Building Better Soils and Bigger Roots.
Building Better Soils and Bigger Roots.
Most farming enterprizes have been exposed to declining profitability over the past decade. A whole array of factors have been eating into the profit margins of farmers, and farmers are struggling to stay ahead of the cost crunch. Factors that have had an impact on farm sustainability are rising costs of production, increased competition on the global market, climate change and volatile political- and economic conditions.
This has lead to a situation where each farmer has to re-evaluate his farming enterprize from all angles in an effort to optimize farming operations in order to reduce the cost of production per unit produced. All of this has to be done without causing harm to the environment and the opportunities of the next generation.
When looking at the so-called “low hanging fruit” in achieving sustainability, improving soil fertility and growing resilient, healthy crops are the first things that farmers need to address.
It all starts with building better soils, that are conducive to bigger roots, which results in healthier crops.
1. Soil amelioration
A comprehensive soil amelioration aproach which aims to improve crop production, by unlocking natures full potential, would focus on the following aspects:
▪ Soil physical and chemical attributes
▪ Soil aeration and decompaction
- ▪ Soil microbiology and humus
- ▪ Soil water holding capacity
a. Soilphysicalandchemicalattributes
In order to address soil physical and chemical issues, detailed geo- referenced soil analyses by an accredited soil lab need to be done. The main reason for a geo-referenced soil-analysis is, to be able to address the short commings of the poor yielding areas on a field and to focus the ameliorants only on the portions of a field that show defficiencies or imbalances. An old-style composite sample will not be able to supply this critical information . It is generally accepted that it is easier to improve average farm yield by addressing the deficiencies on the poor yielding areas, than trying to increase yields on the top yielding portions of the fields. The analyses should include information about the soil type, sand- ,clay- and silt content, soil pH and acidity, organic carbon content and the full range of macro- and trace elements.
The first critical step in improving soil fertility is to address soil acidity and pH. Soil acidity has a huge influence on the availability of nutrients to the plant for uptake as can be seen from the table below:
| pH 4.5 | pH 5.0 | pH 5.5 | pH 6.0 | pH 7.0 |
N 30 % P 23 % K 33 %
43 % 31 % 52 %
77 % 48 % 77 %
89 %
52 % 100 %
100 % 100 % 100 %
Any consideration of crop nutrition and fertilization rates is futile, unless soil acidity is addressed. This should be done at variable rates using the geo-referenced soilmaps as guide. The key factor when considering liming, is the reactivity of the lime and this is mainly determined by the fineness of the lime. Granulated micronized lime is a highly reactive and user friendly option to concider, especially when logistics are very expensive and long term access to land is not guaranteed.
The choice between dolomitic and calcitic lime needs to be guided not only by the acid neutralisation capacity of the lime, but also by the Calcium to Magnesium ratio of the soils. The reason for this is that Calcium is a very big ion, and in solution, it moves inbetween the soil colloids and flocculates the soil. Magnesium has the opposite effect and disperses (compacts) the soil. Therefore it is important for optimal aerobic soil conditions, to try and achieve a 4:1 base saturation ratio of Calcium to Magnesium. The next important nutrient in the soil is phosphate. This nutrient is key to plant energy and especially important for root health. The biggest challenge in phosphate management is the fact that phosphate does not move well in soils and that it tends to react with cations in the soil, which causes the bulk of the phosphates in the soil not to be plant available. To determine the portion of phosphate that is plant available, it is useful to analyse the phosphate levels using a weak citric acid extraction (Bray 1 method) and to measure the locked up phosphate reserves, using a strong citric acid extraction (Bray 2 method). This will indicate how much phosphate needs to be added in the form of fertilizer, and how much can be mineralized by using catalysts like polyphosphates or phosphate mineralizing microbes like mycorrhizal fungi or Pseudomonas bacteria . The last important soil chemical factor
affecting soil fertility is soil salinity and sodicity. The moment the Sodium levels go beyond 2% of the base saturation balance or the soil resistance drops below 500 Ohms, the accumulation of salts around the roots starts burning the root tips and root development is restricted. Soil sodicity also collapses soil structure, and causes anaerobic and compacted soil conditions, which are conducive to plant diseases and cause stunted plant growth.
These are the critical soil chemical factors that need to be addressed in order to lay the foundation for building healthy soils.
b. Soil aeration and compaction
In order to achieve big roots, it is essential to have a well aerated, non compacted soil, throughout the whole soil profile.
It is important to establish right from the start whether there are compaction layers in the soil, where they are, and what the cause of the compaction is. The causes for compaction can be linked to soil type, soil chemical composition, tillage practices or a lack of soil organic matter. Surface crusting is mainly caused by high silt content, low organic matter or a lack of calcium. To addres soil capping, retaining organic material on the soil surface is step one. This can be followed by adding soluble Calcium products which help to break the crust. It sometime requires adding a wetting agent and organic acid , to efficiently break the crust and compaction. Planting a cover crop with a deep root system is also a very efficient way of breaking soil compaction. In some cases, where the compaction is throughout the whole soil profile or deeper down in the profile, starting off with a deep ripping action might be neccesary and
then adding Calcium and organic acids to the soil to kick-start root growth and humus building.
