Ed Sarobol

Soil Organic Carbon Loss and Turnover Resulting from Forest Conversion to Maize Fields in Eastern Thailand

Soil organic carbon (SOC) content and its stable carbon isotopic composition (within the upper 1 m) were measured to determine the effect of land-use changes from dry evergreen forest to maize fields in eastern Thailand. Digital land cover maps, derived from aerial photography and satellite images for years 1989, 1996, and 2002 were used in association with field surveys and farmer interviews to derive land-use history and to assist in study site selection. Conversion from forest to maize cultivation for the duration of 12 years reduced SOC stocks at the rate of 6.97 Mg C ha−1 year−1. Reduction was most pronounced in the top 10 cm soil layer, which was 47% after 12 years of cultivation. Stable carbon isotope data revealed that the main fraction lost was forest-derived C. Generally low input rates of maize-derived C were not sufficient to maintain SOC at the level prior to forest conversion. After 12 years of continuous maize cultivation, the maize-derived C fraction made up about 20% of total SOC (5 Mg ha−1 of the total 25.31 Mg ha−1).

AMELIORATION OF ZINC DEFICIENCY OF CORN IN CALCAREOUS SOILS OF THAILAND: ZINC SOURCES AND APPLICATION METHODS

A variety of zinc (Zn) fertilizer sources are applied with varied responses on calcareous soils in Thailand. Seed treatment is an alternative method to deliver Zn to corn and alleviate Zn deficiency. To address this Zn delivery methods we conducted greenhouse studies on corn grown in three calcareous soils of Thailand to three Zn fertilizer sources [zinc sulfate (ZnSO4), Zn-ethylenediaminetetraacetic acid (EDTA) and Zn citrate]. We also evaluated effectiveness of soaking corn seed in three concentrations of ZnSO4 (0.4, 0.8 and 1.6%) prior to planting compared to soil applied methods. Applications of zinc increased the growth, dry matter yield and zinc uptake of corn with few differences observed among the types of fertilizers. Seed soaking with ZnSO4 solution also increased Zn uptake, growth rate and yield comparable to soil-applied Zn. Seed soaking prior to planting is an effective and efficient method to supply Zn to corn grown in Zn deficient calcareous soils of Thailand.

Effects of Vetiver Grass and Green Manure Management on Properties of Map Bon, Coarse-Loamy Variant Soil

A vetiver grass and bean cropping system could be used for improving physical properties of deteriorated soils. The objective of this research was to study effects of vetiver grass (Vetiveria zizanioides Nash) and green manure management on properties of Map Bon, a coarse-loamy variant of sandy loam, with low organic matter and medium erosion, at the Khao Hin Son Research Station, Chachoengsao, Thailand, from March 2001 to April 2003. The experiment was carried out in a split-plot design in a randomized complete block design with three replications. There were two main plots (with and without vetiver grass) and four subplots (without bean and with either Vigna sinensis, Canavalia ensiformis, or Dolichos lablab). This work showed that the treatments with vetiver grass could increase organic matter and saturated hydraulic conductivity; however, bulk density and soil hardness decreased and total porosity and available water-holding capacity were not affected. The use of green manure affected soil hardness and saturated hydraulic conductivity. The treatments with vetiver grass and green manure could increase available water-holding capacity of the soil also.

Effects of Chicken Manure and Chemical Fertilizer Management on Yield of Cassava Grown on Map Bon, Coarse-Loamy Variant Soil

The objective of this research was to evaluate the effects of chicken manure and chemical fertilizer management on cassava growth and yield. The experiment was carried out in randomized complete block design with three replications from June 2009 to June 2010, using HB 80 cassava cultivar grown on Map Bon, a coarse-loamy variant, at Khao Hin Son Research Station, Phanom Sarakham District, Chachoengsao Province, Thailand. There were 10 treatments: T1, no fertilizer application (control); T2, application of 15N–15P2O5–15K2O chemical fertilizer at the rate of 312.5 kg ha−1 at 1 month after planting; T3, application 15N–5P2O5–20K2O chemical fertilizer at the rate of 312.5 kg ha−1 at 1 month after planting; T4, application of chicken manure (CM) at the rate of 6.25 t ha−1 before planting; T5, application of CM at the rate of 3.125 t ha−1 before planting + 15N–15P2O5–15K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 1 month after planting; T6, application of CM at the rate of 3.125 t ha−1 before planting + 15N–5P2O5–20K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 1 month after planting; T7, application of CM at the rate of 6.25 t ha−1 before planting + 15N–15P2O5–15K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 1 month after planting; T8, application of CM at the rate of 6.25 t ha−1 before planting + 15N–5P2O5–20K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 1 month after planting; T9, application of 46N–0P2O5–0K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 1 month after planting + 15N–15P2O5–15K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 2 month after planting; T10, application of 46N–0P2O5–0K2O chemical fertilizer at the rate of 312.5 kg ha−1 at 1 month after planting + 15N–5P2O5–20K2O chemical fertilizer at the rate of 156.25 kg ha−1 at 2 month after planting. It was found that the treatments with various rates of CM or chemical fertilizer that contained N, P, and K were not different in fresh root yield but treatments with CM and chemical fertilizer tended to give greater fresh root yield or have greater effect on it, and plant height was not affected. The treatments with 3.125 kg ha−1 of CM and 156.25 kg ha−1 of 15–15–15 gave significantly greater fresh root yield of cassava (52%). All fertilization treatments were not different in fresh stem weight but treatments with 3.125 kg ha−1 of CM and 156.25 kg ha−1 of 15–15–15 tended to give significantly greater fresh stem weight of cassava (62%). All fertilization treatments were not different in root starch percentage and root number as compared with control.