Effect of long-term application of animal manure on physical properties of three soils

Surface soil samples to 15 cm depth were taken from replicated plots in an ongoing long-term field experiment involving application of animal manure on three soils in Virginia. The sampled plots had received either no manure or the equivalent of 289,000 kg ha^–1 of manure as dry weight. The manure was applied annually at the beginning of each spring for 15 years from 1978 through 1992. The plots were cropped similarly since 1978. Soil textures were a fine sandy loam at Holland in the Atlantic Coastal Plain region, a silt loam at Blacksburg in the Appalachian region, and a clay loam at Orange in the Piedmont region of Virginia. The following measurements were made on subsamples: liquid and plastic limits, wet aggregate stability, aggregate size distribution, dispersible clay percentage, water retention at 0. 03, 0.1, 0.3, 0.5, 1.0, and 1.5 MPa tension, and modulus of rupture of moulded briquettes at a water content corresponding to 0.1 MPa tension. Organic matter content by the Walkley-Black method was significantly higher in the manure-treated soils at all three locations. Increases were 3% for the sandy loam and 25% for the silt loam and clay loam. From these values it was estimated that at least 95% of the total applied manure had been degraded over the 15 years. Results showed that the liquid and plastic limits for all three soils were higher (p<0.05) for the manure-treated samples. However, the differences in the limits were only 2 to 3%. The modulus of rupture values were lowered by addition of the animal manure. Decreases (p<0.05) occurred for the silt loam and clay loam samples. The wet aggregate stability increased and the dispersible clay decreased in the manure-treated soils. Increases (p<0.05) in wet aggregate stability occurred for the sandy loam and silt loam samples. Decreases (p<0.05) in dispersible clay were measured for the sandy loam and clay loam samples. Water retention was consistently, but only slightly, increased by manure addition. The increases, in the order of sample texture, were clay loam > sandy loam silt loam. Increases tended to be higher at the lower values of tension. Manure addition consistently increased the weight percentages of aggregates passing a given mesh size. Increases, in order of sample texture, were silt loam > clay loam > sandy loam. In their entirety, these results show that the manure produced measurable changes in the soil physical properties. The magnitude of the changes, in most cases, were small and depended on the soil texture. Given the high total amount of manure applied, the results indicate that manure-induced physical changes in the soil were small and evidently did not accumulate over time. Rapid microbial degradation of the manure could be responsible for the lack of marked changes in the soil physical properties.     

Characterisation of Phosphate Solubilising Bacteria in Sandy Loam Soil Under Chickpea Cropping System

With the aim to explore the possible role of phosphate-solubilizing bacteria (PSB) in phosphorus (P) cycling in agricultural soils, we isolated PSB inhabiting naturally in the sandy loam soils under chickpea cropping of Patiala (Punjab State). A total of 31 bacterial isolates showing solubilizing activities were isolated on Pikovskaya agar plates. The potent phosphate solubilizers were selected for further characterization. These isolates were shown to belong to the genera Pseudomonas and Serratia by partial sequencing analysis of their respective 16S rDNA genes. ERIC-PCR based fingerprinting was done for tracking the survival of introduced populations of the PSB during mass inoculation of these strains under chickpea plots. The results showed positive correlation (r² = 0.853) among soil phosphatase activity and phosphate solubilizers population, which was also positively correlated (r² = 0.730) to available phosphorus. Identification and characterization of soil PSB for the effective plant growth-promotion broadens the spectrum of phosphate solubilizers available for field application.     

Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

温度对不同粘粒含量稻田土壤有机碳矿化的影响

模拟了亚热带地区3种不同粘粒含量的水稻土(砂壤土、壤粘土、粉粘土)在5种温度(10、15、20、25和30℃)下的有机碳(SOC)矿化特征,分析SOC矿化对温度变化的响应.结果表明:在160d的培养期内,温度对3种水稻土SOC矿化量的影响有一定差异,30℃时砂壤土、壤粘土和粉粘土SOC矿化量分别是10℃时的3.5、5.2和4.7倍.在较低温度(≤20℃)下,SOC矿化速度较低且相对稳定;在较高温度(≥25℃)下,前期SOC矿化速度较高,随着培养时间的延长逐渐降低,并趋于稳定.3种水稻土SOC矿化的温度系数(Q10)随培养时间出现波动,砂壤土的Q10平均值最低,为1.92,壤粘土和粉粘土的Q10平均值较接近,分别为2.37和2.32;3种土壤矿化速率常数(k)与温度呈极显著的指数相关(P<0.01).3种水稻土有机碳矿化对温度变化的响应敏感度依次为壤粘土>粉粘土>砂壤土.     

