Abstract

The objective of this study was to investigate the spatial variability of soil physical properties and growth of taro (Colocasia esculantum) in an unfertilized 42 m ridge covered with black plastic mulch. The study was conducted at the National Agriculture Research Centre Tsukuba (Japan). The experimental field was made of 3 adjacent ridges of 42 m long and 0.90 m width each. Uniform taro corms were planted in the middle of each ridge at 0.30 m spacing. At the end of growing season, soil samples were taken for measurements of air content (¦_a), bulk density (r_b), gravimetric (q_g) and volumetric water contents (q_v), total pore space (TPS), pore tortuosity (t), gas diffusion coefficient (D_SD_O) and water-filled pore space (WFPS). Taro plants were harvested, separated into leaves (LFW), petioles (PFW), corms (CFW), roots (RFW) and tubers (TFW). All autocorrelation functions (r(h)) for soil properties and taro growth dropped sharply after one lag. Except forq_g, (r(h) for q_a, r_b, Ds/Do and WFPS dropped below zero at about 16 lags, which revealed that these soil properties could be sampled at 4.8 m for independent observations. For taro growth parameters, only PFW, TFW and RFW could be sampled together at 14 lags or 4.2 m for uncorrelated observations. Except for RFW, all taro growth parameters significantly correlated among themselves and with q_g, ¦_a, r_b, Ds/Do, WFPS and t with correlation coefficients ranging from 0.16 to 0.99. Plastic mulch improved soil properties which in turn improved the relationship between these properties and taro growth parameters. 

Key words: Soil physical properties, taro growth parameters, plastic mulch, volcanic ash soil.