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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 2): Grapevine performance
Johan Fourie1 & Pieter Raath2
1 ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Grapevines, 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.
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). The amount of organic fertilizer or compost necessary to supply sufficient amounts of N to non-irrigated grapevines resulted in an over-supply of K and P in the top soil layers of a medium textured soil (Fourie & Raath, 2009). Zuur (1989) observed that grape yields are reduced by 15-20% in vineyards farmed organically, while Reganold et al. (2001) reported that apple yield and quality was not affected negatively by an organic production system.
Given the luxurious supply of K and P in the top soil layer of the medium textured soil on which the Sauvignon blanc/99 Richter vines were established (Fourie & Raath, 2009), it was important to quantify the reaction of the grapevines. This contributed towards the evaluation 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 detailed experimental lay-out and soil analyses are presented in Fourie & Raath (2009). 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 1. The amount of macro-nutrients applied per treatment per annum is presented in Table 2.
Table 1 (Click image to enlarge)
Table 2 (Click image to enlarge)
Measurements
Shoot mass and grape yield
Shoot mass was determined early August and grape yield determined during harvest. All treatments were harvested on the same date.
Leaf analysis
Leaves, directly opposite the clusters, were collected at berry set for five consecutive seasons. The leaf-blades and petioles were separated immediately after sampling. The samples were analysed for macro- and micro-nutrients as described in Kalra (1998).
Juice analysis
The grapes were harvested when the sugar concentration averaged 22°B. A representative sample (approximately one bunch per experimental vine) from each plot was crushed in a hydraulic press. Free run juice was analysed for sugar content (temperature compensated Abbé refractometer), pH (654 Metrohm pH meter) and titratable acidity (50 mL juice titrated with 0.333 M NaOH to pH 7.0 and expressed as g tartaric acid/L). Total juice N was determined by means of an automated colorimetric method (The Non-Affiliated Soil Analysis Work Committee, 1990), following digestion with selenous acid/sulphuric acid. Total P, K, Ca and Mg concentrations in juice were determined by means of atomic absorption spectrophotometry, following digestion with nitric acid/perchloric acid. These analyses were done for five consecutive seasons (2001/02 to 2005/06).
Experimental wines
Forty kg of grapes were harvested for each replication of the selected treatments. The grapes were crushed, de-stemmed and immediately pressed to 100 kPa in a small-scale pneumatic press. Wine was made from the grapes of each treatment as described by Fourie et al. (2006). The wines were stored at 14°C for three months before they were evaluated. Sensory evaluation was carried out by an experienced panel of 14 members on a nine point scorecard (Tromp & Conradie, 1979). The wines were presented in coded form and evaluated for overall wine quality, as well as for aroma and taste.
RESULTS AND DISCUSSION
Grape yield and shoot mass
The shoot mass in the COP treatment was significantly higher than that of the CP, IP, IPSA, and OP treatments during the 2001/02 season (Table 3). This was attributed to the 95 kg/ha N applied to this treatment compared to the 42 kg/ha N applied to CP, the 49 kg/ha N applied to IP and IPSA, and the 60 kg/ha N applied to OP (Table 2). The soil activators applied in the OPSA treatment resulted in a significantly higher cane mass compared to OP, which received the same amount of N (Table 3). Although not significant, the same trend occurred between the IP and IPSA treatments. This trend occurred in these treatments to a greater or lesser extent throughout the duration of the trial.
Table 3 (Click image to enlarge)
The grape yield in the OP treatment was the lowest throughout the study (Table 4), although the amount of N applied during the growing season was increased by 50 % and 67 % during the 2003/04 and 2005/06 seasons respectively (Table 2). The average grape yield of the OP treatment was between 30% and 42% less than that of the CP, IP and IPSA treatments (Table 4). Adding a soil activator to the compost one week after application (OPSA treatment) resulted in an average yield similar to that of CP, IP and IPSA. As in the case of the shoot mass (Table 3), the grapevines in the IPSA treatment also benefited from the application of a soil activator (Table 4).
Table 4 (Click image to enlarge)
Leaf analysis
The percentage N in the leaf-blades and petioles of the COP treatment was significantly higher than that of the other treatments during the 2001/02 season, with the exception of the OPSA treatment (Table 5). This was attributed to the 95 kg/ha N applied to this treatment compared to the 42 kg/ha N applied to CP treatment, the 49 kg/ha N applied to the IP and IPSA treatments and the 60 kg/ha N applied to OP treatment (Table 2). The soil activators applied in the OPSA treatment seemed to make the organic N more available to the grapevine, while the slow release of N from the compost must have provided a continuous supply of N to the grapevines during the growing season.
Table 5 (Click image to enlarge)
The amount of N applied in the COP treatment was reduced from 95 kg/ha to 38 kg/ha during the 2003/04 season, while the N applied in the OP and OPSA treatments was increased from 60 kg/ha to 90 kg/ha and 100 kg/ha during the 2003/04 and 2005/06 seasons, respectively (Table 2). Despite this, no significant differences could be detected between treatments from the 2002/03 season onwards (data not shown). The % N in the OP and OPSA treatments, however, was slightly higher than that of the other treatments in the 2005/06 season (Table 5). The lack of significant response to the high amount of N applied to the OP and OPSA treatments during the 2003/04 and 2005/06 seasons, was, inter alia, attributed to the high amounts of K applied simultaneously with the N (Table 2), thus suppressing the uptake of the N by the grapevines (Saayman, 1981). Another neutralizing factor could have been the leaching of the excess N from the root zone as a result of high rainfall during October 2005 (145 mm). The lack of plant response to the reduction in the amount of N applied in the COP treatment from the 2003/04 season onwards was attributed to the carry-over effect from the high amount of N applied during the 2001/02 and 2002/03 seasons.