中小型土壤动物组成对复垦铜尾地土壤养分的影响

通过盆钵生物试验研究了中小型土壤动物不同类群的组成对复垦铜尾矿废弃地土壤养分的影响。整个培养试验根据需求对不同中小型土壤动物组合设置四个处理措施,每种措施分为有无凋落物两种水平,即:(1)无土壤动物(Re),无土壤动物+凋落物(Re+Li)(2)跳虫(Co),跳虫+凋落物(Co+Li)(3)跳虫+蜱螨类(Co+Ac),跳虫+蜱螨类+凋落物(Co+Ac+Li)(4)中小型土壤动物(剔除大型土壤动物Me),中小型土壤动物+凋落物(Me+Li)。另设一组对照(CK)处理,并于培养实验开始前完成测定,作为本底值。分析表明,土壤p H随着中小型土壤动物类群的增加而降低,最低值出现在Me和Me+Li处理,且二者之间无显著性差异;对照(CK)处理下的各养分含量均显著低于其他各处理,各处理中有机质、有效磷和水解性氮的含量的最大值均出现Me+Li处理,且与其他各处理呈极显著差异(P0.01);土壤全磷含量最大值出现在Re和Me+Li处理,最低值出现在Co+Li处理且之间呈显著差异(P0.05);土壤全氮含量最大值出现在Co+Ac和Me+Li处理,最低值出现在Co+Ac+Li处理且彼此间也呈显著差异(P0.05)。相关分析表明,有机质与有效磷以及全氮与水解性氮之间相关性达到极显著正相关关系(r=0.886,r=0.898),有机质与全氮及水解性氮分别呈现显著正相关关系(r=0.735,r=0.780),全氮与有效磷(r=0.782)以及有效磷与水解性氮(r=0.755)也呈现显著正相关关系。p H与有机质呈现显著负相关关系(r=-0.782),全磷与有机质、全氮、有效磷、水解性氮均无相关关系。     

Development and reproduction of two populations of Heterodera zeae under stress of soil texture in Egypt

The effect of different natural types of soil collected from some Egyptian localities namely, El-Tal Alkabeer, Belbais, El-Ameria, Giza and Dekernes on the behaviour of either Belbais or Giza populations of Heterodera zeae revealed, in general, that Belbais and El-Tal Alkabeer soils which represent sandy clay loam and sandy loam, respectively, were highly favourable to multiplication of the nematode. Giza and Dekernes soils (clay loam and clay, respectively) also, favoured the nematode multiplication but to a lesser degree. On the other hand, the El-Ameria soil (loamy sand) did not favour the multiplication of both nematode populations.     

Effects of soil compaction and mechanical damage at harvest on growth and biomass production of short rotation coppice willow

The effects of soil compaction and mechanical damage to stools at harvesting on the growth and biomass production of short rotation coppice (SRC) of willow (Salix viminalis L.) were monitored on clay loam (CL) and sandy loam (SL) soils. Moderate compaction, more typical of current harvesting situations did not reduce biomass yields significantly. Even heavy compaction only reduced stem biomass production by about 12% overall; effects were statistically significant only in the first year of the experiment on sandy loam. Heavy compaction increased soil strength and bulk density down to 0.4 m depth and reduced soil available water and root growth locally. Soil loosening treatments designed to alleviate the effects of heavy compaction did not markedly improve the growth of willow on compacted plots. Hence the focus fell on harvesting. Extensive mechanical damage to stools caused a 9% and 21% reduction in stem dry mass on the clay loam and sandy loam soils as a result of fewer stems being produced. The particularly severe effect on the sandy loam soil probably resulted from a combination of dry conditions in the year of treatment, root damage and soil compaction under stools and might have been aggravated by the young age of the plants (1 year) at the time of treatment.     

