Tzaneen, South Africa
Tzaneen, South Africa

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Oosthuyse S.A.,HortResearch SA | Desmet B.,Charlie SQM 31 Soi Soi 138 | Wongin W.,Charlie SQM 31 Soi Soi 138
Acta Horticulturae | Year: 2015

Bearing 'Nam Doc Mai Si Thong' trees in a non-irrigated orchard in the Chachoengsao Province, Thailand, were either soil-treated in mid-July, 2011, when new terminal shoot development was commencing, with paclobutrazol (PPZ) or were left untreated in this regard. The treated trees were either sprayed or not sprayed with potassium nitrate in October and November to effect terminal bud and inflorescence development. Potassium nitrate (KNO3) was sprayed on October 10, 20 and 27, and on November 3, 2011. In addition, some of the KNO3 sprayed trees were also sprayed with Ethrel/SOP in early September (September 1 and 8) as a measure to prevent early bud development from the new shoots arising after PPZ treatment. Terminal bud swell was first noted on October 20. Tree flowering intensity was recorded on November 10, 24, and on December 8 and 22, 2011. A weather station recorded maximum, average and minimum temperatures, and precipitation. Ethrel/SOP treatment had no apparent effect on the flowering period or flowering intensity. Only one flush materialized after mid-July from which new shoots or inflorescences developed during October and November. The trees not treated with PPZ and KNO3 (control) generally produced new shoots during Nov. and Dec., whereas those treated with PPZ only, generally produced inflorescences during Nov. and Dec. Here, terminal bud development was not concentrated, occurring over the entire period, and had not occurred or had occurred very little by November 10. In the PPZ treated trees sprayed with KNO3, 40-50% of the terminal shoots exhibited extending or flowering inflorescences on November 10. During the 12 days that followed, terminal shoots showing inflorescence development in the PPZ-only treated trees increased to 58%, attaining the flowering intensity level of the PPZ-treated trees sprayed with KNO3. By November 24, 55-65% of the terminal shoots showed inflorescence development in the treated trees, this increasing to 70- 80% by December 22. New shoots as opposed to inflorescences developed from the terminal shoots on the untreated trees in a similar pattern and in the same time period as in the trees treated with PPZ only. The data clearly indicate that PPZ induced the trees to produce inflorescences, and the KNO3 sprays acted to stimulate and concentrate terminal bud development. Vegetative flushing of the untreated trees during November and December indicates that soil water status and air temperatures were not flowerinductive during the period of the study.

In a first experiment, the effect of foliar spray applications on 10-year-old 'Tommy Atkins' trees of potassium nitrate (KNO3), low biuret urea, GA3, CPPU, and NAA on fruit retention, average fruit weight, and tree yield at harvest was evaluated. Urea or KNO3 were sprayed during the inflorescence development period twice, and the growth regulators or hormones after flowering (fruits a pea size), but before the commencement of natural fruit drop shortly after flowering. KNO3 was applied at 4% (w/v), LB urea at 1% (w/v), GA3 at 40 ppm, NAA at 40 ppm and CPPU at 10 ppm, Applications were made singly or in combination. Pruning of the inflorescences during their development to prevent them from becoming large was also evaluated, as was a Boron formulation applied twice on the inflorescences they were developing. In a second experiment, KNO3, LB urea, and growth regular and hormone spray applications on 10-year-old 'Tommy Atkins' trees were made after flowering just prior to the onset of fruit drop, when the fruits were "marble" size, with the same objective as the first experiment. In a third experiment, KNO3 at 2 or 4% (w/v) was sprayed once or twice during the inflorescence development period on young 'Tommy Atkins', 'Heidi' or 'Kent' trees, again with the same objective as the first and second experiment. In the first, the only treatment to result in a clear increase in fruit retention, fruit size and yield was inflorescence application of KNO3. Low biuret urea was phytotoxic, causing blackening of the flowers and developing ovaries. KNO3 + NAA + GA3 also noticeably increased fruit retention, but not tree yield. Inflorescence pruning gave rise to an increase in fruit size, but not retention. Boron application had no apparent effect. In the second experiment, CPPU + GA3 or NAA spraying apparently increased fruit retention. Both treatments increased yield. In the third experiment, KNO3 spray application always increased yield in increasing fruit retention. KNO3 spray application during the inflorescence development period was considered the best option to reduce fruit drop after flowering and to increase tree yield.

