Effect of grazing intensity on protozoan community,microbial biomass,and enzyme activity in an alpine meadow on the Tibetan Plateau

Purpose

The alpine meadow has received mounting attention due to its degradation resulting from overgrazing on the Tibetan Plateau. However, belowground biotic characteristics under varied grazing stresses in this ecosystem are poorly understood.

Materials and methods

Here, the responses of soil protozoan abundance, community composition, microbial biomass, and enzyme activity to five grazing patterns including (1) artificial grassland without grazing (AG), (2) winter grazing (WG), (3) grazing for 7 months within a fence (GF), (4) continuous grazing for a whole year (CG), and (5) natural heavy grazing (HG) were investigated for two continuous years. Soil protozoan community composition was investigated using the most possible number (MPN) method, and soil microbial biomass and enzyme activity were analyzed using chloroform fumigation extraction and substrate utilization methods, respectively. Multivariate statistical analysis, the analysis of variance (ANOVA), multiple comparisons, and correlation analysis were together performed.

Results and discussion

The WG treatment had the highest abundance of total protozoa (2342–2524 cell g^?1). Compared with AG treatment, HG treatment significantly reduced the abundance of soil total, flagellate and ciliate protozoa, and protease activities in 2012 and 2013. Significantly, lower soil microbial biomass nitrogen (MBN) was also observed in the HG (6.60 and 14.6 mg N kg^?1) than those in other four treatments (22.3–82.9 mg N kg^?1) both in 2012 and 2013, whereas significantly higher microbial biomass carbon (MBC) was observed in HG than that in AG treatment in 2012. Moreover, significantly positive correlations were detected between the abundance of soil protozoa and soil moisture, pH, organic C, total N, and MBN. Our results indicated that soil protozoa showed a negative response to increasing grazing intensities and therefore, suggesting that aboveground grazing practices also exerted strong impact on belowground protozoa, not only on soil microbial characteristics.

Conclusions

Soil protozoan community composition was apparently different between the HG treatment and other four grazing patterns and was potentially impacted by altered soil properties and MBC and/or MBN. Our results suggested that moderate grazing may sustain better belowground biotic diversity and ecosystem functioning in this alpine meadow on the Tibetan Plateau.

     

Soil Fertility Index,Soil Evaluation Factor,and Microbial Indices under Different Land Uses in Acidic Soil of Humid Subtropical India

A study was conducted to examine the impact of land use on soil fertility in an Entisol in the Jalpaiguri District of humid subtropical India. The natural forest served as a control against which changes in soil properties were compared. Soil samples were collected from four different depths (0–25, 25–50, 50–75, and 75–100 cm) of soil from four land uses (viz. forest, home garden, arecanut plantation, and agriculture) and examined for pH, organic carbon (OC), electrical conductivity (EC), cation exchange capacity, available nitrogen (N), phosphorus (P), exchangeable calcium (Ca), magnesium (Mg), potassium (K), aluminum (Al), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and dehydrogenase activity (DHA). Soil pH (5.7), OC (2.29%), N (386 kg ha^?1), and P (22.54 kg ha^?1) were greatest in forest soil, followed by soil from arecanut plantation, agriculture, and home garden. The greatest Ca (0.892 cmol kg^?1), Mg (0.527 cmol kg^?1), and Al (1.86 cmol kg^?1) were found in the arecanut plantation, whereas K (0.211 cmol kg^?1) was greatest in forest. The greatest content of diethylenetriaminepentaacetic acid–extractable copper, zinc, manganese, and iron (2.25, 1.66, 4.86, and 7.65 ppm, respectively) were found in forest. MBC (558 mg kg^?1), MBN (26.67 mg kg^?1), and DHA (33.03 μg TPF 24 h^?1 g^?1) was greatest in forest soil. Soil fertility index varied from 13.13 in arecanut plantation to 18.49 in forest. The soil evaluation factor ranged from 5.32 in agriculture to 6.56 in forest. Pearson's correlation matrix revealed strongly significant positive correlation of soil fertility index and soil evaluation factor with soil properties.     

