GB2291641A - Fertiliser composition - Google Patents

Abstract

A fertiliser composition for correcting iron deficiency in plants and trees comprises a mixture of an iron salt with a polyhydroxycarboxylic acid and/or a derivative thereof which forms an iron complex in aqueous solution that is stable under alkaline conditions. The acid, preferably D-2,3,4,5,6-penta-hydroxycaproic acid, may be present in the form of a sodium or potassium salt or a lactone of the acid.

Description

FERTILISER COMPOSITION This invention relates to a fertiliser composition for agricultural use and more particularly to a fertiliser composition containing iron for use in alkaline growing conditions.

Iron deficiency in citrus fruit trees resulting in low fruit yields and poor quality is a particular problem in Southern Spain where the soil and irrigation water are highly alkaline.

Under alkaline conditions iron sulphate and most other iron containing products are precipitated from solution in a form unavailable for uptake by the plant thus rendering treatments ineffective by simple fertiliser compositions containing iron sulphate or these other products.

It is already known to solve this problem by the use of chemicals such as ethylenediamine-N,N-bis(2-hydroxyphenylacetic acid) (EDDHA) and diethylenetriaminepentaacetic acid (DTPA) which form stable soluble iron chelates under alkaline conditions that allow uptake of the iron.

Such chemicals, however, are generally inefficient and tend to be expensive so that their use leads to increased cost and reduced profitability for the farmer. Additionally, the use of such chemicals can be undesirable from environmental considerations.

The present invention has been made from a consideration of the above mentioned problems and seeks to provide a fertiliser composition for the efficient supply of iron in alkaline growing conditions.

According to the present invention a fertiliser composition for agricultural use, especially in alkaline growing conditions, comprises a mixture of an inorganic iron salt with a polyhydroxycarboxylic acid and/or a derivative thereof.

The fertiliser composition has been found to increase the concentration and bioavailability of iron for uptake by forming an iron complex in aqueous solution that is stable under alkaline conditions.

As a result, the fertiliser composition is particularly suitable for use in highly alkaline and/or iron depleted growing conditions by addition to the soil, irrigation water or in the case of hydroponics, to the growing medium.

Formulations of the fertiliser composition may be used dry in the form of powders, granules or pellets or in aqueous solution for addition to the soil, irrigation water or growing medium. Solutions of the fertiliser composition can also be used for foliar application by spraying.

Pellets having a pre-determined substantially uniform weight may be provided such that the required dosage for a particular treatment is obtained by using an appropriate number of pellets.

In this way, accuracy and reliability of treatment can be ensured in a simple manner which avoids the user having to weigh out the required quantity for each treatment.

Aqueous solutions can be made up as required from dry formulations of the fertiliser composition or by diluting an aqueous concentrate of the fertiliser composition.

Preferably, the iron content is provided by ferrous sulphate, but other sources of iron may be used including salts of organic and inorganic acids.

Suitable derivatives of the polyhydroxycarboxylic acid are those which, on addition to water, are hydrolysed to the conjugate polyhydroxycarboxylic acid. For example, salts, preferably the sodium or potassium salts, or esters (lactones) may be used. Formulations of the fertiliser composition may contain combinations of polyhydroxycarboxylic acid and/or derivatives thereof.

Typical formulations of the invented fertiliser composition which have been found suitable for treatment of iron chlorosis of citrus fruit trees are provided by the following Examples.

Example 1 A powder formulation containing 12% w/w elemental iron based on: 428.69 FeSO47H20 285.79 D.2,3,4,5,6-pentahydroxycaproic acid (sodium salt) Example 2 A powder formulation containing 12%w/w elemental iron based on: 600.09 FeSO47H20 400.09 D-2,3,4,5,6-pentahydroxycaproic acid Example 3 An aqueous solution containing 54g/l elemental iron based on: 238.1 gel FeSO47H20 152.4gel D-2,3,4,5,6-pentahydroxycaproic acid These formulations produce an iron complex having a stability constant (K) of 37.2 which makes them ideal for use in alkaline conditions.

By way of comparison, the stability constant (K) of iron complexes obtained from mixtures of ferrous sulphate with other chelating agents are given in Table 1.

Table 1

K Chelating Agent 15.9 nitrilotriacetic acid tNTA) 19.8 hydroxyethylenediaminetriacetic acid (HEDTA) 25.1 ethylendiaminetetraacetic acid (EDTA) 28.0 diethylenetriaminepentaacetic acid (DTPA) 34.0 ethvlenediamine-N,N-bis(2-hydroxyphenYiacetic acid) (EDDHA) With the exception of EDDHA these complexes of iron tend to be unstable at high pH values, i.e. alkaline conditions. Furthermore, such complexes contain lower elemental iron contents than provided by the present invention.

Other features, benefits and advantages of the invented fertiliser composition will be further understood from the following Examples in which the pH stability of an aqueous solution of an iron fertiliser composition according to the invention is described in Example 4 and the treatment of growing plants with the aqueous solution of Example 4 is described in Example 5.

Example 4 An approximately 100 ppm (parts per million) iron solution was made by diluting an aqueous solution of an iron fertiliser composition according to the present invention containing 5.4% w/v iron (1.84 cm') to 1 dm3 with distilled, deionised water.

A 100 cm3 aliquot of this solution was transferred to a polypropylene beaker and the pH measured (sample C1) using a Radiometer PHM85 pH meter fitted with a Radiometer GK2401C combination glass electrode. Nine further 100 cm3 aliquots of the solution (samples C2 to C10) were transferred to individual polypropylene beakers and the pH of these solutions was adjusted over the range 6.00 to 11.5 by adding appropriate quantities of standard (2.00M) hydrochloric acid (HCI) and standard (2.00M) sodium hydroxide (NaOH). The colour of the solution changed from iight yellow to green to orange with increasing pH.

