Effects of tillage, fallow and burning on selected properties and fertility status of Andosols in the Mounts Bambouto, West Cameroon

To assess the impact of land use on the Andosol fertility, changes in chemical and physical properties affecting soil quality were monitored on Andosols from Mount Bambouto submitted to four different land use and management systems: natural cover, tillage, burning and fallow. In comparison with the natural cover, tillage reduces Andosol OC (6.5 to 4.8%), total N (4.51 to 2.95‰), CEC (22.0 to 20.9 cmol.kg–1) and the abundance of soil macro-aggregates expressed by the water stable aggregates (WSA) varies from 53.8 to 12.0%;and increases the bulk density (0.69 to 1.09 g.cm–3) and the sum of exchangeable cations (3.58 to 4.84 cmol.kg–1). Burning also reduces Andosol OC (6.5 to 0.8%), total N (4.51 to 0.95‰) and CEC (22.0 to 10.2 cmol.kg–1), but increases soil pH (4.62 to 6.54), the sum of exchangeable cations (3.58 to 5.74 cmol.kg–1) and the abundance of soil macroaggregates (WSA: 38.2 to 57.0%). In comparison with tillage, fallow increases Andosol OC (4.8 to 6.5%), total N (2.95 to 5.04‰), CEC (18.0 to 21.6 cmol.kg–1), the sum of exchangeable cations (3.58 to 5.05 cmol.kg–1) and the abundance of soil macroaggregates (WSA: 12.0 to 48.8%). Globally, the tillage management deteriorates Andosol chemical and physical properties affecting fertility, whereas the fallow management restores them. The burning management also improves some Andosol chemical and physical properties affecting quality, but it won’t last long.

Andosolization of Soils on a Strombolian Cone at Mount Bambouto, Cameroon

Morphology, mineral and geochemical investigations were carried out on two selected soil pedons (ZA and TO) developed on a late Quaternary-aged strombolian cone to better understand andosolization processes in Mount Bambouto, Cameroon. Both pedons have A-BC-C horizonation. They have thick surface (A) horizon with bulk density -3, Alo + 0.5Feo about 2% and P retention >90%. Mineral association consists predominantly of kaolinite, gibbsite, goe- thite, organometal complexes and trace amount of ferrihydrite and allophane. The Ki values between 1.1 and 1.6, the low TRB (45 to 67 mg kg-1), the important IMob (20% to 24%), the CIA between 60% and 70% and the EFs above 1.16 for Al and Fe, and below 0.6 for Si indicate sparingly hydrolysis process in subsoil during which released Al, Fe and Si form allophanic or ferrihydrite minerals undergo crystallization into kaolinite, gibbsite and goethite, respectively. At topsoil, part of released Al (and Fe) is organically bounded with organic acids to form organometal complexes.

长白山山脉火山喷出物发育土壤的特性及系统分类研究

以长白山、龙岗、宽甸火山喷出物发育土壤为研究对象，对供试土壤形态特征进行描述，并对其pH、有机碳、磷酸盐吸持量、铁铝氧化物、火山玻璃等性质进行测定，按照《中国土壤系统分类检索（第三版）》的原则和方法并结合美国《土壤系统分类检索》第11版，讨论了土壤的诊断层、诊断特性，并进行了分类检索。结果表明：火山喷出物发育的土壤未必就是火山灰土。长白山天池火山锥顶部的土壤发育程度极弱，属于新成土；天池火山锥底部的土壤已经形成土壤结构体，且具有火山灰特性，属于火山灰土；宽甸青椅山顶部土壤以及龙岗金龙顶子底部土壤均具有火山灰特性，检索为火山灰土；宽甸大川头底部土壤0．02～2mm粒级含量未达到火山灰特性的要求，但具有雏形层，检索为雏形土。

Low-Molecular-Weight Aliphatic Acids in Soils Incubated with Plant Residues Under Different Moisture Conditions

Incubation experiments were conducted to investigate the dynamics of low- molecufar-weight aliphatic acids in two andosols with and without plant materials. Results showed that amount of low- molecular-weight aliphatic acids in soils alone varied considerably with water regime under which the soil was incubated,duration of incubation and soil organic matter content, ranging from 257-860 pmol kg-1 soil I of which 19%～33% was in free state. Incorporation of plant materials increased greatly both the amount and number of members of low- molecular- weight aliphaticacidst and also the proporticn of low-molec "far-weight aliphatic acids occurred in free state. Generally, among these aliphatic acids detected, acetic, propionic, glyoxalic and formic acids were predominant.

