Cover Crop Secrets – Interview with Jeff (Part 1)

Late last year, during my North American seminar tour, I delivered a four-day course in Niagara, on the Canadian side of the falls. One of my attendees was Jeff Rasawehr, the founder of Center Seeds, a Michigan-based enterprise specialising in the supply of cover crop seed. I soon discovered that Jeff possessed a profound understanding of this key fertility strategy. I asked if he would like to share some of his knowledge with Nutrition Matters readers and, thankfully, he was happy to oblige.

Graeme: Thank you for agreeing to this interview. Recent research suggests that it is "the more the merrier" when it comes to cover cropping response. Nature loves biodiversity and it seems she really shows her appreciation when we follow her rules. Have you noticed increased benefits from multi-species blends?

Jeff: We most certainly have. Our regular field trials with our dealers and customer base will often involve up to ten plots. We start with a monoculture, then some three-ways, five-ways and so on. In the last plot we will often just throw in everything that is left. That might involve 15 to 20 different plants. I promote the concept of "diversity by design" but, in all honesty, the smorgasbord of different species in the last plot usually outperforms all of the other trial plots. We always ask that the farmers don't fertilise or use chemicals in these trials and, when analysing the end result, we usually find some deficiencies in the monoculture. However, as you move up in numbers, those problems dramatically reduce. There is much more nutrient density in the multi-crop blends even though no fertiliser was applied. This is all about the biostimulation associated with diverse exudates from the many different plant roots.

Graeme: That is interesting because I was at a farm recently where permaculture principles were practiced. They had created swales (drains on the key lines) along the sides of a barren hillside and had planted out the hydrated mounds created from digging the swales.There were more than forty different species, from fruit trees to vegetables and herbs in each of these swale beds and these were amongst the healthiest crops I have seen. They all flourished in the midst of such biodiversity. There are many lessons to be learned from nature, in a world where we have focused on large scale monoculture.

Jeff: This year, on our field days around the country, the most diverse blends did best on every occasion. The plants had a higher brix, they suffered less disease and insect pressure and they performed better. It is also about diversity within species. For example, this year, we are encouraging our farmers to include 5 different legumes in their blends. There is a greater synergy, even within the grasses, when multiple species are involved. When moving from corn to beans, for example, we would be recommending four species of grasses.

Graeme: What would these include?

Jeff: Well, in North America we would include a cereal rye, an annual rye, triticale and barley. Each of these serves a specific purpose. Triticale is very closely related to cereal rye, but it does have a different release pattern of the nutrients, so you are spoonfeeding nutrients for a longer period to the subsequent soybean crop. Barley is mycorrhizal in the Spring and at that time it also releases a monosaccharide that increases the availability of phosphorus (P) and potassium (K). An increasing body of research confirms that annual rye is something of a superfood. The amount of sugar and protein coming from the root exudates provides huge stimulation of beneficial biology.

Graeme: That’s great information, but what does the cereal rye bring to the party?

Jeff: I really like cereal rye. It is one of the first plants to break dormancy. It is a real quick scavenger of nitrogen, so it pulls nitrogen out of the soil profile, that will be released later. This can have quite an impact on weeds. There are several weed species that germinate when nitrate levels are at around 50 ppm. If we can pull that nitrate nitrogen early and put it in the bank account it can be very rewarding. The nice thing about soy beans is that they need extra organic nitrogen at pod fill and the decomposing cereal rye gives them just what they need, when they need it.

Graeme: It is becoming quite a science to understand each plant's purpose and the synergies between cover crop species. What is your favourite blend?

Jeff: My favourite summer blend would involve 5 legumes, three grasses and a minimum of three brassicas.

Graeme: What would those brassicas include?

Jeff: In my region in Ohio/Michigan, I would be using purple top turnip, daikon radish, and rape. Remember though, that within the radish family, there are different radishes for different purposes.

Graeme: I hear a lot of talk about "tillage radish". It strikes me that this is essentially a marketing ploy. Daikon radish seems to do pretty much the same thing at a cheaper price. Is this the case?

Jeff: Yes the tillage radish is a brand. There are numerous daikon radishes that are comparable at a cheaper price. We offer both options at Center Seeds.

Graeme: I did not hear you mention chenopods in any mixes. Are you familiar with the research suggesting that when five plant families including cereals, grasses, legumes, brassicas and chenopods are combined in a cocktail cover crop, there is an amazing synergistic response? The plant roots begin exuding phenolic compounds (antioxidants), which send the soil life into hyperdrive. All of the multiple benefits of cover crops are then magnified and this fast-tracks desired changes. The chenopods must be present for this phenomenon to occur.

Jeff: I was not familiar with this finding until doing your course. We will most certainly be looking at this inclusion in future blends. We have been passive to date, but we will now get more aggressive on this front. We are particularly interested in spinach and Swiss chard as potential chenopod inclusions.

