|dc.description.abstract||Tunwath is a mixed farm (laying hens-grains) located in the Annapolis Valley, Nova Scotia, in a cool humid temperate zone. It includes about 2100 laying hens, 35 hectares of field crops and additional garden, pasture, hay and woodland. Field crops were grown by conventional methods until 1976 when the farmer stopped using fertilizer, and pesticides. A regular rotation of crops was initiated in 1979/80: fababeans-oats underseeded with clover-clover (green-manure)-winter wheat. Most of our observations were conducted from 1979 onwards; some data on yields and soil chemistry were available from earlier years.
Soil analyses in 1980 and 1983 indicated no major deficiencies in minerals except for low K on some of the sandier soils. A pasture had the highest organic matter content, and a garden receiving regular applications of chicken manure, the lowest. Historical data indicate that pH, Ca and Mg in surface horizons rose substantially after 1975. Estimated field balances for P, K, Ca and Mg are +12, -47, -161 and -35 kg/ha per annum; the positive P balance is due to an input of dicalcium phosphate as a feed supplement. Chicken manure increased chemical measures of phosphate more than did superphosphate. Mineralization of soil nitrogen during crop growing seasons was estimated from vegetation-N to be in the range 28-85 kg/ha until 1984 when it rose to the region of 100 kg/ha following changes in tillage practices. The effect of manure on available N was highly variable in both laboratory and field studies; the additional N found in plants when manure was applied amounted to 0 to 41% of the manure-N. Nitrogen fixation by fababeans was estimated on average as 146 kg/ha and varied 3-fold; that by clover was estimated as 62 kg/ha and varied 7-fold. Inputs of N via N fixation and manure was sufficient to support cereal yields of 4.7 tonnes/ha, and a fababean yield of 3.5 tonnes/ha; these are 162% (wheat), 223% (oats) and 116% (fababeans) of reference yields (recent provincial averages for wheat and oats and cited expected yield for fababeans). Prior to 1976, yields of oats, wheat and fababeans averaged 111, 119 and 106% of the reference values. Between 1979 and 1985, yields of oats rose from about 50% to 98% of the reference value, fababeans from 72 to 100% while yields of wheat fell from 85% (1979-82) to 51% (1984/5) of the reference value. Various data indicate that oat yields had been depressed by residue-induced phytotoxicity and that initiation of the practice of ridging soil after fall rotovation relieved the phytotoxicity. Improvement in oat yields in 1984 was accompanied by an increase in the % N in grains; total N accumulated in oats (+weeds) in the absence of manure roughly doubled compared to previous years but manured oats (+weeds) did not accumulate more N than non-manured oats. It is suggested that healthy oats form a beneficial association with microorganisms which regulates the mineralization of soil-N, above a certain background level, according to the requirements of the crop. Limited observations suggest that ridging after rotovation, or mouldboard ploughing in the fall prior to planting fababeans benefited fababeans compared to rotovation alone. For wheat, there is evidence that yields are now limited by a combination of, or interactions between, the following factors: low available N, competition from perennial weeds, soil structural factors influencing drainage and aeration, and phytotoxicity (associated with rotovation of clover residues prior to planting winter wheat).
There is general correspondence between life cycles of weeds and those of the crops, with perennial weeds dominating in winter wheat, summer annuals in oats (short season summer annual), and a mixture in fababeans (long season summer annual). There is heavy growth of wild radish, a summer annual weed, in winter wheat fields in the fall but this plant is killed by the winter. Fababeans tend to be very weedy during early vegetative growth, probably because growth of fababeans is retarded when nodule growth is most active. For all crops, and in a variety of situations, there were positive correlations between the percent of the total biomass made up by the crops at harvest, and the total biomass (made up of crops and weeds). One comparison of weeded and non-weeded plots of fababeans in a situation where this correlation was very high, indicated that the presence of weeds caused less than a 10% reduction in crop yield. These observations suggest that the presence of many weeds at sites of low total production is indicative of fertility limitations rather than weed problems. Plots of percent crop versus total biomass are used to compare relative weediness between different fields and years; these suggest that (i) weediness of oats decreased following introduction of the ridging practice in the fall of 1983, (ii) weediness of winter wheat increased between 1980 and 1984, and (iii) that there has been little change in the weediness of fababeans. The data for winter wheat, and other observations indicate an overall increase in perennial weeds between 1979 and 1984. This is attributed to the emphasis on minimum tillage. A comparison of six oat cultivars revealed a pronounced cultivar effect on the relative weediness of oats.
The costs of chemicals required for growing grains at Tunwath by conventional management were compared with the costs of purchasing additional grain to make up for shortfalls in yields during the transition to biological husbandry. The comparison suggests that yields under biological husbandry have to be 75% or better of those under conventional management for appreciable savings to be made. The saving that would be realized when yields under biological husbandry are equal to those under conventional husbandry, which appears to be well within the potential of biological husbandry, is estimated as $189 per hectare of grain (1984 Canadian dollars).||en_US