Nutrient Guide and Turf Disease Management (P1)

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Introduction

The role of plant nutrition is increasing in importance as we strive to improve the quality of playing surfaces under ever more demanding circumstances.

Balanced plant nutrition ensures the grass plant receives an adequate supply of essential nutrients. Each element is required for a number of different functions within the plant. Soil texture, pH, organic matter, nutrient interactions and rainfall all infl uence nutrient availability.

Sherriff Amenity are at the forefront of breakthrough solutions for turf management. Working in conjunction with STRI we run trials to evaluate nutrient input and timing in order to develop nutrient and fungicide programmes and assess product effi cacy as part of an integrated agronomic approach.

This booklet details the role of each element in plant nutrition and how our understanding of these nutrients, along with the results of independent trials, enables us to put together the most comprehensive tank-mix portfolio in the UK amenity market.

The role of plant nutrition

The influence of soil pH on nutrient availability

Soil pH is a measure of the concentration of H+ ions in solution. A low pH value indicates a high concentration of H+ ions and consequently an acidic soil. With alkaline soils the reverse is true; a high pH value signifying a low concentration of H+ ions. The pH scale is logarithmic (to the base 10) so that a change in pH from 7.0 to 6.0 refl ects a 10 fold increase in acidity.

The availability of nutrients to plants is affected by the pH of the soil. Since all nutrients are either weakly positively charged (Cations +ve) or negatively charged (Anions –ve).

The influence of soil pH on nutrient availability

Soil colloids (e.g. clays and humus) have a negative charge and attract positively charged cations. They are held or ‘locked up’ until replaced or released by other cations. In this way they become slowly available to plant roots or are leached through the soil profi le. Anions are not absorbed by soil colloids (both have a negative charge) and so tend to remain in the soil solution.

This makes them readily available to the plant, but also prone to leaching. The exception is phosphorous which behaves chemically as an anion and is held quite strongly in the soil by cations eg. calcium, magnesium and iron.

Clay and humus provide the sites to absorb cations, and ‘Cation Exchange Capacity’ (CEC) is the ability of a soil to hold cationic nutrients. Therefore, soils with higher organic matter or clay content will have a higher CEC than sands, for example. CEC can be determined by soil analysis.

Soil pH infl uences CEC because there is an order of preference in which nutrients are bound to soil colloids.

Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+

FIG 1 Infl uence of Soil pH on nutrient availability.

As soil acidity increases, the concentration of H+ increases (and the soil pH decreases). The H+ ions are attached to the colloids and displace other cations (e.g. Na+ NH4+ K+ Mg2+) from the colloids and into the soil solution. This therefore decreases the CEC of the soil.

Inversely, when soils become more alkaline (pH increases), the amount of available cations in solution decreases because there are fewer H+ ions to push them into the soil solution from the colloids (CEC increases).

A small proportion of soil particles (1-5%) have a positive charge, and similar to the CEC, the Anion Exchange Capacity is a measurement of the positive charges in soils affecting the amount of negative charges which a soil can absorb. Again there is an order of preference of absorption.

H2PO4- > SO4– > NO3- > Cl

AEC generally decreases when pH drops and increases when pH rises. The infl uence of soil pH on the relative availability of each nutrient is summarised in Figure 1.

In general, most micronutrients become less available as the pH increases (eg. manganese, copper, zinc and iron), with the exception of molybdenum and boron (above pH 9) which become more available. Very acidic soils can reduce the availability of potassium, magnesium, calcium and molybdenum. For example, at pH 8 the availability of manganese is reduced in comparison to pH 6.5.

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