Abstract
Spinach (Spinacia oleracea L.) is one of the major agricultural products in Iwate prefecture, Japan. To evaluate the effect of compost made from cattle waste and saw dust, the growth and nitrogen (N) uptake of spinach were examined between 1998 and 2001, compared to those with standard fertilization using a chemical fertilizer. The compost was applied annually at a rate of 45 g N•m−2 before sowing, then spinach was cultivated 2–4 times per year without supplemental N application. In the standard fertilization using ammonium nitrate, super phosphate and potassium chloride, N, P2O5 and K2O were applied to the soil at rates of 16–20 g•m−2, 20–24 g•m−2 and 16–20 g•m−2, respectively. Morphological index, i.e. leaf length, leaf width and number of spinach leaves in plants receiving compost were comparable to those of plants treated with chemical fertilizer. Dry matter production and N uptake in spinach applied with the compost was higher than that applied with chemical fertilizer, while the concentration of inorganic N in soil treated with compost was much lower than that treated with chemical fertilizer after every cultivation. Furthermore, the proportion of nitrate to total N in spinach receiving compost was much lower than that in spinach treated with chemical fertilizer, a though N uptake was higher in spinach treated with compost than that treated with chemical fertilizer. These findings suggest that N uptake in spinach would not be fully explained by the concentration of inorganic N in soil. However, concentration of phosphate buffer extractable organic N, which is considered an easily decomposable organic N, increased in soil treated with compost compared to that in soil treated with chemical fertilizer.
