Apple Orchard Nutrients and Fertilisers
Soil Management and Fertiliser Use
Early orchards were cultivated by hand or using horse drawn machinery. One result of cultivation is that organic matter in the soil is mineralised and nitrogen is made available to the trees, but this practice is not sustainable. Nutrient and organic matter levels run down, soil is lost and land becomes unproductive.
In early issues of the Journal of Agriculture we can find discussion of various approaches to fertiliser use and soil amendments. There is an early report of sale of fertilisers by analysis, and by 1910, there was regular analysis of fertiliser being sold to ensure that farmers were receiving value for money. Various acts of state parliament (eg the Fertilisers Act 1894 and subsequent Acts) required that the nitrogen, potash and phosphoric acid content of artificial fertilisers should be specified in writing to the purchaser. This was the case in SA until well into the second half of the 20th century.
An article in the first volume of the Journal of Agriculture and Industry of South Australia published in 1897 (page 19) points out this requirement and also notes that the Agricultural Chemist at the School of Mines could be asked to analyse a fertiliser sample to confirm that it met the warranted composition (for a fee of 3 shillings for a single component, or 6 or 9 shillings for any two or three). Analyses of fertilisers were periodically published in the Journal of Agriculture by the Inspector of Fertilisers, and interested readers can follow up this aspect by reference to the journals themselves which are held in the Waite Library.
Blood and Bone were common “organic” sources of nutrients: There are anecdotal reports of growers obtaining offal from the Adelaide Abattoir as a source of nutrients for orchards in the early part of the 20th century. Again the first volume of the journal of Agriculture and Industry (p 56) gives a method for converting bones into fertiliser and recommends rates at which it should be used. Commercially manufactured Blood and Bone meal was used as a fertiliser well into the 1980’s. More recently “organic” fertilisers made from animal waste have become available and are widely used.
Phosphatic fertilisers derived from such sources as cave guano and bones were the most commonly used fertiliser in South Australian Agriculture as a result of the work of Professor Custance of Roseworthy Agricultural College in the 1880’s. Farm yard manure and potash were also recommended in early publications.
Mixed and compound fertilisers became more widely used as growers began to understand the concepts of plant nutrition better. The idea of a “balanced” fertiliser which contained the major nutrients nitrogen, phosphorus and potassium led to the use of mixed fertilisers. Perhaps the best known were Complete D (8:4:8) and Complete E (10:4:4) manufactured by Adelaide Wallaroo Fertilisers Ltd whose Top brand was well recognised in SA. These were mixtures of superphosphate, sulphate of ammonia and potassium chloride.
As the fertiliser industry became more “international” various high analysis generic fertilisers like MAP (mono ammonium phosphate), DAP (di-ammonium phosphate), urea, potassium nitrate and ammonium nitrate became available. Some mixtures were also enriched with micro-nutrients (trace elements).
Fertiliser Application Methods
Over the majority of the 20th Century there was continued discussion about the best way to apply the fertiliser, so that it reached the active root system. A long term fertiliser trial at the Nuriootpa Viticultural Research Station showed that there was a delay in the response of wine grapes to superphosphate that could be explained by slow movement of the relatively immobile phosphorus through the soil profile (Seeliger and French 1971). Work on a pair of long term Riverland fertiliser trials in citrus showed similar behaviour, and this led to the technique of applying P fertiliser in a narrow surface band to saturate fixation sites, and maximise the amount of P moving through the profile to part of the tree’s root system (Ben Robinson). This technique has been widely adopted in orchards and vineyards.
Robinson, J. B. (1970) A new look at phosphate nutrition of citrus. South Australian Department of Agriculture, Bulletin 26/70.
Seeliger, M. T. and French, R. J. (1971) Changes in soil chemical properties in a long-term fertiliser trial in a non-irrigated vineyard. Australian Journal of Agricultural Research 22 931-940
Tulloch, H. W. and Harris, W. B. (1970) Fertiliser responses with non-irrigated Shiraz grapevines, 1944-1966. Australian Journal of Agricultural Research 21 243-352
The availability of high analysis soluble fertilisers has also changed approaches to fertiliser use. In the middle of the 20th century fertilisers were generally broadcast and cultivated into the soil once or twice a season. As irrigation techniques became more sophisticated in the 1970’s, soluble materials such as urea were injected into irrigation lines saving the need to mechanically spread the fertiliser. This ease of application led in turn to “little and often” fertilising schedules, better matched to the needs of trees.
Work by Brian Taylor at the Waite Institute (and later at Tatura in Victoria) suggested that there might be benefits in post harvest application of nitrogen to deciduous tree fruits and “fertigation” as it became known made this simple to achieve.
Foliar nutrition has also become an important tool in the orchardist’s repertoire and South Australian agricultural scientists have been involved in this from the beginning. When zinc deficiency was first identified in the late 1930’s, it was noted that apples were the most sensitive orchard trees. Experiments with foliar sprays were carried out by Harry Kemp and Alan Beare. These showed that winter (dormant) sprays of zinc sulphate at high concentrations (equivalent to 50g perL) would correct the deficiency. Lower rates of zinc oxide foliage sprays (3g perL) were also successful. Zinc nails would also correct the deficiency for a few years. In more recent times a susceptibility of some sprayed apple varieties to surface russet has been observed, and when foliar sprays are applied in apple orchards, this has to be a consideration.