N uptake and N status in ponderosa pine as affected by soil compaction and forest floor removal

Soil compaction and forest floor removal influence fundamental soil processes that control forest productivity and sustainability. We investigated effects of soil compaction and forest floor removal on tree growth, N uptake and N status in ponderosa pine. Factorial combinations of soil compaction (non-compacted and compacted) and forest floor removal (forest floor present and no forest floor) were applied to three different surface soil textures. For studying N uptake, four trees from every treatment were ¹⁵N labeled with 130.6 mg m^–2 of ¹⁵N. Tree responses to compaction were dependent on the forest floor removal level. In loam and clay soils, non-compacted+no forest floor was beneficial to tree growth. Tree growth was depressed with compaction+no forest floor in clay soil. In sandy loam soil, compaction+no forest floor showed the best tree growth. No N deficiency was found in any soil type but a graphical method suggested correlation between N status and tree growth. In loam and clay soils, compaction+forest floor present increased N uptake. Nitrogen uptake was explained significantly by potential N mineralization in loam and clay soils. In sandy loam soil, the effects of compaction and forest floor removal were more complex, with the N uptake improved in the compaction+no forest floor treatment and reduced under compaction+forest floor present. Soil compaction may have influenced N tracer uptake because of improved unsaturated flow and root-soil contact. However, N immobilization may have restricted N uptake in compaction+forest floor present in the sandy loam soil. The study illustrates how soil properties and site preparation can potentially interact to affect N dynamics and forest productivity.     

Control of pea cyst-nematode, Heterodera goettingiana, by small amounts of aldicarb, Du Pont 1410, Ciba-Geigy 10576 or Dowco 275 applied to the soil at planting time

Aldicarb, or Du Pont 1410 (S-methyl-I-(dimethylcarbamoyl)-N-[(methyl-carbamoyl)oxy]thioformimidate), at 2.8–22.4 kg a.i./ha incorporated in the seed-bed before sowing greatly increased the yield of peas in a clay loam and two sandy clay soils infested with pea cyst-nematode, Heterodera goettingiana, and lessened or prevented increase in the number of nematodes. CibaGeigy 10576 (an organophosphorus compound) at 5.6–22.4 kg a.i./ha was similarly effective in a sandy clay soil. Dowco 275 (O, O-diethylO-(6-fluoro-2 pyridyl) phosphorothioate) at 5.6 or 11.2 kg a.i./ha also controlled the nematode well in the clay loam and in a sandy clay soil but although it greatly increased the yield of peas in the clay loam, it did not increase yield in the sandy clay.     

Development and use of a short-term nutrient-absorption technique for evaluating soil magnesium status

Summary A greenhouse investigation was undertaken to study and evaluate the use of a short-term nutrient-absorption technique for evaluating soil magnesium status. Barley (Hordeum vulgare), variety Arivat, was used as the test plant. The investigation included four experiments with the following objectives: (1) to determine the need for base applications of nitrogen and phosphorus in a soil-magnesium study using a short-term nutrient absorption technique; (2) to study the effect of base applications of N and P on Mg-uptake by plants under three time periods of root-soil contact; (3) to study the effect of increasing soil moisture from 75 to 100 per cent of the soil moisture equivalent on the plant uptake of Mg; and (4) to evaluate the short-term nutrient-absorption technique in determining the magnesium status in six different soils: Gila silt loam, Tours silty clay loam, Cajon clay loam, La Palma fine sandy loam, Yavapai sandy clay loam, and Casa Grande loam. Magnesium was applied in the form of MgSO₄ and Sul-PO-Mag.Plant growth, potassium, calcium, and magnesium uptake were increased by the base application of nitrogen and phosphorus using a 7-day period of root-soil contact.Plant growth was not affected by soil moisture level. Potassium and calcium concentrations in the plant were decreased with increasing soil moisture, but the total plant uptake of these nutrients was not affected. Total plant uptake and concentration of magnesium were increased by increasing soil moisture level.The results obtained in this study agree with previous observations that soil response to Mg does not depend upon the amount of exchangeable magnesium in the soil.Published as Arizona Agr. Expt. Station Technical Publication No.848.     