The percentage K in the leaf-blades and petioles of the organic soil management treatments was significantly higher than that of the CP and two IP treatments throughout the duration of the trial (Table 6). This was attributed to the application of K in the first-mentioned treatments, while the latter received none. The level of K in the leaf-blades and petioles of the OP and OPSA treatments exceeded that of the maximum norms for leaf-blades (1.2%) and petioles (2.9%) as reported by Saayman (1981) throughout the trial (Table 6). Similar results were achieved with the COP treatment in the 2001/02 and 2002/03 seasons. The amount of K applied in this treatment being reduced from 61 kg/ha K in 2002/03 to 24 kg/ha K thereafter (Table 2) resulted in the level of K being reduced to approximately the maximum acceptable levels (Table 6). The application of organic compost or Neutrog® (Bounceback) and Seagro® to supply the N needs of the grapevines on this medium textured soil resulted in an over-supply of K. On sandy soils, however, grapevines may benefit from the supply and slower release of K from these organic fertilizers.
Table 6 (Click image to enlarge)
The percentage P in the leaf-blades and petioles of the COP and OPSA treatments were significantly higher than that of the other treatments from the 2001/02 to 2003/04 seasons (Table 7). It also exceeded the maximum acceptable level of 0.55 % for leaf-blades and 0.60 % for petioles as reported by Saayman (1981). The high P content in the leaves of the COP treatment was attributed to the 44 kg/ha P applied. The application of 27 kg/ha P in combination with the application of soil activators in the OPSA treatment, which must have made the P more readily available to the grapevines, resulted in an increased uptake of P by the grapevines from the early stages of the trial. To ensure a sufficient supply of N from the compost applied in the OP and OPSA treatments parallel applications of 27 kg/ha P from the 2000/01 to 2003/04 seasons and 13 kg/ha and 34 kg/ha of P during the 2004/05 and 2005/06 seasons, respectively, took place. This resulted in the level of P in the leaves of both these treatments being above the maximum acceptable levels mentioned above after the 2001/02 season (Table 7). To ensure a sufficient supply of N in the COP treatment, the amount of P applied could not be reduced to less than 17 kg/ha. Once again this resulted in the P content of the leaves being elevated above the generally accepted maximums throughout the duration of the trial.
Table 7 (Click image to enlarge)
Juice analysis
The sugar and acid content, as well as the pH of the juice did not differ between treatments (data not shown). This indicated that the higher soil water content (Van Huyssteen & Weber, 1980; Wooldridge, 1992; Buckerfield & Webster, 1996) and cooler soil temperatures (Van Huyssteen & Weber 1980; Van Huyssteen et al., 1984) associated with mulches, did not have an effect on ripening of the grapes.
No significant differences in the N content of the juice occurred between treatments throughout the study (data not shown). The K content in the juice of the organic soil management treatments was significantly higher than that of the CP and IP treatments and tended to be higher than that of the IPSA treatment during the 2002 harvest (Table 8). During the 2005 harvest the K content in the juice of the organic soil management treatments was significantly higher than that of all the IP treatments. This trend was detected in the juice of the 2004 harvest as well. The K content in the juice of OP and OPSA was significantly higher than that of the other treatments during the 2006 harvest. These trends reflected the K status of the leaves at berry set. The P content in the juice of the organic treatments tended to be higher than that of the CP and two IP treatments during the 2001/02, 2002/03 and 2003/04 harvests (Table 9). This trend manifested stronger and became significant during the 2004/05 and 2005/06 harvests. Similar to the K content, this trend reflected the P status of the leaves at berry set. No trends were detected in the Ca and Mg content of the juice (data not shown).
Table 8 (Click image to enlarge)
Table 9 (Click image to enlarge)
Wine quality
Only from the 2002/03 season onwards, were enough grapes harvested in the different replications to facilitate statistical analyses of wine quality parameters. Although significant differences did occur between treatments in some years, as far as the total intensity, fullness and overall quality of the wine is concerned, no definite trends could be detected (data not shown).
CONCLUSIONS
Using only compost as nutrient source in a non-irrigated vineyard may reduce grape yields by as much as 42%. Adding a soil activator to the compost one week after application may prevent this from happening. 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. This caused the levels of K and P in the leaves to exceed the generally accepted norms. The luxurious supply of these two elements did not, however, influence the quality of the juice and wine negatively over the medium term, indicating that managing a medium textured soil organically in a non-irrigated vineyard is sustainable over the medium-term. However, the long-term effect of the luxurious supply of P and K by the compost on these medium textured soils and the grapevines needs clarification. Where large amounts of compost are used and microbial activity increases, long-term excessive P availability might affect zinc nutrition of grapevines. 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
Fourie, J.C., Louw, P.J.E. & Agenbag, G.A., 2006. Cover crop management in a Chardonnay/99 Richter vineyard in the Coastal region, South Africa. 2. Effect of different cover crops and cover crop management practices on grapevine performance. S. Afr. J. Enol. Vitic. 27, 178 - 186.
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. The percentage K in the leaves of the organic soil management treatments was significantly higher than that of the IP soil management treatments for the duration of the study and exceeded the generally accepted maximum levels after the 2001/02 season. The percentage P in the leaves showed a similar trend after the 2002/03 season. The level of K and P in the juice reflected the trend that manifested in the leaves, but did not exceed the generally accepted norms. The average grape yield of the organic treatment in which only compost was applied was between 30% and 42% less than that of the IP treatments. Adding a soil activator to the compost one week after application resulted in yields similar to that of the IP treatments. Application of soil activators to the compost and cover crop improved vegetative growth and grape yield during most years in both the IP and organic treatments compared to similar treatments in which no soil activator was applied. Wine quality did not differ between treatments.
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