S Zauyah

Decomposition and nutrient release of maize stover and groundnut haulm under tropical field conditions of malaysia

Recycling of crop residues is essential to integrated and sustainable agricultural management system. Thus, it is of crucial importance to study the decomposition of these residues particularly in the humid-tropics. A litterbag experiment was carried out on an acid soil of the humid tropics of Malaysia. Haulm from groundnut and stover from were placed inside nylon 2 mm mesh bags (20 cm×20 cm) and placed on the soil surface in the field with a groundnut–maize rotation system. A total of 21 bags for maize and an equal number for groundnut residues were placed in a field plot. Three bags of each residue type were retrieved at 1, 3, 5, 7, 9, 11 and 13 weeks of decomposition. The decomposed tissue was analyzed for remaining dry matter weight (DMW), nitrogen (N), carbon (C), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) contents. Dry matter disappearance rate constant (0.158% week− 1) from groundnut haulm was significantly (P=0.01) faster than that from maize stover (0.099% week− 1). A 50% loss of residue N was found after 2 weeks for maize residues and only 1.5 weeks for groundnut residues. Generally, nutrient loss from both residues was in the order of K≥P=N=Mg≥Ca. The results indicated that sowing time of subsequent crop after residue application is crucial to synchronize nutrient release with plant uptake.

Changes in chemical properties and growth of corn in volcanic soils treated with peat, ground basalt pyroclastics, and calcium silicate.

Volcanic ash-derived soils have high pH0 and very low cation exchange capacity attributed to their highly reactive colloidal constituents, the short-range-order minerals. Fertility is in doubt unless the effects of positive adsorption sites are masked and the increment of negative charge improved. Laboratory and glasshouse experiments were conducted to assess the masking effects of peat, ground basaltic pyroclastic and calcium silicate viz. effect on pH0 and CEC of volcanic soils of Camiguin Island, the Philippines, and to evaluate the growth of corn (Zea mays L.) grown on these soils after the treatments. In the laboratory experiment, Andic Haplumbrept (Soil 1) and Typic Dystrochrept (Soil 2) were incubated with 20% (air-dried) peat, ground basaltic pyroclastic and calcium silicate for nine months. In the glasshouse experiment, the treatments consisted of four rates of the above materials: 20, 10, 5, and 0% per unit weight soil. Corn was planted after nine months of incubation period. The results showed that incubation with peat reduced pH0, increased the CEC, and improved their ion retention. Addition of ground basaltic pyroclastic improved the charge properties but indicated that more incubation time is needed to get an optimum effect. Calcium silicate effect was uncertain due to a relatively high application rate. Corn response showed that nutrient uptake increased with the applied amendments. It also showed that relative plant heights and weights were linearly correlated with Mg concentration in the soil solution.

Effect of calcium silicate and superphosphate application on surface charge properties of volcanic soils from West Sumatra, Indonesia

Silicate and phosphate are known to change soils charge properties. A study was conducted to determine the effects of their application on charge of volcanic soils of Sumatra, Indonesia. This study showed in the beginning that calcium (Ca)-silicate application increased soil pH and zero point of charge (pH0). The cation exchange capacity (CEC) increased from 3 to 15 cmolc kg−1 in direct relationship to the rate of silicate application and from 3 to 8 cmolc kg−1 after applying superphosphate. The inverse relations obtained between pH0 and the CEC as well as with the sum of basic cations verify the beneficial effect of applying silicate and superphosphate in increasing cation retention of volcanic ash soils. The AEC values were unchanged as the soil pH values were well above the pH where amphoteric surfaces can generate positive charge. For silicate application, it is believed that nine months incubation period is sufficient to make a major improvement in cation retention and significantly increase soil pH and negative ΔpH values.

Utilization of drinking-water treatment residue to immobilize copper and zinc in sewage-sludge-amended soils

In situ immobilization of copper and zinc using alum-treated drinking-water treatment residue (WTR) was selected for the remediation of sewage-sludge-amended soils. The WTR has a pH of 7.07 and, although its acid-neutralizing capacity (ANC) is low, utilization at high rates (>2.5%) can help to increase the pH of the soil system. The minerals present in WTR, such as kaolinite, gibbsite and Fe-oxides, provide surfaces for the adsorption of heavy metals. From the soil-solution study, results showed that application of WTR had reduced Zn concentrations in the soil solutions, as compared to the control treatment. Removal of Zn occurred via precipitation, adsorption and possibly organic-matter complexation or chelation. From the glasshouse study, results showed that by using WTR, Zn uptake by maize can be reduced. Although the decrease in Cu concentrations in the soil-solution study was not apparent, due to the very low concentrations of Cu present, the glasshouse study did indicate a reduction in Cu uptake by the maize plants; suitable rates of WTR application for maize growth should be less than or equal to 10%. In fact, there is an additional benefit of WTR application, whereby the rate of 2.5% can increase the dry weight of the maize plants. Thus, WTR can be recom-mended as a potential soil amendment to immobilize Zn in contaminated soil.

Co-application of red gypsum and sewage sludge on acidic tropical soils.

The agroenvironmental impact of co-utilization of red gypsum and sewage sludge was investigated. Both laboratory and greenhouse studies were conducted. The treatments were soil + sewage sludge (5% w/w) + red gypsum (0, 2.5, 5, 10, 20, and 40%, w/w). Corn was grown in the greenhouse, and the highest rate of red gypsum application was excluded. The residual calcite in red gypsum was able to increase the pH of the red gypsum–sewage sludge acidic soil system. Hence, gypsum reduced the zinc (Zn) concentrations in the soil solution released by sewage sludge. Phosphorus (P) and potassium (K) were insufficient for corn growth. At the rate of 2.5% red gypsum and 5% sewage sludge application, no dry-matter reduction was observed compared to the control. The uptake of Zn, copper (Cu), and iron (Fe) by the corn plants decreased. Therefore, co-utilization of red gypsum and sewage sludge is a better option than using these by-products separately.