A qualitative assessment of the N Status of Young Rubber Trees as Affected by Interrank Crops in Northeast Thailand

Chlorophyll-meter readings on leaves and measurements of trunks girth of five years old rubber trees (Hevea brasiliensis ) were carried out during the rainy season 2009 within an experiment comparing three treatments, at two positions in a landscape of Northeast Thailand: i) a rank of trees without cover crop in both inter-ranks surrounding it, ii) a rank of trees with Pueraria phaseoloides and iii) a rank of trees with Vetiveria zizanioides in the inter-ranks. These perennial inter-rank cover crops were set up from 2007 and they were cut and their residues spread as mulch at the soil surface every three months. In 2009, rubber trees growing with Pueraria in their interranks had the highest rate of growth and SPAD values. Differences between treatments were smaller upslope than downslope where the soil water reserve was higher. These results suggest that despite the chemical fertilizer application, N nutrition rather than water could be the most limiting factor for the growth of rubber trees in some fields of this area. Managing a legume cover crop in their interranks could be an interesting option.