c. Soil microbiology and humus
Humus is the foundation upon which soil fertility is built and in the past farmers have tried to increase soil humus by just adding carbon containing materials. In nature, however, humus is built by big root systems in the presence of microbiology. Crops that photosynthesize optimally, produce excess photosynthates (carbon based exudates) which are leached via the roots into the soil. The microbiology in the rootzone is then stimulated by these root exudates to proliferate and perform essential plant and soil functions, of which the building of soil aggregates and humus are core. Mycorrhizal fungi, which grow in symbiosis with plant roots, excrete a carbon rich compound called glomalin. This is the “glue” which sticks soil particles together in aggregates, and builds humus via the humification process. Planting a mixture of various cover crops, speeds this natural humus building process up by hosting a wide variety of soil microbiology, which lives from the root exudates. The breadown of organic matter on the soil surface also contributes to humus in the soil. This process needs to be driven by saprophytic fungi, which are specialists in converting organic material into plant available nutrients and humus. These saprophytic fungi often get killed by chemical fungicide and herbicide sprays. So it is important to re- inocculate the organic matter with saprophytic fungi like Trichoderma Asperrellum. The humus building proces happens in an aerobic environment (mainly top 0-10 cm), and therefore it is important to
control soil oxygen levels. Over irrigation of soils reduces soil oxygen, and therefore proper irrigation scheduling is critical.
d. Waterholding capacity
The waterholding capacity will be dramatically improved if the soil fertility boosting steps are implemented as mentioned in the above paragraphs. By balancing Calcium to magnesium ratios, leaching salts, uplifting soil- compaction and building humus in the soil, the water infiltration rate will also be dramatically increased. This will mean less run-off or erosion, and more rainfall water captured in the soil per rain event.
A cover crop or organic mulch greatly reduces the impact of water droplets on soil compaction and reduces soil water evaporation. The soil aggregates formed in humus rich soils, create macro-pores, which increase water infiltration. It also helps to maintain the ideal moisture to oxygen ration for optimum root growth. These action will reduce the occurence of moisture induced stress and will carry the crops through seasons with sporadic rainfall
2. Bigger roots
Big roots follow oxygen in the presence of water, biology and nutrients
a.Root definition
Roots are the interface between the soil and the plant. This interface is full of microbiology, metabolytes, growth hormones, nutrients and water. The environment in which the roots grow, has a huge influence on root development, nutrient uptake efficiency, the hormonal balance of the plant and the type of microbiology that dominates the root zone. When analysing
roots, we differenciate basically between 3 root types. The big roots are called structural roots and are mainly responsible for plant stability and water uptake. The secondary thinner roots, are called oxygen roots, and mainly transport massflow nutrients like Nitrogen, Sulphur and Boron. The fine hair roots are called the feeder roots and are essential for the uptake of Calcium, phosphate, postassium and the trace elements. These fine hair roots are basically the “mouth” and the “brain” of the plant. The prevalence and distribusion of these various root types, will determine the efficiency of nutrient uptake as well as the balance between vegetative and reproductive plant growth.
b.Optimal plant nutrition with the help of microbiology
Optimal plant nutrition happens in a chemically well balanced soil, with the ideal oxygen/water balance, with a well defined big root system, in the presence of microbiology. This can only be achieved when the soil fertility steps are followed as explained earlier. It is important to keep in mind the varying methods of uptake, which the different nutrients have. Nutrients like Nitrogen, Sulphur and Boron are called “mass-flow” elements, and move easily into the plant by dissolving in the soil water and following the water into the plant. These elements can be taken up by any roots. The second group of nutrients get taken up by the plant via diffusion, meaning that they need to be in higher concentration around the roots than competing elements to be taken up by the plant. Examples of these nutrients are Potassium, Sodium, Magnesium and Calcium. The last group of nutrients do not move easily in the soil profile, and need to be taken up by root contact. An example of such a nutrient is phosphate. For the last two groups of essential nutrients, massive amounts of fine hairroots are essential for their uptake.
Especially Calcium, being a big ion, needs “elastic” white root tips to be taken up by the plant. These are the basic soil chemical factors influencing plant nutrition. In nature however, there is an essential link added to this process, and that is the microbiology, that lives in and around the plant roots. This so-called microbiome, can be seen as the plant’s “kitchen”, where the microbiology combines essential plant nutrients with organic compounds like aminoacids and metabolites and feeds the plant these organic compounds. The moment the plant starts feeding on organic metabolites, instead of fertilizer salts, the reserve plant energy status starts increasing dramatically, because the plant does not need to spend much of its own energy on converting salt based fertilisers into plant nutrients. The result is a plant that has excess energy in the form of complex sugars, proteins, lipids and starches. Such a plant is much more resilient against abiot stress and attacks by pests and diseases. This increases on farm sustainability dramatically!
c.Plant hormonal balance via big roots
Another very important function of big roots is the fact that most of the essential plant growth hormones that regulate plant development, are produced on and around the tips of roots. These hormones include cytokinines, gibberellins, ethylene and absisic acid. Without big root systems, that continuously produce new white root tips, the plants balance between vegetative and reproductive growth , is always out. The reason for this is that plants produce auxines in their new shoots. These auxines drive cell elongation and vegetative growth. To counter this auxine dominance, cytokinines and gibberellins are released from the new root tips, which stimulate cell division, new bud breaks and more fruit. Overly vegetative,
lush plants are often thought to be the results of too much nitrogenous fertilizers. However in many of the cases, it is rather a lack of root volume and the absence of cytokinine producing white root tips that cause these overly vegetative crops. Therefore in order to have well balanced, highly productive crops, it is essential to have a big, healthy rootsystem driving plant growth.
Conclusion
Based on all these factors explained, it is clear that long term farm sustainability can only be achieved by building better soils and bigger roots !