Soil Agricultural Potential in Four Common Andean Land Use Types in the Highlands of Southern Ecuador as Revealed by a Corn Bioassay

In the Andes, little is known about the relationships among current land uses and their effect on soil fertility. Corn (Zea mays L.) was used to evaluate soil quality for plant growth on soils of four land uses, along an expected gradient of fertility: native forests (Nf) > pastures (Pa) > Eucalyptus globulus Labill. plantations (Eg) > Pinus patula Schlecht. plantations (Pp). Corn was grown in soils taken from four different areas, for the four land uses in each. In a common garden, a randomized block design was used with four treatments: controls (C), ammonium nitrate (N), triple superphosphate (P), and combined N and P fertilizers (N + P). On soils from Nf, Pa and Eg, fertilization response was N + P > P > N > C;corn biomass (g/pot-1) averaged 4.5 in N + P, 3.3 in P, 1.8 in N, 1.7 in C;P content (mg/pot-1) averaged 12 in N + P, 11.9 in P, 2.3 in N, 2 in C. N + P enhanced growth the most. Mortality was high on Pp soils, growth weak, and fertilization response was P > N + P > C ≥ N;corn biomass (g/pot-1) was 0.9 in P, 0.5 in N + P, 0.8 in C, 0.4 in N;P content (mg/pot-1) was 4.4 in P, 2.3 in N + P, 1.8 in C, 1 in N. All soils had P, K, Ca and Mg deficiencies. Al toxicity possibly occurred only in Pp soils. All control soils had low fertility. Responses to N and P were high except for Pp. Pastures and plantations were once natural forests converted to agriculture, then to pastures as soil fertility declined. Plantations were likely established on poorest pastures;only pine grew on poorest soils. This land use endpoint has the lowest agricultural potential;other land uses have limitations in P, N, and potentially K.

长白山脉火山碎屑物发育土壤特性研究

以吉林省长白山天池火山锥和辽宁省宽甸县黄椅山火山锥上火山碎屑物发育的土壤为研究对象,按照中国科学院南京土壤研究所主编的《土壤调查实验室分析方法》,探索火山碎屑物发育土壤的形态学、化学和矿物学特性。研究结果表明,供试土壤pH（H2O）值介于5.32-6.47,pH（KCl）值介于4.15-5.73,pH（NaF）值介于8.40-10.55;表层有机碳含量介于31.51-59.48g/kg之间;磷酸盐吸持量介于7.08%-75.89%之间;阳离子交换量（CEC7）介于2.35-39.90cmol（＋）/kg;交换性盐基以Ca^2＋、Mg^2＋为主;盐基饱和度为15.33%-55.68%;连二亚硫酸钠-柠檬酸钠-碳酸氢钠（DCB）、酸性草酸铵和焦磷酸钠浸提的铝、铁值分别表现为Alp〈Ald〈Alo,Fep〈Feo〈Fed;水铝英石含量介于0.73%-9.05%,水铁矿含量介于0.46%-4.86%。4个土壤剖面相比较,天池火山锥土壤的发育程度低于宽甸火山锥的土壤;同一火山锥,锥上部土壤的发育程度弱于锥下部的土壤。研究表明：火山碎屑物发育的土壤不同于其他一般母质发育的土壤,水铝英石等无定形矿物的存在导致土壤的Alo值大于Ald值;土壤的pH（NaF）和磷酸盐吸持量与土壤中水铝英石含量呈极显著的正相关,所以,可以通过测定土壤中的pH（NaF）、磷酸盐吸持量预测供试样品的水铝英石含量。

