Studies on Soil Sustainability: The Effect of Forages and Livestock in Organic Agricultural Systems

Kui Liu, Dr. Andy Hammermeister and Dr. Ralph Martin

The benefits of including perennial forage crops in an organic farming system have long been recognized. Forage crops help build soil organic matter, which can become a source of nutrients for subsequent crops and also help improve soil structure. The improved soil can hold more water, is better aerated, and is less likely to erode or compact. A perennial forage crop also breaks the cycles of weeds, diseases, and insect pests. Many organic farms raise livestock to utilize forages from the crop rotation. The livestock help to diversify farm income and utilize the by-products of other crops. Also, since different animals are suited to utilizing different types of feed, they have different roles in the organic system. For example, ruminants such as cattle and sheep can make good use of forages whereas mongastrics such as chickens and pigs, which are less effective at digesting forage, can utilize surplus grain or protein crops.

However, many organic farmers do not raise livestock for reasons relating to land suitability, farming background, markets, profitability, or personal philosophy. On these farms growing perennial forages can represent an economic loss, as it removes land from production for up to five years. Selling hay could reduce farm sustainability by removing nutrients that would otherwise stay on the farm and be used in the production of alternative cash crops. It can also be argued that in an organic system the benefits of perennial forages can be achieved through careful management of crop rotations. Diversifying the rotation and growing fall-seeded and green manure crops are techniques commonly used to break pest cycles and improve soils in stockless organic systems.

The manure from livestock can be a valuable resource for managing soil fertility in an organic system. The high availability of nutrients, especially nitrogen and phosphorus, in manure makes it valuable in areas such as the prairies. However, in areas such as eastern Canada, the land base available for safely disposing of manure is smaller so nutrient loading may become a problem on livestock operations. Also, the manure produced by ruminants and monogastrics can be quite different in nutrient content, and will need to be managed appropriately if the system is to be environmentally sound and sustainable.

The question of whether to include perennial forage crops and livestock in an organic farming system is therefore an important one for individual organic farmers as well as for the organic farming industry as a whole. It is not known for certain whether livestock and forages are essential for cycling energy and nutrients on the farm, or whether organic farms can be sustainable without livestock and forage crops.

To help address these issues, the Organic Agriculture Centre of Canada and the University of Manitoba are partnering in a four year crop rotation experiment. The experiment is designed to address questions related to the agronomic, economic, and environmental benefits of including perennial forages and livestock in an organic system. The researchers will examine the optimum number of years to include forages in a 4-year rotation and assess whether ruminant or monogastric livestock can help increase soil sustainability on organic farms. Specifically, they hope to determine how the number of forage years in a rotation and the inclusion of livestock in the organic system affect soil properties; weed biomass and nutrient uptake; crop growth, development, biomass, and nutrient uptake; and crop yields and economic returns.

The experiment was established in 2002, on cultivated research land in Manitoba and on fall (2001) ploughed pastures in Nova Scotia. There are three forage systems combined with four livestock systems, for a total of twelve treatments:

• Forage systems: 0, 1, or 2 years of forage in the rotation;
• Livestock systems: stockless without amendment, stockless with amendment, monogastric livestock (poultry), and ruminant livestock (beef and sheep).

The basic crop rotation under study is wheat, soybean, barley, and potato, with forages replacing soybean and/or barley in the rotations including forages. The forages will be underseeded in the previous crop. Alfalfa meal and other organically approved mineral nutrient sources will be used in the stockless system with amendments. Composted manure (poultry for the monogastric and beef/sheep for the ruminant) will be used in the systems with livestock, and organically approved mineral nutrients will also be used if required. Amendment application rates will be based on soil test recommendations for each crop.

While livestock are not directly part of this experiment, each system will be managed according to the normal practices for that particular system. In the monogastric-forage rotation, it is assumed that the forages will be sold off the farm and the monogastric animal manure will be returned to the field through monogastric compost. In the ruminant-forage rotation, it is assumed that the forages will be consumed by the ruminants and ruminant animal manure will be returned to the field through ruminant compost. In the stockless forage rotation, it is assumed that the forages will be used as mulching between the rows in the potato plots.

Input costs and financial returns will be monitored so that the economic sustainability of each system can be evaluated. To assess how the number of years in forage or the inclusion of livestock affects soil properties, crop production, and weed populations, the following measurements will be taken:

• Soil: The capacity to provide plant available nutrients will be determined with a plant root simulator (PRS^TM) probe using root exclusion cores. Measurements will also be taken for total carbon, readily oxidizable organic carbon, mineral nutrient concentrations, enzyme activities, and microbial biomass.
• Plant: Measurements will be taken for plant density, biomass, yields, and nutrient content in the biomass.
• Weeds: Weed density and biomass will be recorded.

Preliminary (2002) results from the plots in Nova Scotia indicate that plots receiving no compost (i.e. where alfalfa meal was used as a nitrogen source) were delayed in their early development as compared to plots that received compost. This delay in development seemed to result in a slightly lower crop yield and kernel weight. There was also some indication that the number of weeds in a plot did not affect yields, which seemed to be more affected by the size of weeds and their total weight.

Researchers:
Kui Liu (Ph. D. Student), Dr. Andy Hammermeister, and Dr. Ralph Martin
Organic Agriculture Centre of Canada
PO Box 550
Truro NS B2N 5E3
Contact: Andy Hammermeister ahammermeister@nsac.ca
Tel: 902-893-8037

Funding Sources:
This project is funded as a NSERC Core Experiment.


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