Abstract: The interaction effects of water stress and nitrogen fertilizer on sunflower variety "Shmas" were studied in pot cultivation. Urea as nitrogen fertilizer was applied and water stress was sporadically induced by a cycle of 10 day watering and 10 day stress period after 20, 30, 40 and 50 days of sowing. Node number and Root length were significantly affected by the interactive effect of water stress and nitrogen fertilizer dose. These two parameter will significantly decrease when either sporadic stress period is increased or urea dose is decreased. The nitrogen applied in three dose had effectively balanced the adverse effects of four sporadic stress periods.
Introduction
Water stress is one of the most serious condition that effects crop productivity. Deficiency of water modifies plant water relationship by lowering tissue water potential (Akhtar et al., 1993). Water deficits that occur during the crop growth period influence its various physiological processes associated with growth, development and economic yield (Begg and Turner, 1976; Pandey et al., 1984a,b). Such effects of water deficit depend on the degree of water stress and stage of crop development at which stress occur (Pandey et al., 1984a,b). Moisture stress at any growth stage reduces crop yield. Similar observations were recorded in a study by Malik and Ahmad (1993) who found that moisture stress reduced grain yield. They were of the view that moisture stress at tillering and grain development stages badly affected the crop and resulted in poor harvest. Palmer et al. (1996) have reported that the availability of nitrate had a strong effect on leaf expansion in sunflower. Saeed et al. (1998) have concluded that water stress caused substantial reduction in seed yield and total plant biomass production of soybean compared with control. However, magnitude of such reduction varied with time and duration of water stress. Meo (1999) determined that sporadic stress and urea fertilizer have highly significant response on leaf area of sunflower. Meo and Baig (1999) deduced that parameters like plant height, head diameter and seed yield were significantly affected by fertilizer doses and sporadic stress in sunflower. A reduction in leaf area index of soybean in response to water stress has also been reported by Chinchilla et al. (1988). Ghani et al. (1999) have observed that interactive effect of nitrogen and water stress on yield and biomass had highly significant response in wheat. Meo et al. (2000) indicated that the response of water stress and nitrogen fertilizer on fresh matter production of sunflower (Helianthus annuus L.) was highly significant. Judicious use of fertilizer is considered one of the most important factor which could increase sunflower yield on per unit area bases. Among nutrients applied nitrogen is one of the most essential element for plant growth. Fertilization for the adequate nutrition of all crop play a major role in efficient use of water (Tisdale et al., 1985). The central idea was that fertilizer application time could be one approach to minimize the adverse effects of water stress occured at different growth stages. With a view to test the aforesaid idea, the present study was undertaken to identify the interaction effects of water stress and nitrogen fertilizer on node number and root length of sunflower (Helianthus annuus L.).
Materials and Methods
The trial was carried out in the net house of Botanical Garden, University of Agricultural, Faisalabad. The entire experiment was conducted in 120 pots. The seeds were sown in pots having 9.5 kg garden soil. The size of each pot was 23 cm in diameters. One plants per pot was maintained. Urea as a nitrogen fertilizer was applied in solution form in three doses in the following ratio:
| Full dose(Normal) | = | 1.41 g for each pot |
| 1/3 rd dose (Normal) | = | 0. 46 g for each pot |
| 1/8 th. dose (Normal) | = | 0.17 g for each pot |
Three urea doses and four water stress levels were created. Completely Randomized Design (CRD) was applied with eight replications and three treatments. The number of pots per stress treatment was 24 whereas the number of pots per urea dose was 8. Before application of urea fertilizer, 120 pots were divided into five groups of 24 pots each as follows. Group I having all the three nitrogen levels was kept as control in which water was applied continuously. In rest of the four group of each nitrogen levels sporadic drought was applied by a cycle of ten-day watering and ten-day stress period at the following stages:
The data for number of node and root length per plant was calculated and analysed statistically by using Duncan's Multiple Range Test (Steel and Torrie, 1980).
Result and Discussion
Number of Nods/Plant: The data given in Table 1 revealed that the number of nodes just before flower initiation significantly differed in fertilizer means. The Maximum significant node number was found at full dose of urea and maximum significant decrease in node number was found at 1/8th urea dose. The stress treatment means differed significantly. The maximum significant value was observed in S0 and maximum significant decrease was found in S. Intermediate values were recorded in stress treatments stressed 30, 40 and 50 days after sowing. Stress and fertilizer interaction differed non-significantly.
In full dose of urea, the number of nodes was maximum in So and minimum in S1. In 1/3rd urea, the maximum value was observed in S0 and minimum in S1. The same pattern was observed in 1/8th urea. It is evident that both fertilizer doses and sporadic stress level have highly significant response for node number. When either sporadic stress period is increased or urea dose is decreased, the number of nodes will decrease significantly. These results are in agreement with Buttrose (1974), Memzel et al. (1996) and Meo et al. (1989).
| Table 1: | Number of Nodes before flower initiation |
Fertilizer Level | |
| Any two means sharing the same letter differ non-significantly. F1 = Fertilizer full, F2= Fertilizer 1/3, F3= Fertilizer 1/8 |
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| Table 2: | Length of root at maturity |
Fertilizer level | |
| Any two means sharing the same latter differ non-significantly. F1 = Fertilizer full, F2 = Fertilizer 1/3, F3 = Fertilizer 1/8 |
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The reduction in growth is due to reduction in turgor potential (Ashraf et al., 1994).
Length of Root/Plant: Table 2 shows that length of root at maturity was highly significantly differed among fertilizer means. The maximum significant root length was recorded at full dose of urea and maximum significant decrease was observed at 1/8th urea dose. The stress treatment means differed significantly. Maximum significant value was found in So and maximum significant decrease in S1. Intermediate values were recorded in stress treatments stressed after 30, 40 and 50 days. The interaction between fertilizer and stress means non-significantly differed. In full dose of urea, the maximum root length was noted in So and minimum in S1. In 1/3rd urea, the maximum value was observed in So and minimum in S1. Similarly in 1/8th urea dose, the highest value was recorded in So and lowest in S1. Therefore, at all sporadic stress levels including control, the highest values for root length were found at full urea dose. When it was applied as 1/3rd dose, the values were intermediate and lowest at 1/8th urea dose. These results are in conformity with Carceller and Fraschina (1986).