A field experiment was conducted to determine the effects of nitrogen (N) fertilizer and planting density on growth and yield of long grain rice. Four levels of N fertilizer (0, 40, 80 and 160kg N ha^-1) application at three levels each of planting density (20, 40 and 80 hills m^-2) were treated. Dry matter (DM) per hill increased almost linearly with the increase in N fertilizer; but its effect was more conspicuous before the heading stage than after. The increase in planting density generally made plant size to small. Tillers per plant increased linearly with the increase in N fertilizer levels. Grain yield and most of the yield attributes varied significantly. The highest grain yield obtained was 160kg N ha^-1, which was similar to the yield obtained at 80kg N ha^-1.

We examined development and host-stage selection by Cotesia plutellae, a larval parasitoid of the diamondback moth, Plutella xylostella. There were three larval instars in C. plutellae. Like in other solitary endoparasitoids, first instar larva had sclerotized madibles, which may function to destroy other larvae of conspecific or heterospecifics in the same host. Third instar larva tore out the side of host larvae and emerged. Then, they span the cocoons within 2-4 hours after larval emergence. Females usually laid a single egg in each host, though they superparasitized hosts of the second and third instars more often than the hosts of the first and fourth instars. Although females parasitized all four larval instars of P. xylostella, they preferred to oviposit in the hosts of the second and third instars than rather the hosts of the first and fourth instars. When 50 hosts of either the first, second, third or fourth instar were exposed to two females, the hosts of the second and third instars yielded more parasitoid cocoons than the hosts of the first and fourth instars. Developmental time from oviposition to adult emergence decreased with the increasing host instar at oviposition. Based on the results on acceptance, preference and suitability, the second and third instar larvae of P. xylotealla were suitable for parasitism by Cotesia plutellae.

The study was carried out to determine the duration and grain-filling rate in rice varieties of Kajalsail and Nonabokra under different levels of salinity using BRRI farm soil under greenhouse conditions. Salinity adjusted in soil at the heading stage was 8 ds/m, 16 ds/m and 24 ds/m, respectively. Similarly, tap water was comprised in EC-1.5 ds/m as the control. The duration of the grain-filling period showed variations between two varieties irrespective of salinity levels, and was 15 days after in Kajalsail and 20 days after in Nonabokra. The variety of Kajalsail was more sensitive to salinity levels compared to Nonabokra in respect to the grain-filling rate. Although the relative water content (RWC) of the flag leaf was similar under tow levels of salinity in both varieties, a significant level of RWC was observed in the Nonabokra variety.

An evaluation of effects of succinic acid-2-2-dimethylhdrazide (SADH) (0.0gl^-1, 0.5gl^-1 and 1.0gl^-1) for three cassava cultivars, TMS 30572, TMS 30555 (IITA improved cultivars) and Durungwo, a local Okigwe cultivar, was carried out at a pot trial at Abia State University, Uturu, using a complete randomized block design. Treatment of three cultivars with SADH was applied at 14 weeks after planting foliarly. Parameters were plant height, total dry matter production and fresh root tuber yield, respectively. The data obtained by the variance analysis showed that cassava cultivars contrasted sharply in the responses to SADH treatment after 22 weeks growing cassava. Fresh root tuber yield increased significantly in TMS 30572 due to application of SADH at the rate of 0.5gl^-1, whereas the response of TMS 30555 and Durungwo was not remarkable. In this experiment, plant height of TMS 30555 (119.3cm) showed significant differences between TMS 30572 (76.2cm) and Durungwo (98.8cm) with SADH treatment. The highest rate of SADH treatment, i. e., 1.0gl^-1 depressed the plant height, total dry matter production and fresh root tuber yield in TMS 30572 and Durungwo. Therefore, it would appear that the response of the cultivars to SADH treatment depended on the rate of SADH concentration and cassava cultivars. On the basis of results in this trial, we suggested that field investigation will be undertaken to explore the usefulness of growth regulators (such as SADH as part of the agronomic optima) to achieve the increase of cassava root tuber yields for considering current high global demand for cassava as human food, animal feed and industrial raw material.

A study was conducted at the Bangabandhu Sheikh Mujibur Rahman Agricultural University Experimental Field in July-December 1997 to investigate the effects of green manuring with Sesbania aculeata and Sesbania rostrata on rice productivity and soil environment. Green biomass of Sesbania spp. of 15t ha^-1 was applied to the soil along with inorganic N 0, 20, 40, 60, and 80kg ha^-1, respectively, two weeks before the transplant of a modern rice cultivar of BR11. The highest rice yield of 4.87t ha^-1 was obtained when green biomass was supplemented with inorganic N 80kg ha^-1, which had an increase of 102% and 12% compared to the control plot and the plot where N 80kg ha^-1 alone was supplemented, respectively. No significant yield difference was observed between the plots except the control and where S. aculeata alone was supplemented. However, the highest N-use efficiency was observed in treatments where N 20kg ha^-1 was supplemented with S. rostrata green biomass. Results on soil environmental parameters indicated that green manuring had a beneficial impact on pH, organic-C, NH₄⁺-N, and CO₂-C of soil. Results revealed that CO₂-C were comparatively low in plots where inorganic N was supplemented with or without green biomass at later crop growth stages, which might be due to a probable detrimental effect of inorganic N on the microbial population. From the study, it is concluded that green manuring with S. rostrata of 15t ha^-1 along with inorganic N 20kg ha^-1 might be sufficient for maintaining both satisfactory rice yield and favorable soil environment in acid rice soil under humid sub-tropical conditions.

New isolates of Rhizoctonia oryzae were obtained from contaminated paddy soils in northern Vietnam. These isolates showed different culture types compared to standard isolates from diseased rice sheath. Fatty acid composition of two culture types of Rhizoctonia oryzae, i. e., new and standard isolates from diseased rice sheath and contaminated paddy soils, was analyzed by gas-liquid chromatography. The major fatty acids identified were palmitic, palmitoleic, oleic and linoleic acids, which constituted 96-97% of all cellular fatty acids identified and each fatty acid composition showed differences in quantity. Principal component analysis and cluster analysis revealed that these two isolates were able to divide into different types based on fatty acids composition. ‘The results suggest that our new isolates could indicate one of the mutations of R. oryzae isolates.

Recently, crops have been converting from rice monoculture to combination cash crops and rice in the Red River Delta, necessitating rational estimation of agricultural water demand. Here, annual and monthly water demands for agriculture and for domestic and industrial use in the RRD were estimated by using the Cropwat Model, As a result, these annual demands, for instance in 1999, were 6,761 and 761 Mm³/year, respectively. Though the highest monthly water demand for agriculture occurs in January, water supply potential then still meets this demand. If the crop conversion were further developed, the water demand in agriculture would be reduced. On the other hand, industrial effluents from obsolete wastewater treatment facilities in urban areas, and overusing chemical fertilizers and pesticides in rural areas have been degrading water quality, leading to less opportunity to access clean water in agriculture, thus, some water environment protection management is becoming necessary.

The indiscriminate forest clearings and land conversion to agricultural purposes has caused the country’s once rich natural resources to be at their most endangered state. The overzealous extraction brought by poor logging, unchecked illegal logging and cultivation for agriculture purposes at unstoppable rates have caused the rapid denudation of the forest. At present, less than 20 percent of the total land area is covered by vegetation. This scenario has challenged the national government to find and implement appropriate actions toward restoring degraded areas. The Philippines has implemented various rehabilitation programs with the task of employing conservation measures to cater with immediate needs of land transformation through developing more appropriate land-use systems to sustain growing population, and at the same time improve degraded areas and alleviate deforestation.