The benefit of ameliorating the effects of salinity when using KNO3 as opposed to KCl or K2SO4 as the potassium source in making up fertigation solutions was demonstrated. Three identical experiments were carried out, each on a different crop plant. Nursery 'Valencia' orange trees, and 'Williams' banana and 'Rodade' tomato plants, were transplanted into 2.7-L pots containing river sand or river sand/calcium carbonate (80:20 v/v), and treated with one of four nutrient solutions. One solution contained only Ca(NO3)2 and NaCl, and was applied to all the plants. The remaining three solutions were made up using the same fertilizers except for that supplying K. The K source was KCl, K2SO4 or KNO3. As a consequence the NO3- to NH4+ ratio differed between solutions as well as the Cl- or SO4 2- content. NaCl was added to every solution to impose salinity stress. Elemental content except for that of S and Cl was equal in the K-containing nutrient solutions. Identical experiments were performed on each plant type. In each experiment, growth was most vigorous in the plants treated with the solution made up with KNO3 and least vigorous in the plants treated with the solution made up with KCl. This was reflected by height increases, and fresh weight and number of leaf differences when the plants were lifted. Number of primary roots in banana was commensurate with vigour. Number of leaves showing marginal necrosis in banana or number of wilted leaves in tomato indicated greatest salinity stress following fertigation with the solution made up with K2SO4. In tomato, number of flower trusses, fruit number and yield were greatest where the KNO3 solution was applied and least where KCl solution was applied. Differences in individual fruit weight were not observed. The results clearly indicate a benefit in using KNO3 as opposed to KCl or K2SO4 in fertigating crops growing in desert soils where the irrigation waters are generally saline.

In a consideration of desert tomato (Solanum lycopersicum) culture, three acidic, NaCl-enhanced complete-nutrient solutions differing essentially in potassium (K) source, being either KCl, K2S 4O or KNO3, were applied to indeterminate 'Rodade' tomato seedlings. The plants were grown in pots under shade in river sand. The aim was to assess differences in health as affected by differences in NO3, S4O, NH4, and Cl levels. Plant chlorosis severity was an adequate indicator of plant health, correlating strongly with height growth, fruit set, fruit size, and leaf necrosis incidence. Where KNO3 was the K source, the plants were healthy. Ill health occurred where KCl or K2S 4O was the K source. Presumed inhibition of Na+ and Cl- uptake, and promotion or inhibition of nutrient cation uptake adequately explained the diverse differences in plant health. It was concluded that health may be better assured using KNO3 as opposed to K 2S4O as the K source in sodic sandy desert environments. Addition of K2S4O would be expected to enhance salinity, mainly due to the lower propensity for S4O as opposed to NO 3 uptake. Excess S4O has been associated with suppressed Ca++ and enhanced Na+ uptake.

Oosthuyse S.A.,Hortresearch SA | Holwerda H.T.,SQM Belgiummmm | Desmet B.,Charlee SQM
Acta Horticulturae | Year: 2013

Two experiments, one carried out by the Makin Group, and the other by the P.T.J.A. Wattie, Indonesia, were conducted to determine whether reduced rates of Speedfol B were as effective as conventional rates of Borax in affecting leaf B concentration of oil palm (Elaeis guineensis Jacq.) In both experiments, leaf samples were taken 2, 6, 10, or 12 weeks after B application to assess if differences in rate of effect would occur. In the experiment carried out by the Makin Group, where fiveyear-old palms were used, 100 g of Borax applied per palm was compared with 88 or 53 g of Speedfol B applied per palm. Fifty-three grams per palm of Speedfol B was applied in both dry powder form, and in suspension with 10 L water around the main stem. The B concentration in leaves from trees receiving dry Speedfol B applied at 88 g or 53 g per palm did not differ from those of trees receiving 100 g Borax per palm. In contrast, leaves from the trees receiving the low rate of Speedfol B suspended in water had lower B concentrations than those from trees receiving the higher rate of B as Borax. Leaf B concentration bore no apparent relation to the time delay in taking leaf samples after application. In the experiment carried out by P.T.J.A. Wattie, where three-year-old palms growing in peat-soil were used, 50 g of dry Borax, or 40 or 30 g of dry Speedfol B was applied per palm. Thirty grams of Speedfol B per palm also were applied in 5 L of water around the main stem. The B concentrations in leaves from trees receiving 40 or 30 g of dry Speedfol B or 30 g of wet Speedfol B were not different from those of trees receiving 50 g of Borax. Leaf B concentration bore a quadratic relation with the time delay in taking leaf samples after B application. In both experiments, a difference relating to B product or rate or method of application in relation to leaf sampling date was not apparent.

Tissue cultured banana plants were grown in a mix of river sand and CaCO3 and fertigated with acidic solutions salinized with NaCl. This was done to replicate the typical soil and fertigation condition of desert growers. Two different K sources (K2S4O or KNO 3) were used; either in low concentration fertigation solutions, or in higher (1.5-fold) concentrations. In each set of solutions, the nutrient concentrations, (excepting those for S), were identical when using K 2S4O or KNO3. The experiment was carried out twice, once in summer and once in winter. The aim was to assess differences in growth with time depending on the solution concentration and K source. Fertigation with the lesser concentrated solutions did not lead to a difference in growth between the K sources. Growth was enhanced during winter using the concentrated solutions, with the superiority of KNO3 as the K source not being clear. During summer, growth was depressed using the concentrated solutions when K2S4O was the K-source, whereas it was enhanced when KNO3 was the K source. A number of additional parameters were measured in the winter trial: a greater number of leaves exhibited marginal necrosis when the more concentrated solutions were used, leaf number was slightly greater in the plants fertigated with the lesser concentrated mixes and differences in primary root number were not found. The study suggests high fertigation nutrient rates can be applied to banana plants grown in desert soils with positive effects regarding growth. However, if higher rates are applied, combinations of fertilizers rendering low EC's should be a prime consideration, with KNO3 being the preferential K-source in these conditions.

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