3Phase program for growing celery on sandy soils

Introduction

The research which led to development of the 3Phase fertiliser program started in response to the need to phase out poultry manure because of community concerns with its use in near-metropolitan areas. Although a useful soil amendment and source of nutrients, poultry manure stockpiles provided a breeding ground for stable flies and created odour problems.

This 3Phase fertiliser program is based on four years of fertiliser research on celery grown on the sandy soils of the Swan Coastal Plain with sprinkler irrigation. It gave the highest yields and best quality throughout the year, is practical to apply with mechanised equipment, saves labour and minimises nutrient losses to the environment.

The sandy soils of the coastal plain provide a free-draining, easily worked growing medium. Nutrients are freely available in the soil solution. Some nutrients are highly mobile and easily lost through leaching. Nitrate-nitrogen is particularly susceptible to leaching and is a major groundwater pollution concern.

A good commercial fertiliser program should:

• maximise yield and quality with minimum fertiliser input and cost
• minimise adverse off-site effects, including loss through leaching, wind drift or overspray.

The 3Phase fertiliser program is based on research conducted on some of the most infertile sandy soils in Australia and is aimed at developing cost-effective strategies for producing high yield in a ‘worst case’ situation.

Trial sites chosen for this research had no previous vegetable cropping history and irrigation water did not contain nutrients from past cropping activities. No soil amendments such as compost and manure were used (except as commercial controls), but trials were grown in rotation with lettuce and broccoli and there was some carryover of nutrients from crop residues.

Fertiliser and cost savings are achieved in the 3Phase program by making informed choices about fertiliser type, application rates, methods and timing — matching fertiliser application to crop demand. To achieve this, the life of the crop is considered in three phases: establishment, rapid growth and maturation (Figure 1).

Different fertiliser strategies are used to optimise growth in each of these phases and meet the criteria of a ‘good program’.

 Figure 1 Growth phases from planting to harvest

Three growth phases

Phase 1: crop establishment

Good growth in the first two to four weeks of crop life is critical for achieving high marketable yields. Maximising growth in this phase has a major impact on final yield and reduces the number of days from planting until harvest. The benefits of maximising early growth cannot be made up in later growth phases.

To maximise crop nutrition and growth in the establishment phase it is important to keep fertilisers in the top 10–15cm of soil — where young roots are growing — for as long as possible.

During crop establishment on these sandy soils, fertiliser containing low rates of nitrogen and potassium should be applied twice weekly by spraying or broadcasting. Both methods place enough fertiliser within the reach of roots to maintain a steady nutrient supply without excessive loss to the environment, as long as irrigation practices are good and rainfall is not excessive (see Figure 2).

Figure 2 Broadcast or spray applications of fertiliser during crop establishment place nutrients near young developing roots of these plants 15 days after transplanting

Applying granular NPK fertiliser to the soil surface on the day of planting is critically important for achieving maximum yield, whether spraying or broadcasting is used for following applications.

It takes about four weeks in summer and five weeks in winter for the root zone of a celery crop to become extensive enough to intercept nutrients placed everywhere on the soil surface. By maturity, the roots can access water and nutrients from the top 20–30cm of soil.

Phase 2: rapid growth

Once the root system is established, fertilisers are most effectively applied weekly by banding (Figure 3) until row closure.

Figure 3 Banded fertiliser application in the space between pairs of rows is an efficient way to achieve root uptake during the rapid growth phase. These plants are shown 43 days after transplanting

Fertigation or broadcasting can also be used in this phase. Applying the required rates of fertiliser with these methods is difficult without unnecessary water use or the risk of damaged foliage and heads from fertiliser granules lodging among the stalks.

Banding with compound granular fertilisers is most suitable as it minimises labour costs for application compared to single nutrient fertilisers.

Phase 3: maturation

After row closure, the head and frame of plants fill out, drawing accumulated nutrients from the frame developed in earlier stages, as well as from the soil. Weekly application of nitrogen through fertigation is required in the four to eight weeks between row closure and harvest.

This can involve some unavoidable losses from overspray on adjacent crops, younger plantings or uncropped ground, but other methods used in earlier phases are less safe for the crop or practical in this phase.

3Phase fertiliser program

A ‘year-round’ fertiliser program for celery grown on the sandy soils of the Swan Coastal Plain is shown in Figure 4.

Figure 4 3Phase annual fertiliser strategy for celery according to planting date. Planting dates are shown at fortnightly intervals in some months to account for rapidly changing temperatures, rainfall and sunshine hours

This program combines the methods outlined above with recommended rates and preferred products based on current research. Recommendations may change following more research.

Important notes

• Nitrophoska Blue Special® was used as the granular compound fertiliser. It proved the most effective fertiliser for broadcast and banding for efficacy and labour saving. This fertiliser contains 12% nitrogen, 5.2% phosphorus and 14.1% potassium. Other fertilisers with similar analysis may be suitable but need to be tested.
• Trace elements should also be considered in your fertiliser program. Maintaining soil pH with regular soil testing, liming as required and the use of supplementary magnesium should provide adequate calcium and magnesium. An annual broadcast application of complete trace elements is good practice for all crops grown in rotation, while a fertigated application of borax at 15kg/ha three and six weeks after planting is recommended as a precaution against boron deficiency.
• Broadcast or spray applications in Phase 1 can be applied once a week (at double rates) with little or no reduction in final yield when rates of irrigation are low or heavy rainfall is not expected. Twice-weekly applications are recommended when rainfall is expected or irrigation requirements are high.
• If fertiliser in Phase 3 is applied by boomspray, wash residue off foliage to prevent fertiliser burn, as higher rates of fertiliser are applied at this time compared to Phase 1.
• Urea is a suitable all year round source of nitrogen in Phase 3. Sulphate of ammonia has proved less effective than urea during cooler months.

Nitrogen application benchmarks

Figure 5 shows the levels of nitrogen that give maximum yield over the life of a celery crop grown on sandy soils of the coastal plain.

The totals are reported according to planting time.

Figure 5 Nitrogen application benchmarks for life of crop in kg/ha according to the time of planting

If fertiliser application rates exceed those outlined in Figure 4 you are applying too much and losing unacceptable amounts to the environment. Future research is expected to lower these benchmarks even further.

Acknowledgement

Aileen Reid, Dennis Phillips and Helen Ramsey authored the original version of this material.