Paul Fixen, Potash and Phosphate Institute, Brookings, SD

1996 will begin the eighteenth consecutive year of our involvement in a sustainable-organic farming system. The last time any chemicals or synthetically produced fertilizers were used on our farm was in 1978. Until that time we practiced "conventional" farming. But no matter what the focus is in any particular method of farming there are a few basics that are becoming more clear to me as time moves on:

1. we are able to exist because photosynthesis takes place in plants.

2. Plants thrive when anchored in a healthy, vibrant fertile soil.

3. If soil fertility can be maintained, many other goals are more easily attainable, therefore the focus of any system should be to build and maintain a fertile soil.

In our system we have tried a number of things, some were quite successful some not quite so successful. Of these I would like to zero in on three or four that we deem essential in maintaining soil fertility.

1. Green manure crops - CLOVER - Yellow Blossom Sweet Clover plays a vital role in our soil maintenance system in at least three ways.

(a) Nitrogen fixation - 80% of the atmosphere by weight is nitrogen gas - over each acre of land there is 70 million pounds of nitrogen - enough to provide the nitrogen needed to grow one million bushels of wheat - if it were available to the crop. In our area, clover seems to be the most efficient legume to fix nitrogen. A crop monitored on our farm showed a yield of 4300 pounds per acre of dry matter in the top growth and 800 pounds in the roots. That yielded 105 pounds of actual N in the tops, 15 pounds in the roots for a total of 120 pounds of actual N placed in the soil. Testing over the next three years showed availability of 25% of this the first year, 40% the second and 10% the third, indicating a slow but rather efficient release.

(b) Soil building and structural improvement - as well as fixing nitrogen, the deep penetrating clover roots bring up phosphorus that is out of reach of cereal grains. This is translocated into the clover plant and returned to the soil surface. The roots also open up the soil, enhancing water retention and root development of future crops.

(c) Clover is an excellent weed suppressant, being very competitive, breaking weed cycles and having an allelopathic effect on many weeds.

(2) A second essential is crop rotation. As different crops have different requirements and contribute differently to the soil, a crop rotation on one field over the past six years is as follows:

• 1990 - Green manure
• 1991 - Wheat
• 1992 - Oats
• 1993 - Peas
• 1994 - Rye
• \995 - Oats - underseeded to brome & alfalfa

We have found about 5 years to be the limit of our rotation, after this we need a green manure crop to boost the fertility again. Also we try to place a legume - peas, lentils - somewhere in the middle.

(3) Diversification: Livestock play an important role in the overall plan to maintain soil fertility.

(a) At any given time about 1/3 of our cultivated acreage is seeded down to grass and legumes. These grass-legume mixtures improve soil fertility and structure. We practice mostly a three or four year rotation - underseed with a companion crop, harvest and or graze for three or four years, then back to cereal production. Three years "down" seems to be the most efficient time frame for soil building, water conservation and weed control.

(b) Manure from the livestock - some raw, some composted, provides valuable nutrients as well. Our cattle operation allows us to manure about 40 acres per year.

(4) Quirks and observations:

• Although legumes are the main source of green manure, on occasion we will use anything - cereal crops, weeds, etc.
• Plants in a vital soil seem to have the ability to seek out the micro-nutrients they need composted manure releases nutrients immediately - seems to "mix" with the soil and aid growth.
• Nitrogen release from a green manure crop is a slow release - over three years or so.
• Just when you think you have all the answers, someone goes and changes the questions!