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Fertilisation of rootstock mother blocks
Kobus Conradie, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: rootstock mother blocks, fertilisation, nitrogen, grafting material, quality.
INTRODUCTION
Grafted vines are required for the establishment of new vineyards, due to the fact that ungrafted vines are generally not planted in South Africa any more. To satisfy this demand, nurseries usually obtain rootstock material from registered mother blocks. The production practices that prevail in mother blocks may have a significant effect on the quality of the grafting material. One such practice entails the levels at which fertiliser, especially nitrogen (N), is applied. Since producers strive towards optimal cane production, an application of approximately 250 kg N/ha/a is common practice. The necessity of such application, as well as the effect thereof on the quality of grafting material, however, has not been investigated. As far as the demand for other essential nutritional elements is concerned, very little information is available regarding rootstock mother blocks. The bunches of bearing vines contain large amounts of potassium (K), consequently one may expect rootstocks that do not bear to demand less K. Canes and leaves contains large amounts of calcium (Ca), however, which means that rootstock mother blocks, where cane production is the only priority, might require more Ca than bearing vines.
The most important objective of this project was to determine the effect of nitrogen fertilisation on the quantity and quality of rootstock cuttings used for grafting purposes. Secondly, the seasonal demand for nitrogen, as well as that of other macro-elements (P, K, Ca and Mg), had to be determined. Thirdly, broad guidelines for the fertilisation of rootstock mother blocks had to be created.
MATERIAL AND METHODS
Three existing mother blocks were used in the investigation. For the first two, situated in Stellenbosch district, experimental material consisted of 99 Richter (clone RY 13A) and 101-14 Mgt (clone AA 219A), respectively. Soils contained more than 15% clay and could in both instances be classified as Clovelly. Vines were planted 3m x 1.5m, but only the 99 Richter was trellised. In the third block, situated in Wellington, experimental material consisted of Ramsey (clone SC 18S). The soil (Longlands/Fernwood) was sandy (< 6% clay), while organic material content ranged from 0.73% C to 0.48% C. Separate experimental sites were demarcated on sections with high (HO) and low organic material (LO). Planting width was 2.5m x 0.8m and vines were not trellised.
Four fertiliser treatments, namely 100 kg N/ha (N100), 175 kg N/ha (N175), 250 kg N/ha (N250) and 325 kg N/ha (N325) were applied. At the Stellenbosch sites fertiliser was applied by hand, and in Wellington application took place through the drip irrigation system. In all instances 15% of the total amount was applied in September, followed by 25% in each of the following two months (October and November), 20% in December and 15% in January. All treatments also entailed an application of 60 kg K/ha. Fertiliser was applied over three seasons (1997/98 to 1999/2000) and each treatment was replicated five times. Apart from differential fertilisation, normal cultivation practices were followed. These practices included the regular removal of lateral shoots of 99 Richter throughout the season. For 101-14 Mgt and Ramsey, no lateral shoots were removed.
Aerial organs (main shoots, lateral shoots and leaves) were sampled quantitatively, three times during the growing season (end of January, end of March and end of leaf fall). For this purpose one vine per site was used at a time. The mass of the various organs was determined and then analysed for N, P, K, Ca and Mg. Results were used to calculate seasonal uptake patterns for the various elements. Grafting trials were conducted with canes that had been gathered at the end of the growing season. Chenin blanc (clone SN 1061) was used as scion, whereafter grafted vines were planted in a commercial nursery. Percentage take, shoot mass and root mass of these vines were determined approximately eight months after being planted in the nursery.
RESULTS AND DISCUSSION
Total cane production of different cultivars: Total cane production (not necessarily the rootstock component for grafting) was higher for Ramsey than for 101-14 and 99 Richter (Fig. 1). Although Ramsey is usually known as a vigorous grower, different planting widths and trellis systems might have played a role as well. Lower cane mass for 99 Richter can partly be ascribed to the removal of lateral shoots.
Dry mass of canes (ton/ha).
