ASHS Press Releases

American Society for Horticultural Science

  • Increase font size
  • Default font size
  • Decrease font size
Home HortScience “Green Mulches” Sustain Christmas Tree Production
E-mail Print

EAST LANSING, MI—Organic groundcovers are being investigated for their natural ability to improve the sustainability of intensive forestry and agricultural production systems. These versatile groundcovers, also referred to as "green mulches", can be exceptionally effective; the plants can contribute organic matter to soil, reduce soil compaction and crusting, and improve water infiltration. Selected organic groundcovers can also reduce erosion, add or retain soil nutrients, suppress weeds, and improve the chemical and physical characteristics of soil.

Yingqian Lin, Alexa R. Wilson, and Pascal Nzokou from the Department of Forestry at Michigan State University investigated the performance of a low-input cropping system by testing legume cover crops Dutch white clover (Trifolium repens) and alfalfa (Medicago sativa) in combination with low rates of inorganic fertilizers. "High rates of inorganic fertilizers are currently used in conventional intensive production systems such as fraser fir cropping systems for Christmas trees," said Nzokou. "Our research examined these organic groundcovers to determine their effectiveness as green mulches in helping reduce the use of farm chemicals and providing environmental benefits."

The scientists studied the effects of combining legume cover crops with low rates of nitrogen (N) fertilization on fraser fir productivity and nutrient status, then evaluated the impact on soil fertility and determined the impact of the systems on nutrient leaching below the root zone. The full study was published in HortScience.

Experiments in the study featured the use of one cover crop and one of three applications of reduced rate inorganic fertilizer (75%, 50%, and 25% of the recommended rate). A conventional system using herbicides for weed control and the 100% rate of inorganic fertilizer was used as a control. "A significant positive growth response (height and diameter) was obtained in all alfalfa-based cropping systems," Nzokou noted. "This was accompanied by foliar nutrient concentrations similar to conventional plots and a reduction in nitrate-N leaching."

According to Nzokou, the growth response was reduced (both height and diameter) in white clover-based cropping systems, suggesting competition for soil resources. "In addition, the total nitrate-N leaching was higher in this system, suggesting an imbalance between mineral nitrogen availability and use in white clover-based cropping systems."

The researchers predict a bright future for legume groundcovers. "If the potential competition between cover crops and trees can be properly managed, legume cover crops can be effectively used to make intensive production tree-based systems more sustainable," they said.


The complete study and abstract are available on the ASHS HortScience electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Combining Legume Groundcovers and Low Nitrogen Fertilization in a Short-rotation Fraser Fir (Abies fraseri) Cropping System: Effect on Productivity, Soil Fertility, and Nutrient Leaching
Yingqian Lin, Alexa R. Wilson, and Pascal Nzokou
HortScience 46:481–486. [Abstract] [Full Text] [PDF]

Corresponding author. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it