The solutions were allowed to stand, with occasional shaking, for 14 days at ambient temperature. After this period, the pH of each solution was recorded. Each solution was then filtered through Whatman GF/C fibre glass filter paper. A 10 cml aliquot of the filtrate was transferred to a volumetric flask (100 cm3) and diluted to the mark with distilled, deionised water. The total iron concentration was recorded using a Pye Unicam Atomic Absorption Spectrophotometer. The results are set out in Table 2.

Table 2

y | Sample Initial pH Final pH Fe (ppm) % Difference C1 3.96 3.60 104.5 C2 6.10 4.38 103.5 -1.0 C3 6.95 4.61 103.5 -1.0 C4 8.05 5.22 104.5 0.0 C5 8.57 6.18 104.0 -0.5 C6 9.02 7.09 103.5 -1.0 C7 9.56 7.53 104.0 -0.5 C8 10.03 9.48 107.5 2.9 C9 10.57 10.28 106.5 1.9 C10 11.52 11.62 104.5 0.0 The above results show (within experimental error) that the solution is stable and that there is no reduction in iron concentration over the pH range 6.0 to 11.5.

Example 5 Tomato plants (Lycopersicon esculentum cv "Moneymaker") were raised from seed in perlite using water for irrigation. After four weeks growth under glasshouse conditions individual plants were moved into 7 cm plastic pots, again using perlite as the growing medium.

A first group of ten control plants was treated with a complete micronutrient solution minus iron (Fe). A second group of'ten trial plants was treated with a complete micronutrient solution containing an iron fertiliser composition according to the present invention as an iron (Fe) source.

Each solution was buffered to pH 7.5 prior to application. Nutrient solutions were applied twice weekly, and plants were watered with distilled water at other times on demand.

Plants were cultivated under these conditions for eight weeks, then harvested for evaluation. A visual comparison showed growth of the control plants was less than that of the trial plants and the leaves of the control plants showed signs of Fe-deficiency chlorosis whereas comparable leaves of the trial plants showed no signs of Fe-deficiency chlorosis.

The following parameters were measured for each replicate plant: 1) Total leaf fresh weight 2) Total leaf dry weight 3) Total stem fresh weight 4) Total stem dry weight 5) Chlorophyll 'A' content of leaf 6) Chlorophyll 'B' content of leaf The performance of the iron fertiliser composition according to the invention was evaluated on the basis of this data and the results are set out in Table 3.

Table 3

Control Plants Trial Plants Total leaf dry weight (1) 2.50 + 0.030 3.15 + 0.21 Total stem dry weight 1 1.04 + 0.006 1.63 + 0.19 Chlorophyll 'A' content of leaf 2 7.30 + 0.240 14.60 + 0.85 Chlorophyll 'B' content of leaf (2) 2 4.20 + 0.110 8.30 + 0.23 (1) mean dry weights (g) in relation to Fe source (2) mgig fresh weight values given + se, n = 10.

The above results reflect the improved growth and absence of Fedeficiency chlorosis found by visual comparison of the trial plants with the control plants and clearly indicate the effectiveness of the invented iron fertiliser composition as an efficient iron (Fe) source for crop plants under alkaline conditions.

Other advantages of the invented fertiliser composition include low production costs and compatibility with other chemicals for use in irrigation systems, hydroponics and sprays. The invented fertiliser composition is also environmentally friendly being a derivative of naturally occurring compounds (starch) and being biodegradable.

Claims (16)

Claims:

1 A fertiliser composition for correcting iron deficiency in plants and trees comprises a mixture of an iron salt with a polyhydroxycarboxylic acid and/or derivative thereof capable of forming an iron complex in aqueous solution which is stable under alkaline conditions.

2. A fertiliser composition according to Claim 1 wherein formulations of the mixture are in the form of powders, granules or pellets.

3. A fertiliser composition according to Claim 2 wherein pellets are of pre-determined substantially uniform weight.

4. A fertiliser composition according to Claim 2 or Claim 3 wherein the elemental iron content is approximately 12% w/w.

5. A fertiliser composition according to Claim 1 wherein formulations of the mixture are in the form of an aqueous solution.

6. A fertiliser composition according to Claim 5 wherein the elemental iron content of the solution is approximately 5% w/v.

7. A fertiliser composition according to Claim 5 or Claim 6 wherein the solution is provided as an aqueous concentrate for dilution prior to use.

8. A fertiliser composition according to any one of the preceding Claims wherein the iron content is provided by an iron salt of an organic or inorganic acid.

9. A fertiliser composition according to Claim 8 wherein the iron salt is ferrous sulphate.

10. A fertiliser composition according to any one of the preceding Claims wherein the polyhydroxycarboxylic acid is in a form which is hydrolysed on addition to water.

11. A fertiliser composition according to Claim 10 wherein the mixture contains the sodium or potassium salt or the ester (lactone) of the polyhydroxycarboxylic acid.

12. A fertiliser composition according to any one of the preceding Claims wherein the polyhydroxycarboxylic acid is D-2,3,4,5,6-pentahydroxycaproic acid.

13. A fertiliser composition for correcting iron deficiency in plants and trees substantially as hereinbefore described.

14. A method of supplying iron to a plant in alkaline conditions by application of a fertiliser composition according to any one of the preceding Claims

15. A method according to Claim 14 wherein the fertiliser composition is applied to the soil, growing medium or irrigation water for increasing the concentration and/or bioavailability of iron for uptake by the plant.

16. A method according to Claim 14 wherein the fertiliser composition is applied foliarly for uptake by the plant.