Evaluation of compost quality through germination index, plant yield and nitrogen use efficiency on Japanese Watercress (Nasturtium officinale)

This study aimed to (i) evaluate phytotoxicity, (ii) and quality of two composts, based on plant yield and nitrogen use efficiency of Japanese watercress (Nasturtium officinale}). The germination index (GI) of seeds of mung bean (Vigna radiata L.) was used to assess the phytotoxicity of compost extracts (1:10, w/v) at 0, 10, 20 and 30 days after composting. A separate field experiment growing Japanese watercress was arranged in a randomized complete block design (RCBD) with five treatments and three replications. The treatments were: NT1 (soil only), NT2 (100% NPK chemical fertilizer), NT3 (100% compost A), NT (100% compost B) and NT5 (100% commercial micro-organic fertilizer). Treatments from NT2 –NT5 received the same amount of total applied nitrogen. The results showed that composts in the preliminary study reduced the phytotoxicity of the raw materials by improving the GI from 49% to 58% - 90%. Total dissolved solids in compost A and the heavy metals concentration in compost B were both lower than permissible limits but could be responsible for limiting root growth. Two composts A and B in the experiment gave a comparative vegetable yield (1663.2 - 1762.2 kg/1000 m2) to chemical fertilizer, but significantly lower (P < 0.01) than commercial micro-organic fertilizer (2476.3 kg/1000 m2). After 25 days of fertilizer application, the plants used half of the total N from chemical fertilizer or commercial micro-organic fertilizer, which was twice as many as those from two composts.