| dc.contributor.author | Abboud, Antonio Carlos de Souza. | en_US |
| dc.date.accessioned | 2014-10-21T12:38:42Z | |
| dc.date.available | 1992 | |
| dc.date.issued | 1992 | en_US |
| dc.identifier.other | AAINN80083 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55311 | |
| dc.description | Organic farms are often characterized by no addition of soluble fertilizers. Crops have to rely on poorly soluble sources of nutrients, using biological mechanisms to make them available. The effects of 3 P-containing fertilizers (Rock phosphate (RP), superphosphate (super-P) and compost) were examined on 3 organic and 3 conventional farms to identify some of the critical parameters for the mobilization of P in fields cultivated with barley. The farms provided a gradient of conditions ranging from long-term organic to moderately intensive conventional. Soil P, plant P and yields were used to judge the effectiveness of P fertilizers. The biological variables examined were root mycorrhizal (VAM) infection, root acid phosphatase (P-ase), root length and soil acid P-ase. | en_US |
| dc.description | There was no indication that RP and compost were more effective on organic than on conventional farms. Compost was, in most cases, as efficient as super-P in raising soil P levels, plant P and yields. Super-P tended to decrease VAM infection, while compost had no effects, compared to control. Root P-ase did not, in general, respond to the treatments, but it was correlated with a parameter of the internal plant P demand. Soil P-ase was in most cases unaffected by the treatments. There were not consistent differences in treatment effects between organic and conventional farms when variables were examined individually, but nutrient uptake occurred in a slower fashion in the organic than in the conventional farms. A multivariate analysis showed that the 2 longest-standing organic and the most intensive conventional farm were each clustered separately, whereas the other 3 farms were clustered together. | en_US |
| dc.description | Three other experiments examined how crop, soil and residue management practices on a long-standing organic farm affect mobilization of native and applied P. In the 1$\sp{\rm st}$ experiment, discing with straw retained from the previous crop and discing alone were tested in comparison to mouldboard ploughing (straw not retained). Mouldboard ploughing increased yields of green manure crops in the first year. Discing with straw had the most residual effect, increasing soil P levels and maize yields in the 2$\sp{\rm nd}$ year, oats biomass in the 3$\sp{\rm rd}$ year and % Mg in clover in the 4$\sp{\rm th}$ year, compared to the other treatments. | en_US |
| dc.description | In the 2$\sp{\rm nd}$ experiment, RP was used with 4 green manures (GM): oilseed radish, buckwheat, faba beans and weeds. In the plots that received RP, higher levels of soil P$\sb{\rm res}$ were found over the ensuing 3 years. Effects of the GM were observed in the 1$\sp{\rm st}$ year. Faba beans increased the % N and % P in oat grains in the 2$\sp{\rm nd}$ year. In the 3$\sp{\rm rd}$ year, buckwheat decreased maize yields as a result of competition from volunteer buckwheat. The VAM infection tended to be lower in maize roots on plots on which the GM were non-mycorrhizal type. | en_US |
| dc.description | In the 3$\sp{\rm rd}$ experiment, oat hulls were applied to the soil with RP, and hairy vetch grown. Oat hulls reduced soil NO$\sb3\sp\cdot$ levels, increased N$\sb2$ fixation and stimulated uptake of other nutrients by vetch. A possible boost of P accumulation by vetch under the higher levels of oat hulls occurred. No residual effect of the treatments was evident on a 2$\sp{\rm nd}$ crop. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1992. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Agriculture, Agronomy. | en_US |
| dc.title | Mobilization of phosphorus in organic and conventional farming systems in southwestern Ontario. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
