Effect of phosphate rock and triplesuperphosphate on growth and leaf N, P and K contents of groundnut (Arachis hypogaea L.) grown on a clay soil.

A pot experiment was carried out to investigate the agricultural value of a local phosphate rock (PR) as a source of plant phosphorus compared with that of the currently imported triplesuperphosphate (TSP) . The PR was applied at the rate of 0, 55, and 110 kg P2O5 /ha and the TSP was at the rate of 0, 45 and 90 kg P2O5 /ha. The growth and leaf contents of N, P and K of groundnut (Arachis hypogaea L.) grown on a clay soil were measured. The experiment continued for two seasons. Phosphatic fertilizers are of low recovery; therefore, they can remain for the next crop. Thus, the pots of the first season were set to study the residual effect of phosphorus in the second season. The results indicated that PR and TSP significantly (P>0.05) increased dry weights of shoot and root, leaf contents of N , P and available soil phosphorus. However, plant height was significantly increased by TSP only. The leaf content of K was neither affected by PR nor TSP application. The results showed a positive effect of the residual PR and TSP on the measured parameters. Moreover, the results revealed that the plant measurements obtained from PR treatments were comparable to those obtained from TSP treatments which indicate that PR can be used as a potential source of phosphorus fertilizer. INTRODUCTION Phosphorus is an essential element in plant nutrition. It is often deficient and of low solubility and, therefore, it has to be added as a fertilizer. In Sudan, with a possible exception of nitrogen, phosphorus is the main limiting factor in crop production (El Saeed 1997). This was the concern of many research workers in Sudan who pointed out the good response of crops to phosphorus addition (El Tilib et al 2003). Phosphate rock (PR) is the base for the production of all water soluble phosphorus fertilizers. Finely ground PR ore had been applied directly to the soil as a low-cost fertilizer as an alternative of the water soluble phosphate fertilizers where indigenous deposits of PRs ore located. Phosphorus fertilizers normally have a high carry over effects from one year to the next. Regarding this, residual effect of PR was studied by many workers (Abdalla 1993 and El Saeed 1997). In Sudan, groundnut is produced on large areas under rainfed and irrigation systems. Mostly, the crop is not fertilized in spite of the inherently low soil fertility in terms of nitrogen and phosphorus. However, experiments conducted in different parts of the country gave an erratic and inconsistent results (Hago, Personal Communication, 2005). Triplesuperphosphate, as a source of phosphorus in Sudan agriculture, is an imported commodity, hence, it is expensive. It is, therefore, necessary to try a local and cheaper source of phosphorus. This study was meant to try a local phosphate rock as El-sheikh M. ; El Tilib; E. Elsheikh and Awad Elkarim Arab Univ. J. Agric. Sci., 15(1), 2007 198 source of plant phosphorus. Phosphate Rock is present in different parts of Sudan in considerable amounts, particularly, in Nuba Mountains “Kurun”, Western of Sudan (Abdalla 1993). The aim of this work was to determine the effect of PR and TSP and their residual effect on growth and N, P and K leaf contents of groundnut (Arachis hypogaea L). MATERIALS AND METHODS Pot experiments were carried out at the Faculty of Agriculture, University of Khartoum, Shambat (latitudes 15 ̊ 40 َ N; longitude 32 ̊ 32 َ E) for two summer seasons (2001 and 2002) to examine the effect of PR and TSP on growth and leaf N, P and K contents of groundnut (Arachis hypogaea L)grown on Shambat clay soil. Along with this, another experiment was conducted in the second season (2002) to study the residual effect of the applied phosphatic fertilizers of the first season. Surface samples of Shambat soil, (0-30cm) were used in this study. The physical and chemical properties of the soil used were as follows: pH = 8.1; ECe= 0.52 dSm;K= 0.1 meq/l ; P= 3.3 ppm; N= 0.056%; clay =54.1%. Plastic pots (33 cm diameter and 23 cm deep) were used as experimental units and each pot was filled with 10 kg soil. Uniform size seeds of groundnut cultivar MH 383 were sown in the first week of July in all growing seasons. Five seeds were sown in each pot, and, then thinned to two plants per pot after two weeks from sowing. The treatments were arranged in a factorial completely randomized design replicated thrice. The treatments comprised three PR levels (0, 55 and 110 kg P2O5 /ha) and three TSP levels (0, 45, and 90 kg P2O5 /ha). The local PR used in this study was collected from Jabel Kurun in the Nuba Mountains, South Kordofan State, Western Sudan. The two phosphatic fertilizers were applied at sowing by band method. Seedlings were either inoculated or uninoculated with Bradyhizobium sp. strain TAL 1371 obtained from NIFTAL project in Hawaii, U.S.A. The pots were irrigated with tap water at 60% field capacity every three days. Plants were harvested on the third week of November of each growing season. The parameters measured were plant height, shoot and root dry weights. Leaf mineral contents of N, P, K and available soil phosphorus were determined according to procedures described by Tandon (1993). RESULTS AND DISCUSSION Application of Bradyhizobium sp. showed no significant effect on all measured parameters (data not shown). The results of this study showed that the plant height was significantly increased (P>0.05) by addition of TSP in both seasons (Table 1). Plant height is an important growth factor. Hago et al (2002) reported similar effects for phosphorus fertilizers on Roselle (Hibiscus sabdariffa var. sabdariffa L.). This could be attributed to the positive effect of water soluble phosphatic fertilizers on plant photosynthesis and, hence, plant height. The effect of PR addition on plant height was not significant (Table 1) . This may be due to the relatively low solubility of the phosphorus in PR and, hence, the phosphorus level in the root sorption zone is low, particularly, in early growth stages. It may also be attributed to the low development of plant compared with its rapid growth when soluble form of phosphorus is applied (Hammond et al 1986). There were no significant differences between the overall effect of PR and TSP on plant height. Table 1. The effect of phosphate rock and triplesuperphosphate on plant height (cm)