Study on sources of chemical fertilizer with magnesium for tangerine
(Citrus reticulata Blanco.) on limed acid sulfate soils : Rangsit very acid phase

Nongkran Maneewon Jumpol Yuwaniyama Surachai Muensank
Bunjirtluk Jintaridth and Charoen Charoenchamratcheep.

ABSTRACT

The Study was conducted a farmer 's rice field, Klongyai sub-district, Ongkalak district, Nakonnayok Province during 1991 - 1995. The experiment was designed in Split plot with a replication comprising

1) Main plot of 4 chemical fertilizer formular : 13-13-12 , 15-15-15 , 20-10-10 and 21-7-12 were applied in the rate of 1 and 2 kg/plant/year in the first and second year respectively (200 and 400 grams/plant/year with magnesium oxide in the rate of 20 grams/1kg fertilizer.

2) Sub plot of chemical fertilizer 14-14-21 in the rate of 3 and 5 kg/plant/ year in the third and fourth year respectively. The size of planting pit is 50 x 50 x 50 cm. Marl in the rate of 5 kg/pit was applied and compost of 20 kg/pit was
incorporated into the soil before planting.

The result showed that chemical fertilizer formular 15-15-15 and 20-10-10 with MgO affected on the tangerine's growth development in the early growth period (2 years). Tangerine's height and crown diameter of this two formular were significant difference from the others. Average height and crown diameter were 130-140 cm.and 123-127 cm, respectively . For the third and fourth year, application of 14-14-21 in the rate of 5 kg /plant year (high rate ) the height and crown diameter was greater than the rate of 3 kg/plant/year. The
high rate gave the height and crown diameter of 210 and 230 cm respectively. Furthermore, it was found that application of chemical fertilizer with MgO, tangerine's growth development was better than chemical fertilizer alone .
Soil and plant analysis showed that in tangerine 's best growth development , amount of magnesium in soil was lower than the other formula and higher amount was found in tangerine's leaves.

Key words: tangerine , marl, chemical fertilizer, magnesium