ABSTRACT

An experiment was conducted at the Agronomy Filed Laboratory, Bangladesh Agricultural University, Mymensingh from 5 January to 20 April, 2008 to investigate the effect of rate and timing of nitrogen application on the yield of soybean var. shohag. There were five levels of nitrogen viz. 0, 25, 40, 55 and 70 kg N ha-1 and three application timing viz. basal, 2/3 at basal + 1/3 at 25 DAS and 1/3 at basal + 1/3 at 25 DAS +1/3 at 35 DAS. The experiment was laid out in a randomized complete block design with three replications having unit plot size of 4 m×2.5m. Both the rate and timing of nitrogen application had significant influence on all the characters except stover yield plant-1. The performance of 25 kg N ha-1 and two timing of nitrogen application at 2/3 basal + 1/3 25 DAS was found to be the best. Interaction effect of rate and timing of N application significantly influenced all the characters except, number of filled pods plant-1, stover yield plant-1 and stover yield. The highest seed yield (2.08 t ha-1) and stover yield (2.82 t ha-1) were produced in plots applied with 25 kg N ha-1 in two splits as 2/3 basal + 1/3 25 DAS. However, the application of 25 kg N ha-1 at 2/3 basal + 1/3 25 DAS could give high yield of soybean var. Shohag.

Key words: Rate, timing, nitrogen application, yield, soybean.

Introduction
Soybean (Glycine max [L.] Merril) is one of the leading oil seed and grain legume crops of the world belonging to the family leguminosae, sub-family papilionaceae. It grows well in different regions of the world, particularly in the tropics to the mid temperate zones. According to FAO (2003) the area, production and average yield under soybean of the world in 2003 are 83,695 thousand hectares, 189234 thousand tons and 2.26 tons ha-1, respectively. In Bangladesh the area under soybean is about 5 thousand hectare with a production of 4 thousand tons and the yield ranges from 1.50 to 2.30 tons ha-1 (BARI, 2005). It is a new and prospective crop in Bangladesh. Soybean may be called the “Golden bean” or “Miracle bean” or the “Nugget of nutrition” or the “Protein hope of future” because of its high nutritive value containing about 42-45% protein, 18-20% edible oil and 42-46% carbohydarde (Gowda and Kaul, 1982). It also contains essential amino acids. It is a source of Calcium, Phosphorus and Iron including vitamin A, B, C, D and can meet up different nutritional needs of human beings (Rahman, 1982). On an average about 8-10% of the protein intake in Bangladesh diet originates from animal sources (Begum, 1989) and the rest can be met from plant sources by increasing the consumption of vegetables and pulses including soybean. Now a days, a variety of saya product such as “soya dal”, “soya chatni”, soya-khichuri”, “ soya-milk”, “soyacurd”, soya-flour” and roasted soybean snacks becoming familiar to the people of Bangladesh (Smith, 1975). The lower yield of soybean at farmer’s level is mainly attributed to the lack of improved agronomic management practices of which judicious fertilizer application is an important determinant for better performance of soybean. Among the nutrients, nitrogen is a major essential plant nutrient element and has favorable effect on yield and yield contributing character of soybean (Lahoria et al. 2004). It has the quickest and most pronounced effect on plant growth and yield of crops. It tends primarily to encourage above ground vegetative growth and to impart deep green colour to the leaves. Improper use of nitrogen fertilizer instead of giving increased yield may even reduce the same. Plants receiving insufficient nitrogen are stunted in growth with restricted root system; the leaves turn yellow or yellowish green and tend to drop off. Proper timing of nitrogen application reduces the loss of nitrogen in the soybean field and gives higher 68