Contribution of hay harvest losses and "leaf fall" to N cycling and the N nutrition of intercropped alfalfa and bromegrass

Non-Peer ReviewedA significant amount of forage plant biomass is deposited on the ground as senescent leaves, petioles and flowers (leaf fall). In addition, a varying amount of plant biomass is lost during harvest of hay crops (hay loss). These two sources of plant biomass and nitrogen (N) were quantified over a 3-year period in replicated plots of single or inter-cropped alfalfa (Medicago sativa cv. Beaver) and meadow bromegrass (Bromus riparius Rhem. cv. Fleet) swards grown under irrigation near Outlook. Another experiment in the same field provided an estimate of the quantity of N in the hay losses or leaf fall that was recycled between or within the two species. Alfalfa plants grown on 15N-enriched soil supplied 15N-labelled leaf fall and hay loss biomass which was applied to inter-cropped swards. The proportion15of N taken up by bromegrass or alfalfa was estimated. Similarly, N labelled bromegrass biomass was applied to inter-cropped swards and the uptake by each of the species was estimated. Leaf fall from alfalfa, bromegrass or alfafa+bromegrass swards contained an average of 22, 6, and 16 kg N ha-1 yea-1, respectively, whereas hay losses returned an average of 26, 9, and 22 kg N ha-1 year-1, respectively. The accumulation of 15N from those two N sources was detected in neighbouring plants as early as 13 days following application of the simulated leaf fall or hay losses

Herbage and protein productivity of single or inter-cropped alfalfa and bromegrass under zero nitrogen fertilization

Non-Peer ReviewedNitrogen (N) fertilizer enhances the growth of grass in grass-legume associations and frequently inhibits N2 fixation by the legume-Rhizobium symbiosis. The cost of N fertilizer and environmental concerns related to contamination of groundwater make the use of N fertilizers a less attractive alternative. The herbage and crude protein production of single or inter-cropped alfalfa (Medicago sativa cv. Beaver) and meadow bromegrass (Bromus riparius Rhem. cv. Fleet) grown under irrigation, without N fertilization, were evaluated near Outlook, Saskatchewan, from 1990 to 1992. Hay yield alfalfa increased from 4.5 t ha-1 in the first year to 10.6 t ha-1 in the third year following seeding. The hay yield of bromegrass decreased from 5.3 t ha- in the second year to 1.2 t ha-1 in the following year due to limited availability of N for plant growth. Alfalfa+bromegrass hay yield increased from 4.1 t ha-1 in the first year to 10.5 t ha-1 in the third year. Crude protein yields of single alfalfa or alfalfa+bromegrass were above 750 kg ha-1 year-1 in the first year and increased to 1700 kg ha-1 year-1 in the third year whereas the crude protein yield of bromegrass declined from 300 kg ha-1 in the first year to 80 kg ha-1 in the third year. Crude protein yield bromegrass seeded in alternate rows with alfalfa was up to 25 % higher than that of single bromegrass (not sharing resources). The amount of nitrogen fixation (kg ha-1) on inter-cropped alfalfa in the third year was as high as that of alfalfa not sharing space with bromegrass

Bi-directional nitrogen transfer between legume and non-legume plants

Non-Peer ReviewedNon-N2-fixing crops inter-cropped with legumes may benefit through transfer of symbiotically fixed N from the legume crop. The pattern of N transfer by mechanisms non dependent on decomposition of plant tissues was studied in a greenhouse. In addition, a study accessed the effect of inter-cropped alfalfa (Medicago sativa L.) on meadow bromegrass (Bromus riparius Rhem.) forage and N yield by a combination of N transfer mechanisms occurring under field . conditions. In the first study, shoot portions of one alfalfa or one bromegrass plant (donor) were foliarly fed with N labelled ammonium sulphate. No 15N from bromegrass was transferred to alfalfa, whereas 15N from alfalfa plants was transferred mainly to bromegrass plants. Transfer of 15N between plants of the same species was not significant in alfalfa and only detected in the nearest plant of bromegrass. The 15N content of the receptor plants showed that underground movement of N between plants occurred within 3 days. In the field study, swards of single bromegrass and alfalfa inter-cropped with bromegrass were seeded in rows 17. 8 cm apart. In the fell owing year individual rows of plants, adjacent to each other, on both sides of the edge between the different swards were harvested separately for dry matter (DM) and N yield. Results of bromegrass were related to distance from the nearest row of alfalfa. Forage yield gradually increased from 427 to 1230 kg ha-1 and N yield increased from 53 to 184 kg ha-1 as the distance between the bromegrass row and the alfalfa row decreased from 71.1 to 17. 8 cm. Yield of bromegrass located up to 35.6 cm from alfalfa was significantly increased, indicating transfer of N from alfalfa to bromegrass in agronomically relevant amounts

Spatial Light Modulators for the Manipulation of Individual Atoms

We propose a novel dipole trapping scheme using spatial light modulators (SLM) for the manipulation of individual atoms. The scheme uses a high numerical aperture microscope to map the intensity distribution of a SLM onto a cloud of cold atoms. The regions of high intensity act as optical dipole force traps. With a SLM fast enough to modify the trapping potential in real time, this technique is well suited for the controlled addressing and manipulation of arbitrarily selected atoms.Comment: 9 pages, 5 figure