Understanding your deficiencies

Maintaining high performance turfgrass stands is a difficult and sometimes thankless task. I mean, how difficult and complicated can it be? Actually, very!

The goal, our aim, is to produce a vigorous turfgrass stand(s) on a continual basis throughout the plants life, regardless of the type of usage received. We need to do this both inside and outside the plants natural growing cycle and at the same time, we must achieve the growth characteristcs and development of the plant we desire in the most economical and practical way. So, what do we need to know? Here's a starter for 10.....

Nutrients and their availability help us manage turf effectively, aid the development of a grass plant that is constantly subject to consistent mowing (physical removal of plant tissue) and forced wear and tear. Fertilisers and their use are a very important tool for a turf grass manager. The nutrients within them affect growth cycles, colour, recovery from wear, encourage a dense and uniform grass stand, help develop the extent of rooting we can effectively achieve. They can encourage and equally discourage diseases, we could go on.

Fertilisers provide the plant with the essential elements for growth and each element of the fertilisers we apply throughout the year will affect the use and availability of other elements.

Back in the 19 Century, Liebig and other scientists discovered that certain elements (N, P, K, Mg so on) are critical for effective plant growth and development. Now, here is the important bit, ‘each element MUST be present in the soil in a specific concentration range for effective plant growth’. If the concentration of any given element in the soil-rooting zone is too low then it will become ‘restricted’ and a deficiency of that element will exist. Eventually, plant growth will be limited in one form or another. Likewise, if one element in the rooting zone is too high then toxicity will occur and plant growth, once again, in one form or another will be limited.

Figure 1- Nutrient concentration in plant.

At this point you may be wondering, why am I continuing to read this? Well, what I aim to do with this short article is to help you identify (by eye and in the field) the signs of nutrient deficiencies that enable you to make informed decisions with future planning.

How can I tell (visually) if I have a problem or not?

Fortunately, for us turf managers, plants will exhibit or express nutrient deficiency symptoms on their leaves or other plant parts just like they do when disease strikes. The good thing is that we can adjust our style of management to suit what is discovered and quickly fix the problem encountered, the bad thing is that by the time the deficiency symptoms are expressed it is too late and some damage will be seen on the plant leaves.

Visually observable symptoms include stunted growth of roots, stems or leaves and chlorosis (yellowing) or necrosis (browning/death) of various organs.

Characteristic symptoms often help us fix the issue with little fuss. Luckily, most of the symptoms we see will be seen on the plants leaves. Root symptoms cannot be easily seen unless the plant is very carefully removed from the soil, washed and then studied! For this reason root symptoms are lesser understood and described by the plant science community.

Expressions of deficiencies

Nitrogen (N) – Soils, especially sand based sports turf soils are more commonly deficient of nitrogen than any other element. The plant will be light green in colour, lower leaves yellow and drying to a light brown colour. Stunted or slow growth may be seen as N is needed in many essential plant compounds.

Phosphorus (P) – Second to Nitrogen, Phosphorus is the second most often limiting element in soils. The plant will be dark green (in contrast to those lacking N), often developing red and purple colours on the leaf and leaf margins. The plants and seedling plants will often be stunted in growth with maturity of young plants being delayed.

Potassium (K) – After nitrogen and phosphorus soils are usually most deficient in potassium. As a note, it is because of the importance of these three elements (N P K) that commercial fertilisers list the percentages of these on the bags as a comparison to others.

Sulfur (S) – As enough sulphate is present in most soils deficiencies of this mineral are quite rare. However, if deficient the plant will exhibit Paling of the older leaves (entire leaf) and tip scorch.

Magnesium (Mg) – Chlorosis of older leaves being the initial symptom, but in this case you will see interveinal chlorosis (yellowing between the veins or yellow stripes). Mg deficiency is almost never limiting to grass plant development.

Iron (Fe) – Pronounced interveinal chlorosis similar to Mg but this time the younger leaves will be affected first. Occasionally, it has been found that with Fe deficiencies the veins of the leaf will turn yellow also. In severe cases the younger leaves will develop necrotic (dead) spots.

Manganese (Mn) – Initial symptoms are similar to that of Iron and Magnesium with interveinal chlorosis but on either the youngest or oldest leaves followed by necrotic spots. Whena deficiency of Fe, Mg or Mn is suspected the best course of action is to use a soil nutrient status test to confirm exactly which element is deficient.

Zinc (Zn) – Leaf margins can be distorted and stunted growth of the plant will be exhibited.

Copper (Cu) – Grasses are rarely deficient in this element as the plant needs so little of it. If there is a deficiency then the youngest leaves will exhibit a dark green colour and be twisted and/or otherwise misshapen.

Molybdenum (Mo) – Quite rare again, mid-stem and older leaves develop interveinal chlorosis, progressing to the younger leaves. The youngest leaves may be severely twisted and then die.

Boron (B) – Visual symptoms take a long time to develop as it is slow moving within the plant. Deficiency symptoms develop around the disintegration of internal plant tissue – Soil analysis needed to establish levels with this one!

What to do if a deficiency is discovered?

Once the plant has expressed a deficiency via it’s leaves or by stunted/reduced growth, the best course of action would be to immediately have the soil tested for nutrient levels. It would be possible to have the sap in the leaf tested but this would not give any detail on how bad the deficiency is in the soil nor tell us how much of the ‘missing’ nutrient (quantity) we should apply. So for purposes of effective management a soil test is the ideal first course of action.

But this is not to say that fertiliser application is strictly needed; sometimes it may be necessary to look at the soil itself and decide if an application of nutrient will really help or simply disguise the real issue. Are we managing the soil correctly? Is it aerated, free of compaction, free draining, is it panned? Is there excessive organic layers? Are our irrigation practices really helping or hindering? Is the plant simply suffering from environmental stress? We could go on, but, for the purposes of this particular article we will not.

Of the six major factors affecting the growth of plants (a) Light (b) Mechanical support (c) Heat (d) Air (e) Water and (f) Nutrients only light is not supplied by soils. Soil also supplies the seventeen or so plant nutrients that are essential for plant growth. It makes sense to know what’s going on down there!