Soil aggregation and potential carbon and nitrogen mineralization with cover crops under tropical no-till

Authors: GONSIORKIEWICZ RIGON, JOAO PAULO - Sao Paulo State University (UNESP); Franzluebbers, Alan; CALONEGO, JUAN CARLOS - Sao Paulo State University (UNESP)

Submitted to: Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2020
Publication Date: 8/7/2020
Citation: Gonsiorkiewicz Rigon, J., Franzluebbers, A.J., Calonego, J. 2020. Soil aggregation and potential carbon and nitrogen mineralization with cover crops under tropical no-till. Soil and Water Conservation Society. 75:601-609.

Interpretive Summary: Agricultural production in hot and dry tropical conditions can only be sustained if soil surface condition is preserved with some forms of conservation agriculture. The components of a conservation system have not been fully investigated. A scientist with USDA Agricultural Research Service in Raleigh NC collaborated with scientists at São Paulo State University in Brazil to determine the impacts of winter and spring crop management effects on soil aggregation and organic matter in a long-term study in São Paulo State. Keeping soil covered with a spring-time crop rather than managed without a cover and occasional tilling was essential to maintain strong aggregation and robust soil biological activity. The best winter-spring combination of crops in rotation with soybean in the summer with regards to soil aggregation and organic matter preservation was triticale as grass secondary crop after soybean and sunn hemp as legume cover crop in spring. The combination of grass with legumes in this low-input cropping system provides long-term sustainability in yield and soil condition. These results have important implications for farmers in tropical regions, as well as areas of the southeastern USA.

Technical Abstract: Sustainability of agriculture with no-tillage (NT) production requires appropriate cover cropping, and not a simple and random approach of any cover crop. However, relatively little is known of the long-term soil surface impacts of different cover crops in rotation with soybean (Glycine max) under NT in the tropics. We evaluated the impacts of different cover crops on soil aggregation, soil C and N fractions, and soil microbial activity after 12 years under NT in Sao Paulo state of Brazil. Treatments included two main plots during the winter dry season [triticale (x Triticosecale) and sunflower (Helianthus annuus)] and four sub-plots during the spring cover crop season [pearl millet (Pennisetum glaucum), sunn hemp (Crotolaria juncea), forage sorghum (Sorghum bicolor), and fallow with occasional chiseling). All eight of these treatments followed soybean grown in the summer. Secondary winter crop had no effect on soil aggregation, but total organic C and N concentrations were at least 5% greater with triticale than with sunflower. Across soil depths, soil aggregation and soil C and N fractions were generally more enriched when sunn hemp was cover crop than with fallow. Triticale followed by sunn hemp provided complementary inputs for enhancing soil quality in this unfertilized (N) soybean-based cropping system. Our results suggest that not only is maintaining soil cover important to improve soil aggregation and soil C and N fractions, but the quality of organic inputs determined by cover crop species is an important factor controlling the dynamics of these soil responses.