September 5, 2023

AGRONOMY NEWS

Plan Now For El Niño Planting

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As speculation over an impending El Niño continues to build, growers are advised to plan ahead to ensure that they are not caught out at planting and are in a position to make the most of what could be a high-potential season.

Several farmers familiar with the 1997/98 El Niño have told me “Be careful what you wish for!” and “When it starts raining you might not have a chance to plant again until April 2024!”. With this in mind, there are several steps that farmers can take to prepare…

Make a clear plan of the planting priorities for each field or block based on soil type, weed pressure, depth of moisture and the planned crop.

Firstly, review the options you have in each field. If a field has a relatively low grass weed burden and is on heavy Black Cotton soil, that points towards prioritising it for early planting – either dry or deep moisture seeking.

We don’t know when the rains will arrive but for most regions, it is a sensible assumption that mid-October is the latest safe sensible date to have most planting complete.

If planting normally takes you two weeks, you therefore probably need to start at the end of September. For fields where there is good surface residue and moisture 7-10cm deep, moisture seeking is a real option if you have a planter on 30cm or wider rows (if not, now is perhaps the time to modify in the workshop!).

For fields that are very dry – especially those heavy soils that typically get wet and then cannot be driven on – target these to plant dry and shallow. Cereals are okay to sit in dry soil for a month, beans and pulses are okay, but sunflowers and canola are not so good as their germination declines rapidly after two weeks in hot, dry soil.

Grass weed pressure Access in the wet Current soil moisture Conclusion/action
Block 1 Low Difficult Good moisture at 10cm Dry plant
Block 2 High Easy Dry Wait and plant last after rain and flush of weeds
Shamba mzuri Low Difficult Totally dry Dry plant but only if very good rain is forecast to fill the profile
Shamba mti Low Difficult Very good, moisture at 7cm Moisture seek in late September
Examples of individual field assessments and actions.

One option worth considering is placing your planting fertiliser into dry soil so that a big part of the workload has been completed. You can then come back over with just the seed in advance of rain. This makes planting a lot faster, and in marginal conditions means that there is less weight to tow in the planter. You will have better germination and vigour. You can even broadcast canola seed – this is a great way to establish a crop in the wet.

As a general rule, also bear in mind the grass weed pressure. After this long, dry period there will no doubt be a big flush of grasses, so either A) delay planting your weediest fields and hope there is some rain to give a flush and stale seedbed, or B) put these fields into a break crop like canola or a legume so that you have herbicide options to control the grasses.

Field Focus: Bafumbile Field, Nakuru, Kenya

Bafumbile field is a light volcanic pumice soil on the slopes of the Menengai Crater, Nakuru County, Kenya. Having historically grown a lot of wheat, the field is now in its sixth year of crop rotation and has been direct drilled for 10 years. So after sunflowers and peas last year, the foundations have been laid, and the prospects for maize are exciting, to say the least.

The field was planted into moisture in the first week of March, despite having last received rain in early December. The key to this was ensuring that last year’s peas were harvested in early December, before they used all of the moisture, and keeping the residue from the peas on the surface to stop the sun from drying out the soil.

The benefit of getting crops established early like this is manyfold; the soil temperature is uniformly warm so emergence is fast and even, meaning plants are not competing with each other. Weed germination is less, the crop is harvested earlier and yields are almost always higher from March plantings compared to April in my experience.

The farm has also used a controlled traffic system for over 10 years, which involves driving machinery in exactly the same part of the field every year so that soil compaction is limited to a very small area of the shamba.

Previous cropping history:

2018 Sorghum Fantastic deep roots improve the soil structure
2019 Maize Cash crop, good residue cover
2020 Lupins Reduce nematodes, fix N, reduce Take-All and Rhizoctonia
2021 Barley Cash crop, good control of broadleaved weeds
2022 Sunflowers, Peas So many benefits including grassweed control!
2023 Maize Cash crop

The field is split between DK 777 and P3812W maize varieties. In our trials on this farm, P3812W is often one of the highest yielding, with good quality denty grain. It is a very tall hybrid so we planted at 75,000 seeds/ha, and established 72,300 plants.

DK 777 on the left, and P3812W on the right.

DK777 has always performed well in trials on this farm. It is rarely the highest yielding, and in fact has a very abrupt and stubborn yield limit that is hard to push above, but it has excellent grain quality and disease resistance. We planted at 85,000 seeds/ha and interestingly, established 77,500 plants/ha, so we had a lower establishment than the P3812W.

Planting depth was 7cm. Relatively deep, but this is where there is consistent moisture and soil temperature; maize does not appreciate uneven emergence which results in the plants competing with one another.