Microbial Biomass in Relation to Soil Properties under Integrated Farming Systems of Meghalaya,India

The effects of different integrated farming systems on microbial biomass was studied 20 years after their adoption at Meghalaya, India. The soil fertility was relatively greater in agricultural and agri‐horti‐silvi‐pastoral systems as a result of accumulation of leaf litter/crop residues and addition of inorganic and organic manures. Microbial biomass carbon was greatest in agricultural (378 mg kg^?1) followed by the agri‐horti‐silvi‐pastoral systems (291 mg kg^?1). The most microbial biomass nitrogen (N) and phosphorus (P) (32.4 and 17.07 mg kg^?1, respectively) were recorded in agricultural followed by agri‐horti‐silvi‐pastoral systems. Microbial biomass carbon (C) had a significant relationship with organic C, microbial biomass N, and biomass P, indicating that the living part of soil organic matter is involved in the transformation of nutrients into the labile pool and governs their availability to the plants. Application of inorganic fertilizers and organics along with lime has contributed more microbial biomass that led to more biological activity attributed in nutrient transformations and also maintained the soil fertility.     

Influence of lanthanum on microbial biomass C,P and C- and P-cycling enzyme activities in tea garden soil

At present, reports of the effect of lanthanum on nitrogen cycling in the soil are very detailed, but information on carbon (C) and phosphorus (P) cycling is less reported. We present an investigation into the effects of lanthanum on the pH, microbial biomass C and P and enzyme activities (such as that of β-glucosidase, peroxidase, polyphenol oxidase, acid phosphomonoesterase, phosphodiesterase and phosphotriesterase) in soil in an indoor culture experiment. The results show that the application of lanthanum decreased the pH and had an inhibitory effect on microbial biomass C and P throughout the experiment. The application of lanthanum significantly inhibited most of enzyme activities at the 14th day of the experiment. However, soil samples treated with 100 mg kg^?1 of lanthanum significantly stimulated the activity of polyphenol oxidase at the 14th day, and the range 100–300 mg kg^?1 stimulated the activities during the 28th day to the 56th day. From the 42nd to the 56th day, the pH and all enzyme activities gradually increased. We inferred that the lanthanum had different effects on microbial biomass C and P and enzymes. We recommended that the amount of the rare earth element applied in a tea garden should be lower than 100 mg kg^?1.     

添加秸秆碳源对土壤微生物生物量和原生动物丰富度的影响

为了研究引入秸秆碳源对根结线虫(Meloidogyne spp.)病害严重土壤中微生物生物量和原生动物的影响, 以番茄为供试作物, 设置4个梯度的小麦秸秆添加量[CK(0 g·kg^-1), 1N(2.08 g·kg^-1)、2N(4.16 g·kg^-1)和4N(8.32 g·kg^-1)], 研究不同种植时间(6个月和4个月)下土壤微生物生物量碳、氮和原生动物丰度的变化。研究结果表明: 添加秸秆对微生物生物量碳、氮和原生动物丰富度有明显促进作用, 添加的秸秆量越多, 这种促进作用越明显。不同秸秆添加量处理中, 微生物生物量碳、氮和原生动物丰度为: 4N>2N>1N>CK。秸秆对原生动物的群落结构也有显著影响, 在各处理中, 鞭毛虫和肉足虫占有绝大比例, 分别占总丰度的29.44%和66.19%, 纤毛虫仅占4.37%。在相同添加秸秆量条件下, 土壤原生动物丰度随种植时间的延长而提高, 而微生物生物量碳、氮量随种植时间的延长而降低。而在种植时间相同条件下, 随着秸秆量的增加土壤微生物生物量碳、氮量和微生物生物量碳氮比和原生动物总丰度相应增加。     

Response of soil microbial community and diversity to increasing water salinity and nitrogen fertilization rate in an arid soil

