Agriculture Reference
In-Depth Information
Soil analysis
Soil samples are collected before planting from a soil depth of between 10
and 30 cm with a shovel or auger. It may also be necessary to sample the
subsoil. In fairly uniform soils, soil is sampled at various points, following a
'W' pattern across the fi eld. The soil samples are mixed for analysis. If the soils
appear to vary in a fi eld, each dif erent area should be sampled and analysed
separately. The analysis results will provide the soil's pH and an estimate of the
available macronutrients and, when data are available, a recommendation
as to the fertilizer needs. For nitrogen content, the results will not be as exact.
Any defi ciencies noted at this time should be corrected. It is important to
remember that the soil analysis indicates what is present but not necessarily
available for the plants; sometimes an extreme pH can block the availability
of some nutrients. So the soil's analysis has to be complemented by the plant
analysis. The soil analysis can be repeated every 2 or 3 years to detect any
signifi cant changes.
Plant analysis
Plant or foliar analysis indicates the level of a particular element present in
the plant. The amount is compared with a standard table, which have been
developed for many species after long fi eld studies. This analysis makes it
possible to know if the level found in the tissue is normal, defi cient or excessive.
For leaf analysis, it is important to know how the standards were developed, as
the type, number and age of leaf, what type of shoot (with or without fruit)
and at what time of the year samples were taken can change the standard
values. The samples taken will need to duplicate this sampling protocol
carefully in order to have comparative results. In banana, leaf or petiole pieces
are used instead of whole leaves. The sampling has to be performed by trained
personnel and the samples analysed by a certifi ed and trusted laboratory. The
analysis results will indicate what nutrients are insui cient for the plant's
growth or what is in excess. A decision can then be made to correct a nutrient
that is limiting growth by applying more or less of that nutrient in your
fertilizer programme (Table 4.3).
Dosages will initially follow recommendations from other growing areas
until reliable local or your own information is available. The nutrients most
commonly defi cient are nitrogen, phosphorus and potassium, and sometimes
magnesium, and these are included in a regular fertilization programme.
Roughly, in the adult stage plants need around 100 kg of nitrogen, 50 kg of
phosphorus (P
2
O
5
) and 100 kg of potassium (K
2
O) per hectare per year. These
very broad referential numbers vary signifi cantly with species, soil type and
plant growth stages. Banana, plantain and pineapple normally need much
more nitrogen and potassium than other tree crops. A common problem
