The influence of nutrient solution adjustment and replacement (management), its electrical conductivity (EC) and plant spacing on yield and quality of strawbeny fruit (var. Torrey) produced in a recirculating hydroponic system was studied at Gosford, New South Wales. Four ways of managing the nutrient solution were examined: (i) pH and EC adjusted daily and the solution replaced every 8 weeks (current grower practice); (ii) as above except that a topping up solution with lower potassium to nitrogen (K: N) ratio was used for EC adjustment; (iii) no daily adjustment of EC or pH and one-third of solution replaced every 2 weeks; and (iv) no daily adjustment of solution volume, EC or pH and full replacement after 8 weeks. Compared with grower practice, these alternative solution management strategies provided no advantage in yield, fruit number, or in the �Brix, citric acid, sweetness or flavour of fruit. Use of a topping up solution supplemented with ammonium nitrate (NH4NO3) and calcium nitrate [Ca(NO3)2] to reduce the K : N ratio from 1.7:1.0 to 1.4:1.0 had no effect (P>0.05) on yield but significantly increased (P<0.05) berry weight and improved fruit aroma. Regardless of which method of nutrient solution adjustment and replacement was used, the chemical composition of the recirculating solution changed markedly over 53 days. The method of nutrient solution management significantly (P<0.05) affected leaf phosphorus (P), calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn) but only Mg fell to a suboptimal level for growth of strawberries. Reducing the EC of the nutrient solution from 3 to 2 dS/m at early fruit set gave heavier (P<0.05) berries compared with constant EC of 2 dS/m. Increasing the EC from 2 to 3 or reducing it from 3 to 2 at early fruit set resulted in sweeter (P<0.05) berries and reducing the EC from 4 to 2 improved fruit aroma. Yield declined (P<0.05) when EC was increased from 2 to 4 dS/m. Solution EC bad significant effects (P<0.05) on leaf P, Mg, Mn and Zn. An increase in planting density from 5.35 to 9.35 plants/m2 lowered (P<0.05) marketable yield per plant and fruit acidity but gave 41% higher (P<0.05) yield on an area basis.

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We studied the behaviour of tomato mosaic tobamovirus (ToMV) in a recirculating nutrient solution. Particles of tomato mosaic virus were found in the nutrient solution 3 days after leaf inoculation of plants and we demonstrated that the level could increase to a concentration readily detectable by electron microscopy. Virions remained infective in nutrient solution for at least 6 months, could infect bait plants and induced systemic symptoms within 10 days. This is the first report of measurement of infective virions in recirculating nutrient solutions. Hydroponic producers should be aware of the potential for rapid spread of virus diseases in soilless growing systems as one infected plant can serve as a source of inoculum that can ultimately result in an epidemic.

The nutrient composition of foliage from mature vines of the kiwifruit varieties, Hayward and Bruno was monitored monthly over 3 consecutive growing seasons in an orchard on the central coast of New South Wales. Within a season, concentrations of N (5.07-2.74%), P (1.0-0.44%), K (3.29-1.95%) and Zn (36-19 mg/kg) in the first leaf after the fruit generally declined while concentrations of Ca (1.4 1 - 4.21%), Mg(0.28-0.50%) and Mn (151-275 mg/kg) increased. Leaf composition was relatively stable in February and this is proposed as a suitable standard sampling time for leaf analysis in New South Wales. Only minor differences in nutrient composition were found between the first leaf and other potential index leaves remaining on shoots at this time. Using this leaf sampling procedure, commercial kiwifruit orchards in New South Wales were surveyed over 3 consecutive seasons. The applicability of the New Zealand leaf analysis standards for use in New South Wales was assessed by comparing the predicted and actual performance of orchards in the survey. Where unreasonable divergence between the two was noted the standards were amended to make them more relevant to field conditions in New South Wales.

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