At the recent Grain SA Congress, American producer and maize-yield record holder Kevin Kalb delivered a keynote address that challenged many conventional assumptions about fertiliser use.
Kalb’s family has farmed the same land near Dubois, Indiana, for five generations. In that time, he has watched nitrogen use across the United States climb steeply while yield gains have quietly flattened. It is a pattern that could be termed ‘the efficiency paradox’, and he believes it holds a warning for grain producers everywhere, including those in South Africa.
He argues that too many farming systems have fallen into a cycle of applying more fertiliser to compensate for declining soil biology, rather than building the kind of resilient soil that makes every kilogram of nutrient count.
For South African producers squeezed by rising input costs (fertiliser making up between 30 to 50% of their variable production cost), climate variability, and thinning margins, it is a message worth listening to.
Half your fertiliser never reaches the crop
Research consistently shows that only 30 to 50% of applied nitrogen is absorbed by the plant. The rest disappears and is lost to volatilisation, leaching, or microbial immobilisation.
‘For every dollar you spend on synthetic fertiliser, the best-case scenario is that about half reaches the plant,’ Kalb said.
On his own farm, he has set a far more ambitious target: 75 to 80% nutrient recovery. Reaching it has required rethinking almost everything about how fertiliser is applied.
Thirty years without dry fertiliser
The most striking feature of Kalb’s system is one that raises eyebrows wherever he speaks. For more than 30 years, his farm has used 100% liquid fertiliser and no dry product at all.
The reason is that liquid fertiliser can be precisely banded near the root zone, placing nutrients exactly where young plants need them. It also allows producers to blend in additional products such as micronutrients, sugars, and humic acids to support the soil biology. According to Kalb this is the true engine of productivity.
Dry fertilisers, particularly those with high salt content, work against that goal. ‘Salt is basically a steriliser,’ Kalb said. ‘If you run a lot of high-salt fertiliser, you’re hurting the biology that helps your crop.’
Feeding the microbes that feed the crop
It all comes down to a simple biological cycle. Through photosynthesis, plants produce sugars that are released through their roots into the surrounding soil. Those sugars feed bacteria and fungi, which in turn break down organic matter and release nutrients the plant can absorb.
A healthy maize crop can produce hundreds of kilograms of sugar per hectare, sustaining a vast microbial ecosystem beneath the surface. When that system is functioning well, crops access nutrients more efficiently and the need for external inputs drops.
Get your pH right before you spend on fertiliser
When acidity creeps beyond optimal levels, nutrient availability falls sharply. According to Kalb, a drop from pH 6 to 5,5 alone can reduce availability by up to 40%.
‘If your pH is too low, don’t spend money on fertiliser,’ he said. ‘Spend it on lime first.’
It’s a simple intervention, but one that ensures the nutrients already in the soil, as well as those being applied, can actually be taken up by the crop.
Place it, don’t spread it
Fertiliser placement is another cornerstone of Kalb’s approach. On his farm, nutrients are never broadcast across the field. Every application is banded close to the seed row, putting fertiliser directly within reach of developing roots.
The efficiency gain is significant. According to Kalb, simply switching from broadcast to banded application can improve nutrient uptake by around 30%. Plants respond visibly as maize roots grow directly toward the nutrient bands, developing deeper, stronger root systems that also improve drought resilience.
Proof of this concept lies in Kalb’s own results. His highest recorded maize yield reached approximately 33,6 t/ha without irrigation. What surprised the audience even more was the nitrogen rate behind it: roughly 180 kg/ha, well below typical recommendations for yields of that calibre.
The small nutrients with big impact
While nitrogen, phosphorus, and potassium dominate most fertiliser conversations, Kalb urged producers not to overlook micronutrients. Boron, zinc, and manganese each play outsized roles relative to the small quantities required.
Boron is closely linked to pollination success. Zinc increases leaf size and photosynthetic capacity, supporting stronger grain fill later in the season. These are gains that cost relatively little but can shift the yield needle meaningfully.
He also stressed the importance of keeping the crop green and photosynthesising as deep into grain fill as possible. ‘We want that plant green all the way to black layer,’ he said. ‘The longer the factory runs, the heavier the grain.’
Sampling: the key to fine-tuning nutrition
Another practice Kalb strongly emphasised was regular plant sampling throughout the growing season. He encouraged producers to make tissue and sap testing a routine part of crop management rather than relying only on soil tests at the start of the season. According to Kalb, these samples provide a real-time picture of what the crop is actually experiencing in the field. ‘Everybody here should be pulling tissue samples,’ he told the audience, stressing that plant tests reveal nutrient imbalances long before visual symptoms appear. By monitoring nutrient levels during key growth stages, producers can make targeted adjustments and avoid yield losses caused by hidden deficiencies.
Kalb shared a practical example from his own experience, highlighting again the importance of boron levels during pollination. Through tissue testing, his team monitors boron concentrations closely and aims to keep levels above a specific threshold throughout the season. Maintaining adequate boron, he explained, can significantly improve pollination success and grain set, ultimately translating into higher yields. For Kalb, plant sampling is not simply about collecting data, it is a decision-making tool that allows producers to fine-tune nutrition, protect crop health, and maximise the return on every fertiliser investment.
The phosphorus trap
He highlighted another area where many producers may be spending without return. When soil phosphorus levels are already high, the probability of a measurable yield response drops sharply. Applying more phosphorus to high-testing soils often delivers little economic benefit.
For producers managing tight margins, this reinforces a straightforward principle: test accurately and fertilise accordingly.
What this means for South African producers
South African grain producers operate under different climatic and economic conditions, but the core principles Kalb outlined translate well:
- Improving nutrient efficiency delivers better returns than simply increasing rates.
- Protecting soil biology builds resilience against drought.
- Correcting pH before investing in fertiliser ensures that money isn’t wasted.
- Precision placement lifts uptake.
- Small investments in micronutrients can unlock disproportionate gains.
Start with a small field
Kalb closed his address at the Grain SA Congress with a challenge to producers. While agriculture has rapidly adopted advances in machinery, genetics, and data technology, he believes many fertiliser practices have remained largely unchanged for decades.
‘Everything else in agriculture has evolved,’ he said. ‘But many of the practices that affect our profitability haven’t.’
He advised producers to start small. Dedicate a single field, or even a few strips within a field, to testing new ideas. Focus on one nutrient at a time and observe how the crop responds. Understanding what each nutrient truly contributes to plant health and yield, he argued, is one of the most valuable lessons a producer can learn.
