Economics of Most Limiting Factors in Agriculture

The most limiting factor (MLF) has been accepted for many years. However we tend to ignore that there are always other factors influencing or masking ‘The Most Limiting Factor’ and these need to be ‘factored’ in. We also need to include the concept of most influential factor (MIF). These are those factors that tend to have most influence on minimising the effects of limiting factors.

There are usually correlations between limiting factors. What may at first appear to be the most limiting may be the result of masking due to a high correlation with the real limiting factor(s).

A consistent observation over the past 3 seasons has been that the best performance is usually related to low phosphorous and potassium. Why then when soybeans are high users of phosphorous and potassium? The answer is simple. In the best areas the crop removes more phosphorus and potassium. Hence the condition of the soil is predominantly more important than fertility. While soil fertility is very important, it is seldom more limiting than soil characteristics. This is very important.

As we understand this concept we realise the importance of balances and ratios in agriculture. Not every application is beneficial and excesses usually impact negatively on performance.

Rating and Identifying the Most Influential Factors?

There are many factors – such as fertilizer, soils, and water – which affect crop performance (yield & quality) simultaneously. Maximising profitability lies in identifying which factors are the most limiting and taking action negate their effect. Some factors, such as clay content, are not easily negated but can be planned around if we understand their limitations.

Graph 1: Economic effect of adjusting intensity of influencing factors

The graph above illustrates how factors influence performance and economics.  Optimum benefit will usually occur at the intersection of zones 2 and 3. Above this point it is more beneficial to direct money and time to optimising other factors. The graph is divided into zones 1 though 5. The relevance of the zones is summarised below.

Zone 1 – Huge deficiency zone

This is the most important zone. Factors lying in this zone need to be addressed before all others. Response initially is slow until a good foundation is laid. Some factors which lie in this zone are not economical to remedy and in such cases areas affected should be abandoned. E.g. Shallow soil: (slope of the graph is fairly flat in this zone)

Zone 2 – Most influential zone

When the foundation (zone 1) is in place small additions have a big effect in this zone as Return on Capital (ROC) is highest. This is the best area to spend money when correcting important factors: (Steep graph slope)

Zone 3 – Target or optimal zone

Once this zone is reached economic benefit of improving the factor is negated by the cost of the product/action: (Gentle graph slope)

Zone 4 – Maximum productivity zone

This is the area of maximum performance, but usually the cost of achieving it is higher than the return (negative ROC). Good savings can be made by cutting back on inputs. Many farmers waste a lot of money trying to achieve this ‘STATUS’: (No slope).

Zone 5 – Overdose zone (Greatest savings potential)

Need to decrease significantly. Further addition is not only costly but decreases performance. This is an important zone as money is saved by reducing input and in so doing yield increases. This is as important as zone 2: (Steep negative graph slope)

The break even line

The Break Even Line takes into account the cost of applying the factor concerned. This could be fertiliser, land preparation, pH adjustment, pest and disease control etc.

• Note in Zone 3 the performance increase is parallel to the cost of application. I.e. no financial benefit and tying up money that could better be spent somewhere else.
• In Zone 4 you see that achieving maximum yield usually costs money as the increased benefit costs more than the money you get back.
• In Zone 5 you spend money to lose money. And there are many farmers who spend money in this zone not realising what they are doing.

Too often key soil characteristics such as compaction, low soil organic and pH sit in zones 1 and 2. Until these are remedied things like fertiliser sit in zones 3-5. I.e. applying the fertiliser is a waste of time and money until the soil is corrected in order to be able to use them effectively. Once rectified factors such as fertility suddenly drop into zone 2 where application is now very profitable.

What are the Major Groups of INFLUENTIAL Factors?

The following play a major role in reducing the effect of most if not all LIMITING factors:

• Topsoil pH (nutrient availability)
• Subsoil pH (root access to sub-soil moisture)
• Soil Organic content and Soil Biology
  • Improved soil structure
    • Better rainfall penetration and infiltration
    • Improved germination
  • Nutrient release
  • Increased plant health
  • Nutrient and Cation Balances (nutrient availability and soil structure)
  • Barriers to root access to subsoil (compaction, sub soil pH)
  • Planting Date

What are the Major Groups of LIMITING Factors?

Different people will choose different groups. These are the ones consistently showing with me.

• Knowledge, Planning and Management
• Climate
• Soil condition (Soil Reservoir)
• Nutrition
• Pest, Disease and Weed Control

Knowledge, Planning and Management

This applies to all the above, however it is good to reinforce the importance of it. The best farmers are those who have perfected this.

Climate

Apart from irrigation and greenhouses there is little we can do about controlling the climate. However we CAN plan around it and do things that optimise the climate we are given. E.g. If much of our rainfall runs off the land it is wasted, hence by increasing water penetration and infiltration we effectively increase our rainfall. The same goes for enabling roots to access this stored water.

Soil Condition

The most critical area of focus for most climates is to maximise the condition of your soil. A deep soil with high organic content and optimal pH, allowing deep root growth which can easily be filled by the rain we get is first prize. This, I believe, is where the biggest improvement can be made. We however tend to neglect our soils in favour of ‘quick fixes’, like extra fertiliser.

Nutrition

We can save a lot of money by optimising our soils nutritional balances. Precision farming has already proved this. However the efficacy of improving soil nutrition is determined by the condition of our soil reservoir. The better the soil reservoir the better the plant can utilise fertilisers we apply, AND the more available those fertilisers will be.

Pests & Disease

There are some exceptions but generally, the ‘fitter’ your plant, the better it is able to fight off pests and disease. A soil in good condition where nutrition is balanced will generally result in reduced pest and disease problems. Sulphur plays an important role in most of a plant’s natural defence chemicals. Getting sufficient Sulphur into your fertilisation program is a must. The least expensive of your N, P and K fertiliser options contain NO Sulphur. Very noticeable reductions in insect attack on soybeans were noticed this last season in Cradock where gypsum was applied, and I believe we will see the same effect on plant diseases.