Agriculture Reference
In-Depth Information
and energy (e.g. organic residues) from nature.
The concept of cycling of nutrients and energy
within a farm is fundamental and vital to its
potential to be a sustainable (sub-) system.
Sustainable agricultural production must be
viewed as a managed flow of energy and nutri-
ents among soil, plants and animals within a
cycle in a whole farming system. Flow is cyclic,
although at times, it may not be continuous and
sometimes is incomplete, or there may be some
leakage. Management of the inevitable leakage
from the cycle via soil, water and air is crucial to
the (sub-) system's degree of potential sustaina-
bility. Flow may be strictly within one farm (sub-)
system or it may be across levels of aggregation
as illustrated and described by the interaction
arrows 'a', 'b' and 'c' in Fig. 18.1.
Figure 18.2 is the illustration of an exam-
ple mixed crop-animal system (dairy farm) used
as an extension education tool in Michigan
(Michigan State University Extension Dairy Team
https://www.msu.edu/user/mdr/nutrientcycle.
html). In particular, the cycle illustrates the
major qualitative flows of phosphorus (P, and
other nutrients) and four key management criti-
cal control points in the most common dairy
farm system currently in Michigan. The cycling
and recycling are by no means continuous or
quantitatively complete because there are
inflows, outflows and movement across the farm
boundary, and there is risk and may be leakage
from the (sub-) system. Sources of energy and
nutrients (e.g. purchased feeds and fertilizers)
are transported into the (sub-) system; and out-
flows such as milk and animals are exported
across the farm boundary. Additionally, other
nutrients such as nitrogen (N) leave the farm
either by intentional transport such as in milk,
animals or manure, or may be lost to air and
surface and ground-waters with potential risk of
pollution. Inevitably, a significant fraction of N
from manure volatilizes into air; whereas, other
Purchased N, P and K
supplements
Purchased
-feeds and
by products
Milk and animals
sold
Animals
purchased
Feeds
sold
Manure sold
or exported
Crops
sold
Nutrient loss
to water and air
Fertilizers
purchased
Nutrient loss
to water and air
Fig. 18.2.
Simplified example of a farm nutrient cycle of a mixed crop-animal (dairy) sub-system.
Courtesy of Michigan State University Extension Dairy Team (2006) (https://www.msu.edu/user/mdr/
nutrientcycle.html). The shaded area presents a single farm (sub-system) within its boundary. Large dark
bold arrows indicate the flow of nutrients and energy in a cycle. Smaller arrows show the import and
export flow of products (nutrients and energy) back and forth across the farm boundary. Four critical
control points (CCPs) denote farm practices to optimize or maximize management of and use of nutrients
as: CCP1, use accurate and precise ration formulation and feeding management; CCP2, capture and
retain nutrients in the farmstead to eliminate or reduce nutrient pollution into water and air; CCP3,
maximize nutrient uptake in the plant root zone by strategic and timely application of manure and
commercial fertilizer; and CCP4, minimize loss of nutrients and energy during harvest and storage of
crops whether for animal feed or for export sale.
