Métodos y Manual para Bajar

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En inglés: Soil Tool Kit Manual, Version 6.3, April 2019

En españolManual del kit de salud de suelos, versión 6.3, noviembre 2018

Para obtener guías rápidas de cada protocolo, consulte los enlaces desplegables en la pestaña “Protocolos y manuales del kit de herramientas” en la parte superior de esta pagina.

El kit de herramientas de salud del suelo reúne varios métodos para evaluar la salud del suelo en el contexto de proyectos y redes que trabajan con pequeños agricultores. Aquí en el sitio web describimos los protocolos y el manual para el pH del suelo, el carbono del suelo oxidado por permanganato (POXC o carbón activo), la materia orgánica en partículas (POM), la estabilidad de los agregados del suelo y el fósforo disponible en el suelo. En el manual descargable (enlaces anteriores), hay protocolos adicionales para estimar la humedad del suelo, medir la textura del suelo y evaluar la macrofauna del suelo, así como una demostración / prueba de materia orgánica del suelo utilizando peróxido de hidrógeno. Actualmente estamos trabajando para validar, mejorar y simplificar estas pruebas, y agregar pruebas para la infiltración de agua y la respiración del suelo.

Overall sampling strategy for soils

Taking a soil sample using an auger

Strategies for sampling need to adequately represent a farm field. 8 to 10, or more, sampling locations within each field are generally needed to deal with high variability of soils from meter to meter in smallholder fields.  In general soil is cored to the depth of the plow layer (0-15 cm or 0-20 cm) where roots are most abundant – thus the zone that plants depend most on in terms of biological processes and soil fertility. It is also possible to substitute a traditional soil corer with a square-tipped shovel or even a machete, that can slice the edge of a hole cleanly, followed by trimming the slice with a knife to create a “core-like” square section of the soil e.g. 4 x 4 cm. This is more time-consuming but no worse for rigor than a soil core from a corer (which can cost hundreds of dollars).
However if assessing soil macrofauna is of interest (see section 6 below), it is necessary to excavate larger volumes (e.g. 20×20 area, x 20 cm depth), and then this becomes the strategy for also gathering soil for testing of soil carbon, physical health, and fertility – no corer or corer is needed, just some straight spades or square-tipped shovels, for precisely excavating.

Finding Reagents

It is likely that finding chemical reagents will be a serious challenge to address in many regions. Starting early and identifying potential suppliers in larger cities is fairly important. Below are the five major chemicals required for the available soil phosphorus (Olsen P) and active C tests.  See each test protocol (at top right) for the exact amounts, recipes for reagent solutions, etc.

For soil available phosphorus (P) testing using the Olsen Extraction:

  1. Small molybdate blue reagent packs that are supplied by Hanna Instruments, the company making the colorimeter (Hanna Low Range Phosphate reagent , Hanna Instruments catalog number 93713-03 is enough packets for 300 tests)
  2. Sodium Bicarbonate (NaHCO3):  Cean baking soda from the supermarket usually works but needs to be tested by preparing Olsen solution and testing it without mixing with soil to calculate a blank value (see method) .  If analytic grade NaHCO3 is available, this is excellent. 1.05 grams are required per sample analysis. Each kit requires about 350 g, figuring a little extra for calibration, testing etc.
  3. Sodium Hydroxide (NaOH): lye from a hardware store usually works, or analytic grade. Very little of this reagent is needed, just under 10 g per kit for 300 samples.
  4. Sodium Bisulfate – also called Sodium Hydrogen Sulfate (NaHSO4) — this is a much safer and easier to dose alternative to sulfuric acid or hydrochloric acid. It is sold cheaply as a swimming pool chemical to lower pool pH in the U.S, and it is worth checking that means of purchasing in a capital city in Africa, like Nairobi etc. About 150 g is required for 300 tests (0.45 g per test) so it is not out of the question to import it, but is good to find locally.  Dilute sulphuric acid sold as battery acid can also work, though sodium bisulfate is safer.

For the Active Carbon Test:

  1. No additional reagent packs are required, like the phosphate reagent packs above.
  2. Potassium Permanganate (KMnO4) — only 64 mg is needed per test or 20 g for 300 tests. This means that if absolutely necessary, a small plastic container of KMnO4 can be flown in with travelers to the region.
  3. Calcium Chloride (CaCl2; Magnesium chloride, MgCl2 may also work).  0.3 g are needed per test or 90g for 300 tests.

For the pH test, pH buffers or calibrants for the 4.0 and 7.0 level are needed to calibrate the meter, and can usually be found in chemistry or medical supply stores.