Impact of Organic Production and Reduced Chemical Inputs on Soil Nutrient
Depletion and the Functional and Nutritional Quality of Crops
C.A. Grant, R.B. Irvine, D.A. Derksen, D.L. McLaren, K. Buckley, M.
Monreal, A. Moulin, R. Mohr, Jim House, Brian Marchylo, Nancy Ames
Financial returns from crop production on the Canadian prairies have been
falling, leading to increasingly smaller margins for production. Producers
have attempted to counter this trend by increasing farm size, turning
to off-farm income and attempting to increase productivity and decrease
the cost of production through efficient use of crop inputs. An alternative,
long-term approach could be to increase the value of the crops that we
grow by segregating them from competing products based on higher functional
and nutritional quality. Production systems which reduce or eliminate
inputs of pesticides may enhance the perception of crop quality to consumers
and may also reduce the potential for negative environmental impacts from
crop production. It may also be possible to use crop management practices
to enhance the nutritional quality of western Canadian crops and capture
the value of enhanced nutritional quality for the producer.
Diets worldwide are frequently deficient in micronutrients:
Tremendous strides have been taken since the inception of the "Green
Revolution" to increase global food production in pace with the expanding
food population (Welch & Graham 1999). While malnutrition is prevalent
worldwide, the market views our current food status as excess, with burdensome
supplies depressing prices. However, although caloric production has increased,
nutritional quality of the food supply internationally has not kept pace.
"Micronutrient malnutrition diminishes the health, productivity,
and well being of over half the global community, with impact primarily
on women, infants and children from low-income families (Welch & Graham
1999). An estimated 40% of the worlds population are deficient in Fe,
iodine and vitamin A, while Zn, Se and other micronutrients are increasingly
of concern. Anemia and Zn deficiency are also wide-spread in North America,
particularly among low-income, pregnant females.
Food trends and demographics may increase risk of micronutrient deficiencies:
A number of food trends may influence supply of nutrient in the developed
world. Vegetarianism is becoming increasingly popular. Meat products are
good dietary sources of Zn and movement to diets lower in meat, to reduce
dietary fatty acids will likely result in increases in the number of people
deficient in iron and zinc. A Nova Scotia food survey conducted in 1990
(Gibson 1994) noted that the primary source of iron was pasta, rice, cereals
and breads (44%) while 20 years before meat, poultry, fish and eggs were
the major sources of dietary iron (The nature and dimension of nutrition
and diet-related problems www.hc-sc.gc.ca).
Consumption of organic produce is also increasing. There is a public perception
that current farming practices with inputs of pesticides and chemical
fertilizer produces food of lower quality. However, little information
is available regarding the nutritional quality of grains and pulses grown
using organic as compared to conventional farming methods.
Finally, the population of the industrialized world is aging rapidly.
In Canada, the proportion of people over 65 years is expected to increase
from 12% to 25% by the year 2030 (Guylaine Ferland Diet and Aging: New
Frontiers for Functional Foods? Hc-sc.gc.ca/food-aliment). Older individuals
generally have lower total food intakes, but requirements for some nutrients
increases during aging, due to changes in metabolism. So the diet of elderly
people is often inadequate in certain micronutrients. Foodstuffs with
enhanced micronutrient content may be beneficial to an aging population.
Management practices can influence nutritional content of crops:
Nutrient content of crops is affected by genetics, weather, fertilizer
management, crop rotation, background soil characteristics, and other
agronomic practices which impact on nutrient availability. Western Canadian
producers may have a competitive advantage in the production of crops
with high micronutrient content, since most of our soil resource contains
adequate levels of micronutrients for crop production. However, in the
past, most of our evaluation of micronutrient management was directed
towards increasing crop production through micronutrient application.
There has been little evaluation of the effect of practice such as reduced
input systems or use of compost on crop function or nutritional quality.
Management practices can influence nutrient removal from the soil:
Nutrient accumulation or depletion from the soil will depend on the amount
of nutrients added to the system and amount removed in the harvested crop
or though environmental losses. Long-term sustainability depends on avoiding
excessive depletion or accumulation of nutrients in the soil.
Therefore, nutrient inputs and removal should be balanced both to optimize
production and to avoid environmental damage. This requires an assessment
of the ability of different cropping systems to provide nutrients to the
growing crop and of the long-term balance between nutrient inputs and
This study is designed to evaluate the impact of several cropping systems,
ranging from organic, through pesticide-free production to conventional
management, on soil quality, cost of production, agronomics and final
MATERIALS AND METHODS
A field study was initiated in 2001 on a Newdale Clay Loam soil, located
on the Brandon Research Centre Philips Farm. The study was located on
an area that had oats removed as a green manure crop the previous season.
Pre-plant soil samples were taken and archived for soil nutrient content
and quality analysis.
The experimental design was a split plot with cropping systems as main
plots and crops as subplots. All phases of the rotation were present each
year giving 5 treatments by 4 years by 4 reps for a total of 80 plot per
site. Plot size was 4 m by 10 metres. Total seeded are of trial in treatments
equals 3200 m2.
