By David Jones, Broad Acre Agronomist, Msc. Agriculture
In most parts of the world growers have confidence in optimum seed rates and row spacing for cereals for their conditions, which strike a balance between high yields in good years and stable, consistent yields and grain quality in drier years.
This is the product of comprehensive work and experimentation on local conditions and varieties, and requires many seasons to fully understand the outcomes in different weather scenarios. We do not have such detailed guidance in Kenya so where do we start with selecting an appropriate seed rate for different environments?
The first thing to be aware of is that plants are very adaptable so do not get too carried away.
Canadian work over 4 years showed that in their conditions, yield was unchanged as row space moved out from 10 to 16 inches (25 to 40cm) in three of the years. In one year however – the highest yielding year in the study – there was a significant yield penalty of 700 kg/ha (3 bags per acre) from row spacings over 12 inches (30cm).
Looking at research in Australia there is a vast amount of very high quality data for different yield environments. Department for Primary Industries research in Queensland concluded that in a 2 t/ha (9 bags per acre) yield environment there was no effect on yield from row spacings up to 50cm, compared to 25 and 37.5cm rows.
In a 2-4 t/ha yield environment the same work concluded that yield potential was decreased slightly when row width increased beyond 25cm, and in a 4 t/ha (18 bags per acre) environment yield was significantly decreased – by up to 600 kg/ha – by going from 25 to 37.5cm rows.
But what happens in a high yielding environment where crops have reliable, regular rainfall? Research in France concluded that at yield above 7.5 t/ha (33 bags per acre), there was a measurable and consistent reduction in yield when row width increased above 20cm. This was consistent across four varieties and six sites.
However, wide row spacing does markedly reduce screenings in a dry year – whether this is because of fewer, larger grains or because of rationing of soil moisture this is not always clear, but if you suffer from high screenings moving to wider rows can be very positive.
But yield is not everything. Wide rows and GPS guidance allow growers to plant between rows of previous crops to avoid residues blocking the planter in no-till systems. But is this the wrong way around? Why should optimum row spacing be dictated by previous crop residues?
Planting into residue can be achieved with a disc, however disc vs tine depends entirely on the system you are running and your soil types, and tines on wide rows allow moisture seeking in dry conditions where a disc would place the seed too deep.
Where residue cover is good however and moisture is protected in the soil by a mulch or cover crop, in some areas of the country a disc plater may be a real option, particularly if you are waiting for a flush of Brome ahead of planting, then want to minimise disturbance at planting to avoid further germination.
In the longer term, a system using cover crops could potential reduce (but never eliminate) the need to moisture seek, by reducing evaporation and keeping moisture close to the surface – this is something a see a lot of in poorly spread combine chaff lines in Kenya.
Narrower rows – in tandem with higher plant populations – tend to reduce the competitive effects of Brome and other weeds. Not only does the early canopy closure reduce later germinations of weeds, but it can be a very important tool in reducing seed set – a Brome plant with less space will tiller less and produce less seed.
Some varieties are particularly adept at responding to high seed rates, for example work in England showed that the barley variety KWS Irina could withstand up to 500 seeds/m plant populations before screenings and lodging became an issue, and that this reduced Blackgrass heads by well over half from the standard 300 seeds/m.
Just be aware that inter row cultivations can also play a very important part, and require at least a 12”, ideally 15” row to work effectively.
In most environments, a 12 or 15” row is perfectly sensible. However there are many areas of Kenya where we have seen well over 6 t/ha (27 bags/acre) in trials that will see a slight reduction in yield from rows above 10-12”.
If you are regularly short of moisture at planting, the ability to moisture seek with a 15” row is far more important however, allowing the crop to establish and benefit from rains at a later growth stage.
If Brome is an issue and you are comfortable to delay planting until the first rains, crop competition from narrow rows makes a lot of sense – in areas such as Molo or Timau that are less likely to be moisture limited perhaps.
Whatever you do, choose a well-made planter, maintain it properly and set it up correctly. Do not lose sight of this because it is infinitely more important than row spacing!
Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the future of how we feed the planet.
Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health.
The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).
Till next time,
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.