It is in every grower’s interest to protect the topsoil of their farm as the protection of this valuable resource is essential for the long-term future of any turf business. United States TurfGrass Researcher and soil expert, Professor Dave Kopec was in Australia recently at TurfBreed’s Annual Conference. He dug deep into the importance of soil profiles and rode home the message about looking after this precious, and essential, resource. Here is what he told GROWTH.
Above: Professor Dave Kopec at TurfBreed’s 2019 Conference field day.
How important is it for growers to know their soil profile?
Sod (turf) growers are interested in growing a crop on 3 centimetres (cm) of soil, harvesting, and repeating. Just like growing any plant in a pot (including a grass), the soil should be the same soil from the top of the pot, to the bottom (even if it is not the best soil to begin with).
- Is a visible difference in soil colour, and particle sizes then water movement throughout the entire soil profile can be a real issue. The more the discordant differences there are in the horizon layers, the greater the degree to which water movement will be a problem. If this is the case, the next item to ask and look for is …
- At what soil depth does any change in the entire soil profile occur? If this occurs at a depth of 15cm, you are ok for while … until you harvest soil down to that point. If there is an abrupt layer change close to the surface, then you must realize that surface water penetration may be a problem, because water is hung-up where the two different soils “come together”. In that case, it will perhaps be necessary to aerate with narrow diameter solid tines, so water runs past the hang-up point. Again, the more discordant the different horizons are from each other (in texture and to some extent- colour) the more likely this will result in a potential water management issue.
Many of the farms that I visited in Australia had more or less a uniform soil that was quite deep, although the soil was high in silt and even clay sometimes. The growers in these cases were either (1) using a soil aggravator after harvest to stir up the soil (after fertilisers were applied), or (2) after using a soil aggravator, they followed-up with chicken manure topdressing and lightly dragged it across the surface (to fill in any holes). Or, they re-aggravated again after the manure was distributed, for best results.
What are the basic principles all growers need to know when having their soil profiled?
Dig some holes first! Be able to look down clearly to depth of 45cm. Your eyeballs are your first and usually correct estimation of what is going on. Then if the soil is uniform, sample the top 10cm. Take enough soil that the lab requires for EACH of the following types of soil tests.
Standard chemical test: Provides element amounts of nutrients, soil pH and organic matter content. You are usually adding nitrogen regardless of the soil test results, but extremes in elements can be a tip off to other soil conditions. Disregard iron values in soil and plant tissue tests. The appearance of leaf yellowing on the uppermost younger leaves is a much better indicator that the turf needs iron. The percentage sodium, or Exchangeable Sodium Percentage (ESP), is an important item to look at, since soil sodium often creates soil structure and water infiltration problems.
Mechanical analysis test: Based on the amounts of sand, silt and clay in the lab test results, the lab will tell you the soil textural class (loam, sandy loam, silt clay loam etc…). This will give ballpark hints on how much fertiliser nutrients will be “stored” in the soil, the water infiltration rate of the soil, and the general tendency for that soil to become compacted when mechanical equipment travels over it (especially after irrigations).
If the soil profile is NOT UNIFORM: Perform the same two tests noted above. Look and see how different the result is between the two distinct soil profiles submitted. Certain nutrients may build up in either the “upper” or “lower” soil profile horizons, depending on the two soil textures or “which one lies over the other one”.
If you suspect a saline (salty) soil condition: Whereby you see (1) salty crusts on the outside edges of the irrigated soil and/or (2) poor overall and slow growth (3) short and narrow turf leaves (4) slow pegging of surface stolons (5) poor fill in time between cuts, then perform two standard soil chemistry tests, as two different soil samples.
- Get enough soil by scraping ONLY the top 1cm of soil.
- After you scrape away the above, then sample from 2cm to 15cm, separately.
Dig some holes first! Be able to look down clearly to depth of 45cm. Your eyeballs are your first and usually correct estimation of what is going on.
For both of these separate samples, look at the results for total salinity, and the percentage soil sodium (ESP). The results will tell you the immediate soil surface condition, and the problem happening on the surface only.
In areas of high rainfall, salinity and sodium is usually not an issue, unless the supplemental irrigation water source is saline, for whatever reason.
What are the basic steps for doing the soil-water test on farm?
For soils (see above).
Take enough soil volume that the lab requires for each soil test. For a uniform paddock without a localized problem, you can combine soils from multiple spots within the paddock, mix them up by hand, and then submit a “bulk” sample. If suspect areas exist, sample them and submit them independently but always include a fresh soil sample from a “good area” from the same paddock at the same time.
For water samples:
Get the water from an irrigation head that runs for 5 minutes, not from the dam/water storage. Usually 600 cubic centimetres (0.6 litres) of water is enough. Send the water to the lab in a pre-washed and triple rinsed plastic or glass bottle. If it is warm outside, freeze the sample allowing room for expansion so the container will not crack (remember what happened to the frozen beer bottle you said you would take out of the freezer after work, but forgot). In warm weather, nitrogen and the water pH can change suddenly and drastically in a closed container and give very strange results.
The following recommendations could assist in improving soil management on farms:
- Collate soil data to prepare a soil management plan to address and prevent loss of topsoil.
- Maintain a vegetative buffer surrounding the production area with at least 80 per cent groundcover to reduce erosion risk and dust/sediments entering waterways.
- Apply rubber matting, sand, asphalt, cement or rubble to high traffic areas to reduce dust, mud and soil erosion.
- Avoid slopes greater than 10 per cent due to the increased risk of soil erosion, particularly if minimal vegetation, (however a slight slope encourages drainage).
- Use soil aerators where appropriate to ensure water and nutrients are incorporated into the soil and to minimise runoff. It is common for turf growers to aerate straight after harvest followed by an addition of chicken manure to manage compaction and encourage quicker re-growth. Aeration straight after harvest is reported to provide up to 50 per cent quicker re-growth for up to four weeks weeks after the harvest.
Source: NSW Department of Primary Industries_primefact