Enhancing Soil Quality and Fruit Tree Growth with Arachis pintoi Cover Crops in Hawai’i Orchards

Funded by:

Hawaii Farm Bureau Federation, 2007-2008

Grad student conducting research on perennial peanut

Investigators:

Farmer Cooperators:

Summary

Perennial Peanut groundcover

The use of living mulch (ground cover grown with the fruit trees) is an innovative management strategy that can improve soil quality, reduce grower reliance on synthetic inputs and improve the overall sustainability of tropical fruit orchards in the State (Hensley et al., 1997; Mullahey et al, 1994; Shen and Chu, 2004). Perennial peanut was introduced to Hawai’i almost 20 years ago for use as a living mulch for orchards, and has since been used by growers throught the state as a living mulch in perennial cropping systems (CTAHR, 2009). Its ability to fix atmospheric nitrogen, produce dense cover with little maintenance and protect soil from erosion makes it an appealing groundcover. Fruit tree growers who employ perennial peanut have reported improved tree growth and reduced reliance on fertilizers (CTAHR, 2009), but now data on soil quality under established peanut in Hawai’i is available. Clement and DeFrank (1998) observed a decrease in yield of peach palm grown with perennial peanut up to 18 months after peanut living mulch establishment. These authors suggested yield reductions were due to N competition, but neither plant tissue nor soil nutrient levels were reported. Overall, there is far too little information available on contribution of perennial peanut to soil physical, chemical and biological quality under Hawaiian conditions. Also, we have no knowledge of how perennial peanut influences the growth and development of newly planted fruit trees during the critical period of initial establishment in the first year. Hawai’i fruit tree growers who wish to improve the sustainability of their operations by using nitrogen fixing ground covers cannot make economic or environmentally sound decisions about reducing the application of fertilizers and other off-farm inputs because we have no reliable information regarding the contribution of legume cover crops to soil quality in Hawai’i orchard systems or its effect on fruit tree growth.

This project will: (1) Determine the relationship between soil quality and perennial peanut density at two ommercial fruit tree orchards on O’ahu, and (2) Compare the cost of initial propagule type and density with differences in rate of canopy establishment, soil nutrient content and early growth of three tropical fruit species.

Assessing coverage with perennial peanut

Recommendations

To maximize the benefits of perennial peanut as a living mulch in orchards, we recommend the following:

  1. 1. Use seed at 40-50 lbs/acre or cuttings spaced at 1’ x 1’ for most rapid establishment.
  2. 2. If using cuttings, prepare them well and irrigate thoroughly until establishment
  3. 3. Light nitrogen fertilization (50 lbs N/acre) may improve peanut establishment.
  4. 4. To avoid competition:
    a. Make sure trees are well fertilized during peanut establishment (at least one year).
    b. Avoiding planting peanut directly adjacent to newly planted trees.
  5. 5. Use appropriate herbicides to control weeds during canopy closure. If growing organically, it is especially important that peanut be planted densely to complete cover as quickly as possible. After canopy has closed, close mowing may be used to control most weeds.
  6. 6. Benefits of perennial peanut living mulches are long term. Do not expect significant contributions to soil quality or fruit tree growth in the first year or two of peanut establishment.

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