Effect of nitrogen fertilisation on cane production: Nitrogen fertilisation did not have a significant effect on the cane production of 99 Richter and 101-14 Mgt, although cane mass tended to be higher (p = 0.12) for treatments N175 and N250, compared to N100 and N325 (Fig. 1). It is therefore possible that both insufficient and excessive fertilisation may have had a detrimental effect on shoot growth. The latter was possibly the result of nutritional imbalances, which may be induced by excessive applications of N. For Ramsey on soil with higher organic material, fertilisation had no significant effect on cane production and 100 kg N/ha was clearly more than sufficient. For Ramsey on the soil with low organic material, N175 performed significantly better than N100, which means that it was insufficient to apply only 100 kg N/ha. Application of 250 kg N/ha did not result in any further increase, while cane mass tended to be lower for N325.
If the goal is maximum cane production only, the results may be summarised as follows:
Seasonal demand for nutritional elements: Uptake of the different nutritional elements, calculated at a nitrogen fertilisation level of 175 kg N/ha, are indicated in Table 1. Although total cane production (ton/ha) was much higher for Ramsey than for 99 Richter and 101-14 Mgt (Fig. 1), the uptake of N (g/vine) did not differ much between cultivars/soils. This result corresponds with the fact that cane production /vine (not indicated) was comparable for cultivars/soils. Although the P-content of the soils on which 99 Richter and 101-14 Mgt had been planted were comparable (approximately 20 mg/kg), the P-demand of 99 Richter was approximately 40% higher than that of the 101-14 Mgt. In comparison to the 99 Richter and 101-14 Mgt, the Ramsey used even more P, which may have been the result of high P-contents (>120 mg/kg) in the Ramsey soils. It is possible, however, that Ramsey, just like 99 Richter, had a larger P-demand. The K-demand of 99 Richter and 101-14 Mgt were comparable, but 25-30% less than that of Ramsey. Since K-contents were relatively low for the sandy soils on which the Ramsey had been planted, it indicated that the Ramsey had a larger K-demand. Comparable amounts of Ca were taken up by 99 Richter and Ramsey. For 101-14 Mgt, uptake was considerably lower, however, which may be ascribed in part to a lower pH, together with a lower Ca-status for the soil on which this rootstock had been planted. Comparable amounts of Mg were taken up in all instances.
Figures for the seasonal uptake of N, P, K, Ca and Mg (average for the four experimental blocks) indicate that these five elements are taken up in a ratio of 6.7 : 1.0 : 4.4 : 5.1 : 1.8. In the case of bearing vines the corresponding ratio is 5.4 : 1.0 : 4.2 : 2.8 : 0.8. From this ratio, P and K therefore appear to be equally "important" for bearing vines and rootstocks. In rootstocks the relative N-requirement is slightly higher (24%) than in bearing vines, while the demand for Ca (82%) and Mg (115%) is much higher in rootstocks.
Nutritional uptake during the latter part of the growing season: Since lateral shoots were still being removed from 99 Richter towards the end of January, the relative importance of nutritional uptake during the latter part of the growing season (end of January to leaf fall) could not be determined accurately for this cultivar. Percentages should, however, be comparable to that of 101-14 Mgt (Table 2). Uptake of N was higher for 101-14 Mgt (23.3% of annual demand) than for Ramsey (11.1-13.6%). This result can possibly be ascribed to the fact that at the end of January, 101-14 Mgt was growing more vigorously than Ramsey. In comparison to bearing vines (in which approximately 35% of the annual demand is taken up during the post-harvest period) rootstocks take up little N during the latter part of the growing season. In contrast to N, relatively large amounts of P and Ca (approximately 36% of annual demand) were taken up by 101-14 Mgt during the latter part of the growing season. Ramsey, planted on soil with high organic material, took up a smaller fraction (approximately 26%) of the annual demand for these two elements. An even smaller fraction (14.6% for P and 19.0% for Ca) was taken up by Ramsey on soil with low organic material. Uptake patterns for these two elements are therefore to a certain extent influenced by cultivar and/or soil. As with bearing vines, little K (less than 10%) was taken up in the latter part of the growing season. For Mg, however, a very large fraction (34.9% to 43.6%) of the annual demand was absorbed.
