Nitrogen transfer in an alfalfa-bromegrass mixture
| dc.contributor.committeeMember | Slinkard, Alfred | en_US |
| dc.creator | Tomm, Gilberto Omar | en_US |
| dc.date.accessioned | 2004-10-21T00:02:16Z | en_US |
| dc.date.accessioned | 2013-01-04T05:02:37Z | |
| dc.date.available | 1994-01-01T08:00:00Z | en_US |
| dc.date.available | 2013-01-04T05:02:37Z | |
| dc.date.created | 1994-01 | en_US |
| dc.date.issued | 1994-01-01 | en_US |
| dc.date.submitted | January 1994 | en_US |
| dc.description.abstract | Knowledge about cycling of N is the basis for management decisions in order to maintain crop productivity, reduce dependency on N fertilizers, and reduce the negative impact of agriculture on the environment. Research was conducted in the field during three growing seasons using 15N isotope dilution techniques to study the intensity of N cycling in an alfalfa (Medicago sativa L.)-meadow bromegrass (Bromus riparius Rhem.) mixture managed as a hay crop. In addition, two greenhouse experiments were conducted to compare short-term and long-term N transfer from bromegrass to alfalfa and vice versa. Nitrogen removed by hay harvest amounted to 171 and 32 kg ha$\sp{-1}\ yr\sp{-1}$ for alfalfa and bromegrass, respectively. The average accumulation of N in stubble + roots to 30 cm depth was 115 kg ha-1 for alfalfa and 73 kg ha-1 for bromegrass. Alfalfa derived 210 kg N ha$\sp{-1}\ yr\sp{-1}$ from the atmosphere. At least 31% of this fixed-N was accumulated in stubble + roots. Most of the N (59 to 74%) of intercropped bromegrass and about 40% of intercropped alfalfa N was allocated to the stubble + roots and, thus, had a marked effect on N-cycling. Nitrogen returned to the soil through fallen leaves of alfalfa and bromegrass amounted to 13 and 4 kg ha$\sp{-1}\ yr\sp{-1}$ respectively. An additional 15 kg N ha$\sp{-1}\ yr\sp{-1}$ for alfalfa and 7 kg N ha$\sp{-1}\ yr\sp{-1}$ for bromegrass were recycled through losses that occurred during cutting and removal of hay. Studies in the field and in the greenhouse demonstrated that N can be transferred from grass to legume even when the growth of grass is limited by severe N deficiency. This implies that calculations of the net N benefit from a N2-fixing species to an intercropped grass must include the amount of N transferred from the grass to the legume. Fourteen kg N per ha$\sp{-1}\ yr\sp{-1}$ was transferred from alfalfa to the forage of bromegrass, of which 5 and 9 kg N ha$\sp{-1}\ yr\sp{-1}$ was derived from the soil and from N2 fixation by alfalfa, respectively. On average, 70% of the transferred N (33 kg ha$\sp{-1}\ yr\sp{-1})$ was accumulated in the stubble + roots of bromegrass, indicating the importance of including all plant parts when evaluating N transfer in perennial swards. Larger estimates of N transfer were found in the 2.7-day than in the 79-day greenhouse study, likely due to a negligible transfer of 15N from the recipient plant back into the 15N-donor plant during the 2.7-day period. Field estimates indicated that the average percentage of N in bromegrass derived indirectly from N2 fixation, increased from 13% in the first year to 32% and 34% in the second and third year, respectively. These results show that short-term N transfer measurements on young stands do not accurately estimate the net N transfer between perennial species during a growing season. | en_US |
| dc.identifier.uri | http://hdl.handle.net/10388/etd-10212004-000216 | en_US |
| dc.language.iso | en_US | en_US |
| dc.title | Nitrogen transfer in an alfalfa-bromegrass mixture | en_US |
| dc.type.genre | Thesis | en_US |
| dc.type.material | text | en_US |
| thesis.degree.department | Plant Sciences | en_US |
| thesis.degree.discipline | Plant Sciences | en_US |
| thesis.degree.grantor | University of Saskatchewan | en_US |
| thesis.degree.level | Doctoral | en_US |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) | en_US |