We applied flumetsulam + clopyralid + acetochlor pre emergence – with the decision to use this product driven the weed spectrum which we know is likely to include Amaranthus, Gallant Soldier and Blackjack.
We then returned at around the 4-5 collar stage with atrazine, nicosulfuron and mesotrione to control later emerging weeds. I was disappointed by the control of Brome was poor considering the nicosulfuron is normally highly effective. We added extra atrazine as the product has a very low loading, and mixed halosulfuron for Watergrass control.

I have been saying over the past few years that Fall Armyworm (FAW) pressure is a lot less than it was in 2017 and 18, and 2023 was similarly low. We applied imidacloprid + beta-cyfluthrin early for MLND vector control in the P3812W (DK777 is MLND resistant) and early FAW control, followed by indoxacarb at 4-5 collar, then emamectin at the 7-8 collar stage. This has been more than adequate.

Uniform seed depth is crucial for a strong maize crop. Last year’s peas help the smoothness of planting by leaving a very soft, well-structured soil.

Getting nutrition right has been a big focus on this farm in trials over the past few years, and based on the results of on-farm trials, soil testing and leaf testing, we applied 200kg/ha of DAP and 100kg/ha magnesium sulphate in the seedbed. Foliar copper and boron were applied twice as these are often limited on this farm, and two doses of magnesium sulphate were applied.

A big discovery on this light pumice soil has been the need to feed the crop with small, frequent doses of nitrogen. Because we planted early when there was the chance of not receiving rain for several weeks, we placed 75kg/ha of urea 7cm deep into the soil, BETWEEN the maize rows with the planter; crops on this soil need nitrogen by the 3 leaf stage, at which point their roots will be reaching this line of urea in the inter row.

We then topdressed with two doses of 75kg/ha urea at 5 collar and 8 collar stage.

The farm has been relatively lucky with the rainfall pattern this year, but the biggest benefit has been the ability of maize roots to grow deep into the soil, unimpeded by diseases, nematodes, and soil compaction thanks to the crop rotation and soil management including the controlled traffic system.

The overriding lesson for me on this farm is that profitable farming comes down to taking sensible long-term decisions, rather than throwing expensive inputs at a crop.

Row Spacing

For years, I assumed that the narrower the row spacing, the more yield you harvest from a wheat or barley crop. To a point, this is true – we are ultimately capturing sunlight and converting it carbohydrates, so the larger our crop’s ‘solar panel’, the better. Where this falls down is when it meets the realities of farming, and it can sometimes be used to your advantage…

Barley planted between the previous rows of wheat stubble to reduce infection from soil-borne diseases.
  1. Stubble isolation – when sowing wheat or barley into a previous cereal stubble, planting in between the rows will reduce the incidence of Crown Rot, Rhizoctonia and Take All soil-borne disease, because it provides some separation distance from where the disease inoculum is highest.
  2. The ability to plant uniformly through residue – if you can leave as much of the previous crop standing in the stubble lines as possible, there is less loose residue to block the planter. Of course, technology has given us planters that are much better are penetrating thick straw, but in the most severe cases, hair pinning of the straw with the seed and blockages can result in very poor establishment. Any advantage you potentially gain with narrow rows will be lost by the gaps in the planting.
  3. Moisture seeking – The ability to get a crop germinating on moisture stored 5-10cm deep in the soil has transformed many farms in Kenya. It means that they can plant and get the crop established before the rains arrive so that when the rain finishes, the crop is that much more advanced and is already at the grain fill stage. Moisture seeking requires wide rows to create a ridge and furrow, otherwise you bury the seed too deep.
  4. Herbicide separation – e.g. imazethapyr PRE planting (NOT pre emergence) in peas is permitted in some countries. If you spray after sowing but pre-emergence you will often see crop damage. Spraying before sowing and using tines spaced 30cm or further apart pushes the chemical away from the seed furrow and gives much better crop safety whilst still allowing a very useful herbicide to be employed.
Normally, narrow rows (18cm) are higher yielding than wider rows (36cm), until you look at what you can actually do on wide rows with moisture seeking, stubble isolation etc.

All other things being equal, narrow rows will tend to produce higher yields. So if you are planting wheat after beans or canola into good moisture for example, where soil-borne diseases are unlikely to be a major factor and crop residue is minimal, narrower rows will be of benefit.

If grass weeds are a problem, narrow rows could also help suppress and compete with them. The major lesson is that there is no one single correct approach; evaluate the specific challenges on your farm and choose what is appropriate for you.

Till next time,
David Jones
Independent Agronomist

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