The cropping systems included a range oaf input intensity, from organic,
with no input of nutrient though to a conventional no-till cropping systems,
with inputs of nutrients and pesticides as required. Crop rotations and
management systems are described in Table 1. Management is responsive
to the conditions of the season, within the constraints of the system.
For example, if disease become a problem on the conventional systems,
fungicides may be used, but will not be used otherwise. Harrowing can
be used for weed control in the organic systems if needed.
Best management practices for each cropping system were used. Weed control
measures in the organic and other herbicide-free systems included tillage
and in-crop harrowing. Nutrient inputs for the systems where fertilizer
use was allowed were based on an assessment of nutrient availability and
requirements for target yield. Compost application in the first year of
the study was based on N requirements and will be adjusted annually.
Table 1: Cropping systems and crop rotations used in the experiment.
C. Nutrient inputs but no pesticides
|| E. Conventional
||durum u/s sweet clover
||durum u/s sweet clover
||durum u/s sweet clover
PFP1 = Pesticide-Free Production: No pesticides are applied to the growing
crop and no residual pesticides may be used. But, pesticides may be used
before and after crop growth begins and in other crops in the rotation.
NOTE: In year 1 of the study, annual alfalfa was seeded where the sweet
clover was called for, since sweet clover is a biennial.
RESULTS AND DISCUSSION May through July of 2001 was very wet at
the experimental site, leading to high disease pressure. Spraying operations
were difficult to time due to the frequent rainfall.
Table 2: Stand density (plants m-2) as a function of management practices.
|C. Continuous PFP
|E. Conventional ZT
Stand density: No major differences in stand establishment occurred
due to management practice (Table 2). Stand density was slightly lower
with conventional NT as compared to the PFP system. This may have been
due to the pre-plant tillage in the PFP system.
Biomass yield: Biomass yield at heading did not differ due to
treatment in the field pea, durum wheat, sweet clover or flax (Table3).
However, biomass production of oats was much higher in the PFP than the
other systems and in lower in the organic than any system which received
Table 3: Biomass yield at heading as a function of management practices
|C. Continuous PFP
Plant diseases were measured in field pea, durum wheat, flax and oat.
The field pea rating for mycosphaerella was from 0 to 9, where 0 was no
disease and for sclerotinia was percentage. Durum wheat and oats were
rated for leaf disease, on a scale of 0 to 11, where 0 was no disease.
Flax was rated for stem and leaf Pasmo and lodging, on a scale of 0 to
9, where 0 was no disease or lodging. There was no sclerotinia, mildew
or rust present in the flax at the time of sampling.
Incidence of leaf and stem mycospaerella was moderate and was not greatly
affected by management (Table 4). In contrast, sclerotinia in pea was
failry low, but was greatly much higher on the organic, organic compost
and continuous PFP systems than on the PFP or conventional systems.
Leaf disease in durum wheat was relatively high, with main diseases present
being septoria leaf spot and tan spot. There was little difference among
the management systems in leaf disease incidence.
Incidence of Pasmo in flax was relatively high while lodging was low.
Again, there was little difference in either disease incidence or lodging
between the two management systems for flax.
Leaf disease in the oats was high. Disease incidence was lower in the
conventional management system than in th other treatments. However, the
difference would not likely be of economic importance.
Table 4: Plant disease rating 1 as a function of management practices
|Plant and disease
||C. Continuous PFP
|Field Pea - Leaf mycosphaerella
|Field Pea - Stem mycosphaerella
|Field Pea - Sclerotinia
|Durum - leaf diseases
|Flax - Leaf Pasmo
|Flax - Stem Pasmo
|Flax - lodging
|Oat - leaf disease
1. Mean rating is given with rank given in parentheses where 1 = best
and 5 = worst.
Seed Yield: Seed yield of field pea, flax and oats did not differ
due to management system (Table 5). The higher biomass yield at head in
the oats did not translate into higher final grain yield. Lodging was
a severe proem in many locations in 2001 and higher biomass production
due to higher N availability may have resulted in greater lodging and
a lower harvest index and grain production. Seed yield of durum wheat
was higher (p<0.0536) under conventional NT management than in the
other production systems, indicating that the durum wheat benefited from
the combination of weed control and nutrient inputs. The organic system
without nutrient input produced the lowest seed yield of durum. There
was little difference in durum yield among the system receiving compost,
the continuous PFP system or the PFP system.
Weed populations were assessed, but statistical analysis has not been
completed yet. Samples of field pea, durum and oats were collected and
submitted for quality analysis to Brian Marchylo of the Canadian Grain
Commission (durum), Nancy Ames of AAFC-Cereal Research Centre in Winnipeg
(oats) and Jim House, Department of Animal Science, University of Manitoba
(field pea). Nutrient concentration will also be measured on all harvested
material. These results are not available yet.
Table 5: Seed yield as a function of management practices
|C. Continuous PFP
We plan on continuing this study for 2 cycles or a total of 8 cropping
years. This will allow maturation of the cropping systems. We expect the
cropping system responses will change over time, as weed, disease and
nutrient dynamics shift in relation to the various cropping systems.
December 21, 2001