川西亚高山三种森林恢复途径对土壤生物有效磷的影响

土壤生物有效磷在提高森林生产力和生物地球化学循环中起着至关重要的作用,研究不同森林恢复途径对土壤生物有效磷的影响对于退化森林的适应性恢复和可持续经营具有重要意义。选取川西亚高山不同恢复途径下形成的3种森林类型,即粗枝云杉人工林（人工种植,PF）、岷江冷杉-红桦天然次生林（自然更新,NF）和粗枝云杉阔叶混交林（人工种植后自然更新,MF）,采用基于生物有效性的土壤磷分级方法测定土壤生物有效磷（CaCl₂-P、Citrate-P、Enzyme-P和HCl-P）,探究不同森林恢复途径对土壤生物有效磷的影响。结果表明：不同森林恢复途径对土壤生物有效磷影响显著（P<0.05）,NF和MF的土壤Citrate-P和Enzyme-P显著高于PF（P<0.05）,而PF的土壤HCl-P显著高于NF（P<0.05）。自然更新是3种森林恢复途径中最能提高土壤生物有效磷的方式。3种森林恢复途径下的土壤生物有效磷组分与速效磷均呈现显著的正相关关系,且NF的土壤速效磷与生物有效磷的相关性更强（CaCl₂-P除外）。显著影响NF土壤生物有效磷的土壤理化性质有全钾、铵态氮含量和pH值,且全钾对NF的土壤生物有效磷变异的解释程度最高（r²=0.63,P=0.001）。土壤pH值、钙和可溶性有机碳含量是显著影响MF土壤生物有效磷的主要土壤理化性质（P<0.05）。对PF的土壤生物有效磷具有显著影响的土壤理化性质是土壤有机碳、铁和可溶性有机碳含量。土壤理化性质对3种恢复途径下森林土壤生物有效磷的解释率均超过了80%,森林恢复途径对土壤生物有效磷的影响与土壤理化性质有关。     

Effects of a soil conditioner on some physical and biological features of soils: results from a greenhouse study

A soil amendment substance-organic bio-stimulator, Terralyt Plus (TP), was used to observe its impact on the properties of clay loam (CL), sandy clay loam (SCL) and sandy loam (SL) soils and the growth of corn (Zea mays indentata L.) and wheat (Triticum aestivum ssp./vulgare Vill. v. lutescens) under greenhouse conditions. The diluted TP solutions (1:500, 1:1000 and 1:2000) were sprayed onto the soil surfaces. The wheat growth increased for CL and SCL with the application of TP at 1:1000. The highest dry weights were detected with 1:500 TP and corn in all the soils. Penetration resistance of CL containing corn increased with increasing TP concentration. TP was also effective in improving the aggregate stability for CL but not for the other soils. Catalase enzyme activity (CEA), soil evolution (SE) and the total aerobic bacterial population (TABP) were significantly increased (P<0.05) by spraying TP at 1:1000 onto CL.     

Soil composition affects the nesting behavior of blue-tailed bee-eaters (Merops philippinus) on Kinmen Island

The blue-tailed bee-eater (Merops philippinus) is a summer migrant that breeds on Kinmen Island, located off the west coast of Taiwan, about 5 km from the southern coast of mainland China. The aim of this study was to investigate why blue-tailed bee-eaters build their nests in sandy loam and sandy clay loam, but not in clay loam. Soil chemical and physical properties, and mineralogical composition were measured for the different soil types. Clay loam had a significantly lower pH, Na, and base saturation than did sandy loam or sandy clay loam. Clay loam had a significantly higher N, cation-exchange capacity (CEC), K, and free iron (Fe_d) and aluminum oxide (Al_d) contents than the other soil types. Clay loam had significantly lower sand and higher clay content, and higher bulk density and penetration resistance than the other soil types. The correlation coefficients (r ²) between penetration resistance and Fe_d, Al_d, and clay contents were 0.997, 0.848, and 0.779, respectively. Soil strength and compaction are important criteria for bee-eaters nesting-site selection. The lower pH of clay loam would enhance the exchangeable Al and acidity, further increasing the soil aggregation. Thus, it might prevent the bee-eaters from excavating nesting burrows.     

