As with the N and K supply experiments, rootstock genotype was the major source of variation in shoot dry matter production under varying Si supply treatments, and volkameriana seedlings were more vigorous than seedlings of the other three rootstock genotypes (Table 10). Overall, plants grown with 2 mM Si in the nutrient solution produced approximately one third less shoot dry matter compared to seedlings grown without added Si.
As with the K and Si supply experiments, the major source of variation in shoot dry matter production under different pH treatments was rootstock (Table 14), and volkameriana seedlings were more vigorous than seedlings of the other three rootstock genotypes. The nutrient solution pH had no effect on dry matter production by any of the rootstock seedlings or on %N in shoot dry matter at harvest (Table 15).
Choosing cover crops to enhance ecological services in orchards: A multiple criteria and systemic approach applied to tropical areas
Conventional agriculture is based on a high level of chemical inputs such as pesticides and fertilisers, leading to serious environmental impacts, health risks and loss of biodiversity. Pesticide reduction is a priority for intensive agricultural systems such as orchards. Reintroducing biodiversity in single crop systems can enhance biological regulations, and contribute to reduce the use of chemicals and to provide additional services such as run-off and erosion control. In tropical wet areas, weed control is difficult to manage without herbicides especially when orchards are not located in easily mechanised areas and when labour force is costly. Cover plants can be easily introduced in orchards and could be efficient in weed control and other functions. Based on this assumption, we developed a specific approach for the choice of adapted cover plants in single crop orchards to control weeds and provide additional ecological services. The approach was undertaken on citrus orchards in the French West Indies.
Institute for Micronutrient Technology, India
Potassium is an essential element for plant growth and is an extremely dynamic ion in plant and soil system. As an ion, potassium is highly mobile in the plant system but only moderately mobile in the soil system. Just like humans require a balanced diet with appropriate amounts of carbohydrates, proteins, vitamins, minerals, fats and water, plants too require conditions of balanced nutrition. There is a pre-determined ratio of nutrients that is required by the plant system, depending on its life cycle, environment and its genotypic characteristics, to realize its maximum genetic potential.
Hiu-Ling Liao, Huiqin Chen & Kuang-Ren Chung
University of Florida, IFAS Citrus Research and Education Center
Postbloom fruit drop (PFD) of citrus is caused by the fungus Colletotrichum acutatum. The fungus infects flower petals causing brownish lesions that result in young fruit drop, leaf distortion, and formation of persistent calyces (commonly called ‘buttons’) after the fruitlet drops. Previous studies suggested that an imbalance of plant growth regulators such as auxin, ethylene, and jasmonic acid in C. acutatum-infected flowers, may contribute to young fruit drop.
Girdling increases carbohydrate availability and fruit-set in citrus cultivars irrespective of parthenocarpic ability
F. Rivas, M. Juan, V.Almela, M. Agusti
Departamento de Producción Vegetal, Cátedra de Citricultura, Universidad Politécnica de Valencia.
Departamento de Citricultura, Instituto Valenciano de Investigaciones Agrarias. Valencia, Spain
Department of Fruit Tree Sciences. Israel
The effects of girdling performed at various dates were evaluated during two consecutive years in high- and lowbearing commercial orchards of ‘Fortune’ mandarin and ‘Clausellina’ Satsuma mandarin. The time-dependent response was evaluated through fruitlet abscission, final fruit-set and yield as related to carbohydrate contents in developing fruitlets. A few days after treatment, girdling increased the soluble sugars content (SSC) in fruitlets, reduced the daily fruit drop, and thereby diminished abscission. Application of girdling to low-bearing ‘Fortune’ mandarin orchards was most effective 15 d before anthesis (DBA) and 35 d after anthesis (DAA). It increased yield by 125%. In high-bearing orchards, the best results were achieved by girdling 35 DAA, which increased yield by 28%.
Use of the Cover Crop Weed Index to Evaluate Weed Suppression by Cover Crops in Organic Citrus Orchards
Jose Linares, Johannes Scholberg, and Kenneth Boote
University of Florida, Agronomy Department
Carlene A. Chase and James J. Ferguson
University of Florida, Horticultural Sciences Department
University of Florida, Entomology and Nematology Department
Citrus is one of the most important crops in Florida. During the past decade, increased international competition and urban development, diseases, and more stringent environmental regulations have greatly affected the citrus industry. Citrus growers transitioning to organic production may benefit from premium prices, but they also face many challenges, including development of effective weed management strategies. Cover crops (CC) may constitute an environmentally sound alternative for improved weed management in organic systems.
Harsimrat K. Bons, H.S. Rattanpal
Department of Fruit Science, Punjab Agricultural University, Ludhiana, Punjab, India.
Department of Botany, Punjab Agricultural University, Ludhiana, India.
Citrus is one of the most important fruit tree species in the world, as the fruits are a valuable source of nutrients, vitamins and other antioxidant compounds. The citrus productivity depends on various factors, among these the plant growth regulators holds a prime position. The use of plant growth regulators has become an important component in the field of citriculture because of the wide range of potential roles they play in increasing the productivity of crop per unit area. The plant growth regulating compounds actively regulate the growth and development by regulation of the endogenous processes and there exogenous applications have been exploited for modifying the growth response.
The effects of organic and inorganic mulches on the yield and fruit quality of ‘Cripps’ Pink’ apple trees
Van der Merwe, Johannes Dawid Prins
Thesis (MScAgric)–Stellenbosch University, 2012.
Limited research is available on the effect of mulches on established orchards. Most of the information available stems from research conducted in newly planted orchards or on annual crops such as green peppers and strawberries under greenhouse conditions. To increase the current knowledge on the effect of mulches in established orchards, two field trials were conducted on 14 year old „Cripps‟ Pink‟ orchards. The one trial concentrated on the influence of mulches on the root environment and the other trial on the effect of mulches on growth, yield and fruit quality.
Effects of soil surface management practices on soil and tree parameters in a ‘Cripps Pink’/M7 apple orchard 2. Tree performance and root distribution
John Wooldridge, Johan Fourie & Marlise E Joubert
There are around 22 000 ha of commercial apple orchards in South Africa. Of these, 70% are located in the upland areas of the Western Cape. The apple industry exports c. 40% of its production and supports an on-farm labour force of 27 800 (Hortgro 2012. Apple producers are currently adjusting their production techniques to meet increasing consumer demands for organic over conventionally produced fruit.