火山喷出物发育土壤的比重及颗粒组成测定

利用比重瓶法对火山喷出物发育土壤的比重进行测定,结果表明:玄武岩质火山喷出物发育土壤的比重大于粗面岩质火山喷出物发育土壤的比重;基于粒径小于1 mm土粒测定的比重,玄武岩质火山喷出物和粗面岩质火山喷出物发育土壤的比重均小于一般土壤的平均比重2.65 g cm^(-3);基于粒径小于0.1 mm土粒测定的比重,除个别玄武岩质火山喷出物发育土壤外也小于2.65 g cm^(-3)。分别取比重值为2.65 g cm^(-3)、粒径小于1 mm土粒的实测比重和粒径小于0.1 mm土粒的实测比重,计算不同粒级土粒的沉降时间,并进行颗粒组成的实验研究表明:取不同比重值测定的土壤颗粒组成含量相差较大而且影响土壤质地定名。由于成土母质的矿物组成决定土壤的比重,且土壤颗粒组成的静水沉降实验是在粒径小于0.1 mm土粒的悬液中进行的,所以,准确测定土壤颗粒组成含量,需要区分成土母质的矿物组成,并测定其小于0.1 mm粒径的土粒比重,重新计算沉降时间。

Pretreatment of Soil Samples Rich in Short-Range-Order Minerals Before Particle-Size Analysis by the Pipette Method

The possibilities of combining the dissolution of short-range-order minerals （SROMs） like allophane and imogolite, by ammonium oxalate and a particle size distribution analysis performed by the pipette method were investigated by tests on a soil sample from Reunion, a volcanic island located in the Indian Ocean, having a large SROMs content. The need to work with moist soil samples was again emphasized because the microaggregates formed during air-drying are resistant to the reagent. The SROM content increased, but irregularly, with the number of dissolutions by ammonium oxalate： 334 and 470 mg g-1 of SROMs were dissolved after one and three dissolutions respectively. Six successive dissolutions with ammonium oxalate on the same soil sample showed that 89% of the sum of oxides extracted by the 6 dissolutions were extracted by the first dissolution （mean 304 mg g-l）. A compromise needs to be found between the total removal of SROMs by large quantities of ammonium oxalate and the preservation of clay minerals, which were unexpectedly dissolved by this reagent. These tests enabled a description of the clay assemblage of the soil （gibbsite, smectite, and traces of kaolinite） in an area where such information was lacking due to the difficulties encountered in recuperation of the clay fraction.

Nitrification inhibitor nitrapyrin does not affect yield-scaled nitrous oxide emissions in a tropical grassland

Urea is the most common nitrogen(N)fertilizer used in the tropics but it has the risk of high gaseous nitrogen(N)losses.Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields.In a field trial on a tropical Andosol pastureland in Costa Rica,gaseous emissions of ammonia(NH_(3))and nitrous oxide(N_(2)O)and grass yield were quantified from plots treated with urea(U;41.7 kg N ha^(-1)application^(-1))and urea plus the nitrification inhibitor nitrapyrin(U+NI;41.7 kg N ha^(-1)application^(-1)and 350 g of nitrapyrin for each 100 kg of N applied)and control plots(without U and NI)over a six-month period(rainy season).Volatilization of NH_(3)(August to November)in U(7.4%±1.3%of N applied)and U+NI(8.1%±0.9%of N applied)were not significantly different(P>0.05).Emissions of N_(2)O in U and U+NI from June to November were significantly different(P<0.05)only in October,when N_(2)O emission in U+NI was higher than that in U.Yield and crude protein production of grass were significantly higher(P<0.05)in U and U+NI than in the control plots,but they were not significantly different between U and U+NI.There was no significant difference in yield-scaled N_(2)O emission between U(0.31±0.10 g N kg^(-1)dry matter)and U+NI(0.47±0.10 g N kg^(-1)dry matter).The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site.