Graeme: I didn't hear you mention forage kale amongst your favoured species. It is popular in Australia and NZ.

Jeff: Kale has become very popular as a food of late and this has driven up the price of seed. We find that rape pretty much does the same thing. The amount of protein and sugars pouring off the roots of rape is very similar to kale, but the price is much cheaper.

Graeme: I have always been a little concerned about the inclusion of brassicas in cocktail cover crops in that they could potentially inhibit the potential of the other species. They release isothiocyanates that dissuade root knot nematodes, but this biochemical also repulses mycorrhizal fungi. I felt that the presence of this biochemical amongst the intertwined roots of other species that love to host mycorrhizal fungi, might inhibit that hosting.

Jeff: Yes, there is always that potential if you overdo the brassicas. We talk about cover crop recipes as being equivalent to a spaghetti recipe. You have the pasta that makes up the vast bulk of the recipe, then you have the seasoning. We might uses grasses in the summer or oats in the winter as the pasta bulk, but we only ever want to see brassicas as a seasoning. For example, I would never include more than 2 Ibs of daikon radish per acre in my mixes. You need to think like a chef. You would never pour on the whole bottle of seasoning and the same applies with the use of "seasonings" in the cover crop blends. Legumes, brassicas and chenopods are generally used as seasoning.

summer cover crop

Example of a Summer cover crop

winter cover crop

Example of a Winter cover crop

Graeme: You mentioned earlier that in your many presentations around the country you like to highlight six core strategies in relation to cover crops. Would you like to share those six strategies?

Jeff: Certainly. When I see people not achieving the full benefits of a biological program it is usually because you are missing one of the six steps. Number one is respecting the sanctity of diversity. You can sit back with your monoculture and think you are doing the right thing by your soils, but you are not. You must use a diversity of cover crops. Nature loves biodiversity and she always responds when it is provided. You must respect the concept of "green". You must keep the soil covered in green. In the Fall, you plant your cover crops but in the Spring, if you are not happy with plant diversity, then you beef it up. It is all about ensuring good exudates to fire up the soil organisms in spring. Before a corn crop, I may not be happy with the legumes, so I might go in with some fava beans and some lynx peas. Before a soy crop I will check the diversity of the grasses, and, if I am not content, I will plant annual rye. It might only have time to grow three or four inches but, again, it is all about producing sugar exudates to feed the microbes.

Graeme: I guess in your region you have plenty of water. It is a struggle to convince dryland farmers in Australia about the multiple gains of cover crops, because they are always thinking that the cover crop will steal their limited moisture. What would be your response to these growers?

Greg: Actually, moisture efficiency will go up once you get some soil health back. It all changes once you get some fungi going and get some macro aggregates back in your soil. Then, the soil can actually absorb and retain so much more water. In fact, a soil that contains these all important fungal aggregates can absorb between 8 to 20 inches an hour of a single rainfall event. If you have dead sand or dead clay, water will not absorb. It just washes off and floods. I have often been in the desert and seen a one-inch rainfall cause flooding. Sand that has no macro aggregates can not absorb water.

Graeme: We have huge areas of non-wetting sands in Western Australia. Do you believe there is a place for cover crops to help counter this issue?

Jeff: Absolutely! You need to choose species that are very efficient with water. We call them "Summer sippers". You also need to mix in plants whose leaves will go up and then fold down. The idea is to create condensation.

Graeme: Do you have any suggestions for the most suitable plants in our dryland regions?

Jeff: A lot of the brassicas have the right leaf structure. The key is to create humidity and trap condensation. It is trial and error in different areas. I would suggest daikon radish, rape and kale would be worth a trial. Millets are "Summer sippers". They are a super-efficient species that would also be worth considering.

Graeme: Thats some good practical advice. Our growers can try a combination of millet with a little kale and radish. Back to our list of six. What was the second suggestion in your list?

Jeff: Number two is that we avoid all toxicity, to nurture our biology. I visit farmers who think they are becoming more sustainable, but they are still using anhydrous ammonia or heavy doses of salt-based fertilisers. I ask farmers to question every input. They need to ask the question, "Will this input support or compromise my soil biology?", and then make their choices accordingly. I am at your conference because you so obviously understand this issue and you promote an approach where we always work with nature rather than against her.

Graeme: Does this extend to fungicides? In Australia, it can be quite difficult to find seed that has not been "pickled" in a fungicide.

Jeff: No, no, no, no! We should never use fungicide treated seeds in a cover crop. We are trying to promote biodiversity and if we use treated seed we are compromising it from the get go.

