Monitoring Myths

Crop and soil monitoring is an integral part of the biological farming approach. In fact, it could be argued that the comprehensive and integrated testing technologies involved are what differentiates biological agronomy from conventional agronomy. I have argued for years that this proactive monitoring approach is infinitely superior to the simplistic “record and react” response of the chemical system. During 15 years in the field I have seen nothing that sways me from that opinion. The seven essentials for proactive response include the following:

1)A good CEC-based soil test that includes base saturation and measures the more obscure trace minerals like molybdenum, cobalt, selenium and silica.

2)A conventional, dry analysis, leaf test in conjunction with the soil test and repeated at least once during the crop cycle.

3)Occasional monitoring of soil life activity and variety, using either simple fungi and bacteria counts or more comprehensive Soil Foodweb analyses.

4)A Refractometer, which essentially monitors nutrient density within the plant and offers a good guideline of photosynthesis efficiency and associated pest resistance.

5)A Sap pH Meter, which also measures plant health and resistance but can also indicate key nutrient imbalances. This meter can also be used to ensure “ideal” pH of spray solutions.

6)A Horiba Sap Meter for potassium. This is very important because it allows more intensive monitoring of a mineral notoriously difficult to monitor with conventional leaf analysis.

7)A Horiba Sap Meter for nitrate nitrogen. Nitrate excesses compromise crop quality and increase pest pressure and yet we find them everywhere in intensive horticulture.

There are also other valuable tools that may be part of a bio-growers kit including a Sap Conductivity Meter. This tool can be used in the soil or with plant sap to monitor nutrient availability and presence, i.e. most minerals are in salt forms so deficiencies and excesses can be monitored with conductivity. Another tool is the Penetrometer which offers an insight into the expected soil structure changes associated with the adoption of a biological approach. Finally, an infra-red temperature gun is an inexpensive tool to measure water requirements during the crop cycle.

There are a number of myths that have developed during the widespread adoption of this more sustainable approach and these issues need to be addressed.

Myth 1- A good soil test is all that should be required for nutrition programming.

Reality Check:A soil test supplies a picture of nutrient balance and a broad perspective of potential nutrient delivery to the crop. However, different soils give up their nutrients at different rates, based upon their structure, clay component, and biological activity (often indicated by organic matter levels). In classic Albrecht tradition, for example, it is suggested that all soils require around 68% calcium base saturation to ensure adequate calcium for the crop. While this concept is relevant in many soils there are some soils that give up their calcium more easily than others and these soils do not repay the investment associated with unnecessary liming. Similarly, excesses of one mineral can impact the availability of another mineral in one soil but not in another. The solution to this inevitable variability in response and nutrient delivery between different soils is to always include a leaf test with your soil test. The leaf test shows you what the plant is accessing. You may only have 50% base saturation of calcium in a heavy soil (when 68% is considered ideal) but if there is adequate calcium in the leaf then this all you need in that soil. Again, you might have a massive phosphate excess in your soil which could potentially lock up zinc, manganese and iron but this rule is not applicable in every situation. Leaf analysis removes the guess work and increases the precision and cost-effectiveness of fertiliser programmes.

Myth 2 – The relatively new, sap-based leaf tests are of more value due to their faster turn-around time.

Reality Check: Conventional dry leaf analysis has been around for decades and in that time there has been considerable research to determine “ideal” levels for different crops and different stages of the crop cycle. The sap-based analysis, by contrast, is a new technology and the suggested levels are the intellectual property of the developers. Growers are obliged to simply accept that minerals are low, medium or high based upon criteria that are unknown. I have always preferred the “tried and true” for this reason.

Myth 3 – Conventional leaf tests are easily interpreted – you simply address the shortages.

Reality Check: It can be as simple as this but often you need to be aware of other issues. Potassium, for example, is incredibly mobile within the plant and is rapidly dispatched to where it is required. It is usually needed for the growing tips or to size up the fruit. The flaw in conventional leaf testing is that potassium may have moved from the lower leaves to satisfy needs higher up the plant but this early stage of a potassium deficiency remains undetected due to the testing site. There is something you can use to pick up this shortage even though potassium levels appear adequate on the leaf test. If zinc levels suddenly plummet and manganese levels on the leaf test escalate, this is a classic sign of an unrecognised potassium deficiency. The standard “see and correct” approach would not work here. The plant does not need zinc and it doesn’t have too much manganese. The simple correction of the potash deficiency will rapidly correct the other issues. An excess of copper can hinder uptake of phosphorus, zinc and iron and the solution is not necessarily to apply large amounts of these nutrients but to reduce copper inputs, through the use of bio-control agents, and to immobilise the excess copper in the soil using soluble humate granules. 20 kg of soluble humate granules per hectare is the maximum single application and this is equal to a massive 106 litres of liquid humic acid per hectare. This high dose serves to immobilise copper reducing the antagonism of these other minerals but it also has a very valuable biological benefit. Humic acid is the most powerful known promotant of beneficial fungi in the soil (including Mychorrizal fungi). Mychorrizal fungi are principally concerned with the delivery of phosphate and zinc to the plant so the humic acid serves a dual function. It stops copper from impacting phosphorus and zinc and it also increases the uptake of these two minerals via serious biostimulation of Mychorrizal fungi.

