Fertilizers are responsible for over half of global food production, but there are areas in world with nutrient deficiency and other areas of nutrient excess.
Managing mineral plant nutrients requires careful application of science and skill to meet production, environmental, and social goals.
Manypeoplehaveattemptedtodefinesoilqualityby measuring various soil characteristics
and relating these to differentmanagementpractices,productivity,environmental
quality,orplantdisease.Butsoilqualitymeansdifferent thingstodifferentpeople,dependingonitsintendeduse. Forexample,farmersgenerallywantasoilthatsupports idealcropgrowthyearafteryearwithaminimumofinputs.
Soil Phosphorus (P):Concentrations of plant-available P (sodium-bicarbonate extractable) increased
approximately 20% during this period, with significant increases occurring in
land used for tree crops, row crops, and vineyards. The average P concentration
in 1945 was 72 parts per million (ppm) and is now 85 ppm. The improved
fertility status that has occurred will enhance the inherent productivity of
the soil and increase the amount of crop residue that can subsequently be
returned to improve the soil.
Soil Nitrogen (N) and Carbon (C): The amount of total
N and C significantly increased between 1945 and 2001— reflecting an
accumulation of soil organic matter. Average soil N concentrations increased
from 0.09% to 0.29% and soil C increased from 1.06 to 1.34% between 1945 and
2001. These changes in soil organic matter are typically reflected in better
aggregate stability and water infiltration.
Check the soil all through the profile
Soil Texture: The clay content of the samples consistently increased
from an average of 10% to 13% for the period between 1945 and 2001. This
increase in clay content may be a sign of accelerated soil erosion…which would have
a negative impact on soil quality. While this increase in clay content is not
great, erosion of topsoil can have very negative effects on crop production and
water quality. Efforts to minimize soil loss should always be part of a farm management
These results indicate that soil
quality has generally been maintained or improved over the last 50 to 60 years
of intensive management and cropping.
Does that mean that the status quo is fine? No, continued efforts must
be made — especially to minimize soil erosion. The documented improvements in
soil chemical properties and fertility reflect hard work over many years and we
can’t afford to lose the advances that have been made.
However, for some soil properties, we
are still losing ground. For example, a survey of soil test results for California
in the 1980s revealed that between 20% and 40% of the samples were rated as
medium or lower in potassium (K). This number has increased to 44 to 48% in the
most recent surveys. We know that soils cannot be continually cropped and
nutrients removed without depleting their native fertility and quality.
A soil scientist can evaluate suitability
Efforts to maintain high yields and
soil quality are essential for long-term sustainability. Careful management and utilization of modern
technology accomplish this. The technology available in 2003 is beyond the
wildest dreams of the farmers in 1945. For instance, the use of satellite-aided
precision agricultural tools, computer-controlled water management, improved
soil-testing techniques, rapid assessment of plant tissue samples… can all aid
in protecting the quality of the precious soil resource and the environment.
Let’s continue the progress that has been made and sustain our efforts to
protect the soil.