clusters and plants without clusters; in the latter case the bunches were removed 15 days before blooming. During the third growth year, shoot length, leaf chlorophyll (Chl), and mineral element concentrations were recorded. At the end of the growing cycle the grapevines were divided into leaves, shoots, berries, cluster stems, trunk, roots, and dry matter and mineral element composition per organ were analyzed. The 41 B rootstock showed its lime‐tolerance by exhibiting little reduction of shoot length when grown in the calcareous soil as compared to the non‐calcareous one, while 3309 C growing in the calcareous soil induced a dramatic shoot length reduction. The rootstock also affected the leaf chl concentration according to the known degree of lime‐tolerance/susceptibility: “Pinot blanc” grafted on 3309 C and growing on the calcareous soil showed chlorotic leaves while the plants grafted on 41 B had green leaves; cluster removal did not affect leaf chl. The fruit load (expressed as berry dry matter) was strongly affected by the soil and the rootstock; in the calcareous soil 41 B rootstock produced twice as high cluster dry matter than did 3309 C. A higher macronutrient uptake for the plants growing under lime‐stress conditions was affected by 41 B rootstock. Cluster removal in plants grown on calcareous soil produced different effects, as follows: in the case of 41 B rootstock, a redistribution of photosynthate to other sinks like shoot tip and roots occurred, while in the case of 3309 C only the roots benefited. Under lime‐stress condition the plants grafted on 41 B took up more iron (recorded as total amount in the leaves) than did those grafted on 3309 C.     

Soil Properties Influencing Iron Chlorosis in Grapevines Grown in the Montilla‐Moriles Area,Southern Spain

Abstract

Iron (Fe) chlorosis, an Fe deficiency commonly observed in grapevines cultivated on calcareous soils, generally inhibits plant growth and decreases yield. The objective of this research was to relate the incidence of Fe chlorosis in vines of the Montilla‐Moriles area, southern Spain, to indigenous soil properties. Thirty‐five grapevines (V. vinífera L. cv. Pedro Ximenez grafted on V. berlandieri×V. rupestris 110 Ritcher) showing different degree of Fe chlorosis were selected from 13 vineyards. The leaf chlorophyll concentration (estimated by the SPAD value measured with a Minolta meter) was positively correlated with the contents in different soil Fe forms but not with alkalinity‐related soil properties (pH, calcium carbonate equivalent, and active lime). The acid NH₄ oxalate‐extractable Fe (Fe_o) was the most useful simple variable to predict the occurrence of Fe chlorosis. A Fe_o/active lime ratio of 25×10^–4 was found to be useful to class soils into two groups according to the probability of inducing Fe chlorosis.     

Effects of Biomethanated Spentwash on Soil Properties,Nutrient Availability,Uptake, and Yield of Soybean–Wheat Sequence on Inceptisol

The research aimed to study the effect of presown application of primary biomethanated spentwash (PBSW) on soil properties, nutrient availability, uptake and yield of soybean–wheat sequence on Inceptisol. The field experiment with randomised block design was initiated during 2007–8 and present observation was recorded during 2009–10 and 2010–11.The five treatments were, recommended dose (RD) of NPK (T₁), 100% RD of N through PBSW without (T₂) and with P chemical fertilizer (T₃), 50 and 25% RD of N through PBSW + remaining N and P through chemical fertilizers (T₄,T₅), respectively. The results revealed that the soil physical properties and microbial populations were improved in T₂ and T₃. The lowest soil pH and pHs were observed in T₂. The soil electrical conductivity, organic carbon, exchangeable sodium percentage and sodium adsorption ratio of soil extracts and available K were increased with the increase in PBSW as compared to RD-NPK. The soil available N and P were decreased as PBSW increased at all the soil depths. The greatest yields and total N,P,K uptake of soybean and wheat were observed in T₅.     

Re‐analysis of the Relationship between Organic Carbon and Loss‐on‐Ignition in Soil

The suitability of loss‐on‐ignition (LOI) as an alternative to direct measurement of organic carbon (OC) has been debated for decades without resolution. The literature contains an abundance of different linear regression models to describe the LOI–OC relationship, most based on untransformed values of LOI and OC. Such regression is suspect because the variables are unable to occupy Euclidean space. Logratio transformation—based on relative rather than absolute differences—eliminates this constraint. Re‐analysis of the relationship on new and 10 previously published datasets using logratio techniques reveals that the relationship is nonlinear and that the profusion of regression models is in part a function of the range of LOI. Although LOI may offer a crude estimate of OC at high LOI levels, OC/LOI ratios when LOI is less than about 25% are too variable for reliable OC estimation, and interstudy comparisons remain dubious. Direct measurement of OC is recommended.     

Relationship between the Agricultural Management of a Semi‐arid Soil and Microbiological Quality

Abstract

The establishment of the incidence of different agricultural management practices on soil microbiological quality has become an issue of wide concern. This study was aimed to (i) determine the effect of different agricultural management practices (ecological, integrated, conventional, and conventional with the addition of pig slurry) on the microbial activity of a semi‐arid soil at two different stages (cropped and fallow) and (ii) adapt an existing quantitative method to assess the microbiological soil quality in the different management systems. Several microbial and biochemical parameters, as well as two water‐soluble carbon (C) fractions, were measured in the soil samples. Significant differences (P<0.05) were found between the different agricultural management systems for most of the microbiological parameters during the cropped period. Factorial analysis indicated that adenosine triphosphate (ATP), microbial biomass C, diphenol oxidase activity, urease activity, and water‐soluble carbohydrates had a high weight in factor 1. These parameters were selected to form part of the equation for calculating a microbiological quality index. During the cropped period, the ecological management yielded the highest score of the microbial quality index, whereas, during the fallow period, no differences were found among the index scores of the different agricultural management systems.     

Use of Agro‐industrial Organic Compound: Yield and Nutrient Absorption in Wheat

Abstract

This study, focusing on the cultivation of wheat, consisted of applying an organic compound to the soil for a period of 2 years. The organic compound was made from a mixture of organic residues from a jelly industry (bovine chips and sharings) and other residues from a sugar‐alcohol industry. The mixture was applied at random into the intergrowth lines in a top‐dressing process, without incorporation, and in cumulative increasing doses. In the first year, the applications ranged from 2 to 25 t ha; in the second year, the applications ranged from 8 to 75, in wheat plants. Comparing the results of the chemical treatment to the organic application, it was observed that the organic compound increased the yield of wheat during the 2 years. Furthermore, the organic compound did not contaminate the plants, such as in the absorption of nutrients by the grains, once they have presented normal patterns of nutrient concentrations.