The scarcity of fresh water has forced farmers to use saline water (SW) for irrigation. It is important to understand the response of the soil microbial community and diversity to saline irrigation water. The objective of this study was to determine the effects of irrigation water salinity and nitrogen fertilization rates on soil physicochemical properties, microbial activity, microbial biomass, and microbial functional diversity. The field experiment consisted of a factorial design with three levels of irrigation water salinity (electrical conductivities (ECs) of 0.35, 4.61 or 8.04?dS?m^?1) and two nitrogen rates (0 and 360?kg?N?ha^?1). The results showed that the 4.61 and 8.04?dS?m^?1 treatments both reduced soil microbial biomass C (MBC), microbial biomass N (MBN), basal respiration, total phospholipid fatty acid (PLFA), bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. In contrast, the SW treatments increased the MBC:MBN ratio. Nitrogen fertilization increased soil MBC, MBN, basal respiration, total PLFA, bacterial PLFA, and gram-negative bacterial PLFA. In contrast, N fertilization decreased gram-positive bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. Average well color development, Richness, and Shannon's Index were always lowest in the 8.04?dS?m^?1 treatment. Carbon utilization patterns in the 8.04?dS?m^?1 treatment were different from those in the 0.35?dS?m^?1 treatment. In conclusion, five years of irrigation with brackish or SW reduced the soil microbial biomass, activity, and functional diversity, which may cause the deterioration of soil quality. Thus, the high-salinity water (EC?>?4.61?dS?m^?1) is not appropriate as a single irrigation water resource. Proper N fertilizer input may overcome some of the negative effects of salinity on soil microbial.     

Potted rice straw increased the antioxidase activity and growth of Chinese green cabbage seedlings and altered the soil microbial community

To reuse rice straw and decrease the environmental pollution and resource waste that are caused by burning rice straw in China, this agricultural resource is increasingly being used to make pots with added formaldehyde and other chemicals for cultivating vegetables. A study was conducted to investigate the effects of rice straw-based pot powder on the growth and antioxidase activity of Chinese green cabbage seedlings and the soil microbial community using a molecular analysis. The results showed that there was no negative effect from the powder on cabbage growth, given that the cabbage plants that were treated with powder (1.2–3.2 g kg^?1 rice straw pot powder) exhibited 1.8 to 2.5 times higher fresh biomass than the control (0 g kg^?1 powder). Minor differences were found among key reactive oxygen system enzyme activities, but the superoxide dismutase activity decreased by 33–55% (1.2–3.2 g kg^?1 powder). The phenylalanine ammonia-lyase activity of green Chinese cabbage that was treated with powder (1.2–3.2 g kg^?1 rice straw pot powder) was 1.5 times higher than the no-powder control. The soil microbial diversity was changed, and the community composition was altered depending on the rates of powder application, according to a polymerase chain reaction-denaturing gradient gel electrophoresis analysis.     

Influence of ciprofloxacin on microbial community structure and function in soils

Microcosm experiments were designed to investigate the effects of the widely used antibiotic ciprofloxacin (CIP) on soil microbial communities by using four different concentrations (0, 1, 5, and 50 mg kg^?1 of soil) and five sampling times (1, 3, 9, 22, and 40 days). Untreated controls only received water. The addition of CIP significantly decreased microbial biomass (p?<?0.05) but did not affect soil respiration at high doses. Potential nitrification rates were stimulated at low CIP concentrations (1 mg kg^?1) and inhibited at high CIP concentrations (50 mg kg^?1) after 9 days of incubation. The nitrate and ammonium contents of soil were not altered after CIP addition at any time. The structure of soil microbial communities was assessed by phospholipid fatty acid (PLFA) analysis. The addition of CIP decreased the ratio of bacteria to fungi and increased the ratio of Gram-positive to Gram-negative bacteria. Principal component analysis of the PLFA data clearly distinguished among the different CIP concentrations. Redundancy analysis indicated that the CIP concentration and incubation time explained 33.5 % of the total variance in the PLFA data. These results confirmed that a single addition of CIP can influence structure and function of microbial communities in soil.     