Kemp, H. K. and Beare, J. A. (1944) Little Leaf in Deciduous Fruit Trees and Vines. Journal of the Department of Agriculture of South Australia XLVII, 470-479
A 1926 paper by AL Warren (Assistant Orchardist, Blackwood Experimental Orchard,) in the Journal of the Department of Agriculture mentioned a crude method of soil testing (percentage of lime in the soil) as a way to decide if amendments such as lime are needed.
In the 1970’s, the use of soil chemical analytical services became more widely available than had been the case earlier, and the value of these techniques to help define the nutrients and amendments needed by orchard crops was demonstrated in survey work done by the Department of Agriculture group at Northfield (Ben Robinson and Louise Chvyl). Working with district horticultural advisers and grower groups, it was shown some orchard soils had become very acid and often had high reserves of phosphorus because of long term applications of nitrogenous and phosphatic fertilisers.
By the 1980’s and 1990’s, commercial soil testing (for pH, salinity, extractable nutrient levels and exchangeable cations) had become widely available from departmental laboratories, and various fertiliser companies. The data provided could assist growers make sensible decisions regarding macro-nutrient and trace element applications, and soil amendments. This greatly reduced run off of nutrients into neighbouring streams and rivers.
Soil acidification was not widely recognised as a potential problem in apple orchards until the 1980’s when instances of manganese toxicity (bark measles) were observed in samples from various parts of the Adelaide Hills.
South Australian scientists were pioneers in understanding the role of micronutrients (also known as trace elements) in plant and animal production (during the 1940’s to the 1960’s). Zinc deficiency commonly occurs in tree crops and apples are very sensitive. Harry Kemp and Alan Beare of the South Australian Department of Agriculture were pioneers in the identification of zinc deficiency as the cause of little leaf symptoms, and developed methods to treat the disorder.
Lime and gypsum are now recognised as soil amendments for the treatment of sodic and acid soils respectively.
Soil and plant analysis services are now routinely used by growers.
Leaf Analysis or Tissue Testing
Scientists recognised that the chemical composition of trees themselves could be helpful in indicating if nutrients were in short supply. In the 1950’s and 1960’s “standard ranges” were developed for the concentrations of important nutrients in leaf samples collected at defined times of the year at pome fruit research stations in the UK and the USA.
Early experimental and diagnostic work with plant nutrition was supported by an analytical service offered by the then SA Chemistry Department, but laborious “wet chemistry” methods were slow. It would sometimes take more than 12 months for analytical data from diagnostic samples and field experiments to become available to orchardists or extension officers, which meant that progress was slow.
The Northfield Experimental Laboratories of the South Australian Department of Agriculture were completed in the late 1960’s and well equipped with modern automated and sensitive analytical equipment, which was used in some orchard research work. However the work of these laboratories was largely targeted at broad acre cropping.
In about 1967, the Mill Laboratory was established in rented premises adjacent to the old Loxton flour mill and first Giles Leith then Trevor Glenn developed a rapid turnaround testing service for leaf and soil analysis. This laboratory provided support for the horticultural industries across SA and made the pioneering survey work in apple orchards by Ben Robinson and Louise Chvyl possible. The objectives of this work were to verify standards developed internationally for South Australian conditions, and to identify any specific problems that might be present in orchards.
Nowadays, leaf analysis services are available commercially and better growers will use the data to monitor the success of their fertiliser programs.
Nutrition and Fruit Quality
Instances of Bitter Pit and other forms of fruit breakdown were linked to low fruit calcium levels in the world literature from the 1950’s. Calcium sprays and dips were trialled at various times from then on. (eg articles by John Jacobsen, David Simons and Barry McGlasson in the Journal of Agriculture – see apple storage), and were shown to contribute to improvements in keeping quality.
The concept, developed overseas, of fruit analysis to determine potential influence of nutritional status on fruit storage behaviour was also tested at the Northfield Laboratories for the variety Jonathan but has not been adopted routinely as far as is known.
The increasing use of irrigation and the consequent establishment of pasture sod on the orchard floor have reduced reliance on bagged nitrogen fertilisers. The input of nitrogen from mown swards containing nitrogen fixing legumes (clovers and medics) has not been measured locally, but international work suggests quite significant amounts of N can be made available in this way.
Mown grass swards also provide a more beneficial environment for predator insects, and more optimal temperatures for fruit growth, quality and maturity. A side effect of managing orchards with bare strips under the trees and sod between the rows is that the bare strip is more prone to acidification as cation cycling is not facilitated unless the clippings are moved onto the bare soil.
Footprints of History
Some parcels of land have been orchards for as much as 100 years.
It is still possible to see plots of land in the Adelaide Hills which once were orchards, where the soil loss that occurred between the trees during the period when cultivation was the main method of soil management (this is still apparent as an undulating soil surface).
During the 80 to 100 years until as late as the 1980’s, pest and disease management relied on the use of copper based fungal protectants and lead arsenate as an insecticide against Codlin Moth. Richard Merry, Kevin Tiller and Angus Alston of the CSIRO and the University of Adelaide examined orchard soils in South Australia and Tasmania for residues of copper, lead and arsenic and published their results in 1983. Values were as much as 25 times background values. Copper and lead were retained in the surface soils and some arsenic moved through the profile. Copper is still used in orchards and work of this kind should probably be repeated every 10 years or so.
Merry, R. H., Tiller, K. G. and Alston, A. M. (1983) Accumulation of copper lead and arsenic in some Australian orchard soils. Australian Journal of Soil Research 21 549-561.