Growing Food: A Guide to Food Production

sophisticated machines are needed to do an efficient job, and these can be difficult to
regulate and maintain.
Most subsistence farmers, and many others, find that fertilisers can be a mixed
blessing. In the case of most very poor farmers it is normally more appropriate to
promote the increased understanding and use of organic manures, composts, mulches
and so on.

Approximate Value (as a percentage) of some Organic Fertilisers

FFeerrttiilliisseerrssoouurrccee N P 2 O 5 K 2 O

Bone meal (raw)

Blood meal

Fish meal

Greensand (glauconite)

Groundnut cake

Guano based

Coconut cake

Cow manure (FYM)

Poultry & Pig manure

Slurry

Wood ash

4

12

5

7

10

1–3

0.4–0.6

0.5–1.5

0.5

22

5

1.2

1.5

1.3

0.1–0.3

0.5–1.5

0.1

1–2

0.1–3

1.5

2.5

0.4–0.6

0.6–0.8

0.4

5–8

These nutrients are not immediately available for plant growth, and only a proportion
are utilised during the first growing season. Calcium, magnesium and sulphur are also
often available present in significant amounts.

• FYM. On a dry matter basis FYM (farm yard manure) contains about 2–0.5–1.5, so
  25 t/ha fresh manure would be needed to apply 160, 22 and 110 kg/ha of N, P and
  K respectively. The P and K in FYM is normally readily available, but the N


• Slurry. The composition of slurries varies widely, according to the dilution rate.
  Undiluted cattle waste contains about 10% dry matter, 0.5% N, 0.1% P, 0.4% K.
  Much of the N is present as ammonia which can evaporate after spreading, so
  slurries should be incorporated into the soil immediately after application, or
  applied just before rain.


• Municipal composts, derived from domestic sewage and other waste. The K
  content can be quite low, which can arise because during sewage treatment the
  liquid (which contains much of the K) is drained off.


• Poultry manure can substantially raise soil pH, and so should not be used if pH is
  already greater than about 6. It is often a good source of nutrients. On a dry weight
  basis, it may contain 2–5% N, 1–3% P, and 1–3% K. About half of the N in poultry
  manure can be available in the first season but much of the N may be lost if the
  manure is dried and then stored.

is available in the first season.

becomes available over a period of a few years—only 25 30% of the N applied –

GROWING FOOD – THE FOOD PRODUCTION HANDBOOK 31