Urea as a source of nitrogen for potato production and its residual effect on forage maize yield on recent Nile Alluvial deposites, Khartoum State

A series of experiments were conducted at farmer's fields in recent alluvial soils deposits on the eastern bank of the Nile in EI-Ezergab (15 72 N 32 54 E) and EI-Kadaro (15 76 N 32 54 E) during 2008/2009 and 2009/2010 seasons. The main objective was to test the effect of different levels of N applied as urea (0, 43, 86, 129, 172, 215 and 258 kg NhaE-1) on potato yield and the effect of residual soil N on forage maize following potato harvest. Experimental design was a randomized complete block design, with four replications. For both seasons potato was planted on the first week of December and harvested on the third week of March. Maize was planted on the third week of March 2009 and second week of. April 2010 for the first and second seasons, respectively on the same plots of potato experiment with the same plot size as a test crop to test the effect of residual nitrogen fertilizer without addition of fertilizer. Parameters measured in the four experiments included the number of plants; fresh and dry weights of shoots and tubers, total yield and concentration of nitrogen in shoots and tubers. Also number of plants, fresh and dry weights of maize plants and concentration of nitrogen in plant tissues were measured. Soil samples were collected after each potato harvest and soil N analysis was carried out. The results showed that nitrogen fertilizer had a significant effect (P 0.001) on tuber yield in both seasons. The highest tuber yields in the first (16190) and the second (17114) kg haE-l were obtained by the application of 86 kg N haE-1, which were equal to (47%) and (45%) higher than the control, respectively. Application of nitrogen levels more than 86 kg N haE-1 resulted in progressively lower tuber yields. Maximum amount of tuber dry matter 4631 and 3823 kg haE-1 were obtained by adding 86 kg N haE-1 in first and second season, respectively. Nitrogen applications have a significant (P 0.05) and (P 0.001) effect on dry matter of shoot in first and second season, respectively. The concentration of nitrogen in shoots was higher than in tubers. Regressions of nitrogen concentrations on both shoot and tuber dry weights were highly significant with square R values of 0.939 and 0.927, respectively. The total yield of tubers decreased dramatically when nitrogen concentration in shoots and tubers increased. Nitrogen treatments had significant effect (P 0.001) on tubers and shoots uptake in both seasons. Uptake increased up to 86 kg N haE-1 and then decreased steadily. Highest tuber nitrogen uptake in the first season (89 kg N haE-1) and in the second season (88 kg N haE-1) were achieved by the application of 86 kg N haE-1, while the lowest nitrogen uptake for respective seasons were (64 kg N haE-1) and (48 kg N haE-1). The results reported here indicated that high agronomic nitrogen use efficiency in the first season (115 kg kgE-1) and the second season (98 kg kgE-1) whereas apparent nitrogen recovery for respective seasons were (158% and 97%) this results were realized due to the application 43 kg N haE-1. After potato harvest, the concentration of total nitrogen left in the upper soil (0-30cm) ranged from (0.053 to 0.066 %) and (0.043 to 0.049%) for the first and second season, respectively. Residual nitrogen fertilizer had significant (P 0.05) effect on maize forage fresh yield. The highest yield of 34610 and 24630 kg haE-1 were obtained by the residual nitrogen effect of 258 kg N haE-1, which is (49%) and (46%) higher than the control for the first and second season, respectively. Also it was observed that increase in nitrogen residual resulted in increase of fresh forage yield. Residual nitrogen also had a significant effect (P 0.01) on dry matter of maize. Maximum amount of dry matter 11590 and 7317 kg haE-1 were obtained by residual effect of the 258 kg N haE-1 treatment in the first and second seasons, respectively. The effects of residual nitrogen were highly significant (P 0.001) on nitrogen uptake for both seasons. The nitrogen uptake was associated with the increase in residual nitrogen levels. Highest nitrogen uptake of 221 and 138 kg N haE-1 were obtained by residual nitrogen effect of 258 kg N haE-1 were obtained by residual nitrogen effect of 258 kg N haE-1