Speakers
Description
1.Introduction
A 39-year field experiment has been conducted continuously since 1984 in Germany, to evaluate the effects of a combined supply of organic and mineral nitrogen on the biomass of two different selected cover crops.
2.Materials, Methods
The field experiment is located at the experimental Station Berlin-Dahlem (Humboldt-Universität zu Berlin, Germany). The site has the following characteristics: 66.7% sand, 20.7% loam, and 12.6% clay, 0.03% of total N content, 0.35 % of total organic carbon, and 0.0 % of CaCO3. Three different regimes of N mineral fertilization and the two cover crop species radish (Rafanus sativus var. oleiformis Pers.) and phacelia (Phacelia tanacetifolia Benth.) were examined. The mineral nitrogen fertilizer used is calcium ammonium nitrate (CAN). The treatments used in plots having spring barley (Hordeum vulgare L.), corn silage (Zea mays L.), and winter wheat (Triticum aestivum L.) as main crops are the following: cover crop or straw with no mineral nitrogen fertilization (CN0), with low nitrogen mineral fertilization rate (CN1), with medium nitrogen mineral fertilization rate (CN2), with high nitrogen mineral fertilization rate (CN3), only high level of mineral nitrogen fertilization (AN3). The leaf chlorophyll content of cover crops was estimated using a SPAD chlorophyll meter. Twenty SPAD measurements were taken for each plot of radish and phacelia, and the average was calculated. Cover crops were harvested on the 24 total plots of phacelia and radish on which the previous year had been sown, in two different field, spring barley and winter wheat. For each plot, four technical replicates of 0.25 m2 were harvested and pooled to provide a single sample, respectively. The fresh matter (FM) of each sample was determined. Samples were dried at 105 ºC to a constant dry weight and dry matter (DM) and dry matter content (DMC) were determined (Shipley & Vu, 2002).
3.Results
FM and DM yields, and SPAD measurements of phacelia and radish were significantly (p < 0.05) associated with N fertilization from CN0 to CN3 treatments. FM of phacelia and radish ranged from > 10 t ha -1 and ~ 5 t ha -1 to ~ 40 t ha-1 and ~ 20 t ha-1 as the phacelia has a higher biomass and therefore a higher availability of organic N. DM yields of phacelia and radish ranged from ~ 1 t ha -1to ~ 3 t ha-1 and ~2.5 t ha-1. SPAD values increased as nitrogen fertilization levels increased for phacelia from ~ 10 to ~ 20, for radish from ~ 30 to ~ 40. DMC was negatively affected by increasing N-fertilization for phacelia from ~ 0.15 g g-1 to ~ 0.05 g g-1 and for radish from ~ 0.25 g g-1 to ~ 0.10 g g-1. Linear regression shows that phacelia responds more strongly to increasing doses of nitrogen up to values of 25 t FM ha-1 compared to radish (~ 15 t FM ha-1).
4.Discussion
Phacelia could provide organic nitrogen to the main crop that has high N requirements. Herrera et al., 2010 reported that phacelia has a high N uptake of 9.85 g N m-2 through a combination of high shoot biomass and root intensity present in the upper soil state. Radish could be a source of organic N for those main crops with low nitrogen requirements. It needs, if used as green manure, an additional dose of mineral N as it alone would fail to fully meet the needs of a subsequent main crop (Ruark et al., 2018).
5.References
Herrera, J. M., Feil, B., Stamp, P., & Liedgens, M. (2010). Root Growth and Nitrate‐Nitrogen Leaching of Catch Crops following Spring Wheat. Journal of Environmental Quality, 39(3), 845–854. https://doi.org/10.2134/jeq2009.0306
Ruark, M. D., Chawner, M. M., Ballweg, M. J., Proost, R. T., Arriaga, F. J., & Stute, J. K. (2018). Does cover crop radish supply nitrogen to corn? Agronomy Journal, 110(4), 1513–1522. https://doi.org/10.2134/AGRONJ2017.06.0352
Shipley, B., & Vu, T. T. (2002). Dry matter content as a measure of dry matter concentration in plants and their parts. New Phytologist, 153(2), 359–364. https://doi.org/10.1046/j.0028-646X.2001.00320.x
| Keywords | Cover crop; long-term experiment; Nitrogen; fertilization |
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