INTERCROPPING – FOR CROPS AND FORAGE

Intercropping is a way that we can introduce diversity into our cropping systems.  There are many reasons why one might chose to do this, including reducing the use (and potential financial risk) of high input fertilisers, reducing pest problems and reducing soil erosion.  Intercropping can also aid in weed control and helping to make the most profitable and productive use of land, through the complementary access to a greater range of the soil’s resources than with a monoculture.

The history of intercropping is long – with developing countries still using it as a common technique.  Developed nations’ farmers however predominantly moved away from it around the 1940’s¹, and into monocultures, but in some cases have now done the full circle and are beginning to incorporate it back into their programmes.  The added bonus now is that they have the use of modern day technology and the value of greater scientific understanding.

What is intercropping?

Intercropping is the growing of two (or more) crops on the same piece of land and at the same time (or same partial time).  One might also term it companion cropping or companion farming.  The key to intercropping is choosing species that work together. [private] When I say work together, I mean species that are not competing in the same manner for light, space, timing, nutrients etc.

Types of Intercropping

There are four recognised types of intercropping:

Mixed intercropping – two or more species sown with no distinct row arrangement

Row intercropping – at least one of the crops is sown in rows

Strip intercropping – growing crops in strips wide enough to separate them, yet narrow enough to allow their interaction.

Relay intercropping where the second is sown often at the stage of flowering or closer to maturity of the first.

The complementarity of the species chosen is obviously critical in the success of intercropping.  Different rooting systems (such as tap root and fibrous), above ground canopy growth (such as a climber with a tall plant) and nutrient needs (a pulse or legume crop with a high nitrogen user) are all things to consider with regard to complementarity. 

Fertiliser reduction

Intercropping can help to create a more resilient cropping system.  The past decade has seen traditional monoculture croppers move to split applications of their nitrogenous fertilisers.  This reduces the upfront cost associated with crop production, reduces overgrowth of early biomass (often not related to yield) and means the second fertiliser application (and associated costs) can be avoided in the event of a dry or unfavourable season.  This helps with the resiliency of the cropping business across the variance of seasons.  Intercropping can take this idea of reducing risk and improving resiliency and take it the next step.  Planting wheat with a legume, with just a starter fertiliser to get the crop going, but then relying on the legume to supply the nitrogen to the wheat ‘as needed’.  As proposed by Stephen Machado of Columbia Basin Agricultural Research Centre at Oregan University – in the event of dry times, the legume will slow or cease N fixation (a moisture reliant process) – meaning that oversupply of nitrogen is avoided.  In the case of a favourable season, the legume can supply the nitrogen necessary for a higher yield potential.³

Growers may not have explored the advantages of intercropping in the past, due to the ease of cheap and readily available fertilisers used in monoculture crops – cropping systems which are also simpler to grow.  Current day pressures of the rising cost and rates of fertilisers (and, with time, decreasing availability) along with the increasing realisation (and on ground effects) of soil degradation associated with high fertiliser inputs means that more farmers are questioning if the traditional monoculture system is the best production model.  It is no longer a given that the advantages of the simplicity of the monoculture system and the results from petrochemical fertilisers that were achieved upon adoption many decades ago, outweigh a system like intercropping, despite it requiring more thought and understanding.

Production increase

Yield advantages, in terms of more production off one area of land may be gained.  It may not be a yield increase in one of the species compared with its equivalent monoculture, but the overall production from the given piece of land may be greater.  Differences in the characteristics of the plants’ growth enable this yield advantage.  Characteristics like different canopy structures means maximum light intersection; different root structures means maximisation of soil resources; improved ground cover with several species means less heating of, and moisture evaporation from soils.  This can result in improved water use efficiency.⁴

Some species mixes will provide improvements in overall yield, while others will result in worse results – the key is to get two (or more) species that don’t have a strong overlap in their demands for all or some of the competing resources of sunlight, minerals, space.

Pest pressure

There is evidence that planting two species together can reduce pest and disease pressures often experienced in monoculture situations.  The combination of several species creates a more varied habitat for beneficial insects, which in turn help to keep pest numbers at bay.  Could it also be that the combination of several crop species (and associated diversity) means plants are accessing different nutrient suites that can then be shared between plants via soil fungi and VAM?  Access to a more diverse nutrient base is likely to be related to better pest immunity of the plant.

Weed incidence can also be reduced as the mix of species means that there is more soil covering and competition with weeds.  There is a downside to this however – that for those using herbicides in their systems – there is less herbicide choice once two crop species are placed together in the one paddock.

Risk Reduction & Resiliency

Consistent production and resiliency across seasons is most certainly more of an issue than it used to be for farmers.  I attribute two main occurrences to this:

1 – many areas of the world are experiencing increasingly unpredictable weather patterns.

2 -many soils of the world have been degraded.  Degradation in soil carbon levels mean that soils have less ability to hold moisture and nutrients.  Degradation in soil biology has affected soil structure and has negative impacts on infiltration.  Less ability to hold moisture and less ability to infiltrate rainfall effectively means that farm businesses are even more impacted by point 1 – less reliable or more erratic weather patterns.

Due to these challenges, farmers are looking for ways to reduce the risk in their businesses.  As described earlier, co-planting a legume with another crop can help to reduce nitrogenous fertiliser inputs (and its associated costs), and help with reducing the risk of high upfront costs at planting.

Growing more than one species of crop via intercropping means that peak resource times will likely vary between species – meaning unfavourable weather conditions (like frost, dry, rain at harvest), may impact one species more than another and this will have less impact on crop returns.  Conversely, particularly favourable conditions at one part of the season may benefit one species more.  The farmer will also be less affected by fluctuations in grain prices when prices are spread across more than one commodity.

Feed Quality – for forage crops and silage

For the graziers amongst you it is interesting to note the differences in forage quality achieved from intercropping.  Adding a legume to a cereal fodder crop can help to increase nutrition for livestock.  Given the advantages for soil and livestock that we have previously learnt about from increasing plant (and root) biodiversity, it seems like a relatively easy move to increase diversity of a forage crop (whether as a straight crop or a pasture crop).

Erosion control

The mixing of several species (depending on the arrangement of sowing) can mean greater soil coverage and reduced erosion as a result.   A sorghum-cowpea intercropping trial reduced soil runoff by 20-30% compared with the sorghum crop alone and by a significant 45-55% when compared with the cowpeas alone.⁵

Adaptations

There are naturally many changes a farmer would need to make to a cropping system to embrace and trial intercropping.  Changes for those growing fodder crops may be simpler, as there are not the challenges of grain harvest.  Harvest of a dual grain crop is clearly going to be more challenging that a single grain – with grading required afterwards if the grains are to be sold into a traditional market, or separate harvesting – depending on the planting arrangement.

Biodiversity

Anywhere that diversity of root systems in the soil can be brought into our farming systems there are many advantages.  Not always immediately apparent or measurable, but with the appropriate associated management and persistence, it can start to have great effects on soil and farming business resiliency.

I will have a look at some specific farmer examples over the next few weeks; the theory of intercropping might all sound great, but I’m sure you will want to know how to manage this practically.

References

1,2&3.  Machado, S. (2009)Does Intercropping have a role in modern agriculture?  Journal of Soil and Water Conservation, Mar/Apr 2009 – Vol64, no2.  http://cbarc.aes.oregonstate.edu/sites/default/files/JSWC64_2_55machado_proof_3.pdf

 4 & 5. Lithourgidis, (2011) A.S., et al.  Annual Intercrops: an alternative pathway for sustainable agriculture. Australian Journal of Crop Science 5(4): 396-410.