We often talk about the importance of healthy plants in reducing pests and diseases, but how often do we actually see the visual benefits?
Reducing fungicide use is important not just for Integrated Crop Management (ICM), but keeping input costs down and reducing the chances of fungicide resistance developing.
Our wheat trials have revealed a particularly good example, where some very slight nutrient deficiencies were identified in a routine leaf test and immediately corrected.
Retaining moisture at planting, ensuring good soil structure, and removing weed competition are some of basic principles to reduce plant stress, and crop rotation is fundamental to reducing soil borne pests such as nematodes and disease like Rhizoctonia and Take-All.
Nutrition also plays a vital role and is often harder to see, until you put two different approaches side-by-side in the field. Two identical plots of the variety Robin in our trials that received no fungicide are shown below, where leaf analysis at Growth Stage 30 highlighted slight deficiency in Magnesium, very low Boron, and still low Copper despite a routine foliar application at late tillering.
2kg/ha of Magnesium Sulphate, 150g of Boron and 200g of Copper were applied immediately to correct the deficiency, with a final small top up of all three applied at Flag Leaf.
Robin was the highest yielding variety in our trials last year in the fungicide treated plots, however its susceptibility to Septoria and Rust are notorious (which is why we always include one untreated plot of every variety in trials).
The difference in Septoria infection is incredible, with the control plot – despite showing no visual nutrient deficiency symptoms – full of Septoria, and the nutrient corrected plot still clean and green!
Leaf testing should be routine for high yielding crops, identifying deficiencies before they occur and checking that money spent correcting them (which is often very cheap!) has worked successfully.
Nutrient corrections – top tips
- Look at the crop for visual nutrient deficiencies.
- Leaf test to pick up early deficiencies; mid-late tillering, and again during stem extension.
- Test the youngest fully emerged leaves from 30 plants.
- Sample different soil type zones separately.
- Do not get hung up on sales people promoting specific nutrients or mixtures; apply what the crop is requires.
- When you apply any nutrient, always leave an area of your crop untreated for reference.
- Follow tank mixing guidelines to avoid crop damage or blocked sprayers.
Making a successful habit of continuous maize
There is no good data on how much of the 2-2.5m hectares of maize grown in Kenya is on land that has repeatedly grown the crop, but one suspects that it is the vast majority.
We all know the benefits that rotation brings to any farming system but when it is not feasible or practical, how can we ensure that maize-after-maize cropping is successful?
Firstly, fertility. If you look at a lot of data from corn growing areas of the USA comparing maize-soybean rotations with continuous maize, the optimum economic rate of nitrogen is typically around 50 kg/ha greater in continuous maize.
Part of this higher nitrogen requirement is attributable to the lack of N fixed after the legume, but a large part seems to be from the requirement of microbial populations to break down the high carbon maize residue.
There is evidence that in full cultivation systems where maize residue is chopped and mixed, the nitrogen lockup is less pronounced, compared to notill systems where residue is retained on the surface.
No good data is available on Fall Armyworm, despite pupae numbers in the soil in theory being greater after a maize crop where larvae have fallen to the ground in the last season. However with no diapause in the life cycle of the Fall Armyworm, adult moths will hatch within 10-15 days of pupation so it is unlikely that the Fall Armyworm risk should be any greater in continuous maize than rotation crops. That said, are adult moths attracted to maize residues? In my experience I feel that there may be some limited truth in this.
Autotoxic compounds from decomposing maize residue have also been identified in work by the University of Minnesota, with evidence showing that row cleaners can reduce the effects of residue close to the seed.
Planting maize after maize certainly creates more challenging planting conditions due to the residue and presence of obstacles for the opener – notably root balls. Planter set up is crucial and justifies a lower forward speed for this reason, to ensure even planting depth.
Variety choice in many countries is also guided by resistance to bacterial diseases such as Goss’ Wilt which cannot be controlled by fungicides, however data in Kenya is simply not available to guide variety selection on these requirements.
Optimum seed rates also tend to be slightly greater in continuous maize. This might be because plants tend to be smaller, perhaps due to lower fertility, but either way it is interesting how many trials identify this trend.
Northern Corn Leaf Blight and Aspergillus risk will be greater however and can be effectively controlled by fungicides – our research has shown that these pay, even in low risk situations so should be considered a must in continuous maize cropping.
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.