Are Livestock And Forages Needed On Organic Farms?

by K. Liu, A. Hammermeister and F. Willick

The sustainability of cropping systems is largely affected by soil nutrient management and crop selection. Generally, organic farmers enhance soil quality by carefully selecting their rotation crops and recycling nutrients through livestock on the farm. Many farmers, however, do not have livestock on the farm, and some do not include forage crops in their rotation. Farmers are asking "How important is it to have forages and livestock on an organic farm?"

A four-year study examining this question was established at the Nova Scotia Agricultural College. The study investigated the sustainability of farming systems with or without forages in rotation, and with or without access to composted livestock manure as an amendment.

Forage, including legumes and grasses, is a valuable crop in rotations because it enhances soil organic matter and nutrient cycling, and breaks pest cycles. In the study, three separate rotations were established: one with no forage, one with one year of forage and one with two years of forage.

Livestock manure is a valuable resource for on-farm nutrient management. Farm livestock may be classified as monogastric (e.g. poultry and pigs) or ruminant (e.g. cattle and sheep). The food these livestock groups eat and the manure they produce are different. When their composted manure is applied to the field, it has different influences on soil fertility. In the study, three soil amendment systems were studied in each rotation.

In the first soil amendment system, researchers used alfalfa meal as the primary nitrogen source, forages for mulch on potatoes, cereal straw was retained on the plots, and phosphorus and potassium requirements were met using approved mineral amendments. In the second system, forages were sold for animal feed, cereal straw was removed for bedding, and composted poultry manure was applied to provide nitrogen and phosphorus to the field. In the third system, the forages produced were used as feed, cereal straw was removed for bedding, and composted beef manure was applied to meet nitrogen and phosphorus requirements.

All of the plots grew potatoes in the last year of the rotation in order to measure the effect of the previous three years of management on crop growth and soil quality. Each potato plot was split into two parts, one receiving soil amendments (compost or alfalfa meal) according to soil test recommendations, and the other receiving none.

All the research plots were established on land that had been in long-term pasture; the land had been grazed and had previously received manure applications. As a result, soil fertility levels were medium to high.

Although the researchers expected to find the best potato yield in the plots with forages in the rotation, they found higher yields in the rotation with no forage. This may be due to the high background fertility of the soil and the effects of tillage on releasing nutrients in the short-term. Potatoes also need good soil structure in the seedbed; the rotations with forages may have had poorer seedbeds because of the slow decomposition of sod and the slower nutrient release.

Considering soil amendments, the highest yields were found in plots with composted beef manure. The combination of composted beef manure with a no-forage rotation had the highest potato yields, followed by the combination of composted beef manure with a two-year forage rotation, but the difference between these two was very small. Rotations using composted beef manure had the highest nitrogen uptake by plants and the highest above all was the two-year forage rotation receiving beef manure.

These results may be explained in part by looking at the amendments. The beef manure compost was made from typical manure with straw bedding. The compost made from poultry manure was mixed with wood chips and some grass clippings. This compost may not have provided as much nitrogen as was expected because wood is difficult to decompose and the process ties up nitrogen. Other studies indicate that alfalfa meal is slow to release nitrogen.

So, how important are forages and livestock on organic farms? Organic farming systems are a complex subject to study. If land is transitioning from fertile old pasture, the benefits of forage in rotation will not be evident, as the benefits of forages come in the long-term. Likewise, the benefits of compost may not be seen in the year of application. Applying compost well in advance of the crop that will need it is recommended.

Kui Liu is a Ph.D. student at the Organic Agriculture Centre of Canada. Please send comments or questions by phone to 902-893-7256 or by email to oacc@nsac.ca.

Posted on the OACC website, March 2006