Search Results
You are looking at 1 - 5 of 5 items for :
- Author or Editor: James J. Ferguson x
- HortScience x
Citrus rootstock improvement has relied historically on clonal selections chosen from traditional field trials and from cold-hardy scion improvement programs. Although the impact of traditional plant breeding programs on citrus rootstock improvement has been limited because of biological impediments and lack of understanding of citrus genetics, newly developed techniques on the cellular and molecular level have provided new opportunities for progress.
Although trends in citrus rootstocks can be monitored through Budwood Registration data, official statistics are generally not available on rootstocks in bearing groves. Traditional screening programs include initial testing for resistance to fungal and viral diseases, nematode susceptibility, and nursery performance followed by evaluation as a budded tree. Rootstock trials underway include hybrids of `Ruby' orange/trifoliate orange, sweet orange/trifoliate orange, pummelo/trifoliate orange, and `Changsha' mandarin/trifoliate orange.
Our objectives were to determine if leaf N concentration in citrus nursery trees affected subsequent growth responses to fertilization for the first 2 years after planting and how N fertilizer rate affected soil nitrate-N concentration. `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on `Swingle' citrumelo rootstock [C. paradisi Macf. × P. trifoliata (L.) Raf.] were purchased from commercial nurseries and grown in the greenhouse at differing N rates. Three to five months later trees were separated into three groups (low, medium, high) based on leaf N concentration and planted in the field in Oct. 1992 (Expt. 1) or Apr. 1993 (Expt. 2). Trees were fertilized with granular material (8N–2.6P–6.6K) with N at 0 to 0.34 kg/tree yearly. Soil nitrate-N levels were also determined in Expt. 2. Preplant leaf N concentration in the nursery varied from 1.4% to 4.1% but had no effect on trunk diameter, height, shoot growth, and number or dry weight in year 1 (Expt. 1) or years 1 and 2 (Expt. 2) in the field. Similarly, N fertilizer rate had no effect on growth during year 1 in the field. However, trunk diameter increased with increasing N rate in year 2 and reached a maximum with N at 0.17 kg/tree yearly. Shoot number during the second growth flush in year 2 was much lower for nonfertilized vs. fertilized trees. Leaf N concentrations increased during the season for trees with initially low levels even for trees receiving low fertilizer rates. Soil nitrate-N levels were highest at the 0.34-kg rate, and lowest at the 0.11-kg rate. Nitrate-N levels decreased rapidly in the root zone within 2 to 3 weeks of fertilizing.
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. Two field experiments were conducted at Citra in north central Florida from 2002 to 2005, to evaluate the effectiveness of annual and perennial CC to suppress weeds in organic citrus groves. To quantify and compare the effectiveness of CC to suppress weed growth, a new weed suppression assessment tool, the cover crop/weed index (CCWI), was developed using the ratio of biomass accumulation of CC and weeds. Annual summer CC accumulated more biomass in comparison with winter CC. Sunnhemp (Crotalaria juncea L.), hairy indigo (Indigofera hirsuta L.), cowpea (Vigna unguiculata L. Walp.), and alyceclover (Alysicarpus vaginalis L.) all provided excellent weed suppression, which was superior to tillage fallow. Single-species winter CC did not always perform consistently well. Use of winter CC mixtures resulted in more consistent overall CC performance, greater dry matter production, and more effective weed suppression than single species of CC. Initial perennial peanut (PP) growth was slow, and summer planting of PP (Arachis glabrata Benth.) was determined to be the most effective date in terms of weed suppression, which was improved gradually over time, but all planting dates resulted in slow initial growth compared with annual CC. For both PP and annual CC, weed biomass typically was inversely related to CC dry weight accumulation resulting from competition for resources. The CCWI was a suitable tool to quantify CC performance in terms of weed suppression.
A stepwise multiple regression analysis, using payment by processors as the dependent variable (Y) and numerous physical and chemical characteristics as the independent variables (X), demonstrated that the primary factor determining `Manzanillo' olive (Olea europaea L.) value at harvest was size. Optimal crop value correlated strongly with the combined percentage of standard, medium, large, and extra-large olives; R' values were 0.93***, 0.93***, and 0.42 (ns) in 1984, 1985, and 1986, respectively. As the harvest season progressed, increased percentages of olives within these size classifications, not weight increases of individual olives within the size categories, produced the increase in value. Individual olives within size categories maintained the same weight through the harvest season, regardless of tree crop load. The best criterion for predicting optimal harvest time “is the total percentage of standard, medium, large, and extra-large olives.