Crop rotation

By David Jones, BroadAcre Agronomist, Msc. Agriculture

It may seem as though the off season is a long way away for many growers in Kenya, but it will arrive quickly and now is a good time to review how best to use the land in the fallow period. Having experienced what for many is the wettest period of Long Rains in living memory, you may decide to repair any structural damage early with subsoiling or cover crops, or depending on what the weather does now, make use of the Short Rains and the moisture in the bank to grow a second crop.

For many growers split cropping their farms 50% each season, the decision is not whether to grow a crop, but what crop to grow, be it a cereal or a break crop. A summary of considerations include:

Weed Burden

  • If you are in a difficult Brome or Ryegrass situation, opting for a non-cereal break such as Canola or Peas is sensible to allow Group A herbicides such as Agil and Fusilade to be used. Adding diversity to the system – particularly as far as Brome is concerned is often very effective. Successive cereal crops planted in March every year for example, select for Brome populations that thrive when a crop is planted. I have seen some very good results from planting Canola in the off season in between two barley crops which seems to send a signal for the Brome to germinate where it can be dealt with.
  • With Ryegrass, if it is resistant to Group A herbicides do not plant a crop that is A) not competitive, and B) relies on Agil / Fusilade. Make use of available residual herbicides, inter-row cultivations and rogueing.

 

crop rotation

As well as making a profit, a good break crop will reduce problematic grass weeds

Soil Moisture

  • Precious little point planting a crop such as Canola or Peas if you are short of moisture and planting straight after a late harvested cereal crop. Sorghum would be a far better option in this situation, provided you have the heat units.

Time of Planting

  • If you are delayed by a late harvested cereal, beware of long season crops. Focus on the output of the main season crop in Feb-March-April and do not compromise it by having to wait for the off season crop to be harvested. Chickpeas for example finish well in the hot weather of Jan and Feb, but will not appreciate a late March finish in the rain.

Insect Pressure

  • In some parts of the country, insect pressure in the last two December – February seasons has been extremely challenging. Choosing crops that are less susceptible to Bollworm and Green Peach Aphids e.g. Sunflowers helps spread the risk, and frees up sprayer capacity for Canola and Peas.

Choose The Right Variety

  • If you are likely to experience a shortage of moisture later in the crops life, selecting an earlier variety and planting at a lower density can help ration what is in the soil. An over thick crop of flowering Kwale wheat might look great in December, but you may wish in January that you planted a smaller crop of Eagle 10 or Korongo.

Related: Understanding The Role Of Cover Crops

 

Evaluate The Potential Returns

Examining Gross Margin projections helps to understand the relative profitability of different crops so that financial returns can be optimised. It also identifies what is the chance of a crop losing money in your likely yield scenario, and secondly, can you reduce the risk of a loss-making crop by setting the planting and agronomy up accordingly?

The graph below is based on a range of crops with the gross margin in blue (the value of the crop MINUS typical input costs for sprays, seed and fertiliser), and in orange the cost of the sprays, seed and fertiliser that we are typically seeing on our Agronomy Clients’ farms.

crop roati

There is an increasingly wide range of Canola varieties available, being trialled here by CropNuts and the Agventure Centre of Excellence for Crop Rotation

I have included maize for a comparison, and you can see that most high yielding crops will provide a worthwhile return to cover machinery and labour overheads if the season goes to plan.

What is interesting is when you start to look at low yield potential sites – where wheat and barley are sub 3 t/ha. Can a profit still be achieved?

The evidence suggests it can, especially where inputs are spent appropriately. Minimal topdressing, a slightly lower seed rate and less focus on wet season (i.e. Septoria) fungicides not only saves money, but in a low rainfall environment can also enhance yields but avoid over-thick crops.

Related: Cover Crops: The Key To Unlocking Soil Fertility?

 

crop rotation

Options for 2018/19

Planted early, into a good seedbed with adequate moisture, canola can provide a very respectable return and improve the yield of the following cereal or maize. Grass weed control benefits are also an excellent reason to grow the crop in an all cereal scenario such as Narok.

A large population of Brome could easily be costing you 1.5 t/ha in yield – this would improve the barley gross margin by over 50,000 Ksh, on top of the benefit on Fusarium and other soil borne diseases.

crop rotation

Sorghum roots have a tremendous ability to penetrate firm or compacted soils

Sorghum is a crop which I am less comfortable with on many farms, particularly in medium and high altitude areas. The attraction is the low growing costs and excellent rooting, but try a small area until you know that it will work on your farm and with your planter – plant populations need to be right. Birds can be a menace too near harvest.

A great legume alternative is peas, provided a clean sample can be harvested and stored. If not, don’t even consider the crop. It also requires rain around flowering to maximise its potential, and the seed and fungicide input is not for the feint hearted!

Sunflowers may be one of the lowest profitability crops, but do not dismiss them. The rooting and rotational benefits to following cereals are superb, and the crop is far more resilient to Armyworm, Bollworm and Aphid pressure than peas or canola. Be realistic about what you can achieve from canola and peas in a drier, hotter environment, and look at Sunflowers as a long term rotational and grass weed option. Spend the money on herbicides pre emergence too as the crop is not competitive like canola.

crop rotation

A good pre emergence herbicide program (left) is an important investment for successful Sunflowers. To avoid weedy, low yielding crops (right).

Topical Grass Weed Update

On almost every farm I have visited through May and June I have been met with the comment that grass weeds are particularly bad this year – notable Brome and Rye Grass.

The effect of above-average precipitation in the main germination periods in encouraging Brome germination is well documented. But most Brome species last for 3 years in the soil, with 20% of the seed surviving from year to year.

In a way this is the antithesis of the situation with Fall Armyworm, where the weather conditions have subdued the pest, but encouraged a very large germination of grass weeds from the seed bank in the soil.

Related: Brome Grass Weed Control

 

Does this mean that levels will be lower next season, as the numbers in the soil have been depleted somewhat? This is unlikely in my experience, particularly if they have been allowed to set seed. What this will be positive for is where break crops have been used, and good control of grass weeds has been achieved. In these situations there will inevitably be less seed left in the soil.

But this reinforces the fact that in bad brome situations, a single season approach (i.e. a one year break between cereals) is not sufficient. Back-to-back breaks or a fallow- break crop approach are required to stop this carryover in the seed bank. More on this next time!

Take care,

David

About David

 

David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.