Ten Reasons to Tissue Test.

A refractometer showing sap extracted from plant

Tissue testing is one of the most valuable tools for proactive crop management and yet many growers ignore or under utilise this technology. A simple leaf test before flowering can make a huge difference to profitability. Here are 10 good reasons why every grower should leaf test on a regular basis.

1) To identify soil-based lock-ups.

Even if you have provided all of the relevant minerals and boosted the biology that delivers these minerals, it is still likely that excesses will influence mineral delivery to the plant. Many minerals are antagonistic to others if they are over supplied. Calcium, for example, directly limits the delivery of seven minerals if it is under supplied, as it stimulates the uptake of these minerals. However, if it is over supplied, via too much lime, in a soil lacking the storage capacity for that amount of added calcium, then those same seven minerals are also shut down. This phenomenon is often called “The Goldilocks Effect” because it’s all about supplying just the right amount of this important nutrient. Leaf tests provide an insight into these mineral dynamics and offer the opportunity to develop a strategy to counter these effects, usually through direct supply of relevant minerals into the plant using foliar fertilising.

2) To ensure everything is right at the business end of the season.

Things change when the plant enters the reproductive mode. There is a dramatic increase in the need for sugar production (and delivery) to fuel the formation of seed or fruit and this requires chlorophyll management. It is the chlorophyll-based sugar factories that determine the production of this extra glucose and the efficiency of these sugar factories is determined by the minerals that govern chlorophyll density. We need to test for the presence of the minerals that can create the undesirable stripes, blotches and pale colours at this critical time so we can deliver the missing minerals and reclaim chlorophyll density. This is the part of the season where profitability is determined and it is a brave or foolhardy soul who enters the business end of the season driving blind. It amazes me that any business person could rely on guess work at this crucial time. However, I acknowledge that there are the more enlightened amongst us who understand the requirements of their plants at any given time through a combination of observation, experience and intuition. The rest of us need leaf tests before flowering, for every crop, so we are not driving blind!

3) To determine the need for liming in your particular soil.

The Albrecht-based, cation balancing philosophy has been oversold in relation to its relevance in every soil type. It is claimed that all soils require a base saturation of 68% calcium and in some cases this is simply not true. Some soils give up their calcium more easily than others and if your soil is one of these then you may be wasting large sums of money on liming. Leaf tests tell you how much calcium your plant is accessing. If the leaf test shortages mirror the soil test shortages then it is time to lime. There is another strategy which can help you decide about the merits of any dry mineral application. Micronised Mineral Suspensions (MMS products) can be used to evaluate the field response of any dry mineral fertiliser. We often hear the comment “I didn’t get as much benefit as I hoped from that liming”. While it is much more common to hear positive responses to liming, it is becoming increasingly unacceptable that some growers are investing in calcium and not seeing the anticipated returns on their investment. Here’s what you can do to take the gamble out of this type of fertilising. If you are contemplating liming, for example, then apply 20 litres of Lime-Life to a single hectare along with a kilo of Solubor to ensure that there is enough boron to ensure a good calcium response. The 20 litres of Lime-Life™ will give a rapid response if you need calcium and then you will know that it is worth liming the rest of the farm. Always remember that “Calcium is the trucker of all minerals and boron is the steering wheel”. During my recent seminar tour of New Zealand it was common to see incredibly boron deficient farms where dairy farmers complained about their lack of response from liming. There is no point in addressing your calcium shortage in soils that contain just 0.2 ppm of boron unless you are also going to address the boron deficiency.

4) To avoid over supply of nitrogen.

