Interview: State of the soil in South Africa
Independent Soil & Crop Consultant, Thomas Strydom, answers a few questions about the current state of the soil in various regions of South Africa.
During the past few years, many parts of the interior areas have experienced droughts, especially in the western parts. Droughts have a negative impact on the land, but may also be positive, what is your opinion about this?
Droughts can have certain positive as well as negative impacts, as they affect the soil’s chemical, physical and biological environment in various ways. A positive may be that it is one of nature’s ways of replenishing the soil, because of less chemical degradation of nutrients due to smaller crop yields and less nutrient extraction, as well as physical protection of soil with less natural water compaction in sandy soils and lower compaction by tractors and implements, in effect, putting the soil in “a resting period”. During these periods there is also less leaching of important elements such as nitrogen, potassium and sulphur. It is almost impossible for a farmer to see or experience any drought as a positive; unfortunately, they remain part of nature’s cycle. With excessive heat, organic materials on top of the soil can burn to “ash” rather than create humus in the top 200mm. In such cases, nitrogen in the soil will also be used by organisms at the expense of plants. Damage after hard rain, which occurs sporadically, followed by strong winds, is another major problem. Wind erosion is common in times of drought. Certain types of sandy soils in the Western parts also tend to harden in drier years, when fine sand particles become firmly pressed into each other. Natural soil compaction occurs that has a negative impact on root development and distribution of roots through the soil profile. It is also essential to look at the chemical composition of the soil through lab analysis and make the necessary corrections. Soils do not always have effective depth for root development and for this reason, chemical balances must be optimal to ensure better plant growth. By utilising grid sampling, chemical variations can be corrected and eventually eliminated.
What is the overall condition of the soil in the summer production area – e.g. What is the impact of fertiliser and other chemicals over decades?
Due to various problematic cultivation practices there are unfortunately big areas that show compacted layers at depths from 250 to 400mm. This has a huge impact on root development and also the ability of the soil to utilise the nutritional elements that are available. Farmers should focus on detailed grid soil analysis to ensure that the soils are managed efficiently as they can become very difficult to fix. Soils only have the capacity to handle a certain amount of lime and if the need is higher, due to acidity, pH and calcium/magnesium levels, it can be very difficult to overcome the problems in a short period of time. Inclusion of other elements can also be adversely affected, as the ability of plants to capture nutrients decreases drastically at lower pH levels. Adequate calcium levels and more alkaline soil gives plants the ability to handle stress and dry periods better, and up to 2 weeks longer.
What are the most important problems with production soils and how should they be corrected and managed?
There are many variations and problems with regard to soil; producers do not always know and understand the variations and characteristics, and generally deal with them in the same way as their neighbours or predecessors. In many cases, they fail to make sure what is best for their specific farming and environmental conditions. By gathering good information and judiciously respecting nature, the correct steps can be taken, with less mistakes and not so many school fees to be paid.
Read another blog from Arthur: Developing a precision farming system in South Africa
Lime is applied to increase the pH of the soil. Why – what is the ideal pH for the different soil types and why is it important?
It is important that a holistic approach be followed when it comes to field management.
- Chemical soil management must be seen as a whole and not only with regard to acidity; pH levels can indicate that soil is fertile, but it may not necessarily be at its full potential. Potassium levels, in topsoil and subsoil, especially for soybeans, peanuts and sunflowers, which tend to make use of subsoil fertility using their tap root systems, should also be taken into consideration.
- Sandy soils, with low cation exchange capacity will become less fertile faster due to the poor holding ability of cations, as opposed to strong clay soils. Long-term management and the gathering of relevant information is vital, then, in the following years, managing the levels according to what the fertility status indicates. In sandy soils, the physical amounts of elements are very important as they tend to get very low. In clay fields, availability and relationships between elements are again very important; they need to be interpreted by an expert adviser with enough experience, understood as a whole and respected in terms of their characteristics.
- Quality of analysis as well as the source of the lime:
Recommendations and their effectiveness are often only as good as the information on which they are based on, and the quality of the product used. Producers know their fields and what variations manifest themselves, not necessarily the reasons, but they can then be determined. The effectiveness of calcium also differs significantly depending on its source and has to be evaluated by means of laboratory analysis as well as the calcium carbonate equivalent, with quality controls of each product, including the reactivity of the lime. - Different soil types with different chemical properties also play an enormous role and since the yield potential of soils differs as well as chemical extraction per crop, it is important to take grid soil analyses every 2 to 4 years and address the variations. High yields should not always be the only goal; sustainable profitability is what must be pursued. The goal is to maximise and realise the specific potential of the farm.
If it starts to rain, what should one do with the fields in preparation for the coming planting season and why?
If possible, producers should collect good information and then decide what corrective action is needed and what should be planted. Information such as soil analysis, profile soil inspections, moisture availability in the soil, crop rotation planning as well as input product prices, should be taken into account before deciding the way forward. Only once all the information has been obtained is it possible to decide which way to go. It is essential to determine what the most important factors are and where the greatest risks lie and save where you can without directly harming profits. Plants growing on a healthy fertile medium can handle stress conditions better and present the opportunity to realise above normal returns in good circumstances.
