Influence of basin‐based conservation agriculture on selected soil quality parameters under smallholder farming in Zimbabwe

The research was carried out to determine the effect of basin‐based conservation agriculture (CA) on selected soil quality parameters. Paired plots (0.01 ha) of CA and conventional tillage based on the animal‐drawn mouldboard plough (CONV) were established between 2004 and 2007 on farm fields on soils with either low (12–18% – sandy loams and sandy clay loams) or high clay levels (>18–46% – sandy clays and clays) as part of an ongoing project promoting CA in six districts in the smallholder farming areas of Zimbabwe. We hypothesized that CA would improve soil organic carbon (SOC), bulk density, aggregate stability, soil moisture retention and infiltration rate. Soil samples for SOC and aggregate stability were taken from 0 to 15 cm depth and for bulk density and soil moisture retention from 0 to 5, 5 to 10 and 10 to 15 cm depths in 2011 from maize plots. Larger SOC contents, SOC stocks and improved aggregate stability, decreased bulk density, increased pore volume and moisture retention were observed in CA treatments. Results were consistent with the hypothesis, and we conclude that CA improves soil quality under smallholder farming. Benefits were, however, greater in high clay soils, which is relevant to the targeting of practices on smallholder farming areas of sub‐Saharan Africa.     

More than eating dirt: a review of avian geophagy‡

Geophagy, the ingestion of earth varying in particle size from stones to soils rich in clay, is a relatively widespread behaviour across avian taxa. We reviewed its occurrence in birds and its hypothesised adaptive functions in birds. Of the ～30 avian orders, 23 exhibit geophagy. However, it has only been documented in ～260 species (～2% of birds) and therefor is relatively uncommon. Ingestion of stones and other large particles (grit) is recorded in 54 extant families across the avian phylogeny and appears to be ancient in birds and has evolved several times. Clay ingestion is recorded in 14 phylogenetically scattered families and might have evolved repeatedly. Furthermore, at least nine families exhibit both clay and grit ingestion. Six hypothesised functions of avian geophagy involve digestion and nutrition. Ingested grit might provide (1) essential minerals, particularly sodium or calcium, but it appears to primarily (2) improve mechanical digestion of food in the gizzard, where ingested stones and sand particles are known as gastroliths. Consistent with this gastrolith hypothesis, ～86% of species ingesting grit consume “hard” food: seeds, leaves, insects or other animals. In contrast, ingested clay appears to be for sodium or other nutrient intake and/or protecting birds from ingested plant secondary compounds, by (3) protecting the digestive tract and (4) adsorbing these compounds. Consistent with this, ～88% of species ingesting clay eat fruit that is often rich in secondary compounds and low in sodium, and clay ingestion is associated with frugivory in a representative sample of genera of which many have been shown to source sodium. The other two hypotheses are buffering gastric pH (5) and acquiring antidiarrheal agents (6), but no documentation of this in birds was found. We suggest additional tests of these hypotheses and additional investigation of these proposed benefits of geophagy in birds.     

湖北省几种土壤的粘土矿物组成与表面化学性质

研究了湖北省棕红壤、黄棕壤、水稻土和灰潮土的粘土矿物组成、电荷性质及对磷的吸附。结果表明：①供试土壤的粘土矿物组成都以水云母为主,高岭石和１．４ｎｍ矿物含量较少,１．４ｎｍ矿物种类不同且比例变异大;②供试土壤的负电荷量（ＣＥＣ８．２）介于９．２￣１９．１ｃｍｏｌ／ｋｇ间,永久负电荷占ＣＥＣ８．２的５０％￣６４％,阴离子交换量（ＡＥＣ）为０．７５￣２．２１ｃｍｏｌ／ｋｇ,电荷零点（ＰＺＣ）介于２．３     

陕西省南部地区土壤粘粒特性研究

陕西南部土壤粘粒特性的研究发现,陕西省南部北亚热带湿润地区,发育在第四纪下蜀黄土母质上的土壤粘粒含量高,粘化层不明显,粘土矿物以伊利石和蒙脱石为主,粘粒铁富集明显;发育在基岩风化物母质上的土壤粘化层明显,粘土矿物以蒙脱石、蛭石为主,且有一定量的高岭石,粘粒中铝富集强烈。中山区暖温带湿润地区的土壤,粘粒含量较低,粘土矿物以伊利石、绿泥石为主,粘粒中铁、铝富集均不明显,元素的淋溶迁移较弱。     

