Author: Mr. Guy Sela, CEO of SMART! Fertilizer Management software and an international expert in plant nutrition and irrigation.
Soon after the dawn of civilization, small groups of humans began to settle in fertile areas where they could surround themselves with land suitable for grain production. In short order, growing human populations sprawled into adjacent areas of food production which were moved and expanded to keep up with the demand for grain.
The human population
Agricultural land use- The continuing decline of arable land per person bodes ill for feeding our growing population, especially considering water shortages, soil degradation, climate change and construction. Graph: Food and Agriculture Organization.
Thus continued the cycle for thousands of years: More population requires more land for agriculture resulting in still more population requiring more land
Man, has consistently turned his efforts toward increasing grain yields. Surprisingly, until the last century, area expansion was still the principal source of growth in world grain production. Then, a transformation occurred.
Emanating from research and trials in Mexico, the Green Revolution employed new agricultural technology to boost yields. Spreading worldwide in the 1950s and 1960s, scientific approaches to crop-raising significantly increased the amount of calories produced per acre of agriculture.
Suddenly, yield-raising technologies exceeded area expansion to become the principal source of growth of grain production.
Green Revolution technologies exponentially increased the amount of grain production, benefiting billions of people and forever changing the way agriculture is managed worldwide. Here are some examples:
Today, in our highly populated world, arable land per capita is, in fact, decreasing. Thus, we are now dependent on increasing yields in order to meet demand for food.
Grain yield is dependent on many factors – soil, irrigation, genetics, climate, cultural practices, pests and disease control and fertilizer application. Crops developed during the Green Revolution are high-yield varieties – domesticated plants bred specifically to respond to fertilizers to produce an increased amount of grain per acre planted. In fact, these high-yield varieties cannot grow successfully without the help of fertilizers.
In fact, research shows that fertilizers can account for 30% to 70% of the yield. This very significant contribution explains why many farmers believe that if they apply more fertilizers, they will obtain higher yields. However, there is a limit to fertilizer effectiveness.
The relation between fertilizer application rates and potential yield is schematically described in the following diagram:
Based on abundant field trials and consequent data analysis, the curve demonstrates the yield response to fertilizer application. We can learn a few things from looking at the graph.
When no fertilizer is applied, yield reaches some minimal level of potential. Then, yield increases along with an increase in the fertilizer application rate.
Eventually, yield reaches its maximum level of potential. Notably, we see that a plant can’t accept more nutrients than it needs, after which addition of fertilizer does not increase the yield.
In fact, when fertilizer application rates become too high, plants suffer from salinity damage and specific nutrient toxicity, resulting in decreasing yield.
Moreover, we have found that since local conditions may vary significantly between fields, a fertilizer-yield curve that was established for one field will not be valid for another, even on the same farm.
In addition, the very same crop might require different fertilizer application rates at different times during the year and in different locales. For example, the potential maximum yield for wheat on this farm might change from year to year due to weather fluctuations.
START YOUR FREE TRIAL OR LEARN MORE
In other words, trying to apply a general fertilizer recommendation across the board is not much better than a wild guess.
To obtain optimal results, you must plan a fertilizer program that is specific to your field in a certain season. Since every field has its own nutrient composition, the accurate approach would be to use soil, plant and water analysis, and to adapt the fertilizer program according to specific conditions.
The yield response curve we presented above shows how fertilizer application rates affect crop yield. But, in fact, it is not only the total fertilizer application rate that is at play here; it is also the application rate of each individual nutrient.
According to Leibig's Law of the Minimum, crop yield is determined by the most limiting factor in the field. This implies that if but one nutrient is deficient, yield will be sub-optimal, even if all other nutrients are available in sufficient quantities.
Not all fertilizer-program recommendations are created equal. We will describe four approaches based on soil tests: (1) buildup and maintenance, (2) sufficiency (both of these are used mainly for phosphorus and potassium), (3) basic cation saturation ratios and (4) the quantitative approach.
Buildup and maintenance refers to the consideration of soil fertility in future years. The objective is to apply more nutrients than the crop removes so that the nutrient level in the soil does not restrict the yield.
The recommendation is made to apply enough fertilizers to meet the nutrient requirements of the crop while building up the nutrient level in the soil to a critical level over a planned timeframe.
Soil test level is maintained at or above the critical level by applying fertilizer at a rate that replaces the nutrients removed by the crop. Nutrient availability in the soil increases over time as more fertilizer is used.
Therefore, risk of nutrient deficiencies related to their availability in soil is decreased, while profitability in a given year increases. Nevertheless, this approach entails the risk of over-fertilizing along with a negative impact on the environment.
The sufficiency approach deals with how fertilizers are applied so as to meet the nutrient requirements of the crop right now. The aim of this approach is to maximize profitability in a given year while minimizing fertilizer applications and costs.
When soil test levels are low, fertilizer rates that are higher than the nutrient removal of the crop are recommended. When soil test levels are high, reaching the critical soil test level, the fertilizer recommendation decreases to near zero.
Mainly concerned with calcium magnesium and potassium, basic cation saturations ratios assume that a certain ratio of cations (positively charged ions) must exist in the soil in order to achieve maximum yield.
Accordingly, the proportion of cations should be 65-85% Ca, 6-12% Mg and 2-5% K. Yet, this approach has many drawbacks since, for example, it cannot be used in sandy soils which hold very small quantities of cations.
In the quantitative approach, the amount of nutrient that has to be applied is the difference between the total nutrient requirement of the crop and the amount of the nutrient available in the soil layer as tested.
This amount is adjusted by dividing it by an efficiency factor (<1), which relates to the efficiency of the fertilizer application and the efficiency of the plant roots in nutrient uptake.
This approach should be used with caution since soil test results are mostly empirical and do not describe the actual amount of available nutrients. However, this approach is very easy to understand and implement and, therefore, is commonly used by many crop consultants and agronomists.
After performing soil tests to distinguishing which nutrients are present or missing and which fertilizer mix we want to apply, we need to decide on the method of fertilization that will work most effectively.
One such method is fertigation through irrigation, where we can add the missing nutrients through the irrigation system (drips or sprinklers).
Another way is to use a basic dressing to add the total amount of nutrients into the ground before sowing. Basic dressing is the only method to fertilize a non-irrigated field.
In our recent studies conducted on corn plants, we found that the use of fertilizer solutions to deal with corn plant macro-element deficiencies has raised the yield production up to 65%.
For comparison, plots that were fertilized according to the corn plants’ general nutrient needs, without consideration of soil analysis, raised the yield production by only 20%, so our method was much more productive.
START YOUR FREE TRIAL OR LEARN MORE
There is only one solution to the modern challenge of feeding our rapidly growing population using smaller growing areas: increase the yield.
The one parameter that can be controlled by growers is the availability of plant nutrients and their application in the right quantities at the right times. Optimal use of fertilization programs that are plot- adjusted can have a significant impact on the yield, expenditure and environment.
Growers must ensure that each plot receives the precise fertigation plan it needs based on its soil characteristics, crop type and the irrigation system. We have proven that using field-specific fertilizer programs and managing them based on tests achieves healthier growth of grain crop resulting in significantly increased yield, lower expense and a better environment.