Notes to broadcasters
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Plants, like people and animals, need food. Plant nutrients such as nitrogen, phosphorus and potassium are needed for the growth and development of crops and trees. But African smallholder farmers are facing a major problem as soil fertility declines from continuous cropping without replenishing soil nutrients. Smallholder farmers have few affordable options which are compatible with both the physical and chemical state of their soils. This is partly because smallholder farmers’ access to inputs such as improved seed, fertilizers and pesticides has deteriorated in many African countries since the removal of subsidies on mineral fertilizers and other agricultural inputs.
One option for farmers is to add nutrients (called plant foods in the script) to the soil by using manure, compost or natural fertilizers. Biological sources of fertility or biofertilizers have the potential to increase yields of legumes and plants which follow them in rotation, as well as reducing the use of chemical nitrogen fertilizers. They are also much more affordable than synthetic fertilizers.
You might want to supplement this script by adding an interview or a post-program discussion with a local farmer or agricultural extension worker who is familiar with the benefits of rhizobial bacteria and biofertilizers.
Script
Characters:
Host
Mr. Tomato, a jovial, jokey character
Ms. Bean, sophisticated and articulate, looks down on Mr. Tomato
Mr. Rhizobium, articulate and straightforward
Host:
Welcome to the program. Many farmers are facing problems with declining soil fertility. But wouldn’t it be a good thing if your crops could talk directly to you and tell you exactly what they need? And what if your soil could talk too? What do you think it would say? (Pause) Well, we all know that plants and soil can’t actually talk, at least in English (replace with language of broadcast). But today, through the magic of radio, we are going to bring you an interview with two very important plants and a very special guest, who you’ll hear from later in the program. So stay tuned – you’re about to hear some important news.
Musical break for 10 seconds, then fade under host and out.
Host:
Plants, like humans, need good food. But have you ever heard a plant talk about what it needs to eat? Today we are privileged to have two special guests in our studio. Welcome, Mr. Tomato and Ms. Bean.
Mr. Tomato:
It’s good to be here. And thank you for providing water for my roots (chuckling).
Ms. Bean:
Thank you for inviting me.
Host:
I’ll start with you, Mr. Tomato. Can you tell me what you need to be strong and healthy?
Mr. Tomato:
Well, we all know how much I like to drink (laughing). Yes, I need a lot of water. But I won’t go into that today. I’ll get right to the point. Here are the kinds of food I need to be big and healthy. The most important three plant foods I need from the soil are nitrogen, phosphorus and potassium. I know that all soils have some of these three foods. But I’ll tell you honestly. Many of the soils I have been in lately were pretty poor.
Host:
I thought all soils contained these foods.
Mr. Tomato:
Not so fast, young (woman or man). We know that crops need to take plant foods from the soil. And we also know that these foods are used up every time a crop is grown, especially when no fertilizers are added to replenish them. But even when these plant foods are in the soil, they’re not always available for me to eat. For example, there’s lots of phosphorus in the soil that I can’t use because I just can’t digest it. And there’s lots of nitrogen in the air… (pause) but I won’t take all the attention, Ms. Bean – you can tell us all about nitrogen later.
Ms. Bean:
Thank you. It would be my pleasure.
Host:
We’ll look forward to that, Ms. Bean. Mr. Tomato, do you have any advice on how farmers can make sure that their soils contain enough plant foods to make their crops grow big and healthy?
Mr. Tomato:
Well, some farmers use synthetic fertilizers. But these can be very expensive. So what I recommend are biofertilizers.
Host:
Biofertilizers? What are biofertilizers?
Mr. Tomato:
Biofertilizers are natural sources of plant foods – things like manure, compost, green manures, and so on. You can use crop residues, kitchen waste, and all sorts of things to make biofertilizers. In fact, although I love a good, long drink of water more than anything else in the world (chuckling), good compost is my favourite food.
Host:
So biofertilizers give you nitrogen, phosphorus and potassium?
Mr. Tomato:
And so much more! They provide all sorts of other plant foods as well – things like calcium and magnesium, as well as other foods that I need in smaller amounts – like manganese, copper, iron and zinc. Composts also help the soil hold lots of water. And you know how I like that (laughing)!
Host:
Thank you, Mr. Tomato. And now I would like to hear more about nitrogen from you, Ms. Bean.
Ms. Bean:
Well, let me start off by informing you that I am a very special type of plant. I am a legume. Legumes have very special talents.
