Legumes fix nitrogen from the air right? Nope!

When we first moved to the Funny Farm 3 years ago I transplanted some Baptisia australis, a native perennial legume with beautiful flowers, into a couple of the vegetable beds. I got the idea after having visited Carl Jordan's Spring Valley Ecofarms where they were doing research on restoring a worn out farm using an allycropping system. In this system, perennial legumes (mimosa) were planted in widely spaced rows and vegetable crops were planted between the rows. The perennial legumes were cut to the ground several times during the growing season. The prunings were used as mulch around the vegetables where they would decay and slowly release nitrogen and other nutrients that would be used by the vegetables. Also, after pruning, the mimosa would slough off roots which would allow nitrogen stored in root nodules formed by nitrogen-fixing bacteria to be released into the soil which would then be available to the vegetables as well. The bacteria are the organisms that fix nitrogen from the air not the plants. If the bacteria are not present to colonize the roots no nitrogen is fixed.

When leguminous crops, (beans, peas, clover, alfalfa, vetch) have been colonized by nitrogen-fixing bacteria, yields are greatly improved. Once the crop has been harvested or, in the case of a cover crop, plowed into the soil, the crops planted next will benefit from the nitrogen as well. We gardeners and farmers also benefit by not having to apply additional costly nitrogen fertilizer.

We can be sure that our crops are being colonized by nitrogen-fixing bacteria by inoculating our seeds. I purchase inoculant from Johnnys Seed Co. and treat my seeds before planting or during planting. Different species of legumes are colonized by different species of bacteria. Soybeans are colonized by Bradyrhizobium japonicum; clovers and alfalfa by Sinorhizobium meliloti, beans by
Rhizobium leguminosarum biovar phaseoli. It is important that you choose the right inoculant for the crop you are growing. Johnnys sells an inoculant that has a mix of different species that will inoculate snap beans, field type peas (black eyed or southern peas), english and sugarsnap peas.

The bacteria may persist in the soil for several years. however, I inoculate my seeds every year to be sure I am getting the benefits of nitrogen fixation. A bag of inoculant is enough to treat 8 lbs. of seeds and costs about $6.00; well worth the investment in my opinion. There are native species of these bacteria but they may or may not be present and they may not be efficient nitrogen fixers. The plants can sense whether or not the bacteria can help them and will select those the best to come colonize their roots. There is much communication between the plants and the bacteria in this symbiotic, mutualistic relationship between species.

It takes about a week for root nodules to be visible and about 3 weeks for nitrogen fixation to start taking place. You can determine whether or not your crops have been colonized by carefully digging up some of the roots with a trowel and looking for nodules. If you slice a nodule open and the inside looks pink or red, nitrogen fixation is taking place. The plants and bacteria together produce a molecule that is similar to the hemoglobin in our blood which carries oxygen from the plant to the bacteria. The red color comes from the presence of iron in the molecule which also makes our blood red. Adequate supplies of iron in the soil are necessary to make this process happen.

Permaculturists often plant leguminous plants in the same hole with fruit or nut trees so that the young food producing trees can benefit from the nitrogen fixation within the roots of the legume. After several years the legume is removed or cut down allowing the food tree to grow on.

This fall I dug the Baptisia out the the beds and moved them to our orchard where they will help feed our apple trees. They were nicely colonized with large nodules of bacteria which you can see in the picture below.

Choosing Varieties that Work in our System

Each year we trial new varieties of crops in the never-ending search for those that produce well for us. We are looking for ones that can withstand the extremes of high temperature, humidity and often low rainfall (drought) that we experience in the summer here in Georgia. Our climatic conditions can put great stress on our crops making them more susceptible to insect and disease pressures. Additionally, night temperatures in the 70's and daytime temperatures in the 90's for days on end cause plants to go into survival mode. They stop producing flowers and fruit.

We grow some hybrid varieties and some open-pollinated varieties. Many hybrids have been bred to withstand disease or insect infestations. Many open-pollinated and heirloom varieties do not have these traits although some do. We take this into consideration when making our choices. We look for varieties that have been grown successfully in our area for a long time. We want varieties that taste good and produce a good yield for a long period of time.

Here are a few examples of how we make those decisions. We will start with zucchini and squash. We stopped growing yellow squash for 2 reasons. The first is that most of the other growers at our markets grow it so we do not need to compete with them. Additionally we have not found a variety that produces well for us. Insects and diseases always take them out early. This year we decided to focus on zucchini. We planted 2 heirloom varieties from Europe. One was ronde de nice, a French variety, and the other was costata romanesco, an Italian variety. Both varieties showed good resistance to disease and insect pests. We only lost a couple of plants to the dreaded squash vine borer. The ronde de nice plants grew well, the fruit was tasty and looked good but produced very little fruit. The costata romanesco grew well and produced great tasting fruit over a long period of time. That variety also produced plentiful male blossoms which we were able to harvest and sell to a restaurant. Guess which variety we will be growing next year. The previous year we had success with an old open pollinated variety called simple long grey. We will be adding it back to the mix next year as well. Delicata is an open pollinated variety that does well for us too.
Next are tomatoes. Our main tomato variety is Big Beef, a hybrid. It consistently produces tasty, good sized fruit and is pretty resistant to the ubiquitous early blight we get every year. We also do well with Tomatoberry, another hybrid introduced by Johnnys Seed a couple of years ago. It produces strawberry sized and shaped fruit that are very tasty. It excels late in the summer when other varieties have given up. We still have one plant that is cranking out lots of fruit in November. Amana Orange is an heirloom variety that is my favorite tomato for flavor. It does not produce a lot of fruit but it is a market favorite so we can get a premium price for it all summer. This year we tried San Marzano. The plants grew strongly at first but were the first to succumb to the blight. We will be looking for another paste type variety next year, probably we will go back to Roma. We also tried Sungold II. It did terribly. Another one we like a lot is Eva Purple Ball, another heirloom variety that does well. Flavorful and crack resistant, it produces well too.
The final example is butterbean. We love them but had not devoted space for them in the past. This year we planted a short row of Violet's Multicolored. Here is the description from Southern Exposure Seed Exchange:

80-90 days [Banks County, GA, saved by 4 generations of Violet Brady Westbrook’s family.] A rainbow of colors – cream, beige, red-brown, and violet-purple, with speckles and swirls. Small seeds have great flavor, good both fresh or dried. 3-5” pods. Semi-bush plants have good disease- and drought-resistance.

They lived up to the description in every way except 1. They were not even close to being semi-bush. The vines grew to be 12' long. It was fortuitous that i did not read the description on the package again before planting so i built a tall trellis for them to grow on. We saved the beautiful seeds for planting next year.

We grew several other crops too. Marketmore cucumbers did great for us. Provider bush green beans have done well in the past but struggled this year with the heat and drought. We have a difficult time with peppers. This season we will continue to hunt for pepper varieties that will do well for us. We will be trying new techniques to protect the eggplants from flea beetles and potato beetles.

I read a research study yesterday about the declining nutritional quality of fruits and vegetables over the last 50 years. The conclusion of the study was that hybrid varieties that were bred to produce a large yield at the expense of nutritional value was a big factor in this trend. We will be taking that into consideration when we are salivating over seed catalogs in the next month or two.

After all we are what we eat!