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

2001 Report

RATIONALE
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 outflows.

OBJECTIVE
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 crop quality.

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.

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.

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 nutrient inputs.

Table 3: Biomass yield at heading as a function of management practices

Plant Diseases:
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

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

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.

en français


December 21, 2001