Mineralization Potential of Atrazine and Degradation Intermediates from Clustered Characteristics in Inoculated Soils

Soil properties impact pesticide persistence. Because these characteristics operate together in situ, identification of their clustered associations can help explain pesticide fate. Factor analysis was used to reduce the dimensionality of soil characteristics by grouping them into clustered independent factors, which were then related to the mineralization of atrazine and selected degradation intermediates. A Sharpsburg silty clay loam, Ortello sandy loam, and Hord silt loam were inoculated with a Hord soil that had a high capacity for atrazine mineralization. The soils were spiked with ¹⁴C-radiolabeled atrazine, deethylatrazine, hydroxyatrazine, N-isopropylammeline, N-isopropylammelide or cyanuric acid and sampled during incubation for 80 d (atrazine) or 40 d (degradation intermediates) at 22°C. Low mineralization in uninoculated soils demonstrated that the absence of atrazine-mineralizing microorganisms was most limiting. In inoculated soils, regression analysis indicated mineralization of atrazine (R² = 0.88) and its degradation intermediates (R² ≥ 0.89) was related to factors associated with bioavailability and microbial activity. For atrazine, this relationship indicated mineralization may be positively influenced by higher pH and available phosphorus, lower NO₃-N, organic carbon and clay contents, and lower adsorption. Our results show how factor analysis can be used in conjunction with multiple regression to determine mineralization potential and thus help identify soils with limited degradation capacities and possible long-term persistence.     

Incidence and survival of non-O157 verocytotoxigenic Escherichia coli in soil

Aims: This study estimated the incidence of non‐O157 verocytotoxigenic Escherichia coli (VTEC) in farm pasture soils and investigated the survival of non‐O157 VTEC in clay and sandy loam soils. Methods and Results: Twenty farms were tested over a 12‐month period by sample enrichment in tryptone soya broth plus vancomycin, followed by PCR screening for the presence of vt1 and vt2 genes. Of the 600 soil samples, 162 (27%), across all farms, were found to contain vt1 and/or vt2 genes. The enrichment cultures from the 162 PCR‐positive samples were plated onto Chromocult tryptone bile X‐glucuronide agar (TBX), presumptive VTEC colonies recovered, confirmed as VTEC by PCR and serotyped. Samples of the two predominant soil types in Ireland (clay and sandy) were homogenized, characterized in terms of pH, boron, cobalt, copper, potassium, magnesium, manganese, phosphorus, zinc and organic matter content, inoculated with washed suspensions of eight non‐O157:H7 soil isolates and six bovine faecal isolates and stored at 10°C for up to 201 days. Inoculum survival rates were determined at regular intervals by recovering and plating soil samples on TBX. All inoculated non‐O157 serotypes had highest D‐values in the sandy loam soil with D‐values ranging from 50·26 to 75·60 days. The corresponding range in clay loam soils was 31·60–48·25 days. Conclusions: This study shows that non‐O157 VTEC occur widely and frequently in pasture soils and can persist in such environments for several months, with considerable opportunity for recycling through farm environments, and cattle, with clear potential for subsequent transmission into the human food chain. Significance and Impact of the Study: This is the first such study of non‐O157 VTEC in farm soils and found that these VTEC are frequent and persistent contaminants in farm soils. In light of recent epidemiological data, non‐O157 VTEC should be seen as an emerging risk to be controlled within the food chain.     

