Knowledge, science, and practice in ecological weed management: farmer–extensionist–scientist interactions - Ecological Management of Agricultural Weeds - page 111

from machinery breakdown, labor problems, and unexpected changes in the
cost of inputs. All these factors can affect the nature and timeliness of weed
control measures.
Thus, on the one hand, weeds are sufficiently predictable that farmers can
use routine control practices to produce crops without being overrun by
weeds. On the other hand, weeds are rarely eliminated altogether, due to the
localized mismatch between routine control practices and the uncertainty of
weed patchiness.Farmer decision-making in weed management aims to mini-
mize this mismatch for more efficient and less risky crop production. How
have advances by researchers and extensionists taken into account weed
patchiness and uncertainty for the wide diversity of the world's farmers?
Since the early 1900s, the routine use of uniformly applied agrichemical
inputs on the better croplands has produced impressive increases in yields and
labor productivity,first in temperate and later in tropical agriculture.Through
multiyear replicated experiments, scientists conducted input-output research
to identify the best broadly applied levels and combinations of different
inputs, each of which has a specific, short-term purpose. Extensionists and
later private crop consultants promoted the use of improved varieties, chemi-
cal fertilizers, and pesticides. This simple production model based on the effi-
cient assemblage of purchased inputs into an end product resembles an
industrial process (Levins, 1986). In the USA maize production quadrupled
from 1940 to 1990 with fewer farmers and less land in production (Hossner &
Dibb, 1995). In more recent years, in China rice and wheat yields have doubled
and quadrupled, respectively (Hossner & Dibb, 1995).
Recently, science and society have begun to realize that a crop field is not a
factory, but rather part of a living and responsive system. Herbicide resistance
in weeds, floristic shifts to harder-to-control weeds, ground and surface water
pollution, and human health effects are now routinely recognized as part of
the risks and external costs of using herbicides and other agrichemicals
(Chapter 1).
In many tropical countries, the standardized, high-input approach to
increased crop yields has not fit productively with the complex landscapes,
incipient infrastructure, and the diverse human cultures and cropping
systems of smallholders (Pretty,1995,pp.31-3).As a result,input use has gen-
erally been irregular and crop yield responses modest and inconsistent. In the
countries of Central America, Phaseolus bean yields have not increased consis-
tently during the past 30 years (FAOSTAT, 1999). In Nicaragua, for example,
since 1965 bean yields have fluctuated from 0.5 to 0.9 Mg ha 1 , but the long-
term yield has increased only slightly (unpublished Nicaraguan Central Bank
files, 1998). Similarly, coffee yields have fluctuated from 0.3 to 0.8 Mg ha 1 .