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Effect of different levels of fertilizer, application interval and container type on growth of seedlings of black locust (Robinia pseudoacacia L.)

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Black locust seedlings were raised in white ray leach super cells from seed of an unknown California source in the shade house at Oregon State University, Forest research Laboratories. When the seedlings were 25 days old, application of 4 levels of nitrogen i.e. zero, low, medium and high (0, 100, 200, 400 ppm) in the form of ammonium nitrate fertilizer was started. Each N level was associated with and without 50 ppm of phosphorus in the form of phosphoric acid to make 8 doses. Positive N doses, both with and without P, were applied after each 5 days (D5) and 10 days (D10) to make 14 treatments. Nitrogen alone had a significant (P < 0.05) effect when raised from 0 to 100 ppm (D5) in all growth parameters i.e. shoot length, diameter, leaf area and total dry biomass. Medium level of N (200 ppm) resulted in significantly higher responses to seedlings that had received P. High N level (400 ppm) did not prove to be effective in increasing different growth parameters which is in agreement to our William H. Emmingham H hypothesis of luxury consumption. Nitrogen and phosphorus interaction caused tremendous positive response in all growth variables generally at low and medium N levels. Phosphorus applied to 0 and low (D10) levels of N caused significantly higher nodulation. On all other growth variables, P had no effect different than without P at these two N levels. Nitrogen application interval (D) had significant effect on P50 seedlings at low (100 ppm) N level on almost all growth variables. Seedlings getting nitrogen fertilizer every 5 days (D5), had higher growth than those receiving fertilizer every 10 days. Concentration of N and P in plant tissue was not affected by presence or absence of P but it was affected by level of N. Nitrogen and phosphorus use efficiency was maximum at 200 ppm (D10) N level in seedlings with added P. This was also the level at which average growth per subsequent additional unit (100 ppm) of N after the first input of 100 ppm was maximum. Another experiment tested the effect of 4 container types (polythene bag, deepot, ray leach cell and Spencer-Lemaire) on growth of black locust seedlings. Results indicated that growth of seedlings was not only dependent on the volume of the container but shape was also instrumental in determining the development of seedlings. Seedlings in deepots had the highest mean growth in shoot height, diameter, leaf area and total dry biomass by the end of the experiment. These were significantly greater (P >0.05) than the seedlings grown in Spencer-Lelnaire and ray leach cells. Seedlings in Spencer-Lemaire had the minimum growth whereas ray leach seedlings were found to be more efficient in growth per unit volume of growing medium. Polythene bags were cost effective as the growth of seedlings in these was not different than deepot which are definitely more costly than polythene bags.

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