An assessment of soil bacterial community structure and physicochemistry in two microtopographic locations of a palustrine forested wetland

We studied redoximorphic features, field indicators and bacterial communities of soils in hummocks and hollows of a palustrine forested wetland in Virginia. We hypothesized that presence of hydric soils, soil physicochemistry and soil bacterial community structure would differ between hummocks and hollows. We fingerprinted soils collected from different microtopographic locations using Length Heterogeneity Polymerase Chain Reaction (LH-PCR) to study their bacterial community structures. Two hummocks had silty/sandy loam soils with mean chroma values of > 4, showing no indication of ‘hydric soils’ (i.e., wetland soils). Two hollows, however, had clay loam soils with mean chroma values of 2 with gleying and redox concentrations observed, indicative of seasonally inundated wetlands. The soils of hollows also had higher organic matter content and soil moisture compared to the soils of hummocks (P < 0.05). Multidimensional scaling (MDS) and Analysis of similarity (ANOSIM) of the fingerprints revealed differences in soil microbial community structures between hummocks and hollows (Global R = 0.30, P < 0.01). The diversity measures of the fingerprints (Shannon’s H′) were also different by microtopography with higher diversity in hollows relative to hummocks (P < 0.05). LH-PCR proves to be a useful tool in examining bacterial community composition of wetland soils in this study. However, cloning and sequencing of specific community LH-PCR profiles of interest is necessary to fully characterize the community down to genus/species level. With species identities we should be able to not only better explain differences observed in the community profiles, but study their relations to hydrologic and/or physicochemical conditions of wetlands.     

Allelopathic effect of Pluchea lanceolata (Asteraceae) on characteristics of four soils and tomato and mustard growth

The effect of the leachate of the noxious weed Pluchea lanceolata was explored using mustard and tomato seedling growth bioassays of four soil types (sandy loam, clay loam, silty loam, and sand). The objectives of the present study were: 1) to determine how soil chemistry changes after addition of leachate and leaves of the weed; 2) to determine what level of input to the soil does not cause significant differences from those of weed-associated soils under field conditions; and 3) to determine whether soil texture affects bioassay results. Leaf leachates of the weed were added to four soil types in different dilutions, and soils were analyzed for pH, electrical conductivity, organic matter, Cl, PO₄, exchangeable Cu^{+ +}, Zn^{+ +}, Na⁺, K⁺, Mg^{+ +}, and Ca^{+ +}, and total phenolics. These results indicated that the leachates of the weed altered chemical characteristics of each soil type. Concentration of phenolics in treatment of each soil type was dilution-dependent. Leachates were more inhibitory on sandy loam and clay loam than on silty loam and sand. Present study indicated that in allelopathic bioassays, amended soils that are nonsignificantly different from weed-associated soils should be taken. Further, present investigations confirmed the significance of good control soil with nonsignificantly altered chemical characteristics from those of natural soils, as well as soil texture to establish allelopathy of ecological relevance.     

Persistence of Viruses in Desert Soils Amended with Anaerobically Digested Sewage Sludge

Pima County, Ariz., is currently investigating the potential benefits of land application of sewage sludge. To assess risks associated with the presence of pathogenic enteric viruses present in the sludge, laboratory studies were conducted to measure the inactivation rate (k = log₁₀ reduction per day) of poliovirus type 1 and bacteriophages MS2 and PRD-1 in two sludge-amended desert agricultural soils (Brazito Sandy Loam and Pima Clay Loam). Under constant moisture (approximately -0.05 × 10⁵ Pa for both soils) and temperatures of 15, 27, and 40°C, the main factors controlling the inactivation of these viruses were soil temperature and texture. As the temperature increased from 15 to 40°C, the inactivation rate increased significantly for poliovirus and MS2, whereas, for PRD-1, a significant increase in the inactivation rate was observed only at 40°C. Clay loam soils afforded more protection to all three viruses than sandy soils. At 15°C, the inactivation rate for MS2 ranged from 0.366 to 0.394 log₁₀ reduction per day in clay loam and sandy loam soils, respectively. At 27°C, this rate increased to 0.629 log₁₀ reduction per day in clay loam soil and to 0.652 in sandy loam soil. A similar trend was observed for poliovirus at 15°C (k = 0.064 log₁₀ reduction per day, clay loam; k = 0.095 log₁₀ reduction per day, sandy loam) and 27°C (k = 0.133 log₁₀ reduction per day, clay loam; k = 0.154 log₁₀ reduction per day, sandy loam). Neither MS2 nor poliovirus was recovered after 24 h at 40°C. No reduction of PRD-1 was observed after 28 days at 15°C and after 16 days at 27°C. At 40°C, the inactivation rates were 0.208 log₁₀ reduction per day in amended clay loam soil and 0.282 log₁₀ reduction per day in sandy loam soil. Evaporation to less than 5% soil moisture completely inactivated all three viruses within 7 days at 15°C, within 3 days at 27°C, and within 2 days at 40°C regardless of soil type. This suggests that a combination of high soil temperature and rapid loss of soil moisture will significantly reduce risks caused by viruses in sludge.     