Factors influencing carbon decomposition of topsoils from the Brazilian Amazon Basin

 The influence of texture and local climate, especially precipitation, on C decomposition was evaluated in topsoils under forest and pastures at different sites located in the western, central, and eastern Brazilian Amazon Basin. Independent of the geographical location and vegetation cover, C decomposition was lower in topsoils of fine texture with a sand/clay ratio of less than 1, compared to topsoils of coarse a texture with a sand/clay ratio ranging from 2 to 8. In the former, the low sand/clay ratio appears to reduce C decomposition. In the latter, besides the effect of the high sand/clay ratio, the local climate, especially the annual precipitation, seems to play an important role in controlling C decomposition. Received: 2 March 1998     

Aspects of the adsorption and degradation of isoproturon in a heavy clay soil

Abstract. Degradation of isoproturon in a heavy clay soil followed first-order reaction kinetics with half-lives at 15 °C of 27 and 208 days in the topsoil and subsoil, respectively. Adsorption when shaken with 3 mm sieved samples of the soil fitted the empirical Freundlich relationship with k values of 3.25 in the topsoil and 1.06 in the subsoil. Adsorption in a static system with different sized aggregates of soil did not reach equilibrium, even after 24 hours contact, and the rate of adsorption was slower with larger aggregates. Following an adsorption period of 24 hours, desorption equilibrium was reached more rapidly with larger (6–10 mm) than with smaller (<3 mm) aggregates. Adsorption isotherms measured in a static system with a soil:water ratio typical of field conditions in winter also indicated less adsorption than that measured in shaken, laboratory systems with low soil:water ratios. The rate of change in water extractable residues of the herbicide was more rapid than that of total extract-able residues following application of isoproturon to the heavy clay soil in the field. The implications of the results for isoproturon leaching under field conditions are discussed.     

土壤粘粒吸附脲酶量的影响因子研究

研究了８种土壤粘粒对脲酶的吸附量,以及不同ｐＨ,温度和Ｚｎ（Ⅱ）、Ａｓ（Ⅴ）、Ｈｇ（Ⅱ）质量浓度对脲酶吸附量的影响。结果表明,８种土壤粘粒对脲酶均有吸附,但吸附数量不尽相同。非最适ｐＨ时,脲酶吸附量在弱碱性介质中的下降率大于弱酸性介质;温度升高,脲酶吸附量下降,且去有机质土壤粘粒的下降率大于原样土壤粘粒;Ｚｎ（Ⅱ）、Ａｓ（Ⅴ）、Ｈｇ（Ⅱ）抑制相同比率的脲酶吸附量时,所需３种离子的质量浓度为Ａｓ（Ⅴ）＞Ｚｎ（Ⅱ）＞Ｈｇ（Ⅱ）,表现为Ｈｇ（Ⅱ）的抑制作用最强。     

Revegetation techniques on clay soil slopes in northern Italy

Several standard techniques currently used in the reclamation and revegetation of former quarry land in Italy's northern Apennine region were compared. The trial site, a 40-degree slope with clay soil, high pH and a little organic matter, was arranged in a randomized block design. The techniques assayed were hydro-seeding+tillage, hydro-seeding on sod, straw mulch+tar, jute mats+tillage+hydro-seeding, jute mats+tillage and a control. Each plot was enriched with equal amounts of chopped straw (120 g m⁻²), worm compost (140 g m⁻²) and the fertilizer Biosol^® (140 g m⁻²); the binder Terravest^® (36 g m⁻²) was also used in the three hydro-seeded plots. Ground cover, species, runoff and erosion were compared in each treatment. The overall 3-year data indicate significant differences in the treatments tested. There is a clear distinction between the treatments that promoted good grass cover growth and checked erosion (straw and tar, jute on tilled soil, and hydro-seeding on jute and tilled soil) on the one hand and the hydro-seeded treatments (on sod and on tilled soil), which showed no differences from control, on the other. © 1997 John Wiley & Sons, Ltd.     

One Dimension Compression Model for Natural Clays Considering Structure Disturbance

In order to investigate the 1D (one dimensional) compression behavior for China structured clays in a simple way, the experimental results on intact and reconstituted clay samples for 12 typical China natural clays located from south to north in China were analyzed. Based on these, a modeling method for destructuration behavior was proposed by introducing the bonding ratio and furthermore extended to disturbance soil model by using disturbance state concept. The proposed model was then validated by simulating 1D compression tests of various natural clays.