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GrnenorN, P., ToLr-cNA,en, M. eNo MuloooN, J. F. 1985. Effect of temporary N starvation on leaf photosynthetic rate and chlorophyll content of maize. Can. J. Plant Sci. 65: 491-500.The photosynthetic rate (P) of maize (Zea may's L.) plants grown under growth room conditions was studied during and after a 1O-day period ofN starvation. The relationships between P and chlorophyll content, and P and nitrogen content were examined. Nitrogen deprivation, from the l8th to the 28th day, induced a decline of maximum photosynthetic rate, respiration and chlorophyll content; this effect was reversible. Recovery of photosynthetic capability occurred within 10 cm of water was placed between the lamp and the chamber to absorb most of the infrared radiation. Screens made of cheese cloth were used to reduce irradiance reaching the leaf. Photon flux density was measured to the top of the cuvette with a quantum photometer (Lambda Instrument Ltd., Lincoln, Nebr.) and corrected for absorbance and reflection by the cuvette. Maximum photosynthesis (PMAX) was measured by a photon flux density incident at the leaf surface of 2050 pEm-2'seg-t (400-700 nm). Photosynthetic rates were also measured at 700, 340, 66 and 0 pE'm 2'sec '. Room temperature was maintained at 25 -+ l'C. Fig. 2. Maximum photosynthetic rate of the 6th leaf of the control plants and of plants grown with N-free nutrient solution from the 18th to the 28th days (conditions: 26-+ l"C;

. 1980. Effects of seed-and soil-applied Rhizobium japonicum inoculants on soybeans in Ontario. Can. J. Plant Soybeans (Glycine max (L.) Merrill), inoculated with 1.75 kg/ha of seed-applied inoculant (Rhizobium japonicum (Kirchner) Buchanan) or 40 kg/ha of granular, soil-applied inoculant, were grown in 1976 and 19'77 , along with uninoculated control plots, in fields planted to soybeans for the first time. Control plots averaged 2.1 tlha, compared to 2.6 tlha for the seed-applied inoculant and 3.1 t/ha for the granular inoculant treatment. However, neither inoculant treatment increased yields over the uninoculated controls on land where soybeans had been grown before. In 1978, two commercial granular inoculants and one seed-applied inoculant were treated at various rates at three sites on new soybean land. Granular inoculants caused consistently higher yields than the seed-applied inoculant. Seed yields increased linearly with rates of granular inoculant which were llt, rlz, lla and I times the manufacturers' recommended rates for soybeans grown in l8-cm rows. However, above the lowest rate, the value of the added yield was only equal to the cost of the extra inoculant. Thus, in the narrow-row soybean cultural system necessary to maximize yields in short-season areas, the manufacturers' recommended rates of granular inoculant were higher than necessary for maximum economic return.

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Two experiments were conducted over 3 yr to study the effects of variability in intra-row spacing on grain yield of maize; effects of non-uniformity in seedling size were also investigated. Experiment 1 consisted of single-row plots which were thinned in the seedling stage to produce stands of equivalent mean densities (i.e., the same number of plants per plot row), but with different lengths of gaps within the row; two additional treatments involved the selection of seedling plants which were either very uniform, or non-uniform, in height. Yield was unaffected by the presence of gaps up to 1 m long within the row. In general, plots of uniform seedling size outyieldcd those where seedling size was more variable. Experiment 2 involved a comparison of plots seeded to produce one, two, three or four plants per hill at an equivalent mean plant density (same number of plants per plot row). On average, yield was not depressed until the number of plants per hill exceeded two. No treatment effect on the intra-plot standard deviation of ear dry weight per plant was measured in any test. Experimental results indicate that uniformity of spacing, within the range commonly encountered with properly adjusted, commercial maize planters, is unlikely to affect yield. Uniformity of seeding depth is likely to be more crucial.