Author: Faustino P. Villamayor

Abstract

Phosphorus (P) is generally considered to be the most limiting mineral nutrient in tropical soils. This study was conducted to determine the amounts of Pin various components of the rainforest ecosystem. Composite samples of rocks, soil, stream sediments, stream water, rainwater, leaves of dominant vegetation, forest litter, wood and moss were randomly collected from a portion of the rain forest in Mt. Pangasugan, Leyte, Philippines. Samples were analyzed for their total P contents.
Findings revealed that P concentration varied substantially in the various ecosystem components evaluated. Higher P concentrations were found in the biosystem components particularly in the leaves of the vegetation than in the geosystem components. The P concentrations decreased in the following order: fresh leaves > moss > litter > soil > sediment >rock > wood > stream water > rainwater. Trace amount of P is brought into the ecosystem by rain. On the other hand, considerable amounts of P are found in the stream water and stream sediments which represent P losses from the rainforest ecosystem. This substantial loss of P is attributed to human disturbance in the forest ecosystem.

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Author: Faustino P. Villamayor

Abstract

Residual soils, whose geology is marine and terrestial sediments, have higher available zinc content than those whose geology is marine elastics. These residual soils come from the upper catchment areas of alluvial soil. Available zinc contents of four alluvial soil series, namely Palo, Umingan, San Manuel and Mattdaue, were observed to vary with the geology of their upper catchment areas. Alluvial soils derived from the residual soils of marine and terrestial sediments have higher available zinc than alluvial soils derived from residual soils of marine elastics. Two out of 8 alluvial soil types derived from marine and terrestial sediments contain available zinc in amounts lower than the critical value of 1 ppm. On the other hand. 3 out of 8 soil types derived from marine elastics have available zinc in amounts greater than 1 ppm. Zinc deficiency would most likely occur in alluvial soils derived from marine elastics and least likely in alluvial soils derived from marine and terrestial sediments.

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Author(s): Juanita B. Moulin and Rodolfo G. Escalada

Abstract

Sixteen varieties of mungbean grown in ViSCA during the wet season were evaluated for their growth and yield performance In the open field. Their agronomic parameters measured such as seedling emergence, flowering, maturity, plant height, and number of nodules developed per plant differed significantly among varieties.
Most of the varieties showed marked differences in their yield and yield components. The highest dry bean yields were obtained from CES ID-21 (916.4kg/ha) and CES N30 (867.3 kg/ha). Varieties which developed more nodules generally produced higher grains yields than those which developed less nodules. Three mungo varieties (CES 87, EGMY 377-21, and EGMY 161-1) were found to be low grain yielders. However, they produced the heaviest fresh herbage yield which is important for forage as well as for green manure.

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Author(s): N. 0. Aparra and N. G. Mamicpic

Abstract

BNAS 51, Centennial and Kinangkong yielded 27.42, 14.32 and 5.41 t/ha of tubers, respectively, with a corresponding coefficient of variation (C.V.) of tuber yield among hills of 41.92, 46.02 and 107.65%. Yield among hills was slightly more uniform at a spacing of 60 x 75 cm (C.V. = 56.39%) than at 30 x 75 cm (C.V. 74.01%), although the difference in variability was not statistically significant. A high C.V. of tuber yield among hills (80.66%) was obtained by applying 200-190-230 kg/ha of N-P205-K20, while a low C.V. (54.81%) was observed at zero fertilizer application. Vine weight, vine number, vine diameter, leaf weight and leaf area were significantly and positively co5rrelated to root yield. Variability in vine weight, vine number and leaf weight were significantly and positively correlated to the variability in root yield.

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Author: Jose R. Pardales, Jr.

Abstract

The factors which limited fruit and seed development in taro were determined through laboratory and field observations in the flowers of 18 selected cultivars from the taro germplasm in the Philippine Root Crop Research and Training Center in ViSCA, Baybay, Leyte. The limited fruit and seed set in some taro cultivars were attributed to the following factors: (1) failure of the staminate flowers to produce pollen; (2) short receptivity period of the stigmas; (3) relatively low pollen fertility; (4) irregular number of ovules in the ovaries; (5) presence of trinucleate pollen; and (6) short life duration of the flowers. Low seed set in taro may also be influenced by (a) fungal infection causing decay in many flowers, especially after controlled pollination; and (b) presence of insects found to be feeding on the pollen grains during pollen shedding.

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Author(s): Alfredo B. Escasinas and Rodolfo G. Escalade

Abstract

Differences in grain yield between the different methods of weed control were not statistically significant; however, highly significant differences were observed on the timing of weed control. Results showed that early application of weed control treatments resulted in increased grain and stover yields. Clean culture and application of atrazine 2 weeks after planting and at pre-emergence resulted in increased yields, while late application at 4 and 6 weeks after planting gave lower yields. Similarly, split application of atrazine produced undesirable results. Hand-weeding at 2 weeks and at 2 and 6 weeks after planting produced results comparable to clean culture. Lowest yields were obtained from unweeded plots. Results indicated that chemical weed control was comparable to hand-weeding in increasing yields of sorghum.

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Author(s): Ofelia I. Dedal, M.K. Palomar and C.M. Napiere

Abstract

Xanthomonas manihotis Starr infected four species of euphorbiaceous plants, namely: Manihot glaziovii Muell.- Arg., Manihot esculenta Crantz (variegated ornamental cassava), Euphorbia puicherrima Willd., and Pedilanthus tithymaloides (L.) Poit. The diagnostic character of the disease on the alternate hosts was similar to that on cassava which served as the control.

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Author(s): Nelson M. Esguerra and Frank H. Haramoto

Abstract

Distribution pattern and population fluctuation of the carmine spider mite and its predators were studied in unsprayed Solo papaya trees grown at the Kauai Branch Experiment Station of the University of Hawaii, at Kapaa from 1978 to 1979. In the field, the carmine spider mites were found exclusively on the undersurfaces of bottom leaves. Initially, they started to infest papaya along borders of the fields. As soon as infestation increased, mites were distributed evenly on most trees. The number of mites decreased from the proximal to the distal portions of bottom leaves. For monitoring and surveillance work, therefore, mites should be counted first on edges of a field and on mature leaves. This procedure saves time, effort and money in surveying for mites especially when the population is low and is starting to build up. In the field, the staphylinid beetle, Oligota sp.; the predatory mite, Phyteseiulus rnacropilis (Banks); the coccinellid beetle, Stethorus siphonufus Kapur; and 2 species of spiders, Theridion spp., preyed on the carmine spider mites. Of these predators, spider, staphylinid beetle and predatory phytoseiid mite increased with slight population buildup of the carmine spider mites. Rainfall and predators prevented outbreaks of carmine spider mites and continuously allowed the population to fluctuate at low levels.

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