When a fertiliser gives a big response it is human nature to apply a little more to test the boundaries of the benefit. This is often unkindly called the “moron approach” but it is a major problem in horticulture, particularly in relation to nitrogen. It is more common to see nitrogen “over done” than any other mineral because it is a mineral required in large amounts for healthy plant growth and consequently it can give a big response if it is lacking. The secret is to know when enough is enough and this is when leaf analysis is essential. This might involve conventional leaf testing or D.I.Y. sap analysis using a Horiba Nitrate Meter. Either way the guiding maxim should always be “How low can I go?”. There are two key benefits in adopting this minimalist strategy. The cost of nitrogen is destined to rise and rise, in line with oil, so only applying what is needed, and no more, has obvious economic appeal. Secondly, high nitrate levels in the plant reflect more than wasted nitrogen. They point to a plant that has become a calling card for insect attack due to the nutrient dilution factor associated with nitrate nitrogen. A chief role of insects in the great scheme of things is garbage disposal. They are able to tune in to infra-red radiation from plants. A healthy, minerally balanced plant emits a steady flow of infra-red while a nitrate-packed plant sends out a staccato stream of infra- red radiation. The insect responds, as it is programmed to do, and attacks the “sick” plant. When nitrates enter the plant they are always carried in by water. If nitrates are over supplied then we have a watery plant where other nutrients have been diluted. Modern agriculture need not be at constant war with nature. It’s just that we keep on firing the first shot! Regular leaf tests ensure that we don’t shoot ourselves in the foot through over doing nitrogen.

5) To monitor levels of “The Big Four”.

American consultant, Gary Zimmer, has determined that achieving and maintaining luxury levels of four minerals, according to leaf analysis data, is a key to achieving maximum productivity with minimum strife. These four minerals are calcium, magnesium, phosphorus and boron. All four minerals are intimately involved with photosynthesis, the most important process in plant production, and they comprise two synergistic pairs. Boron is a huge player in calcium performance and magnesium stimulates the uptake of boron. 35% of all of the leaf tests we analyse are deficient in all four of these minerals and it is an extreme rarity to ever see all four at luxury levels. The game plan, then, is to lift the levels of these key minerals and this involves a precision approach involving high analysis mineral inputs with no tag ons. What is the use of calcium nitrate to lift calcium, for example, if you already have far too much nitrate nitrogen (as is so often the case)? Similarly, why select magnesium sulphate to boost magnesium, when you already have excess levels of sulphur? We have found that Micronised Mineral Suspensions, involving liquid fertilisers containing suspended particles of miniscule size, can be tremendous tools in achieving the elusive luxury levels we are seeking. Lime-Life™, for example, contains 40% calcium compared to just 18% in calcium nitrate and it doesn’t contain any unwanted extras. Similarly Mag-Life™ contains more than double the magnesium than magnesium sulphate in a far more stable form. The problem with this exciting, yield-building strategy is that it is not that easy to achieve. We have found that all movements in the right direction will prove beneficial but you will need regular leaf tests to monitor your progress.

6) To check that potassium is present when it is most needed.

In this instance conventional leaf testing is not the tool of choice. Potassium is the most mobile of all minerals and it often moves from the lower leaves to the top end of the plant, where it is required to size fruit or fuel growth at the growing shoot tips. Hence, the leaf sample, typically selected from the last fully developed leaf, can often reflect K levels in the region to which potassium has moved, rather than supplying an accurate indication of overall potassium status. By the time that the potassium deficiency has extended up to the zone you are measuring, you often have a serious shortage which will prove costly in the final analysis. The Horiba Potassium Meter is an invaluable tool to avoid these costly oversights. It is simply a matter of measuring the lower leaves and upper leaves and K levels should be the same at both sites. The moment the levels in the lower leaves are more than 10% lower than the upper leaves you have detected a potassium shortage and should act immediately. You will be amazed, if you adopt this approach, to realise just how strong the potassium draw-down can be when the plant enters the reproductive mode. You will also be surprised to observe the powerful antagonistic effect of excess nitrate nitrogen on potassium availability. Nitrates, when oversupplied, will shut down potassium faster than a house cat will claw the knee upon which it sits, at the sound of a fridge door opening (dogs are a lot less fickle!)

7) To see that you maintain enough silica for cell-strengthening protection.

