Robert Kratochvil, Extension Specialist – Grain and Oil Crops, University of Maryland; firstname.lastname@example.org
Does choice of cereal cover crop species affect full season soybean? Does cereal cover crop kill date matter? These are questions that soybean farmers are asking as Maryland cover crop acreage continues to increase.
To address these questions, three years of research was conducted by planting three cereal species (barley, wheat, and rye) as cover crops at the Wye Research and Education Center (fall 2009 and 2010) and Central Maryland R&E Center-Beltsville (fall 2010 and 2011). A no cover crop treatment (only fall-winter weed growth) also was included. Three (Wye) and two(Beltsville) cover crop spring kill dates that supported varying amounts of cover crop biomass production were used. The kill dates at Wye are defined as 1) extra early kill for only the rye and the no cover treatments (mid-late March during the two study years); and at both Wye and Beltsville 2) early kill date for all treatments (ranged from 13 April to 23 April); and 3) late kill date for all treatments (ranged from 2 May to 16 May). Soybean varieties Asgrow brand3539RR2 (mid-MG 3) and Asgrow brand 4630RR2 (mid-MG 4) were planted into all cover crop treatments between 2 and 3 weeks after the last kill date. Soybean harvest dates were considered normal ranging from 17 October to 3 November during the three years.
Approximately three weeks post-planting, stand emergence was assessed to see if the cover crop species or kill date treatments impacted stand establishment. Over the three year period, no emergence differences were observed indicating that neither choice of cereal cover crop nor spring kill date had a detrimental effect on soybean germination and emergence. The most important criterion when planting full season soybean into a cereal cover crop is attainment of good seed-soil contact.
Starting approximately mid-June each year, a weekly measurement of growth stage progression was done by randomly selecting 5 plants in each plot, determining the growth stage according to Fehr and Caviness (1971), and averaging the growth stage. The primary growth differences observed were associated with the two varieties. Both varieties progressed through vegetative growth similarly. The onset of reproductive growth always was observed for the earlier of the two varieties, as expected. The weekly readings continued until early-mid September. Occasionally, only very minor differences in growth stage progression for the soybeans were observed for either the cover crop species or the kill date treatments. These differences were inconsistent across the assessment dates and are considered to have no influence on soybean growth and performance.
Soybean yield (72 bu/acre average) was excellent during the three years. The most consistent yield difference observed was associated with variety, however there was no consistent trend favoring one over the other. At Wye, the MG 3 variety produced better than the 6 MG 4 variety during 2009-2010 and the opposite occurred during 2010-2011. During 2010-2011 at Beltsville, the MG 4 variety was best and during 2011-2012, there was no yield difference between the two.
Response of soybean yield performance to cover crop species and kill date varied by location. During the two years at the Wye, a cover crop species × (by) kill date interaction was observed. For the March kill date (extra early), soybeans planted into the no cover crop treatment produced 10% (2009-2010) and 4% (2010-2011) better than soybeans following rye.
For the 2010 April kill date (early), soybeans planted following any of the three cover crop species produced the same (62 bu/acre) but soybeans following the no cover treatment yielded nearly 10% more (68 bu/acre). In 2011, the April kill date produced no yield differences (~67.5 bu/acre average) among the four cover treatments.
For the two years the study was conducted at Beltsville, there was no cover crop species × kill date interaction during 2010-2011 but in 2011-2012 this interaction was significant. At Beltsville in 2010-2011, soybeans planted where cover crops were killed during April produced over 6% greater than soybeans following the May kill date. However during this study year, there were no differences in soybean yield associated with any of the cover crop treatments.
During 2011-2012, soybeans following either barley or wheat cover crop produced the same for the two kill dates. However, soybeans that followed either rye or the no cover crop treatment, produced approximately 12% greater following the May kill date. Based on three years of data collected in this study, answers to the two primary questions about soybean performance following cereal cover crops are:
1. Does choice of cereal cover crop species affect the performance of full season soybean?
The performance of full season soybean following a cereal cover crop cannot be predicted by the cereal species grown. Differences may occur but they will be associated with location and kill date.
2. Does cereal cover crop kill date influence soybean performance?
The optimum kill date for cereal cover crops followed by full season soybean is difficult to predict. Factors that can affect soybean performance for any particular kill date are location, year, weather, and variety.