Notes to broadcasters
The lack of available phosphorus for crops is a serious constraint for many farmers in sub- Saharan Africa. Agroforestry practices such as the use of improved fallows can help farmers to increase nutrient inputs (especially nitrogen) and improve soil structure. Unfortunately, improved fallows alone cannot improve levels of phosphorus in soils. An inorganic source of phosphorus (either chemical or mineral fertilizer) must be added to the soil in order to overcome low levels of phosphorus which cause stunted growth and reduced yields.
The following script reviews some of the benefits of improved fallows, and encourages farmers to consider the need to add phosphorus to their soils before they resume using the land for cultivation.
Script
Characters
In this program, the hosts are named Onyango and Rose. Please use names that your audience will relate to and recognize. Rose is very knowledgeable on the topics of agriculture and agroforestry. Onyango is also very keen and asks many good questions, but sometimes seems impatient. The two have a playful way of responding to each other.
Start of program
MUSIC TO INTRODUCE PROGRAM. FADE OUT MUSIC.
Onyango:
Hello and welcome to the show. Today we want to talk about improved fallows and the importance of adding phosphorus to increase soil fertility when using improved fallows. To begin, can you describe what improved fallows are for our listeners, Rose?
Rose:
Sure, Onyango! First, let’s remind people about the difference between a normal fallow and an improved fallow. A normal fallow is land that is resting – land that is not being cultivated at this time. The farmer has not planted maize or sorghum, but has left the land to re-grow naturally. Often this is done to allow the land to restore its fertility.
Onyango:
Yes, of course. So then what is an improved fallow?
Rose:
Don’t worry, I’m getting there! Improved fallow is also land that is resting, but the farmer has planted a special cover crop to improve soil fertility.
Onyango:
Improved fallows have been very much promoted in our community. Stay tuned to hear more about how farmers can benefit by using improved fallows.
MUSICAL BREAK (5 seconds).
Onyango:
Welcome back to the show. We’ve just been talking about improved fallows – a method that you can use to improve soil fertility on your farm. We’ve said that a farmer plants a special cover crop to help improve soil fertility.
Rose:
Yes. Farmers can plant shrubs on their land. We recommend shrubs such as Sesbania or Crotolaria. Planting shrubs on fallow land improves the soil, prevents soil erosion and reduces the growth of weeds. Farmers also like improved fallows because they can use the shrubs for fuel wood and fodder.
Onyango:
My understanding is that improved fallows are also a benefit because they add important nutrients to the soil. For example, improved fallows can increase the level of nitrogen in the soil.
Rose:
This is true! Nitrogen can be added by a special kinds plants. One of these plants is Tephrosia. The nitrogen is added to the soil when the leaves, pods and roots of the plant decompose.
Onyango:
So improved fallows can help by adding nitrogen to the soil, which is very important for healthy crops. What about another important nutrient – phosphorus?
Rose:
Another good question! Onyango is asking if improved fallows can help farmers by adding the nutrient phosphorus to the soils. The answer is that phosphorus will not be added to the soil if you use improved fallows. In fact, the shrubs actually remove phosphorous from the soil as they grow.
Onyango:
It sounds like improved fallows alone can’t solve the problem of low levels of phosphorus in the soil?
Rose:
You’re right. In fact, when shrubs such as Sesbania or Crotalaria are cut down and harvested, the phosphorus [stored in these plants] is removed from the land. That’s why it’s important for farmers using the improved fallows method to add extra phosphorus to the soil before planting their crops.
Onyango:
Are you saying farmers must purchase fertilizers to add this nutrient before planting their crops?
Rose:
Yes. Adding fertilizer is the best way to add phosphorous to the soil.
Onyango:
But surely adding compost or growing a green manure crop would be cheaper for farmers than buying chemical fertilizers!
Rose:
Yes, this is true! The problem is that most crops are hungry for more phosphorus – they need more than manure or compost can supply to the soil.
Onyango:
So, what is the solution?
Rose:
Well, a farmer has to add phosphate fertilizers. Adding fertilizers will ensure that enough phosphorus is available for the crops.
Onyango:
So farmers can use phosphate fertilizers like DAP, SSP and TSP, or rock phosphate fertilizers before they plant their crops.
Rose:
Exactly.
Onyango:
As we’ve discussed, improved fallows have many benefits for farmers. The shrubs can improve the soil and supply extra products such as fuel wood or fodder.
Rose:
The improved fallow method also increases the level of nitrogen in the soil, which will benefit the next crop planted on that plot. But remember farmers, if you use improved fallows it is important to take care to replace the phosphorus in the soil after you’ve cut the shrubs and before you plant your crops. At the very least you can add compost or manure to replace some of the phosphorus that is removed when the shrubs are cut down.
Onyango:
But, as we said, to really ensure that there is enough phosphorous in the soil, it may be necessary to apply phosphate fertilizers. FADE IN MUSIC AND HOLD.
Rose:
Improved fallows can improve soil, reduce erosion and reduce the growth of weeds. If you use improved fallows, remember that you will need to replace phosphorous in the soil, after cutting the shrubs and before planting your crops.
FADE OUT MUSIC.
Acknowledgements
- Contributed by Heidi Braun, University of Guelph, Ontario, Canada.
- Reviewed by Professor Helen Hambly Odame, Rural Extension Studies, University of Guelph, Canada.
Notes
- This script mentions the use of rock phosphate fertilizers for improved fallow systems. For further information about rock phosphates for sustainable agriculture in Africa, please see the ‘Rocks for Crops’ website at http://rocksforcrops.lrs.uoguelph.ca/
- The full names of the phosphate fertilizers mentioned in this script are as follows:
DAP – di-ammonium phosphate
TSP – triple superphosphate
SSP – single superphosphate
Information sources
- Amadalo, B. et. al. (2003). Improved fallows for western Kenya: an extension guideline. Nairobi, Kenya, World Agroforestry Centre.
- Sanchez, P.A., and C.A. Palm. “Nutrient cycling and agroforestry in Africa.”