Host:
What kind of special talents?
Ms. Bean:
Well, I believe Mr. Tomato let it slip (coughing as if she doesn’t even like to say his name) … that there is a lot of nitrogen in the air.
Host:
Right.
Ms. Bean:
What he didn’t tell you is that legumes have the special talent of being able to remove that nitrogen from the air and turn it into nitrogen that plants can use.
Host:
Really? How do you do that?
Ms. Bean:
It’s quite simple really. (coughing and starting a lecture) You see, a single teaspoonful of soil contains millions of micro-organisms such as fungi and bacteria. Most of these micro-organisms are helpful to the crop and to the farmer. Some of them live together with plant roots in a kind of partnership.
Host:
Can you give me an example?
Ms. Bean:
Certainly. For example, there are little lumps on my roots called nodules. A very special kind of bacteria called rhizobial bacteria live in those nodules. It is this bacteria’s job to make nitrogen. So here’s the bargain we have: the bacteria make the nitrogen and I give the bacteria a place to live – the nodule. I also supply carbon and energy which help the bacteria make the nitrogen.
Host:
So beans have a special relationship with these bacteria?
Ms. Bean:
Not just beans – all kinds of legumes. Pigeon pea, peanut, bambara groundnuts, Leucaena, Acacia, clover… There are many legume crops, shrubs and trees. And almost all of them have this partnership with bacteria.
Host:
I have a question for you, Ms. Bean. If I’m a farmer, how do I know that a legume is taking nitrogen from the air and putting it into a nodule?
Ms. Bean:
Well, I could answer that question, but I think it’s time to introduce our very special guest.
Host:
Yes, I think the timing is right. Thank you, Ms. Bean. Mr. Rhizobium, welcome to the show. Could you tell us a little more about yourself?
Mr. Rhizobium:
Certainly. I am a bacterium. To be more precise, I am a rhizobial bacterium. As my good partner Ms. Bean said, I take nitrogen from the air and turn it into usable nitrogen inside the nodule which she so kindly provides for me.
Host:
How does a farmer know if a legume is taking nitrogen from the air and transforming it in the nodule?
Mr. Rhizobium:
It’s quite simple. Nodules can be easily seen on the roots of crops and trees. It is most easy to see them at flowering time. Good nodules are plump. If you cut them open, they’re pink or red or sometimes black. Shrivelled and small green or white nodules are not working well. They’re not creating nitrogen very well.
Host:
So what can a farmer do if a legume is not fixing nitrogen?
Mr. Rhizobium:
If the legume isn’t fixing nitrogen, it’s often because you don’t have the right kind of bacteria in your soil. You see, certain crops have better relationships with certain types of bacteria than others.
Host:
What can a farmer do in that case?
Mr. Rhizobium:
The best solution is to use an inoculant.
Host:
What is an inoculant?
Mr. Rhizobium:
An inoculant is a product which contains different types of bacteria. You can find inoculants at some farmers’ stores, from Ministries of Agriculture, or from research stations or universities. They’re quite affordable. Usually inoculants are mixed with peat and come in a package with instructions on how to use them.
Host:
Well, that sounds like a good place to stop for today. Let’s summarize all we’ve heard. We’ve learned that plants need plant foods from the soil, and that biofertilizers are an affordable and effective way to add these foods to the soil. And we’ve learned about the special relationship between legumes and the bacteria that live in nodules on their roots. (Pause) I want to thank all our guests very much for speaking with us today.
Mr. Tomato:
Thank you. And can I have another drink of water (laughing)?
Ms. Bean:
It was a pleasure to be with you today.
Mr. Rhizobium:
Thanks for the opportunity to speak today.
Host:
Thank to all our listeners and goodbye for now.
Acknowledgements
Contributed by: Vijay Cuddeford, managing editor, Developing Countries Farm Radio Network.
Reviewed by: Anthony Anyia, Research Plant Physiologist, Alberta Research Council, Canada.
Information sources
- Mike Carter, 1991. Partners in Plant Production: Rhizobia and Mycorrhizae. Footsteps, volume 7, June 1991.
- Hannington Odame, 1997. Biofertilizer in Kenya: Research, production and extension dilemmas. Biotechnology and Development Monitor, No. 30, p. 20¬23.
- Atomic Energy Agency, 1997. Small Farms: Big Gains: Zimbabwe Advances the Natural Way.
- Biofertilizers – the natural way? New Agriculturist, volume 98-7, 1998.