Graeme: You seem to have a very pragmatic approach with cover crop design, where every inclusion has a specific biological purpose. Mycorrhizal fungi are one creature that is seriously lacking in most soils. In fact, there are less than 10% of these creatures remaining in our soils. This shortage is a serious issue. Mycorrhizal fungi may well be the most important creature on the planet at this point in time. We now understand that these organisms, alone, generate 30% of all of our soil humus. Humus creation can reverse global heating. I wondered what you had to share about specific cover crops that will encourage mycorrhizal fungi back into our soils.

Jeff: Well it is all about combination. I am a big fan of Dr Wendy Taheri. She is a very competent US microbiologist who has demonstrated that the combination of oats and crimson clover is highly mycorrhizal. I believe that this synergy can be further pushed by augmenting the clover family. I like to throw in a small white and a yellow clover.

Graeme: So theoretically, if you were to plant a cover crop that included oats, crimson clover and some other clovers, it should be a great strategy to include a little mycorrhizal inoculum, like our Platform® product. That way, the new inductees could hit the ground with maximum support and there should be an enhanced outcome. You could seriously boost your mycorrhizal numbers to provide a mycorrhizal matrix into which you introduce your cash crop.

Jeff: Those are exactly my thoughts. I have just organised some Platform® from Dave, your Canadian distributor, for this purpose. I think it is important to also allow for the fact that many of the other grasses are not particularly mycorrhizal, so when the oats die off, we need a Spring replacement. This is where barley can really shine. It is also highly mycorrhizal, so if I come in with some barley for my Spring green, I can help maintain the mycorrhizal push throughout.

Graeme: We have been talking about cover crops so far, but I would just like to branch out for a moment and talk about interplanting. In my travels around the world, I have seen some impressive results when interplanting legumes with cereals. Even on our own research farm, we demonstrated profound benefits from including soy under corn. It was not just the obvious supply of supplemental nitrogen that helped, I would argue that there is another benefit that is equally beneficial. This involves the ongoing delivery of the two most important minerals for photosynthesis – calcium and phosphorus. Legumes release acids that break the bond between locked-up calcium and phosphorus in the soil, and both minerals are then available to the cash crop. We monitored this throughout the corn crop and it was really quite impressive. What is your feeling about the value of interplanting?

Jeff: It is absolutely essential. I have experimented with this on my own farm and we have encouraged many of our dealers and growers to do the same. We have found that it is essential to have a legume beneath the cereal. However, even here, the benefits can be boosted with biodiversity. We are now encouraging the use of four legume species. In fact, on my own farm this season, I will be including some seasonings of interplanted clover that will include just a quarter of a pound of Dutch white, a half pound of alsike clover, six to eight pounds of red clover, a couple of pounds of balansa clover and two or three pounds of crimson clover. The cash crop does so well with all of this support. I have also found benefit in a light sprinkling of annual rye in Spring, but only in conjunction with cereal rye.

Graeme: I am not familiar with the idea of using annual rye interplanted with your cereal crop. What is this about?

Jeff: The University of Kentucky, and others, have shown that there can be some very good benefits from using annual rye in this fashion. It has been shown that the generous, first exudations of annual rye serve as a superfood for soil life. I will choose the cheapest annual rye seed on the market to achieve this early Spring boost. It will cost less than a dollar per acre for this rapid injection of soil food and it is a very good investment. This simple practice was worth 10 to 12 bushels per acre to me on the farm last year and that was also with less fertilisation. I just used a little urea.

Graeme: Are you familiar with the concept of foliar urea? Here you are applying the nitrogen to the leaf in the amine form, which allows a rapid and energy-efficient conversion through to amino acids and proteins. This is actually the most efficient and most cost-effective way to deliver a nitrogen boost and it comes without adding the salts to the soil.

Jeff: No I was not aware of these benefits. It is part of the learning I am enjoying at your course. We find that nutrient uptake of everything, including nitrogen, improves if we can improve the ratio between fungi and bacteria in the soil.

Graeme: We find this to be the biggest biological imbalance in the soil. Almost every conventional soil we test from around the world is lacking the beneficial fungal component. This spells problems with the fungal aggregates that can be so important in a healthy, productive soil. What is the best cover crop strategy to improve the fungi to bacteria ratio?

Jeff: We can boost fungi by boosting protozoa and the best way to do this is to plant peas in Summer. You might include three or four varieties including cowpeas, and you might toss in a sprinkle of fava beans. Boosting protozoa helps to manage bacterial overgrowth while also stimulating fungal numbers.


I trust you have learned something of value from the first half of this interview. If so, you will be keen to read the second half next week, where Jeff shares the balance of his six secrets of cover cropping.

To read Part 2 of this interview, please click here.

Sign up to our e-newsletter to receive the latest articles, product updates and exclusive offers from NTS. Every new subscription receives a free digital copy of Graeme Sait's book, 'Nutrition Rules!'. CLICK HERE TO SUBSCRIBE

comments powered by Disqus