Echantillonnage du sol et preparation des echantillons: guide de recherche de Iiita, No. 2

La method d'echantillonnage du sol choisie des raisons qui motivent l'analyse du sol. Le sol ne forme pas une masse homogene. La vie vegetale, la topographie, les pratiques agronomiques, etc. affectent l'uniformite du sol. L'exactitude des donnees de l'analyse du sol est fonction de la precision avec laquelle les echantillons sont preleves

Soil sampling and sample preparation

The approach to soil sampling depends on the reasons for soil analysis. Soil is not a homogeneous mass. Plant life, topography, agronomic practices, etc. affect the uniformity of a soil. The accuracy of the soil analysis data depends on the accuracy with which the soil samples are taken. Several definitions and terms are important to describe fertilizers. The "grade", for example, describe the N-P205-K20 content in weight percentage. The exact amount of fertilizer required has to be calculated depending on type of fertilizer and area to be fertilized. Mixing of fertilizers makes application easier, however, not all fertilizers can be mixed

Effect of agroforestry woody species on earthwarm activities and physicochemical properties of warm casts

The effects of five agroforestry woody species (Dactyladenia barteri, Gliricidia sepium, Leucaena leucocephala, Senna siamea andTreculia africana) on the surface aasting activity ofHyperiodrilus africanus were studied in an Alfisol (Oxic Paleustalf) in southwestern Nigeria. Casting activity under the woody species decreased in the following order:Dactyladenia sp. (26.4 Mg ha-1 year-1)>Gliricidia sp. (24.4 Mg ha-1 year-1)>Treculia sp. (22.9 Mg ha-1 year-1)>Leucaena sp. (18.6 Mg ha-1 year-1)>Senna sp. (18.3 Mg ha-1 year-1). These differences in casting activity were partly explained by microclimatic effects. Irrespective of the woody species, the worm casts were higher in clay and silt contents, bulk density, water-stable aggregates, pH, organic C, exchangeable cations, effective cation exchange capacity, and extractable P levels than the corresponding surface soils. The woody species did affect the physicochemical properties and P sorption of the worm casts. The content of water-stable aggregates of worm casts decreased in the following order:Dactyladenia sp.>Treculia sp.>Senna sp.>Leucaena sp.>Gliricidia sp. Large differences in extractable P levels were observed.Senna sp. was associated with the highest extractable P level (11.5 mg kg-1) andTreculia sp. the lowest (4.9 mg kg-1). P sorption was highest on worm casts underDactyladenia sp. and lowest on those underTreculia sp. Without fertilizer application, there were no significant differences in the dry weight of maize grown in the different worm casts. With NPK applications, the dry weight of maize grown in worm casts associated withTreculia sp. was significantly lower than that of maize grown in the other worm casts, mainly due to the low extractable P level. Despite a high organic C and exchangeable K status, maize grown in the worm casts still responded significantly to N and K applications. The N uptake by maize grown in worm casts associated withTreculia sp. was lower than that in the other treatments

Ion exchange equilibria involving aluminum in a kaolinitic Ultisol

Cation exchange equilibria in an acid Ultisol profile involving K-Al, Ca-Al, K-Ca, Na-K, and Na-Ca exchanges were studied. Selectivity coefficients, surface activity coefficients and free energy changes were computed using the thermodynamic formulations. In exchange equilibria involving Al, the magnitude of selectivity coefficients Kc, was affected by pH, surface composition, and hydrolysis of Al. In equilibria not involving Al, good reversibility for K-Ca, Na-K and Na-Ca exchanges was obtained. Potassium was selectively adsorbed in all horizons of the profile. The over-all selectively sequence follows the order of K>Al>Ca≈Na

A new method for the simultaneous measurement of Ph-dependent cation exchange capacity and ph buffering capacity

