MATERIALS AND METHODS

Field study was carried out during January 1997 and 1998 at Mu'tah University, College of Agriculture, Rubba in southern part of Jordan.

Application of chicken and sheep manure, added at rates of 20,40 and 80 t ha^–1 to soil was compared with one treatment of inorganic fertilizers (400kg N ha^–1, 200kg P₂O₅ ha^–1 and 100kg K⁺ ha^–1), in addition to a control treatment

After preparing the soil for planting by plowing, disking and spreading the drip irrigation system and covering with plastic mulch. Onion Allium cepa var. Geza was used in this study. The plants were transplanted at 10-15cm height to the experimental land. Each treatment comprised six rows (50 cm apart) in 2 m long and 6 m² of plot area.

Representative compound bulk soil samples were collected randomly from the upper 30 cm of each treatment. The soil was dried, ground and passed through a 2mm sieve. Analysis of manure, irrigated water and soil are shown in Table 1.

The experimental design was randomized complete block design with three replicates. At harvest, two square meters from each experimental unit were harvested and the following components were measured; yield weight of smallest 5 bulbs, weight of largest 5 bulbs, dry weight and leaf area. Bulb samples were dried at 70°C to a constant weight in an oven to determine the dry weight percentage.

The leaf area of three plants for each treatment were measured using leaf area meter Li 310, Li-cor inc. (USA).

Plant tissue samples were digested and analyzed for total N as outlined by Fleige et al. (1971). Available phosphorus in soil was determined according to Watanabe and Olsen, (1985). Therefore, H₂PO₄ and K⁺ in plant tissue were analyzed according to Meiwes et al. (1984).

MSTAT-C statistical package was used to analyze the data that obtained from the experiment. Analysis of variance was the preliminary analysis. Proper mean separation procedure, least significant differences (LSD) test at 0.05 probability level was used (Lentner and Bishop, 1993).

RESULTS AND DISCUSSION

Leaf area, dry weight and number of plants/m² are presented in Table 2. Data indicates a slight increase in dry weight of bulbs for 1998 season. There were no significant differences between the values of dry weight produced by different treatments of fertilization. The dry weight ranged between 15.6% (Sheep manure at level of 40 t ha^–1) and 17.6% (control).

Leaf area of the plants was significantly affected by the application of different fertilizers. The 20 t ha^–1 of sheep manure gave the highest leaf area for 1997 season (1806.3m²), while 40 t ha^–1 of chicken manure gave the highest for 1998 season (2729 m²). Leaf area was higher at 1998 than at 1997 season in general. This could be attributed to the decomposition of residue of organic matter in the same field and might be due to the fact that manure provides suitable nutrients to the plants (Lekasi et al., 1998). Organic matter content was found to be a reliable index of crop productivity in semi arid regions due to its positive effect on soil water-holding capacity (McDaniel and Munn, 1985).

The total yield response to soil treatments with manures and inorganic fertilizer at 1997 and 1998 were significantly different. Higher total yield was obtained from sheep manure (58. 5 t ha^–1) by using 20 t ha^–1 manure in 1997. On the other hand the highest yield was found using 40 t ha^–1 sheep manure in 1998 (Table 3). Total yield varied with type of manures and levels. However, total yield was not significantly affected by chicken manure during both seasons. Total yield of sheep manure was significantly higher at the similar levels of chicken manure.

Table 1:	Characteristics of soil, irrigated water and organic fertilizer of the investigated area
n.d= not determined

Table 2:	Effect of soil treatments with chicken manure, sheep manure and inorganic fertilizer on leaf area and dry weight of onion. During 1997 and 1998

Table 3:	Effect of soil treatments with chicken manure, sheep manure and inorganic fertilizer on total yield and bulbs weight of onion during 1997 and 1998.

Table 4:	Effect of soil treatments with poultry manure, sheep manure and inorganic fertilizer on the availability of some nutrients

This might be attributed to the stimulating effect of the sheep manure that supplies plants with nutrients required for better yield.

According to Table 3 the chicken manure tend to reduce the yield for all the three levels (20,40 and 80 t ha^–1) in comparison with fertilizer and control. This could be due to the harmful effect of chicken manure resulting from the increase in electrical conductivity of the soil at high level of application. It could also be attributed to the high mineralization process triggered in concentration of salt in soil there after solubilization of organic nitrogen from organic matter present in sheep manure by soil microorganisms compared with chicken manure. Havlin et al. (1999) found that adding organic matter into soil has positive effect on soil microorganisms.

One of the significant findings is that the yields level in 1997 and 1998 were closed in both years. This could be due to the fact that organic matter needs rather long time to decompose by soil microorganisms before it becomes ready to be absorbed by plant roots. As a result those yield values remained too close to the yields resulting from inorganic fertilizers as well as control treatments for both years of experiment. These results are in consistency with the results of El-Koumeyand Abu-Agwa (1993) and Aqeel (2001).

All nutrient contents in soil increased with increasing application rates of chicken manure and sheep manure, except with potassium which gave the reverse (Table 4). This phenomena could be attributed to the fact that potassium fixed in soil, particularly those soils with higher percentages of clay minerals at which composed of two layers of silica teterahedra and one layer of Alumina octahedra (i.e. 1:2) as mica illite or vermiculite which has voids or spaces just fit in size with potassium size Bohn et al. (1985) For a given application rate, the effect of treatment was found in the order : chicken manure >sheep manure >Diammonium phosphate. It is well known that chicken manure has higher nutritional values than sheep manure.

Nitrogen content in onion tissues increased with increasing application rates of fertilizer in general. On the other hand more nutrient contents were obtained in 1998 season than in 1997 season except when using 80 tons ha^–1 where the values decreased in 1998. These results are in agreement with total yield (Table 3).

Potassium and phosphorous content in onion tissues increased but not significantly with increasing application rates of manure and chemical fertilizer treatments but all the values decreased in 1998 than in 1997. In general there was no significant difference between treatment and the control treatment in plant tissue.

Onion yield from chicken manure in 1997 and 1998 did not differ significantly. However, the yield was increased significantly on sheep manure and inorganic fertilizer. The yield of onion was higher in second year compared with the first year. It could be due to plant residue in the soil from the previous years, which help the increase of nitrogen content of the soil through the nitrogen mineralization (Liucero et al., 1995). In general under south region conditions of Jordan, using manures coupled with drip irrigation and plastic mulches is an alternative cropping system that can provide high yields and reduce inorganic fertilizer inputs in vegetable productions. This was with agreement with the findings of Singogo et al. (1996).