Understory cover crops in pecan orchards: Possible management systems.
Bugg, Robert L., Marianne Sarrantonio, James D. Dutcher and Sharad C. Phatak

American J. Alternative Agriculture 6(2):50-62. 1991

Reviewer's Note: This conceptual and review article concerns possible cover-cropping approaches for the pecan orchards of southern Georgia. Many of the cover crops discussed in this article also grow well in parts of California, and several of the suggested techniques may be adaptable to pecan a6d walnut production in this state.

Annual legumes and mixtures of annual legumes and grasses can perform several functions as understory cover crops in pecan orchards, such as providing nitrogen-rich organic matter to improve soil fertility, or by sustaining lady beetles and other arthropods that may aid the biological control of pecan pests. Remaining questions concern selection of appropriate plant materials; whether to use cover crops singly or in mixtures; how to ensure reseeding as well as a substantial N contribution; whether, when, and how to use mowing and tillage; and fertilization options.

Different considerations apply when dealing with cool -vs. warm-season cover crops. With minor adjustments, growers could adapt present cultural practices to include cool-season cover crops. These could be used throughout the orchard by establishing appropriate self-reseeding species and avoiding both excessive mowing and indiscriminate placement of N-rich fertilizers. Within alleys, alternating 2-m strips of cool-season cover crops could be tilled in mid to late April or allowed to mature. The tilled strips would supply N to pecan trees immediately, whereas the adjoining untilled (remnant) strips could be mowed after seed is mature, to ensure dispersal of seed and reestablishment of cover crops over the entire alley. Cool-season annual legumes that die or are killed in late spring will probably furnish N and other nutrients at a suitable time, particularly in orchards with sprinkler irrigation. Soil moisture is essential to the breakdown of cover crop residue and the release of N to the associated pecan trees.

Warm-season cover crops, if desired, should be restricted to alleys to reduce possible competition with pecan. Cover crops in alleys will receive more light than in tree rows, especially during periods when pecan trees are in leaf. Tillage will encourage emergence of warm-season cover crops. If these die or are killed in late summer or early fall, timing of N release may not be optimal, particularly in the absence of adequate irrigation.

Many options and trade-offs need to be explored before choosing a cover-crop system. At times, several objectives may appear to conflict, and even delicately-managed mixtures of species may not fulfill all the desired functions.

For more information write to: Information Group, UC Sustainable Agriculture Research and Education Program, University of California, Davis, CA 9S616.

(DEC.330) Contributed by Robert Bugg