Soil analyses

Soil texture

Soil A and B horizons should be evaluated for soil texture. Aspects that can be documented include: (i) coarse fragment analysis; (ii) particle size by hydrometer and handsieving; (iii) texture by feel; (iv) moisture content; (v) water-holding capacity (water content at field capacity and at 1.5 MPa pressure); and (vi) bulk density.

Soil pH

Soil pH is measured on a saturated paste. This aspect of soil analysis is important for pineapple culture, as serious problems can be associated with alkaline soils. The most serious is the proliferation of water moulds, Phytophthora spp. and pythiaceous fungi, which are parasitic on pineapple roots and stems. Soils of alkaline pH may also limit the availability of important nutrient elements, with iron being a notable example.

Cation exchange capacity (CEC)

CEC may be estimated using the NaOAc/NH4OAc replacement method. CEC data provide a measure of the soils' ability to hold nutrients in a form available for uptake by the plant, can have an impact on the frequency of fertilizer applications and may also indicate whether the fertilizer should be applied to the soil or as a foliar spray.

Organic matter

The organic-matter content can be measured by ashing the soil, with the volume of organic matter being estimated from the loss of weight. As mentioned earlier, pineapple plants respond favourably to soils with a high percentage of organic matter. This is not to be confused with crop residue or other organic material that has not undergone complete decomposition by composting or other means that result in a stable C/N ratio in the soil.

Total elemental composition

Soil elemental composition can be measured by HNO3/HClO4 digestion and analysis by inductively coupled plasma (ICP) spectrom-etry. Metals analysis can be made for Fe, Zn, Cu, Mn, Cd, Cr, Ni and Pb and the water-soluble elements Ca, Mg, Na, K, S and B can be determined.

Nitrogen in the soil can be measured by the Kjeldahl method. Not all soil nitrogen is fully available, though mineralization gradually releases nitrogen in organic matter. Nitrogen in the mineral form should eventually be replaced to maintain an adequate supply for plant nutrition.

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