Potassium Requirements of Lowland Rice

Rice is a staple food for about 50 percent of the world’s population. Potassium (K) is absorbed in large amounts by rice plants and adequate amounts of this element are fundamental to improve productivity and maintain sustainability of the cropping systems. A greenhouse experiment was conducted to determine the adequate rate of K for lowland rice grown on a Brazilian Inceptisol. The K rates used were 0, 50, 100, 200, 400, and 600 mg K kg^?1 soil. Most of the growth, yield, and yield components were significantly and quadratically increased with increasing K levels. Based on a quadratic equation, maximum grain yield was obtained with the addition of 371 mg K kg^?1 soil. Maximum plant height and shoot dry weight were obtained at 414 and 398 mg K kg^?1 soil, respectively. Root growth (maximum length and dry weight) was also significantly increased in a quadratic fashion with the increasing K rate in the growth medium. Maximum root length was achieved at 58 mg K kg^?1 whereas maximum root dry weight was obtained with the addition of 394 mg K kg^?1 soil. Plant height, shoot dry weight, 1000-grain weight, root length, and root dry weight were significantly associated with grain yield. Hence, manipulation of these growth and yield components with the addition of K fertilizer can improve yield of lowland rice in varzea soils of central part of Brazil. Potassium uptake increased significantly in a quadratic fashion with increasing K rate. However, K-use efficiency (mg grain per mg K applied) decreased significantly with increasing K rate in a quadratic fashion. Maximum grain yield was obtained with 117 mg kg^?1 Mehlich 1–extractable K, base saturation of 53 percent, Mg saturation of 9 percent, K saturation of 2 percent, and Ca/Mg ratio of 4.     

Lowland Rice Genotypes Evaluation for Potassium-Use Efficiency

Lowland rice significantly contributes to world as well as Brazilian rice production and information on genotypes potassium-use efficiency is limited. A greenhouse experiment was conducted with the objective to evaluate lowland rice genotypes for potassium (K)–use efficiency. Ten genotypes were evaluated at 0 mg K kg^?1 (low) and 200 mg K kg^?1 (high) of soil. Grain yield and shoot dry weight were significantly affected by K as well as genotype treatments. Genotypes CNAi 8860, CNAi 8859, BRS Fronteira, and BRS Alvorada were the best in relation to K-use efficiency because they produced best grain yield at low as well as at higher K levels. Shoot dry weight, number of panicles per pot, and 1000-grain weight had highly significant (P < 0.01) association with grain yield. Spikelet sterility, however, had significant negative association with grain yield. These plant parameters were mainly influenced by genotypes, indicating importance of selecting appropriate genetic material for improving grain yield. Soil K depletion was significant at harvest, suggesting large amount of K uptake by lowland rice genotypes.     

Accumulations of Cadmium,Zinc, and Copper by Rice Plants Grown on Soils Amended with Composted Pig Manure

A pot experiment, in which composted pig manure was applied to soils at rates of 0%, 0.5%, 1.5%, 3.0%, and 5.0% (W/W) to simulate additions of different amounts of cadmium (Cd), copper (Cu), and zinc (Zn) to soil, was conducted to assess accumulation of metals by rice (Oryza sativa L.) plants from soils treated with manure. Results indicated that Cd concentrations in rice grains were more than the limit of 0.2 mg kg^?1 when 0.14 mg kg^?1 or more Cd was loaded to Ferralsols by manure application, but it was not more than the limit in Calcaric Cambisols. Zinc contents in polished rice grains did not exceed the permissible limit of 50 mg kg^?1 in two soils. Copper concentrations in rice grain were slightly more than the limit of 10 mg kg^?1 in Ferralsols but not in Calcaric Cambisols. Results suggested greater risk of heavy‐metal contamination from manure to paddy rice in Ferralsols than in Calcaric Cambisols.     

Different Fractions of Soil Potassium,Olsen Phosphorus,and Available Sulfur Status of Intensively Cultivated Berpura Soil Series of India and Nutrient Indexing of Rice Crop

