EFFECT OF APPLIED CALCIUM-BORON RATIO ON THE AVAILABILITY OF EACH TO RADISH ( Raphanus sativus L.)

The present study was based on the hypothesis whether Ca/B ratio is significant in soil solution terms or in applied terms. A green house study was carried out in sandy heath land soil, growing radish (cv. French breakfast) as a test crop during 1997 at the University of Reading, England. The experiment was laid out in a randomized complete block design and replicated three times. Varying Ca/B ratios i.e. 2000:1, 1000:1, 500:1, 250:1, 125:1 and 25:1 were applied, corresponding to soil solution ratios 7959:1, 4369:1, 1035:1, 851:1, 486:1 and 45:1 along with a basal dose of all essential nutrients. Results revealed that significant treatment effects were observed in the growth response of radish plants and maximum fresh and dry matter yields were recorded at Ca/B ratio of 1035:1 in soil solution or applied 500:1, corresponding to Ca/B ratio in tops and roots were found to be 187 and 41, respectively. The concentration of Ca decreased and B increased significantly with decreasing the Ca/B ratio in the soil. While, the total uptake of Ca and B showed similar response to radish yield as affected by varying Ca/B ratio either in soil solution or applied. Direct correlations were found between the Ca/B ratio in the soil solution or applied with the Ca/B ratio in radish plants, suggested that both Ca/B ratios are significant from the soil fertility and plant nutrition point of view. Soil pH significantly increased as the Ca/B ratio in soil solution or applied decreases. INTRODUCTION It is well documented that B has a close relationship with Ca both in plant and soil. It appears that Ca increases the B requirement of plants due to similarity in function (Valmis and Ulrich, 1971; Golakiya and Patel, 1988) and in soil reduces its availability perhaps due to the formation of a calcium metaborate complex (Sillanpaa, 1972). Some times this mutuality is indicated by the Ca/B ratio of plants. The concept of a certain Ca/B ratio used for the status of B nutrition in plants, resulted in many publications by a number of investigators (Gupta and Cutcliffe, 1972; Manchanda and Yadav, 1978; Lal et al., 1979 and Golakiya and Patel, 1988). The investigators showed that crops grow normally if a certain balance exists both in the intake and tissue concentration of Ca and B. However, the results regarding Ca-B relationships appear to be conflicting, because some researchers grown plants in culture solution (Brennan and Shive, 1948; McIlrath and Debruyn, 1956) and others grown plants in soils (Manchanda and Yadav, 1978; Golakiya and Patel, 1988) using traditional extractrants for the determination of available Ca and B in soil, however, hardly few studies were carried out on the extraction of soil solution. Because, soil solution is the source of nutrients for plants and most soil chemical reactions involve this phase. An understanding of nutrient concentration in soil solution is therefore essential, because it influences the processes of nutrient supply to the plant. Soil solution chemistry may therefore, provide a valid measure of the nutrient status of a soil (Campbell et al., 1989). Therefore, the main aim of the present investigation was to study the effect of Ca/B ratio on the availability of each in soil solution and their uptake by plants. Secondly, to see whether the concentration of these two elements in soil solution run parallel with plant uptake, or if any adsorption, precipitation and exchange reactions of ions did occur during plant growth. Keeping in view these points an experiment was proceeded to test the general hypothesis as to whether the Ca/B ratio is significant in soil solution terms or in applied terms, using radish as a test crop. MATERIALS AND METHODS Experimental conditions and layout The experiment was carried out in 1997 at the Department of Soil Science, University of Reading, England under green house conditions in randomized complete block design with six Ca/B ratios and replicated three times. Each treatment was represented by a plastic pot in which four healthy plants of equal size were planted. Each block was situated within a distance of 30 cm from each other. The position of each pot was randomly changed once a week, to minimize spatial variation in the green house during the experimental period. The maximum temperature was 22 C and the minimum 18 C. The relative humidity was approximately 