Utilizing cover crop mulches to reduce tillage in organic systems in the southeastern USA

Abstract

Organic systems in the southeastern USA offer unique challenges and solutions to crop production due to regional soil and climate characterized by highly weathered soil types, high precipitation and the capacity to grow cover crops in the winter. Recently, the interest of producers and researchers in high-residue cover crops and conservation tillage systems has increased. Various designs of the roller-crimper to manage cover crops have been invented and demonstrated to growers in the southeastern region of the USA over the past 17 years. The impacts of high-residue cover crop mulches on the agronomic systems in the region are diverse. Legume cover crops assist with meeting N demand from cash crops though they decompose rapidly and are seldom sufficient for N demanding crops such as corn. Cereal cover crop mulches can have the opposite effect by immobilizing N and have a longer impact on soil moisture and weed dynamics. While undesirable for many crops, N immobilization is one possible mechanism for weed suppression in legume cash crops planted into cereal residues. Other cover crop weed suppression mechanisms include physical impedance, light availability, allelopathy and microclimate effects. Regardless of the cause, successful weed control by mulches is highly dependent on having substantial biomass. The southeastern region is capable of producing cover crop biomass in excess of 9000 kg ha − 1 , which is sufficient for weed control in many cash crops, although supplementary weed control is sometimes necessary. Long-term data are needed to predict when farmers should add supplementary weed control. More work is also needed on how much additional N is required for the cash crops and how best to deliver that N in a high-residue environment using organic sources.

Impacts of Organic Zero Tillage Systems on Crops, Weeds, and Soil Quality

“…The two researchers concluded that small-grain cover crops could be killed effectively if rolling-crimping was delayed until advanced growth stages (Zadoks growth stage, ZGS 85; [30]). Recent roller-crimper designs have improved efficacy of killing cover crops and enhanced operator comfort when used in the field [31][32][33]. Current models can kill over 90% of a rye cover crop when terminated as early as 50% anthesis or ZGS 65 in some environments [34].…”

“…The enthusiasm generated among organic farmers spurred a growing number of researchers across North America to investigate organic ZT as an emerging cropping strategy. Results of several studies were summarized in a special issue on organic conservation tillage in Renewable Agriculture and Food Systems in 2012 [33,[37][38][39][40][41].…”

The Current State and Future Directions of Organic No-Till Farming with Cover Crops in Canada, with Case Study Support

“…Choosing early maturing cultivars is beneficial in allowing earlier termination and cash crop seeding in the spring [12]. Cultivar examples that are acceptable in certified organic systems include Québec-bred CETAB-HÂTIF, a fall rye variety that tends to bloom 7-10 days earlier than common fall rye, and North-Eastern USA-bred Purple Bounty and Purple Prosperity, hairy vetch varieties that bloom in late May as opposed to early June [9,34] (p. 88).…”

“…Cultivar examples that are acceptable in certified organic systems include Québec-bred CETAB-HÂTIF, a fall rye variety that tends to bloom 7-10 days earlier than common fall rye, and North-Eastern USA-bred Purple Bounty and Purple Prosperity, hairy vetch varieties that bloom in late May as opposed to early June [9,34] (p. 88). Reberg-Horton et al compare rye varieties and find that an early maturing rye can have 25% more biomass than late maturing varieties even when the early maturing type is terminated in late April rather than in early May as for the late maturing variety [12].…”

“…The methods supported by recent research rely heavily on cover crops to a greater extent than is already practiced in organic agriculture [10]. Since the majority of organic herbicides is ineffective at controlling weeds, mechanically terminated cover crops are placed on the soil surface as weed-suppressive mulch for the following cash crop, a crop considered by this paper to be any crop intended to be marketed [11][12][13]. There are a number of mechanical termination methods, but the roller-crimper is credited with making no-till more available to organic farmers in Canada and is most strongly supported by research [14].…”