Nutritional elements are absorbed largely in February and March, while uptake in April, May and June is very low (data not shown). In practice producers usually apply the final fertiliser increment towards the end of January. Nitrogen fertilisation in particular is avoided from this stage onwards, to allow the shoots to ripen properly. The above results indicate that this approach is a sensible one for N and K, seeing that uptake of these two elements is low during the latter part of the season. It is important, however, for sufficient P, Ca and Mg to be present in the soil. Proper liming and addition of P (where necessary) during soil preparation might help to prevent deficiencies shortages of these three elements.
Results of grafting trial: Nitrogen fertilisation had no effect on shoot mass of the grafted vines (data not shown). The starch content of canes did not differ significantly either, but values were slightly lower for 101-14 Mgt, compared to 99 Richter and Ramsey (Table 3). For 99 Richter and 101-14 Mgt percentage take was not affected by nitrogen fertilisation. For Ramsey on the soil with the higher organic material, however, percentage take was significantly reduced by an application of 325 kg N/ha, while optimal root mass was obtained by the addition of 100 kg N/ha. For Ramsey on the soil with low organic material (LO), percentage take was the lowest for an application of 100 kg N/ha, while application of 250 kg N/ha resulted in an increased percentage take. Application of 325 kg N/ha did not result in a further improvement in percentage take, while root mass did not follow a clear pattern. Application of 325 kg N/ha was apparently excessive for Ramsey on the soil with the higher organic material, while 100 kg N/ha was insufficient for the soil with lower organic material. Nitrogen fertilisation should therefore be adjusted according to the natural N-supply of the soil.
Guidelines for fertilisation of rootstock mother blocks: During the course of the investigation period the production of rootstock cuttings for grafting was in the vicinity of 31 for 99 Richter, compared to 73 for 101-14 Mgt and 50 for Ramsey. No more than 50% of the main shoots produced by 99 Richter could be used for grafting, because the front sections of the main shoots were too thin for grafting purposes during the seasons in question. For 101-14 Mgt the largest parts of the main shoots could be used, while approximately half of the main shoots of the untrellised Ramsey were used as grafting material. For 99 Richter production of rootstock cuttings for grafting (70 000/ha) was therefore half that of 101-14 Mgt (162 000/ha). In the case of Ramsey (with a narrower plant width) production was 250 000/ha. The amount of nutrients required annually by a rootstock mother block, will therefore correlate with total cane production rather than with the number of rootstock cuttings produced for grafting purposes. Although total cane production (ton/ha) was higher for Ramsey (Fig. 1), the different nutritional elements (N, P, K, Ca and Mg) were taken up in more or less comparable absolute quantities (g/vine) by the various rootstocks (Table 1). This means that in practice, nutrient uptake will be broadly dependent on planting width (number of vines/ha). Broad estimates regarding amounts of the various nutritional elements being absorbed over the course of a growing season, are given in Table 4. Calculations were done for a planting width of 3.0 m x 1.5 m (2222 vines/ha) and for one of 2.5 m x 0.8 m (5000 vines/ha). The values in Table 4 are not necessarily identical to the amount of fertilisation that has to be applied, in view of the fact that adjustments have to be made for factors such as soil type and management system. The situation for the various macro-elements may be summarised as follows:
ACKNOWLEDGEMENT
This is a popular extract of a scientific article being prepared for publication in S. Afr. J. Enol. Vitic.. The complete manuscript "Effect of nitrogen fertilization of rootstock mother plantations on quantity and quality of grafting material" is available from the author.
Further queries may be addressed to: Dr Kobus Conradie, tel (021) 809-3025, email: conradiek@arc.agric.za.
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