Berpura alluvial soil series of the Indo‐Gangetic Plains is situated in the Ambala District of the Haryana State of India. Soils of this series had medium concentrations of both potassium (K) and phosphorus (P) and large concentrations of sulfur (S) before 1970. To study different fractions of K, Olsen P, and 0.15% calcium chloride (CaCl₂)–extractable (available) S of soils of the Berpura series and to create nutrient indexing of rice crops growing on this series, surface soil samples were collected from 100 farmers' fields after the harvest of the wheat crop in 2005. During kharif season of same year, samples of upper two leaves at anthesis growth stage of rice crop were also collected from the same 100 farmers' fields that had earlier been sampled for soil analysis. Analysis of soil samples showed more K depletion in soils of this series, of which 86% of farmers' fields were deficient in ammonium acetate (NH₄OAc) K (available K). Thirty and 62% of leaf samples of the rice crop growing on the 100 fields of this series were extremely and moderately deficient in K, respectively. The mean values of water‐soluble, exchangeable, nonexchangeable, lattice, and total K were 10.6, 30.3, 390.0, 8204, and 8635 mg kg^?1, respectively. In soils of this series, 0.123, 0.351, 4.517, and 95.009% of total K were found in water‐soluble, exchangeable, nonexchangeable, and lattice K forms, respectively. On the other hand, long‐term farmers' practice of more application of P fertilizer in wheat crop has resulted in P buildup in the soils of the Berpura series. Olsen P in soils of farmers' fields of this series ranged from 9.0 to 153.0 mg kg^?1, with the mean value of 41.8 mg kg^?1. Eighty‐two percent of leaf samples of rice crops grown on this series without application of P fertilizer were sufficient in P. The analysis of soil and rice crops for P and K proved the suitability of 0.5 M sodium bicarbonate (NaHCO₃) and 1 N NH₄OAc for extracting available P and K, respectively, in alluvial soils of the Indo‐Gangetic Plains. The 0.15% CaCl₂–extractable S in this soil ranged from 9.6 to 307 mg kg^?1 with a mean value of 34.6 mg kg^?1. Four and 26% of soil samples had low and medium, respectively, in 0.15% CaCl₂–extractable S. S deficiency was recorded in rice crops, as 29% of the leaf samples were extremely deficient in S and 58% were moderately deficient in S. This indicated the unsuitability of the 0.15% CaCl₂ to extract available S from the Udic ustochrept utilized for cultivation of rice crops.     

Agronomic Evaluation of Coated and Common Urea in Upland Rice Production

Two greenhouse experiments were conducted simultaneously to evaluate polymer-coated and common urea in upland rice production. The nitrogen (N) levels used for both the N sources were from 0 to 400 mg kg^?1 of soil. Maximum grain yield was obtained with the addition of 167 mg N kg^?1 polymer-coated urea and 238 mg N kg^?1 common urea. Maximum value of other plant traits was obtained with N applied from 233 to 313 mg kg^?1 depending on plant traits and N source. Nitrogen-use efficiency (NUE) decreased with increasing N rate in the two N sources. Based on results of growth, yield, and yield components, and NUE it can be concluded that the N sources were equally effective in upland rice production. Base saturation, pH, and exchangeable calcium (Ca) increased with increasing N rates while iron (Fe), manganese (Mn), and copper (Cu) contents decreased with the increasing N rates.     

Efficacy of Potassium Humate and Chemical Fertilizers on Yield and Nutrient Availability Patterns in Soil at Different Growth Stages of Rice

Potassium humate (PH) is a promising natural resource to be utilized as an alternative for increasing crop production. A pot experiment was conducted during 2009 and 2010 to assess the efficacy of application of potassium humate (0, 5, and 10 mg kg^?1 soil) alone and in combination with chemical fertilizers (75% and 100% recommended dose of nitrogen–phosphorus–potassium) on yield and nutrient availability patterns in soil at different growth stages of rice. Two doses of zinc, viz. 0 and 12.5 mg kg^?1, were also applied. Sole and combined application of potassium humate with nitrogen–phosphorus–potassium (NPK) and zinc significantly (p < 0.05) improved the yield and availability of nitrogen, phosphorus, potassium, sulfur, zinc, and dehydrogenase activity in soil. Application of 10 mg kg^?1 potassium humate along with 100% NPK and 12.5 mg kg^?1 zinc sulfate proved significantly superior when compared to 75% and 100% of NPK alone.     

