By Helen Atthowe. Helen farms in western Montana where there is a 100 day growing season with freezing winters, a dry climate and good loam soil. Her website is

Now that I have stopped using animal manure, people ask me if it is really possible to raise vegetables commercially without it. It has been a journey. I began farming in 1993 using a living mulch system. In this system, clover was planted in between crop rows and maintained as an undisturbed cover crop during the growing season. The cover crop, or living mulch, was mowed several times each growing season to control annual weeds that came up through it and to cycle organic residues back into the system on a regular basis. Each spring the clover was tilled in and became the planting bed for the next growing season. Then I planted another clover cover crop in between the new crop rows. Compost made from manure, clover cuttings, crop residue and hay was added to the entire field and incorporated every spring with the clover living mulch.

Over a twelve-year period, soil nutrient levels and soil organic matter increased. We also found higher numbers of predator and parasite insects in the living mulch. We kept track of soil fertility and our applied amendments, and soon realised that we did not need to add so much compost. We decreased compost application rates from 10 to 5 to 2 tons per acre and finally stopped making and applying compost in 2003. That saved a lot of labour and tractor time and, for the first few years, yields were as high as when we applied manure-based compost.

The experiment

The experimental field, with minimum and no-till rows on either side of the untilled control in the centre

In 2004 we decided to experiment with greater in-field vegetation diversity and further reduce tillage. To do this we moved to a new field and set up organic minimum and no-till experiment plots. The new field had been in pasture for 50 years. In April 2005 we undercut and turned over the pasture 4in to 6in deep, then disked twice (shallow tillage) and let it dry out. We left a 600ft by 30ft strip of untilled permanent pasture in the centre separating two 2.5 acre tilled sections. This strip was our “untilled control”. We performed soil tests on the untilled and tilled sections of the new field two weeks after tillage. Soil nitrogen levels doubled when we tilled this 50-year-old pasture, but organic matter levels dropped slightly. In May we disked twice more and seeded a cover crop of triticale and red clover. The cover crop was mowed to 3in tall in September 2005. By autumn 2005, the six-acre field was virtually weed free and mostly red clover. In the spring of 2006, it was time to plant vegetable crops. We mowed and flamed the red clover in no-till rows and planted Brussels sprouts transplants in double rows into a 600ft by 3ft strip of flamed clover. The row middles were 4in wide and remained as undisturbed, untilled red clover. Broccoli and cabbage were planted in nearby minimum tillage rows. In these rows, twoyear-old red clover was chisel-ploughed with a one-shank chisel plough to make 3ft by 600ft rows. The 3ft rows were tilled using a 3ft cultivator before planting. Double rows of transplants were planted in the 3ft beds. The 4ft row middles were left in undisturbed, untilled red clover and mowed periodically. In 2006, we performed soil tests on the untilled pasture strip control, minimum-till vegetable rows, no-till vegetable rows, the undisturbed and untilled clover planted in 2005, and a strip of the same clover that was mowed in July of 2006.

The results

Healthy rows of peppers with clover cover crop

Nitrogen levels jumped from 16 ppm in April to 83 ppm in May and June after early April incorporation of red clover into the minimally-tilled rows, with no compost added. Where we added manure-based compost to the 3ft row and tilled in the compost and clover, nitrogen levels rose to 103 ppm in May and June. Nitrogen levels in the no-till plots, with no compost, rose to 30 ppm by June first. In July and August, nitrogen levels dropped in the minimum-till plots with and without compost, but nitrogen levels remained stable and increased slightly in the no-till plots.

Nitrogen levels were lowest in the control, untilled pasture strip and continued to drop to extremely low levels by August. In the area of the field that remained in untilled, undisturbed red clover, nitrogen levels also dropped over the season. But nitrogen levels did not drop as low as in the untilled pasture control strip. So, it seems that the clover did not use as much nitrogen during the growing season as the pasture grass, but neither did it release any measurable amount of nitrogen. We mowed a 6ft by 600ft row within the untilled clover field on July 1, 2006 to see if that would increase nitrogen release. We were surprised to find that the opposite occurred in the short run. Four weeks after mowing, nitrogen levels were still dropping and were lower than in the unmowed clover. We suspect that soil microbes, busy decomposing the mowed clover, were tying up available nitrogen temporarily. The crop yield was good in all the minimal till sections and not good in the no-till areas.

The lessons

There are some practical take-home lessons from this journey experimenting with growing my own fertilizer and reducing tillage.

First, it is possible to maintain good levels of plant nutrients for commercial vegetable production without using manure, and instead growing legumes which are minimally tilled-in each season.

Second, growing untilled legumes, either mowed or unmowed, does not provide enough plant nutrients for commercial vegetable production, at least in the first few growing seasons. Mowed, untilled legumes do, over time, increase soil organic matter levels and provide a foundation of slow-release plant nutrients. In our 10-year living mulch study, spring nitrogen levels started at 15 ppm in 1993 and ended at 44 ppm in 2003 with peaks of 80 to 82 ppm during 1996- 1999. Thus, one important thing we learned is that growing clover as a living mulch between crop rows and tilling it in each spring results in a long-term soil nitrogen increase.

Third, a combination of reduced tillage and tilling in legume cover crops (or living mulches) may be the best way to provide the nutrients that crops need for good production and also steward long-term soil health. If we want to maintain soil organic matter levels, we need to till less. Below-ground carbon in plant roots turns over more slowly in the soil, and hence provides a stronger organic matter framework, than does above-ground carbon in shoots and leaves. This is an important thing to consider when comparing the growing of plant-based soil amendments to manure. Long-term soil organic matter will not be maintained as well with manure amendments.

The journey never ends and I am still experimenting with the best ways to grow my own fertilizer!

This article appeared in Growing Green International magazine Num 29 (Summer 2012), p26.