Nutrients and antinutrient constituents of Amaranthus caudatus L. Cultivated on different soils

This study investigated variations in the concentration of nutrients, antinutrients and mineral content of Amaranthus caudatus harvested from different soil types at various stages of maturity. Four out the five soils namely; sandy clay loam, silty clay loam, clayey loam and loam were experimentally formulated from primary particles of silt, clay and sand in line with the United State Department of Agriculture’s (USDA) soil triangle protocol. The unfractionated soil was used as the control. After harvesting at pre-flowering (61 days after planting), flowering (71 days after planting) and post-flowering (91 days after planting) stages, nutrient and antinutrient analyses were carried out following Association of Official Analytical Chemists (AOAC) and other referenced methods while the Inductively Coupled Plasma- Optical Emission Spectrometer was used to determine mineral compositions of the plant samples. The results of the study revealed that particle size and physicochemical properties of the soil influenced the number of minerals deposited in plant tissues. It was further observed that the nutritional properties of the plant change as plant ages. For an optimal yield of vitamins A and E, clayey loam proved to be the best soil particularly when A. caudatus is harvested before flowering but for vitamin C, sandy clayey loam yielded the highest output at the same stage. Similarly, clayey loam and loam soils yielded the highest proximate compositions at flowering and pre-flowering; however, mineral elements (micro and macro) were highest in control and loam soils.     

Electronic nose evaluation of onion headspace volatiles and bulb quality as affected by nitrogen, sulphur and soil type

Edaphic factors affect the quality of onions (Allium cepa). Two experiments were carried out in the field and glasshouse to investigate the effects of N (field: 0,120 kg ha⁻¹; glasshouse: 0,108 kg ha⁻¹), S (field: 0, 20 kg ha⁻¹; glasshouse: 0, 4.35 kg ha⁻¹) and soil type (clay, sandy loam) on onion quality. A conducting polymer sensor electronic nose (E-nose) was used to classify onion headspace volatiles. Relative changes in the E-nose sensor resistance ratio (%dR/R) were reduced following N and S fertilisation. A 2D Principal Component Analysis (PCA) of the E-nose data sets accounted for c. 100% of the variations in onion headspace volatiles in both experiments. For the field experiment, E-nose data set clusters for headspace volatiles for no N-added onions overlapped (D²= 1.0) irrespective of S treatment. Headspace volatiles of N-fertilised onions for the glasshouse sandy loam also overlapped (D²=1.1) irrespective of S treatment as compared with distinct separations among clusters for the clay soil. N fertilisation significantly (P < 0.01) reduced onion bulb pyruvic acid concentration (flavour) in both experiments. S fertilisation increased pyruvic acid concentration significantly (P < 0.01) in the glasshouse experiment, especially for the clay soil, but had no effect on pyruvic acid concentration in the field. N and S fertilisation significantly (P < 0.01) increased lachrymatory potency (pungency), but reduced total soluble solids (TSS) content in the field experiment. In the glasshouse experiment, N and S had no effect on TSS. TSS content was increased on the clay by 1.2-fold as compared with the sandy loam. Onion tissue N: water-soluble SO₄²⁻ ratios of between five and eight were associated with greater %dR/R and pyruvic acid concentration values. N did not affect inner bulb tissue microbial load. In contrast, S fertilisation reduced inner bulb tissue microbial load by 80% in the field experiment and between 27% (sandy loam) and 92% (clay) in the glasshouse experiment. Overall, onion bulb quality discriminated by the E-nose responded to N, S and soil type treatments, and reflected their interactions. However, the conventional analytical and sensory measures of onion quality did not correlate with %dR/R.