Eco Landuse Systems Pty Ltd

e-mail: biala@optusnet.com.au website www.elspl.com.au

---

(D24) Wilkinson, K. and Biala, J. (2001) 'Managing soil nutrients with compost'; The Australian Grapegrower and Winemaker, November 2001 (454), 15 - 16

Dr Kevin Wilkinson¹ and Johannes Biala²

¹Department of Natural Resources and Environment, Institute for Horticultural Development, Private Bag 15, Scoresby Business Centre, Victoria, 3176.
²The Organic Force, PO Box 74, Wynnum, Queensland, 4178.

Introduction

Soil degradation and water pollution are a major threat to sustainable agricultural production. Two of the key causes of these problems are declining soil organic matter and our reliance on inorganic fertilisers for plant nutrition. Compost, a rich source of organic matter, is one means of redressing this problem.

The use of composted organic materials in viticulture is gaining momentum. Various reports of research on the use of compost for mulching have been published in this journal recently (Buckerfield and Webster 1999, 2000; Schefe 2000). Much of this research was conducted in 5 Australian States with funding from the Natural Heritage Trust (Wilkinson 2001).

What is compost?

It is important to answer this question first of all because in order to get the best use out of compost, growers must understand what it is and what it isn’t, and also, what it can and can’t do! Compost is made through the controlled microbiological decomposition of organic materials. Emphasis here is placed on the word ‘controlled’ because it denotes the manufacture of a product to specifications. The Australian Standard for Compost (AS4454-1999) is your best guarantee of quality and ensures that a manufacturer’s claims can be supported. Two important quality issues that the Standard guarantees are the elimination of weed seeds and pathogens during composting and the availability of nutrients from the final product.

Various types of composted materials are available and are used for different purposes. The quality of the end product is determined primarily by the processed materials and also by the extent of the composting process. Pasteurised products are not fully matured but are minimally processed to ensure that weeds and pathogens are eliminated. These products are often used for mulching or broadacre application well ahead of planting. In contrast, fully composted materials are in an advanced stage of decomposition and are usually used as soil improvers with nutritional effects or for pre-planting applications.

How is compost used in the vineyard?

Much of the composted materials used in Australian viticulture are manufactured from garden organics (tree prunings, grass clippings and small shrubs). They are typically applied as mulch 5-10 cm deep in a 0.5-1 m band on the soil surface under vine. We have found that 5 cm deep is generally the minimum depth required for effective, long-lasting weed control and moisture conservation. In Europe, mature compost is also used for its fertiliser value and is applied as a side-dressing under vine at a recommended rate of 25 m³/ha/year (Biala 2000).

Compost can also be used successfully to establish a new vineyard. Due to the relatively low nutrient demand of vines, only low-nutrient value composts should be used. Garden organics composts are ideal, but must be fully composted and mature. The recommended rate of application depends on soil conditions (Table 1).

Table 1: Recommended use of low-nutrient, mature compost in vineyard establishment (Stoeppler-Zimmer et al. 1992).

Soil type and conditions	Recommended application rate
Degraded or disturbed soils
-medium/heavy soils	100 – 150 m^3/ha (once)
-light/medium soil	75 – 120 m^3/ha (once)
Soils low in organic matter (<2%)
-medium/heavy soils	75 – 120 m^3/ha (sufficient for 2-4 years)
-light/medium soil	50 – 100 m^3/ha (sufficient for 2-3 years)
Soils high in organic matter (>2%)
-medium/heavy soils	50 – 100 m^3/ha (sufficient for 2-4 years)
-light/medium soil	50 – 75 m^3/ha (sufficient for 2-3 years)

In vineyard establishment, compost can be applied in the rip-line or directly in the planting hole. If applied in the planting hole, low nutrient, mature compost needs to be blended with the existing soil at a 1:2 to 1:4 compost to soil ratio (Stoeppler-Zimmer et al. 1992).

Do you know what you are putting on the ground?

It is most important to understand what is being applied to the soil when using organic amendments and what effect they might have on your soil and crop. First of all, define what your needs and expectations are so that you can choose a product that will deliver the desired outcomes. A single product may not be able to meet all your needs.

A specification sheet showing a typical analysis should be supplied with all compost products and other organic amendments. Product suppliers should provide additional information as to what the various types of organic products can and cannot do. This enables you to decide on the most suitable product for your individual circumstances. In any case, the use of organic soil amendments should be accounted for in the nutrient budget for your vineyard and needs to be considered when planning the fertiliser application program.

A typical analysis for a composted garden organics mulch product is shown in Table 2. This product delivers both macro- and micro- nutrients and has a liming effect that counters soil acidification due to its pH and high calcium content.

