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Effect of organic and integrated soil cultivation practices on soil nutrient status and performance of a Sauvignon blanc vineyard situated in the Paarl wine district (Part 1): Soil nutrient status
Johan Fourie1 & Pieter Raath2
1 ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Soil mineral content, organic production, integrated production, nutrition.
INTRODUCTION
Organic farming became one of the fastest growing segments of US and European agriculture during the 1990’s (Reganold et al., 2001). South African wine producers also responded to this trend to provide consumers with wine from organic origin.
Organic viticulture aims to work with nature’s diversity to create productive ecosystems and soils rich in biological activity, that are well structured and fertile (Jenkins, 1991). The use of organic methods in grape production is, however, contentious. This is due to uncertainty regarding its long-term environmental impact, cost of production and therefore financial viability, as well as the perception that wine from organic origin is of poorer quality. According to Reganold et al. (2001), the Organic and Integrated Production (IP) systems resulted in higher soil quality than the conventional system. The continuous use of livestock manure on agricultural land resulted in a significant increase in soil P that suggested the practice might not be sustainable over the long-term (Hao et al., 2004). Using livestock manure as fertilizer, therefore, necessitates the consideration of application rate and frequency in order to minimize environmental impacts.
Given the growing interest in organic agriculture, this study endeavoured to evaluate organic agricultural practices as a viable approach to wine grape production in South Africa. The results given are from one of the first independent initiatives that compared the impact of different production systems on soil quality, grapevine performance and wine quality.
MATERIALS AND METHODS
Trial layout
The trial was carried out over a period of six years (April 2000 to March 2006) in a four year old non-irrigated Sauvignon blanc/99 Richter vineyard trained on a four strand extended Peroldt trellis system (Booysen et al., 1992). The grapevines were established on a sandy clay loam soil (Table 1) at Plaisir de Merle farm situated near Paarl (33°44’S, 18°57’E), Coastal wine grape region, Western Cape. Mean annual rainfall during this period was 1033 mm, of which approximately 75% fell during autumn and winter. Vines were spaced 1 m in the row and 2.5 m between rows. Treatments were replicated four times in a randomized block design. Each plot (replication) consisted of 7 grapevines and the two adjacent work rows, resulting in a surface area of 105 m2. Individual plots were separated by two border grapevine rows and 14 border grapevines within rows.
Table 1 (Click to enlarge)
From seasons 2000/01 to 2004/05, rye (Secale cereale L. v. Henog) was used as cover crop in the IP and Organic treatments. In 2005/2006 the cover crop was ‘Pallinup’ oats (Avena sativa L. v. Pallinup). The cover crop was sown annually (seeding dates varying between 14 April and 10 May) at 100 kg/ha (Fourie et al., 2001). Seedbed preparation was carried out using a disc harrow approximately six weeks before the seeding date. After sowing (broadcast by hand), the seeds were covered with a disc harrow.
Six soil management practices, namely Conventional production (CP), IP, IP plus soil activators (IPSA), Organic production (OP), OP plus soil activators (OPSA) and Commercial OP (COP) were applied as described in Table 2. The amount of macro-nutrients applied per treatment per annum is presented in Table 3.
Table 2 (Click to enlarge)
Table 3 (Click to enlarge)
Measurements
Soil was sampled annually after harvest from two positions in approximately the middle of the vine row, just before seedbed preparation was done (early March). Samples were drawn from the 0 - 300 mm soil layer up to the 2002/03 season and from the 0 - 150 mm soil layer from the 2003/04 season onwards. Composite samples were analysed for pH (1.0 M KCl), P (Bray II), exchangeable K, Ca, Mg and Na (extracted with 0.2 M ammonium acetate) and organic carbon by means of the Walkley-Black method (The Non-Affiliated Soil Analysis Work Committee, 1990).
RESULTS AND DISCUSSION
The applied organic fertilizer (COP treatment) and compost (OP and OPSA treatments) elevated the level of P in the 0 - 300 mm soil layer to a more acceptable level during the 2002/03 season (Table 4). The following season, the level of P in the 0 - 150 mm soil layer of the organic soil management treatments was significantly higher than that of the CP and two IP treatments (Table 5), and exceeded the norm of 30 mg/kg for this soil type (Conradie, 1994). The organic fertilizer and compost applied resulted in elevated levels of K in the 0 - 300 mm soil layer of the organic soil management treatments (Table 4). This was even more pronounced in the 0 - 150 mm soil layer (Table 5). The level of K in the soil of the treatments in which organic soil management principles were applied was significantly higher than that of the CP and two IP treatments during both the 2002/03 and 2003/04 seasons (Tables 4 & 5). The same trend was detected for Mg. Despite the high Ca content of the compost and organic fertilizer, the level of Ca in the soil did not differ significantly between treatments.
The organic matter content in the 0 - 300 mm soil layer differed significantly during the 2002/03 season, but no definite trends could be detected (Table 4). The % C in the 0 - 150 mm soil layer of the organic soil management treatments was significantly higher than that of the CP and two IP treatments during the 2003/04 season (Table 5).
Table 4 (Click to enlarge)
Table 5 (Click to enlarge)
CONCLUSIONS
The amount of Neutrog, Seagro or compost that was necessary to supply sufficient amounts of N to the non-irrigated grapevines resulted in an over-supply of K and P in the top soil layers of this medium textured soil. The long-term effect of the luxurious supply of P and K by the compost on these medium textured soils needs clarification. Compost composition differs according to the raw materials used; detrimentally high applications of P and K can, therefore, be prevented.
ACKNOWLEDGEMENTS
Financial support by Winetech and ARC, technical support by Isabella Van Huyssteen, Karen Freitag and the staff of Soil Science ARC Infruitec-Nietvoorbij.
For further information contact Dr Johan Fourie, tel (021) 809-3043, e-mail fouriej@arc.agric.za.
LITERATURE CITED
Booysen, J.H., Steenkamp, J. & Archer, E., 1992. Names of vertical trellising systems (with abbreviations). Wynboer September, 15.
SUMMARY
Six soil management practices (treatments) applied in a non-irrigated Sauvignon blanc/99 Richter vineyard on a sandy clay loam soil near Paarl were evaluated over a period of six years, commencing four seasons after planting. The K and Mg contents in the 0 - 300 mm and 0 - 150 mm soil layers of the treatments in which organic soil management principles were applied, were significantly higher than that of the treatments in which the soil was managed according to Integrated Production (IP) principles after the 2001/02 season (second season in which the treatments were applied). The P content and percentage C in the 0 - 150 mm soil layer of the organic soil management treatments were significantly higher than that of the IP soil management treatments as well, but only after the 2002/03 season.
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