Analysis of Data Materials and Methods

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5.2.3. Analysis of Data

Analysis of variance was employed to evaluate the effects of application rate of SRFs and reference fertilizer on cumulative yield oven-dried plant tops, cumulative uptake of nutrients concerned, and concentration of nutrients in dry tops for each nutrient source fertilizer, growing period, and soil. The occurrence of deficiency and toxicity concentrations of nutrients in plant tops was identified using critical values of nutrient concentration in plant tops proposed by Pinkerton et al. 1997. Care should be taken in this interpretation, however, since these critical values were established based on concentrations of nutrients for various cultivars of ryegrass and for different growing conditions from those used in this research. For example, the critical levels of a nutrient may be shifted due to interactions with other elements Munson, 1968 and may not be appropriate to the present experimental condition. It is also probable that these critical values are too high for nutrient efficient cultivar used in this experiment. The agronomic effectiveness AE of SRFs relative to reference fertilizer was calculated using the values of cumulative uptake of the nutrient concerned. The value of nutrient uptake is a combined response of yield and nutrient concentration to the application of fertilizer, and thus was the preferred indicative measure of AE Mackay et al. 1984. For the present experiment, moreover, total uptake of nutrient may be used to indicate the extent of release of the nutrient by dissolution of SRF in the soil. Principally, the relative agronomic effectiveness RAE of SRF was defined as the ratio of the effectiveness of SRF over that for the reference fertilizer. Different methods of RAE calculation were employed as were appropriate for the data provided by each experiment: 1. The RAE values for Ca and Mg experiments using soil WP-6 can not be defined due to most of the plants in these experiments dying. 2. For Ca and Mg experiments using soil MR-5, there was only minor effect of the application of Ca and Mg fertilizers on nutrient uptake so that response functions were poorly defined. The RAE values were interpreted graphically based on the response curves, and are the ratio of the rate of SRF required to support 50 of maximum cumulative uptake of the nutrient concerned i.e., Ca for Ca experiment and Mg for Mg experiment relative to the corresponding rate of reference fertilizer. 84 3. For K experiment, the RAE values were calculated based on the best fit equations describing response curves of cumulative K uptake as a function of the application rate of K fertilizers. The best fit equations for the response curves of K 2 SO 4 reference fertilizer were linear, whereas those for SRFs were quadratic. If the rate for the +K 2 SO 4 is extended to much higher than 90 mg Kkg, it will result a quadratic equation with the maximum K uptake achieved at a much greater rate than 90 mg Kkg. However, the maximum or half of maximum values of K uptake for the +K 2 SO 4 treatment can not be defined based on its response curves obtained in this present research. Therefore, the RAE values for the K-SRFs were defined as the ratio of the slopes for the application rate of 90 mg K as K-SRFkg i.e., the highest rate of K for the +K 2 SO 4 treatment. The internal efficiency IE functions describing the effect of nutrient uptake on plant yield were obtained by plotting the value of yield dry plant tops versus the value of nutrient uptake for each harvest, and the IE coefficient is taken to be the slope of this relationship. The relative internal efficiency RIE was defined as ratio of the IE value for SRF to that for the reference fertilizer.

5.3. Results and Discussion