Table 2: Typical analysis of a composted garden organics product used as a mulch in viticulture

Characteristic	Units	Typical value
Bulk density	kg/L	0.6
Moisture content	% (w/w)	41
pH		7.3
Electrical conductivity	dS/m	1.8
Organic matter	% (w/w)	51
C:N ratio		35
Ammonium-N	mg/L	4
Nitrate-N	mg/L	0.3
Nitrogen (N)	% (w/w)	0.86
Phosphorus (P)	mg/kg	1,650
Potassium (K)	mg/kg	4,650
Sulphur (S)	mg/kg	1,850
Calcium (Ca)	mg/kg	15,400
Copper (Cu)	mg/kg	54
Lead (Pb)	mg/kg	81
Zinc (Zn)	mg/kg	220

A garden organics mulch is typically low in nitrogen but contains appreciable amounts of calcium and to a lesser extent, potassium (Table 2). Despite this, application of this product at 5 cm deep in a 50 cm bandwidth under vine would supply about 228 kg of total nitrogen (N) per ha (assuming 3000 lineal metres of vines per ha). This is normally far in excess of crop requirements, but in contrast to inorganic N fertilisers, the total nitrogen in compost is only slowly available to the crop over time.

Based on extensive research world-wide, it is estimated that 10-15% of the total nitrogen in compost is available to the crop in the first year. In the example above, approximately one-third to one-half of crop requirements would be met by the compost in the first year (or 23-34 kg N / ha). However, excessive nitrogen may be leached if higher application rates (increased depth or bandwidth of mulch) were administered or if the product contained higher nitrogen levels.

Mulches can also tie-up nitrogen

The above example assumes that a portion of the nitrogen in compost is available in the first year. However, nutrient release figures are generally based on highly matured composts that have undergone an extensive period of controlled decomposition. Many of the composted mulches used in Australia are by contrast less well decomposed and are deficient in available nitrogen. As these products breakdown, they may compete with the crop for available nitrogen in the soil (known as ‘nitrogen drawdown’). A clue that this might happen with our ‘typical’ compost in Table 2 is its relatively high C:N (carbon:nitrogen) ratio. As a general rule, composts need to have a C:N ratio of below 20:1 to reduce the risk of nitrogen drawdown.

In Western Australian trials with pasteurised mulches, the best results tended to be achieved at a low 25 mm application rate. Researchers there suspect that the performance of pasteurised mulch at higher application rates was reduced by nitrogen drawdown. Also, results obtained in Childers, Qld showed that the use of partly composted garden organics as a surface mulch resulted in reduced N levels in the topsoil. However, the reduced nitrogen level brought about by the application of mulch in Childers did not become visible in any way in the vines.

Nitrogen supply has important implications for the control of vigour. This would mean that, where vigour needs to be promoted, additional N may have to be applied at least in the first year to compensate for nitrogen drawdown effects caused by surface mulches. It must be remembered that a counter balance to this effect is the promotion of vigour because of higher soil moisture levels under mulches.

Potassium in compost is readily available

In contrast to nitrogen, the availability of potassium (K) in compost is much higher, probably in the order of 80-100% in the first year. Trials in Qld and Victoria both showed that composted mulches increased soil K levels. At Hickinbotham’s vineyard in Dromana, Victoria, soil K increased from deficient levels to near sufficient levels with the addition of compost. This resulted in an increase in the uptake of K by the vine and a reduction in magnesium (Mg) uptake. High levels of soil K can cause Mg deficiency. However, plant Mg levels in all treatments were still in the adequate range.

Release of nutrients depends on environmental conditions

The level of breakdown of the applied organic materials and hence the release of plant nutrients is also largely determined by environmental conditions. Moisture and temperature are the key factors that govern microbial activity that results in breakdown of organic matter. To date, most available information about the release and uptake of nutrients supplied through compost originates from Europe where climates are moderate and composts are rarely used as mulch.

Considerably more research is needed to understand the mineralisation of nutrients from pasteurised and composted products and the associated nutrient and particularly nitrogen dynamics in Australian vine-growing conditions.

References

Biala, J. (2000). The use of compost in viticulture. A review of the international literature and experience. Report for Natural Heritage Trust, Environment Australia. June 2000.

Buckerfield, J.C. and Webster, K.A. (1999). Compost as mulch for vineyards. The Australian Grapegrower and Winemaker, 27^th Annual Technical Issue. 426a: 112-118.

Buckerfield, J.C. and Webster, K.A. (2000). Vineyard trials show value of mulches- organic matter for better water management. The Australian Grapegrower and Winemaker. 441: 33-39.

Schefe, C. (2000). Composts in viticulture. The Australian Grapegrower and Winemaker. 442:31

Stoeppler-Zimmer, H., Gottschall, R. and Bahlke, A. (1992). Kompost mit Guetezeichen fuer ihren Wein- und Obstbau. Bundesgütegemeinschaft Kompost Region Südwest e.V.

Wilkinson K. (Ed.) (2001). Promoting the use of recycled organic materials in viticulture. Final Report for Natural Heritage Trust, Environment Australia. September 2001.