Silica is becoming the hot ticket for Ag science researchers. This neglected mineral, which was previously considered a ‘non-essential’ nutrient, is now known to be a major star in pest protection. It is also an important player in photosynthesis, stress resistance, heavy metal management, sodium tolerance and nutrient delivery. While there have been no “ideal” leaf levels determined for most crops we have been able to determine general performance zones based upon observation and grower reports. Recently a NSW blueberry grower reported sensational shelf-life for his produce when his leaf levels of silica were at 1200 ppm. When he neglected his regular silica applications and the leaf levels fell to just 300 ppm so did his fruit quality. The shelf-life was a fraction of the original but began to improve as soon as he resumed his applications of Dia-Life™. Dia-Life™ is based upon micronised diatomaceous earth which contains 85% silica dioxide.

We have found that small, regular applications of this suspension via fertigation, results in substantial increases in the levels of silica in the leaf.

8) To avoid the undesirable build up of copper in the plant based on abuse of copper fungicides.

Copper fungicides are often overused and the copper excess in the soil and plant can create several problems. Copper kills beneficial fungi along with the pathogens and it continues to compromise the soil food web for many years if soil levels are allowed to escalate unchecked. Copper can also have an antagonistic effect upon the uptake of several minerals including zinc, iron and phosphorus. The negative effect upon zinc and phosphorus availability is two pronged. There is both a chemical and a biological explanation. The soil species most responsible for the delivery of zinc and phosphate to the plant is mychhorrizal fungi and they are not a big fan of copper. In fact this invaluable creature, which burrows into the roots of the host plant and extends the root’s nutrient uptake potential by 1000%, will fade away as fast as a house cat turns from a nocturnal stalker of native wild life into a the perfect purring pet, come daybreak (It’s not that I don’t like cats …….). The antidote to excess copper levels in the soil (reflected in a leaf test) is a heavy application of humic acid. When humic acid is applied at 20 kg of NTS Soluble Humate Granules™ per hectare the humates buffer the damaging effect of copper while simultaneously stimulating mychhorrizal fungi to deliver phosphate and zinc. The humic acid also solubilises iron to help address the copper-sponsored iron deficit. 20 kg per hectare is the absolute upper limit of humic acid in a single application or you may risk nutrient lock-ups.

9) To monitor herbicide-induced deficiencies of iron and manganese.

When glyphosate, the world’s most popular herbicide, is sprayed upon the entire growing area, as it is in minimum tillage farming and in most orchard and vine crops, there is some collateral damage. Recent research by Professor Don Huber, from Purdue University in the US, has revealed that glyphosate is causing more problems than originally understood. It was known that this popular herbicide can induce spontaneous abortion in pregnant woman and that it kills an important protective species in the soil called Pseudomonas florescens. However it was a surprise to learn that this chemical is also impacting upon the availability of two key nutrients. Professor Huber has shown that when as little as 2.5% of the sprayed chemical comes in contact with the soil it kills the organisms responsible for delivering iron and manganese to the plant. Even with such minimum soil contact Huber measured a reduction in iron uptake of over 60% while manganese fared worse with a reduction of 80%. One strategy to minimise herbicide side-effects is to encourage the rapid removal of glyphosate from the soil after it has disposed of your weeds. This herbicide was originally marketed as completely biodegradable but while bacteria can eat and remove the herbicide residues, they don’t exactly line up for the task! It’s like saying that because bull’s testicles and fish eyes are both edible and nutritious then consumers should queue for the privilege. Recent research has revealed that Glyphosate residues can remain present in the soil for 6 months or longer, during which time the chemical continues to exact a biological and biochemical cost. The key is to encourage the rapid breakdown of residues and this can be inexpensively achieved using the new NTS additive, Herbi-Safe™. Herbi-Safe™ is combined with herbicides at one litre per hectare to remove herbicide residues from your soil within days rather than months.

10) To achieve maximum quality and production.

Profitability is about chlorophyll management. The better you manage the green pigment in the leaf where the glucose building blocks are manufactured, the greater your rewards at the end of the season. Blotches, stripes, pale colours and other cases of chlorosis are examples of poor chlorophyll management. The best way to avoid yield-limiting chlorosis is to conduct regular leaf tests and to correct any deficiencies that are identified. There is also a disease link to trace mineral deficiencies, so ensuring that you maintain good levels of all nutrients in your plants will have many beneficial flow-on effects.