Effect of Nitrogen Fertilizer and Plant Density on Growth , Fruit Yield and Seed Production of Okra ( Abelmoschus esculentus L. Moench )

Abstract

This study was suggested to investigate the effects of inorganic nitrogen fertilizer and plant spacing on vegetative growth characters, fruit yield and its components , seed yield and its components as well as on some chemical contents of Okra leaves ( Abelmoschus esculentus L.Monech ), cultivar Clemson Spinless. Two field experiments were carried out during the summer seasons of 2006 and 2007, at the Experimental Station Farm of Horticulture Department , Faculty of Agriculture , Omar Al-Mokhtar University , Al-Gabal Al-Akhdar region . Twenty treatment combinations, representing all possible compinations among five nitrogen levels; 0 , 70 , 115 , 160 , and 205Kg N/ha and four plant spacing ( 20, 30, 40 and 50 cm ), were studied in a split-plot layout in a randomized complete blocks design , with four replications, in both experiments. The five nitrogen levels occupied the main plots; whereas, the four plant spacing treatments were randomly distributed in the sub-plots. The obtained results could be summarized as follows : 1. Increasing the level of applied nitrogen up to 205 Kg N/ha was accompanied with significant increases in fresh and dry weights of each vegetative growth, leaves and branches/ plant, plant height, number of branches as well as number and area of leaves / plant .

2. Gradual increases in the level of applied nitrogen up to 205 Kg N/ha, significantly increased the total and early fruit yields , number and weight of fresh fruits / plant and the value of nitrogen use efficiency ( NUE ), in the two studied seasons . Meanwhile, the five levels of nitrogen did not significantly differ in their effects on length , diameter, as well as, fresh and dry weights of green fruit .

3. Significant increases in the leaves contents of N , P and total chlorophyll were obtained as a result of increasing the level of applied nitrogen up to 205 Kg/ha . Meanwhile , application of N at 115 and 160 Kg / ha produced the highest leaves content of K, in the first and second seasons, respectively .

4. Fertilizing okra plants with gradual increaments of nitrogen up to 205 Kg/ha, resulted in progressive and significant increases in seed yield either per plant or per hectare , number of matured fruits / plant, average weight of matured fruit and weight of seeds / fruit, in the Two studied seasons, as well as pod length, shelling percentage in the first and second seasons , respectively . However, weight of 100 seeds (seed index) , germination percentage and pod diameter did not significantly respond to the studied N levels, in both seasons.

5. Increasing the distance between adjacent plants from 20 to 50 cm, significantly increased the studied characters of vegetative growth in the two growing seasons. Meanwhile, plant height was significantly decreased with increasing plant spacing .

6. Planting at narrow spacing ( 20 cm ) significantly increased early and total green fruit yields / ha and the value of nitrogen use efficiency in the two studied seasons; while, increasing the distance between plants up to 50 cm, statistically increased number and weight of green fruits / plant. On the other hand , the studied four spacing had no effects on length and diameter of fruit as well as its fresh and dry weights . The widest tow spacings , 40 and 50 cm, did not significantly differ in their effects on early fruit yield and NUE .

7. Increasing the distance between plants to 50 cm, generally, increased the leaves contents of N , P , K and chlorophyll in both studied seasons.

8. The studied four plant densities did not significantly affect weight of 100 seeds, germination percentage and length of matured fruit, in the two growing seasons, number of seeds/fruit in the first season, and pod diameter in the second one, whereas, decreasing the distance from 50 to 20cm, consistently and significantly increased total seed yield / ha , but significantly decreased number of matured fruits and seed yield / plant, as well as weight and number of seeds / fruit .

9. Planting okra plant at widest spacing ( 50 cm ) combined with 205 Kg N/ha , generally, produced the highest increases in the studied characters of vegetative growth in the two growing seasons; whereas , the highest value of plant height was obtained from plants spaced at 20 or 30 cm and fertilized with 115, 160 or 205 Kg N /ha.

10. The highest significant increases in the early and total green fruit yields / ha, as well as the value of nitrogen use efficiency were, generally, achieved from plants spaced at 20 cm and fertilized with 160 or 205 Kg N/ha., meanwhile , planting at widest spacing combined with 205 Kg N/ha produced the highest fruit yield / plant in the first season . The results of the second season, revealed that, the highest early and total fruit yields / ha were obtained at narrow spacing ( 20cm ) combined with 205 and 160 or 205 Kg N / ha ., respectively , meanwhile, growing okra plants at 50 cm with N fertilization at rate of 205 Kg N / ha., gave the highest number and weight of green fruits / plant. On the other hand , the highest values of NUE were obtained from plants spaced at 20 or 30 cm combined with 70 , 115 , 160 or 205 Kg N / ha .

11. Growing okra plants at 50 cm combined with 205 Kg N/ ha increased the leaves contents of N , P and total chlorophyll. However, the studied plant densities, generally , did not significantly differ in their effect under the studied N levels. On the other hand, the highest leaves K content was obtained at 50 cm spacing combined with 115 and 160 Kg N / ha , in the first and second seasons, respectively .

12. Sowing at narrow spacing ( 20 cm ) and fertilizing with 205 Kg N / ha, significantly increased total seed yield /ha ., meanwhile, the highest significant increases in the number of matured fruits and seed yield / plant were obtained at 40 or 50 cm spacing combined with 160 or 205 Kg N / ha ., in the two studied seasons. On the other hand, the present interaction had no significant effect on weight of 100 seeds as well as germination and shelling percentages .

In view of the obtained and discussed results, of the present study, it could be generally concluded that, increasing plant density by decreasing the spacing between plants (20 cm) combind with N fertilization at 205 Kg / ha might be considered as an adequate and economical treatment combination for the production of high yield of green fruits and dry seeds with good quality, under the prevailing conditions of Al-Gabal Al-Akhdar and other similar regions .