Rethinking Agriculture for New Opportunities 413recuperative powers of plants and animals as well as the activity of beneficial and
predator insects to farmers’ advantage.^14 The Indonesian IPM programme, for
example, taught farmers that spiders, previously viewed with antagonism, should
be protected and preserved. Demonstrations showed that rice beyond a certain
stage can sustain extensive leaf damage from insects, as much as 25 per cent, with-
out depressing effects on yield, and even possibly some gain. When sheep in Aus-
tralia and South Africa were fed leguminous forages containing tannins as part of
their diets, their internal parasite loads were reduced, reducing expenditures on
antihelmintic medicines and providing an alternative treatment when antihelmintic
resistance is a problem (Kahn and Diaz-Hernandez, 2000). The presumptions of
modern agricultural science regarding chemical means for pest and disease control
have been broadly challenged, with such means being increasingly reduced and
avoided where possible.
Soil fertility can be enhanced, often more effectively, by
non-chemical means
The most broadly successful component of modern agriculture has been the intro-
duction and use of inorganic fertilizers to supply soil nutrients, particularly nitro-
gen, phosphorous and potassium, where these were lacking. But this success has
led many policy makers and some scientists to equate soil fertility improvement
with the application of fertilizers when, in fact, fertility depends on many addi-
tional factors. Indeed, the misuse or overuse of chemical fertilizer results in adverse
effects on yield by negatively affecting the physical and biological properties of
soil. The advantage of inorganic fertilizers is that they are easier to apply, often
cheap (if subsidized) and have more predictable nutrient content. Also, organic
nutrients are sometimes simply not available in sufficient supply.
When inorganic fertilizers are added to soils that possess good physical struc-
ture, with adequate soil organic matter and sufficient cation-exchange capacity,
they can produce impressive improvements in yield. Where soils are acidic (low
pH) and the nutrients needed for plants are in short supply, the application of
appropriate amounts of lime (calcium carbonate) along with inorganic fertilizers
can result in spectacular crop yield increases and can greatly improve farmer
income. But in many circumstances, especially in the tropics, soils are not so well
structured or well endowed. Then, inorganic fertilizers, especially if used in con-
junction with tractors that compact the soil, can lead to changes in soil physics and
biology that are counterproductive and diminish, sometimes sharply, the returns
from adding chemical nutrients.
We have suggested to dozens of soil scientists in the US and overseas that prob-
ably 60–70 per cent of soil research over the past 50 years worldwide has focused
on soil chemistry and about 20–30 per cent on soil physics. This means that less
than 10 per cent of soil research has been devoted to improving our understanding
of its biology. This estimate has not been challenged by agronomists to date. Why
such preoccupation with soil chemistry? It is the easiest kind of soil deficiency to