Two field experiments were conducted during 1997 and 1998 seasons at the
Hort. Res Farm of Seds, Beniswef Govrenorate to investigate the effect of partially
substituting of N fertilizer with the biofertilizer nitrobein on growth, yield and chemical
constituents of two sweet potato cultivars (Mabrouka and South Africa). Each cultivar
received four treatments including the control one, 30.75 kg N/fed{100%N). The other
three treatments included soil inoculation with the biofertilizer Nitrobein combined with
N fertilizer at rates of 23.06{75%N), 15.38{50%N) and 7.69{25%N) kg N/fed. The
biofertilizer (Nitrobein) was supplied at the rate of 7kg/fed. Results showed that, cv. Mabrouka had longer vine length and higher fresh
weight of foliage per plant than South Africa during 1998.0n the other hand, South
Africa showed greater leaf area than Mabrouka during 1997.Moreover, data indicated
that 50 and 25 % of N+ Nitrobein resulted in lower DWT% of leaves as compared with
the control treatment (1 OO%N). Concerning total yield of tuber roots, no significant difference was observed
between the two cultivars in 1997. While in 1998 cv. Mabrouka exceeded South Africa
by about 39%.Results also showed that applying N!trobein with 50 and 25% of N
fertilizer gave the highest yield as compared with the control during the two growing
seasons. They exceeded it by 12.6 and 10.8% during (1997) season and by 24.2 and
26.7% during 1998 season, respectively. No significant differences were observed in the marketable yield between the two
cvs. during the two growing seasons. Data also showed that 75% followed by 50%of
N+ Nitrobein gave the highest values of marketable yield as compared with the
control treatment (100%N).The lowest marketable yield during the two growing
seasons was always given by the treatment 25% N+ Nitrobein. Differences in average tuber root weight (g), DWT% and shape index of the tuber
root were significant only during the second season. Mabrouka cv. had the highest of
shape index of the tuber root. Also, it was obvious that 50%N+ Nitrobein resulted in
the highest average weight of tuber root .On the other hand, the highest shape index
and DWT % values resulted from 25% N+ Nitrobein . Mabrouka showed higher percentages of N, P, K, protein and sugars than South
Africa. However, fertilizer treatments had no influence on N, P and protein
percentages of tuber roots. Potassium % was higher in tuber root received 50 or 25
%N+ Nitrobein as compared with control (100 % N). On the other hand, plants
received 100 %N without Nitrobein produced tuber roots with 15.3 % and 11.4%
sugar contents higher than those treated with 50 and 25 % of the recommend amount
of nitrogen, respectively.