Evaluating compost and lime effects on soil organic matter, soil microbial communities and the control of Fusarium wilt in commercial tomato grown in Florida's sandy soils

Project Overview

Project Type: On-Farm Research
Funds awarded in 2010: $14,955.00
Projected End Date: 12/31/2012
Region: Southern
State: Florida
Principal Investigator:
Amy Shober
University of Florida

Annual Reports


  • Vegetables: tomatoes


  • Crop Production: nutrient cycling, organic fertilizers
  • Education and Training: extension, on-farm/ranch research
  • Pest Management: chemical control, field monitoring/scouting
  • Soil Management: organic matter, soil analysis, soil microbiology, soil chemistry, soil quality/health


    Single applications of composted yard waste and lime amendments to Florida soils used for commercial tomato production had minimal effect on soil chemical properties and no effect on the incidence of Fusarium wilt. Soil organic matter was higher in soils receiving compost at the 30 ton/acre rate than when compost was applied at lower rates (5 to 20 ton/acre). Soils amended with 20-30 ton/acre compost supported statistically higher numbers of culturable bacteria and lower numbers of culturable fungi during mid-season only. The grower received little benefit from compost and lime additions, suggesting unrecovered costs of processing and applying the compost.


    Vegetable production in Florida and throughout the southeastern U.S. commonly occurs on sandy coastal plains soils. These soils tend to be acidic with low organic matter content. As a result, soils used for vegetable production tend to have low fertility, water holding capacity, and biological activity (Muchovej et al., 2008). Fertility has typically been managed by applying inorganic fertilizers and lime as needed, while soil diseases, nematodes and weeds have traditionally been controlled by fumigation with methyl bromide.

    Producer reliance on inorganic fertilizers to meet crop nutrient requirements does nothing to enhance soil organic matter levels. In addition, fields are commonly left fallow between crop cycles allowing the loss of organic matter as topsoil is eroded by wind or water. The use of methyl bromide effectively sterilizes soils, reducing the level of soilborne pests and pathogens as well as beneficial microorganisms that function to cycle plant nutrients and potentially suppress the effects of harmful organisms. Agricultural transition from methyl bromide has led to a resurgence of diseases caused by soilborne pathogens, especially wilt caused by Fusarium oxysporum f.sp. lycopersici (FOL).

    The management of soil pH with lime has been shown to reduce Fusarium wilt, when nitrate-based N fertilizers are used in place of ammonium-based sources (Jones and Woltz, 1967, 1969, and 1972). Such practices were paramount for the control of FOL race 2 (Jones and Woltz, 1967 and 1969), but efficacy has not been assessed for race 3 isolates. However, pH management varies among tomato growers and is not currently used as a disease management tool because of widespread soil fumigant use (Geraldson et al., 1966; Jones et al., 1966). While commercial tomato cultivars with resistance to FOL race 3 are available, they lack the horticultural traits or resistance to other pathogens that are critical for successful production in Florida. These breeding issues were considered insignificant until recent changes in fumigation practices.

    Research suggests that repeated applications of organic amendments, such as animal manures, biosolids, and composts, can increase soil organic matter level (Darby et al., 2006; Tester, 1990), even in the southeastern U.S., where the organic matter oxidation is rapid (Ozores-Hampton et al., 1998). Soil organic matter has many known benefits, such as increased water holding capacity, improved soil aeration through reduced bulk densities and increased soil fertility (Tester, 1990). Increasing soil organic matter can also enhance microbial activity, which improves plant nutrient uptake and suppression of certain plant diseases (Darby et al., 2006; Stone et al., 2003; Vallad et al., 2003).

    Research clearly indicates that the use of organic amendments and lime can improve soil physical and chemical properties and increase overall crop growth. However, it is unclear whether these practices alone or in combination can sufficiently control soilborne pathogens, such as FOL, when vegetables are produced in sandy soils within a humid, sub-tropical climate regime. It is possible that such practices, if not properly monitored, could actually exacerbate certain diseases caused by soilborne pathogens or lead to physiological disorders due to reduced availability of certain essential nutrients.

    Project objectives:

    The objective of this study was to determine the effect of compost and lime on soil chemical properties (including organic matter), the soil microbial community, including Fusarium spp., and the incidence and severity of diseases caused by soil borne pathogens, such as FOL. Specifically, we evaluated the effect of compost and lime amendments on the severity of Fusarium wilt and soil microbial community structure.

    In addition, we evaluated the effect of compost amendments on soil organic matter under Florida’s humid sub-tropical climate. We also determined the effect of the compost and lime treatments on the availability of essential plant nutrients, including P, K, Ca, and Mg. Both Ca and Mg can form complexes with dissolved organic carbon and be leached from the soil when composts are applied. Losses of Ca and Mg from soils can lead to abnormal fruit development (blossom end rot) and large yield losses.

    Results from this study were shared with the cooperating grower and the greater grower community to provide guidance in the use of soil amendments and soil pH management in commercial tomato. This research was part of a long-term effort by both UF investigators to identify cost-effective cultural practices that reduce the need for chemical pesticides and fertilizers by improving soil conditions that enhance soil microbial populations and activity. Such practices are sustainable, environmentally benign, and have practical applications for conventional and organic crop production in Florida and other southeastern states.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.