The pH dependent cation exchange capacity (CEC) and pH buffering capacity (pH BC) are two crucial properties in soil fertility management of variable charge soils. However, they are rarely measured, since most of the existing methods are cumbersome and time-consuming. We propose a new method, based on the silver-thiourea (AgTU) method, for the simultaneous measurement of pH dependent CEC and the pH BC. In general, this method consists of first increasing the pH of the soil to about pH 7 and then gradually acidifying the soil by titrating with HNO3, while measuring pH and CEC after each equilibration. This way, both CEC at different pH values and the pH BC are measured on the same sample, without the multiple washing steps needed in other procedures. Various aspects of the proposed method were tested and the results obtained were compared with the ion adsorption method. The modified AgTU method obtains field relevant results and is suitable for the routine analysis of large numbers of samples

Amelioration of a degraded Oxic Paleustalf by leguminous and natural fallows

The restorative ability of herbaceous (Psophocarpus palustris, Pueraria phaseoloides) and woody (Leucaena leucocephala, Senna siamea, Acacia leptocarpa, Acacia auriculiformis) legume species and of natural regrowth was studied on an eroded and compacted Oxic Paleustalf in southwestern Nigeria. Compared to the control treatment that was continuously cropped for 15 years, four years of fallowing significantly improved test crop yields. However, fallowing with the above species did not substantially improve soil properties, particularly soil bulk density. A longer fallow period may be needed to amend soil physical conditions of this degraded Alfisol. Soil chemical properties were greatly improved following land clearing and plant biomass burning in 1993. However, the residual effect of burning on soil fertility was insignificant in the second cropping year. Among the fallow species, P. palustris and natural fallow showed the best residual effect on test crop performance. Despite the high biomass and nutrient yields of S. siamea and A. auriculiformis, test crop yields on these plots were low due to the border effects from the uncleared and fallowed subplots

Formas orgânicas e inorgânicas de mobilização do cálcio no solo

A falta de Ca e a presença de Al na subsuperfície do solo restringem o crescimento das raízes. A eficiência da calagem aplicada na superfície do solo na neutralização da acidez subsuperficial é limitada. Foram conduzidos experimentos de laboratório com colunas de PVC para avaliar técnicas orgânicas e inorgânicas na mobilidade do Ca em solo com carga variável. Foram conduzidos dois experimentos com sais de Ca: CaCO3, CaSO4, Ca(NO3)2, Ca-acetato e Ca-citrato, e outro com CaCO3 associado com resíduos de aveia preta, trigo e leucena. Avaliaram-se os teores de Ca trocável em solucão de KCl 1M nas profundidades de 0 a 5, 5 a 10, 10 a 20, 20 a 30, 30 a 40 e 40 a 50cm. A eficiência dos sais na mobilidade de Ca seguiu a ordem: NO3 > Acetado > Citrato > SO4 > CO3. Os resíduos de plantas forma eficientes na mobilização do Ca na seguinte ordem: aveia > leucena > trigo. Atribuiu-se à formação de complexos organo-metálico a responsabilidade pela mobilização do Ca no solo associada com a calagem e os resíduos vegetais.<br>Lack of Ca and often the presence of Al in subsoil restrict crop-root proliferation. The efficacy of soil surface liming in neutralize subsoil acidity is limited. Laboratory experiments were conducted with leaching columns to evaluate some organic and inorganic techniques to accelerate the mobility of Ca in a variable charge soil. Two different experiments were conducted, one with Ca-salts: CaCO3, CaSO4, Ca(NO3)2, Ca-acetate, and Ca-citrate; and another one with CaCO3 plus plant residues: black oat (Avena strigosa), wheat (Triticum aestivum) and leucaena (Leucaena leucocephala). The observations included MKCl exchangeable Ca in 0 to 5, 5 to 10, 10 to 20, 20 to 30, 30 to 40 and 40 to 50 cm soil depth. The effects of CaCO3 without plant residue was limited to the upper 10 cm of the profile. The efficacy of Ca-salts on the mobility of Ca ex followed the order: NO3 > Acetate > Citrate > SO4 > CO3. Plant residues were highly efficient as Ca-carrier in the following order black oat > leucaena > wheat. Metal-organic complexes were assumed to be responsible for the movement of Ca in the profile associated with lime and plant residues