The other proven strategy when interpreting leaf analysis data is to try to achieve luxury levels of the four key minerals that are termed “the big four”. These include calcium, magnesium, phosphorus and boron. There are two synergistic pairs in this group. Boron enables calcium to perform its myriad functions and magnesium is a phosphorus synergist. All four minerals are involved in photosynthesis and hence their importance. If you can successfully achieve luxury levels of all four on your leaf test then you are set for a bumper, disease-free crop. The best tools to achieve this goal are the NTS Micronised Mineral Suspension Products (MMS). These liquids feature very high analysis of just the minerals required without any unwanted tag-ons.

Myth 4 – Refractometers and Sap pH Meters both measure nutritional status so you don’t need both.

Reality Check: The refractometer measures dissolved solids as light passes through or refracts from the nutrients present in the leaf sap. The associated brix reading serves as a guideline for nutrient density and indicates how well the plant is photosynthesising. Low brix levels indicate increased pest pressure as pests always prefer plants with poor nutrition. That substandard nutrition may be linked to a lack of key nutrients like calcium, phosphorus or potassium or it can be related to an oversupply of nitrate nitrogen. Nitrates always enter the plant with water and dilute the other nutrients present, creating a calling card for insect pests. The Sap pH Meter also offers an indication of mineral status but can be more diagnostic when seeking precision. If the sap pH is below the desired level of 6.4 then the plant is lacking one of the major alkalising minerals, i.e calcium, magnesium, potassium or sodium. The lower the pH, the higher the fungal pressure as these pathogens flourish in acid conditions (just like candida in an acidic human host). Conversely, if nitrates are high (they have diluted the alkalising minerals with the water with which they arrive) or if the key acidifying minerals are lacking then the sap pH will be high and this tends to increase insect pressure. What are the acidifying minerals? The two minerals always linked to acidity are phosphorus and sulphur. If a particular food is considered to be acid-forming in the human body, that characteristic is fuelled by relative levels of phosphorus or sulphur in that food. Rice bran, for example, is very acidifying due to its high phosphorus component while eggs can make you acidic due to their sulphur lode. If your plant sap has a pH of 7.5 then you have high nitrates or low levels of sulphur or phosphorus and this problem needs verification and correction. The principal difference between these tools, then, is that the refractometer is monitoring the presence of minerals, amino acids and sugars while the Sap pH Meter is really just about minerals. Using a combination of monitoring tools can offer good diagnostic potential. For example, if brix levels were low but the dividing line on the refractometer was blurry, then calcium is not the culprit and phosphorus may be suspect. If the sap pH is high (above 6.4) and a Horiba Nitrate Meter confirms that nitrates are not high then we have further indication that a lack of phosphorus may be the problem. Using a similar process of elimination, if the plant sap pH was low (below 6.4), then we assume that one or more alkalising minerals are deficient. If the refractometer line is blurry then calcium is not deficient. If you check lower and upper leaves with a Horiba Potassium Meter and no potassium (K) deficiency is detected then your culprit is probably magnesium.A foliar of magnesium sulphate combined with fulvic acid should correct the situation. The point is that both meters are required to realise this diagnostic potential. The refractometer can measure foliar spray suitability, frost damage potential and weed pressure susceptibility while the sap pH meter offers more precise mineral diagnosis and can double as a pH meter to modify foliar spray pH to increase performance. i.e acidic for a reproductive push and alkaline for a vegetative push. The bottom line is that you need both tools in your kit!

Myth 5 – The Reams Test is of more value because it monitors biological availability of minerals.

Reality Check:We include a basic Reams Test as part of our standard Soil Therapy™ package. This test uses a mild acid to mimic the biological acids in the soil that assist with nutrient availability. It supposedly offers a snapshot of biological activity in the soil at any given time and is very popular with some of the American consultants with links to the US energy farming pioneer, Dr Carey Reams. We have found this test to be inconsistent, confusing and of minimal value although it remains as part of our analysis out of curiosity. Virtually every test comes back with low levels of biologically active phosphorus, including organic paddocks. This could theoretically reflect the decimation of Mychorrizal fungi in most soils (as they are the creatures most linked to phosphorus availability), but it should also be consistently reflected in leaf tests. There should obviously be low phosphorus in the leaf if there is very low levels of biologically active phosphorus in the soil and no foliars have been used, but this is not the case. Similarly, we have not seen much crop related significance to the all-important phosphate to potassium ratio promoted by the Reams people. The inherent value of any concept is based on its performance in the field and in this context, the Reams Test hassimply not delivered.