Ameliorating Sandy Soil Properties: Application of Mathematical Model to Explore Spinach (Amaranthus tricolor L.) Plant Response

Amelioration is an effort to increase soil fertility by manipulating chemical and physical properties of the soil. In this study, biochar and manure were adopted for ameliorating sandy soil. The purposes of this study were to identify the response of spinach plants, to apply mathematical model for exploring spinach plant growth, and to determine the appropriate ameliorant dosage. The ameliorant were rice husk biochar and poultry manure. The study was conducted in a greenhouse with 4 different dose comparisons (in kg; sandy soil: rice husk biochar: poultry manure), i.e. 1: 0: 0 (C), 1: 0.007: 0 (B), 1: 0.0035: 0, 0035 (MB1), and 1: 0.007: 0.007 (MB2). Each treatment was repeated 5 times in a Complete Block Design. Growth parameters observed were plant height, number of leaves, and plant weight. Observation was carried out for 70 days. The analysis used was one-way ANOVA test, Turkey test, logistic equation and exponential polynomials models, and linear regression. The study revealed that the best spinach growth response by MB1. The growth rate from plant height side of C, B, MB1, and MB2 treatments were -0.0509, -0.0406, -0.0556, and -0.0489 respectively. In terms of number of leaves, the optimum of growing period of C, B, MB1, MB2 treatments were 48, 65, 96, and 66 days after planting respectively. One-way ANOVA test showed that rice husk biochar and poultry manure ameliorant had a significant effect on plant growth both height and number of leaves (sign. <0.05). While, the wet and dry weight were not significantly effect (sign. > 0.05). Mathematical model with logistic and exponential equations were acceptable to describe spinach plant growth (R2> 80). Ameliorant rice husk and poultry naure 5 tons ha/ha (MB1 treatment) was recommended for optimum spinach growth in sandy soil.