Effect of phosphogypsum application on the growth and Ca uptake of Komatsuna Brassica rapa L. cv. Natsurakuten

Abstract

(pp. 1–7) Application of phosphogypsum PG and limestone to Andisol were compared in terms of their effects on the growth and uptake of Ca in Komatsuna Brassica rapa L. cv. Natsurakuten. The studies were carried out in soil pot cultures, and both PG and limestone were applied to the Andisol at the rates of 0, 0.30, 0.75, 1.50 g kg−1 in the form of CaO. 1. Limestone application resulted in an increase in the soil pH. On the other hand, no change was observed in the case of PG application at pH 6.1 ± 0.1 regardless of the application rate. Both soil EC and water-soluble Ca increased in proportion to the PG application rate, and this increase was approximately 5 times greater than that observed when limestone was applied at 1.50 g kg−1. The w-Ca/ex-Ca ratio (water-soluble Ca: 1 M acetic acid-extractable Ca) was clearly increased from 0.12 up to 0.26 in PG, while the value was slightly decreased from 0.12 to 0.05 in limestone. 2. After 33 days cultivation, both top and root growth of Komatsuna were enhanced by PG application. Specifically, when PG was applied at the rates of 0.30, 0.75, and 1.50 g kg−1 the root fresh weight increased by 31, 14, and 6%, respectively, in comparison with limestone. The root development of Komatsuna was closely related to Ca uptake. Ca uptake by Komatsuna was closely correlated to water-soluble Ca in comparison with 1 M acetic acid-extractable Ca in the soil. In particular, Ca uptake was restricted under the low-water soluble Ca conditions 2.0 mmolc kg−1. Therefore, it was concluded that water-soluble Ca in the soil was useful as an index of plant-available Ca.