Agriculture Reference
In-Depth Information
However, lower production levels, the efficient use of manures and com-
posts and the use of permitted fertilizers, where P and K levels are deficient,
may lead to a balance or surplus of nutrients in organic systems.
Nutrient budgets allow a breakdown of nutrient inputs and outputs
and, in more comprehensive studies, a quantification of internal flows in
farming systems (Watson and Atkinson, 1999). Nutrient budgets have been
compiled at a variety of scales and using various methodological approaches
across the world (Scoones and Toulmin, 1998; Jarvis, 1999). It is impor-
tant that for cropping systems based on crop rotation or mixed systems
including livestock, such as organic farms, nutrient budgets are considered
at the level of the whole farm system (Watson and Stockdale, 1999), so that
all potential inputs and outputs are included. Here we will consider both
nutrient budgets, compiled as farm gate budgets, and the results of some
limited soil analysis to examine whether organic farming in the UK can be
sustainable with regard to nutrient cycling.
Methods
Soil indices
Soils in England and Wales are analysed routinely for available P and K
(MAFF, 1986). Soils can be grouped into categories, the soil P and K index
system, where an index of 0 or 1 indicates a possible crop deficiency
(MAFF, 1994). A sequential Balzer P extraction (Balzer and Balzer-
Graf, 1984) determines soil reserve, plant-available and water-soluble P,
respectively, and is carried out by the Organic Advisory Service (OAS) in
addition to routine analysis (EFRC, 1999). Results from soil analyses
submitted to the OAS during 1997 have been collated and examined
using an Access database. The results have also been compared with
data on the P and K status of UK arable soils (Skinner et al ., 1992).
Traditionally, soil tests have been used to assess nutrient availability
for crop growth. However, no simple method exists for measuring the
potentially available N content of the soil or the longer term release of other
nutrients into available forms.
Nutrient budgets
Farm gate budgets are among the simplest form of budgets. These consider
only flows that transfer nutrients over the farm boundary, e.g. N fixed, feed,
stock, seed, milk and grain (Jarvis, 1999). If the inputs and outputs balance,
the farming system is considered to maintain soil fertility. A surplus of
nutrients can provide an indication of the potential for losses of nutrients,
Search WWH ::




Custom Search