Primary productivity, nutrient cycling and organic matter turnover of tree plantations after agricultural intercropping practices in Northeast Thailand / by Pitaya Petmak

Thesis (Ph.D. - - Forestry : Siliculture and Forest Influences) University of the Philippines, College, Laguna.

Includes bibliographical references.

PITAYA PETMAK, University of the Philippines at Los Bafios, May 1983, Primary Productivity, Nutrient Cycling and Organic Matter Turnover of Tree Plantations after Agricultural Intercropping Practices in Northeast Thailand. Major Professor: Dr. Neptale Q. Zabala

Tree species showed different effects on each crop yield. All agricultural Crops intercropped with Pe ltophorum dasyrachis gave the lowest yield value. Yields were high when intercropped with Acacia auriculaeformis and Eucalyptus camaldulensis, but higher when intercropped with Leucaena leucocephala during the third year of intercropping practices.

All of the equations derived by the allometric model for the various biomass components estimated for each tree species were closely correlated with each particular stem diameter. The coefficients of correlation (r) were also highly correlated with an average value of 95% in all equations.

This shows that the model is applicable for A. auriculiformis,P. dasyrachis, L. leucocephala and E. camaldulensis with stem diameters of 5 cm, 5 cm, 30 cm and 130 em above the ground Respectively.

Acacia auriculaeformis had the highest value both in the estimated net aboveground production rate and in the average fuelwood dry weight with 35.85 t/ha/yr and 43.94 t/ha respectively over the four years period. It also increased over 600% on the monoculture trial compared with the other three tree species,

The rate of production on one hand of the litterfall at four year of age was highest in Acacia with 4.03 t/ha/yr and lowest in Leucaena (1.91 t/ha/yr). However, the annual return/uptake ratio (%) in dry matter of Acacia is far below from Leucaena with 11.24% and 44.11% respectively.

The considerably fastest rate of leaf litter decomposition was found in Leucaena stand (1.84 gm/m*/ month) and very slow in Acacia stand (0.12 gm/m*/month) during the rainy Season In the dry season, Leucaena had 89.3% and Acacia the lowest with 28.8% assumed at 50% of decay rate during the rainy season. From these, it was estimated that leaf litters of Acacia and Peltophorum need almost two years to complete @ decomposition process while Leucaena and Eucalyptus need Only a year.

In the fifth year, it was observed that the effects of tree crops on re-intercropping planted fallow after clear cutting showed an inverse correlation to agricultural crop production especially that the Present status of soil productivity was higher in Leucaena plot than in Acacia. It was also observed that nutrient uptake in L. leucocephala and E- camaldulensis are much lower than 2. dasyrachis and A. auriculaeformis. Finally, the average above ground dry weight of all crops were observed to be higher in Leucaena
stand.

Economic analysis using B-C ratio Showed that the first ten groups of varying combinations obtained a ratio greater than one (1.0) which defined that all of these groups are economically feasible,

Submitted to the University Library 01/07/1994 T-1485