System of rice intensification in promising rice hybrids in north-western Himalayas: crop and water productivity,quality, and economic profitability

System of Rice Intensification (SRI) has spread as an innovation of rice cultivation that can produce higher crop yields and conserve seed and water resources. The SRI innovation is also gaining popularity in north-western (NW) Himalayas on one hand and hybrid rice technology on the other in the region. Moreover, rice productivity in NW Himalayas is quite low owing to the use of low-yielding germplasm and poor crop management. Thus, SRI principles coupled with hybrid rice technology seems to be a boon to boost rice productivity in the irrigated ecosystem of wet-temperate NW Himalayas well known for rice cultivation. Therefore, comparative performance of promising rice hybrids under SRI was assessed at three locations in wet-temperate NW Himalayas (India) using nine promising rice hybrids including state-recommended rice hybrid “Arize–6129” as check cultivar. It was revealed that various hybrids differed significantly w.r.t. days to 50% flowering, days to 75% maturity, plant height, tillers hill^?1, panicles hill^?1, panicles m^?2, and panicle length. Highest number of panicles m^?2 (370) was observed in Arize–6129 followed by US–312, Bioseed–786, and NK–3325, respectively. Significantly longer panicles were observed in Dhanya–2366 followed by Arize–6129, US–312, Bioseed–786, NK–3325, and US–10, respectively. Arize–6129 resulted in significantly higher grain (75 q ha^?1) and straw yield (125 q ha^?1) followed by US–312, Dhanya–2366, NK–3325, PAC–801, US–10, Bioseed–786, Uday–111, and Uday–131, respectively. The production- and monetary-efficiency as well as gross and net returns and B:C ratio also followed the similar trend as that of crop productivity with significantly higher production– (67 kg ha^?1 day^?1) and monetary–efficiency (INR 608.4 ha^?1 day^?1), and net returns (INR 68138 ha^?1) and B:C ratio (3.66) in check cultivar “Arize–6129” over other rice hybrids. Higher grain productivity (49.5–75.0 q ha^?1), net returns (INR 39238–68138 ha^?1), and B:C ratio (2.53–3.66) in current study conclusively inferred that SRI coupled with hybrid rice technology can harness higher productivity and profitability. Protein content (8.30–8.45%) exhibited higher values under Bioseed–786 followed by NK–3325, UDAY–111, and Arize–6129; however, NPK uptake (grains, straw, total) was significantly highest in Arize–6129 followed by US–312, Dhanya–2366, and NK–3325, respectively. Total water productivity (6.4–9.75 kg ha^?1 mm^?1), irrigation water productivity (16.5–25 kg ha^?1 mm^?1), and economic water productivity (64.0–97.5 INR ha^?1 mm^?1) collectively followed the trend of Arize–6129 > US–312 > Dhanya–2366 > NK–3325 > US–10 > PAC–801 > Bioseed–786 > Uday–111 > Uday–131 in current study. Overall, Arize–6129, US–312, and Dhanya–2366 were proved as potential rice hybrids in terms of their higher crop and water productivity and economic profitability among above nine rice hybrids for their large-scale cultivation under SRI in wet-temperate NW Himalayas.     

Agronomic evaluation of rice cultivation systems for water and grain productivity

Field experiments were conducted during summer (March–July) and kharif (June–September), 2008 at the wetland farm, Tamil Nadu Agricultural University, Coimbatore, India, to study the performance of different rice cultivation methods on productivity and water usage using the hybrid CORH-3 as a test crop. Treatments consisted of different rice cultivation methods, namely, transplanted rice (conventional), direct sown rice (wet seeded), alternate wetting and drying method (AWD), system of rice intensification (SRI) and aerobic rice cultivation. Results revealed that maximum number of tillers m^?2, higher shoot and root length at maturity were recorded under SRI followed by transplanted rice, while aerobic rice produced lower growth parameters in both the seasons. Chlorophyll content at flowering was higher under SRI in two seasons studied (42.74 and 39.48 SPAD value, respectively) and transplanted rice compared to aerobic rice and AWD. In both summer and kharif seasons, SRI produced higher grain yield (6014 and 6682 kg ha^?1), followed by transplanted rice (5732 and 6262 kg ha^?1), while the lowest grain yield (3582 and 3933 kg ha^?1) was recorded under aerobic rice cultivation. Under SRI, 5 and 6.7% increase in grain yield and 12.6 and 14.8% water saving were noticed compared to transplanted rice, respectively, during summer and kharif seasons. In respect to water productivity, the SRI method of rice cultivation registered the highest water productivity (0.43and 0.47 kg m^?3), followed by AWD and aerobic rice cultivation. The conventional rice cultivation and direct sown rice produced lower grain yield per unit quantity of water used.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Properties and available micronutrient status of some soils derived from Abeokuta formation in Nigeria