65%, and the lighting period was distributed in 16 hrs day and night. Description of the soil used The soil used was boron deficient, collected from the Bracknell area near Reading. The soil was from sandy heath land, and is an unfertilized acid soil. A bulk sample of the top soil (0-20) was collected from different points at random in the area, after clearing the surface litters, and made a composite sample. The composite soil sample was air dried, ground, passed * Department of Soil and Environmental Sciences, NWFP Agricultural University, Peshawar – Pakistan. ** Department of Soil Science, University of Reading, England M. Tariq and C.J.B. Mott. Effect of applied calcium-boron ratio on the availability of each . 358 through a 2 mm sieve and characterized for various physico-chemical properties by routine standard procedures Pot, seed pre-germination and planting Each pot received 1 kg of air dry soil and four equal size plants. Before use the pots and saucers were thoroughly washed in 3% hydrochloric acid and then with deionised water and dried in oven at 40 C. A glass wool filter paper was placed at the bottom of each pot to cover holes for preventing loss of soil, and the pot placed on a plastic saucer. Equally sized of radish seeds (cv. French breakfast) were selected, and pre-germinated in acid washed sand for five days. Then the uniform seedlings were transplanted to the pots. It was kept around at 20% by weight moisture content with deionized water by successive weighing, throughout the growth period. The plant water consumption was recorded. As the plants were growing an extra amount of water equivalent to the plant fresh weight applied at every weighing, and also one pot without plants was included to measure the water losses by evapotranspiration. Application of Ca/B ratios The soil was prepared by adding solutions of CaCl2.2H2O and H3BO3 in different proportions, to bring the original soil to desired Ca/B ratios. The ratios of total Ca to B in each treatment were as follows:2000:1, 1000:1, 500:1, 250:1, 125:1 and 25:1 corresponding to the soil solution ratios 7959:1, 4369:1, 1035:1, 853:1, 486:1 and 45:1, respectively. The detail procedure for preparing the ratios were as follows:Soil contains a” mg Ca kg and b” mg B kg. We take 1 kg soil for each pot, this contains ac” mg Ca and bc” mg B. For example, to obtain the 1000:1 Ca/B ratio we need to add: d” mL of CaCl2.2H2O containing e” mg Ca L . Total f” mg Ca (a-d), and g” mL of H3BO3 containing h” mg B L : Total j” mg B (b-g). Then ac+f/bc+j = 1000/1. Harvest and measurements The radish plants were harvested at marketable maturity. The plants were washed thoroughly with deionised water, then placed on tissue paper to remove excess water. The fresh matter yield for tops and roots were measured. Then both tops and roots were oven dried at 80 C for 48 hours and had their dry matter yield recorded. Soil analysis At harvest fresh soil from each treatment pot was collected and the soil solution from saturated soil was extracted using centrifugal drainage as suggested by Kinniburgh and Miles (1983), and subjected to elemental analysis for Ca and B by ICP-OES. At harvest sub-samples from each treatment pot was taken for the determination of soil pH (1:2 soil: water suspension), to see any pH changes occurred due to varying Ca/B additions. Plant analysis The dry plant materials were ground using Tema mill which was cleaned thoroughly with a brush and acetone for each treatment, then extracted by dry ashing technique and analyzed for Ca and B for their elemental content followed by ICP-OES (Mozafar, 1989). Elemental standard solutions were prepared for low, moderate and high concentrations in the same matrix as the samples to calibrate the ICP-OES before introducing the samples, and the results printed on Dec-writer II input/output terminal. Statistical analysis Statistical analysis of all the data collected during investigations were analyzed by MSTAT-C computer package, using ANOVA technique and the means were compared by the LSD-test of significance (Steel and Torrie, 1980). In addition, correlation coefficients (r) were determined between the variables of the experiment. RESULTS AND DISCUSSION Results showed that the experimental soil was loamy sand in nature, acidic in reaction, having adequate organic matter, and deficient in hot water solubleboron (Table Ι). Table Ι Physico-chemical properties of experimental soil Properties Units Values