Available iron, zinc, copper and manganese were determined in six pedons located in upper slope, middle slope and valley bottom soils derived from Abeokuta geological materials in Nigeria. The soils had an average of 639.8 g kg^?1 sand, 241.8 g kg^?1 clay and 118.4 g kg^?1 silt. The fertility status of the soils was low–medium with a strongly acid–neutral reaction, 1.3–15.1 g kg^?1 organic carbon contents, moderate–high exchangeable bases and 1.38 mg kg^?1 available phosphorus. Both Fe (122.50 mg kg^?1) and Mn (111.40 mg kg^?1) occurred at toxic levels, whereas the mean Cu (1.27 mg kg^?1) and Zn (2.56 mg kg^?1) contents were found to be adequate for most crops grown in the region. There were significant positive correlations among the micronutrients and also between soil pH, organic carbon, particle size fractions and micronutrients. The high levels of Fe and Mn were probably due to the presence of oolitic ironstone in the parent material.     

Microbial assimilation of atmospheric CO2 into soil organic matter revealed by the incubation of paddy soils under 14C-CO2 atmosphere

Similar to higher plants, microbial autotrophs possess photosynthetic systems that enable them to fix CO₂. To measure the activity of microbial autotrophs in assimilating atmospheric CO₂, five paddy soils were incubated with ¹⁴C-labeled CO₂ for 45 days to determine the amount of ¹⁴C-labeled organic C being synthesized. The results showed that a significant amount of ¹⁴C-labeled CO₂ incorporated into microbial biomass was soil specific, accounting for 0.37%–1.18% of soil organic carbon (¹⁴C-labeled organic C range: 81.6–156.9 mg C kg^?1 of the soil after 45 days). Consequently, high amounts of C-labeled organic C were synthesized (the synthesis rates ranged from 86 to 166 mg C m^?2 d^?1). The amount of atmospheric ¹⁴CO₂ incorporated into microbial biomass (¹⁴C-labeled microbial biomass) was significantly correlated with organic C components (¹⁴C-labeled organic C) in the soil (r = 0.80, p < 0.0001). Our results indicate that the microbial assimilation of atmospheric CO₂ is an important process for the sequestration and cycling of terrestrial C. Our results showed that microbial assimilation of atmospheric CO₂ has been underestimated by researchers globally, and that it should be accounted for in global terrestrial carbon cycle models.     

Phosphorus Nutrition of Upland Rice,Dry Bean,Soybean, and Corn Grown on an Oxisol

Rice, dry bean, corn, and soybean are important food crops. Phosphorus (P) deficiency is one of the most yield-limiting factors for these crops grown on highly weathered Brazilian Oxisols. Four greenhouse experiments were conducted to determine P requirements of these four crops. The P levels used were 0, 50, 100, 200, and 400 mg kg^?1. Growth, yield, and yield components evaluated of four crop species were significantly increased with the application of P fertilization. Most of the responses were quadratic in fashion when the P was applied in the range of 0 to 400 mg kg^?1. Maximum grain yield of upland rice was obtained with the application of 238 mg P kg^?1 of soil, maximum dry bean grain yield was obtained with the application of 227 mg P kg^?1 of soil, and maximum grain yield of soybean was obtained with the application of 224 mg P kg^?1 of soil. Maximum shoot growth of corn was obtained with the addition of 323 mg P kg^?1 of soil. Most of the growth and yield components had significant positive association with grain yield or shoot dry weight. Phosphorus concentration and uptake were greater in the grain compared to straw in upland rice and dry bean plants. Overall, P-use efficiencies decreased with increasing P rates.