Response of soybean varieties to maturity and biomass production under various planting dates

Planting date plays a significant role in soybean maturity and biomass yield. To study the maturity and biomass production potential under different environmental conditions, three indigenous land races (Kulat brown, Kulat white, Mothi) and two improved varieties (NARC-II, Swat-84) of soybean were planted at monthly from April to July during 2004 and 2005 growing season, at New Developmental Farm, The University of Agricultural Peshawar, Pakistan. Data was recorded for full maturity, plant height and biomass production. April planted crop took maximum days (187) to maturity, which decreased gradually with delay in planting. May planted crop gave maximum plant height (91.4 cm) and biomass yield (12598 kg ha) which decreased in later planting. Kulat white took maximum days (170) to maturity and attained maximum plant height (107 cm). However maximum biomass 12606 kg ha yield was given by Mothi. Landraces took 41 days more than improved varieties to mature. In land races the plant height was almost double and the biomass yield was 31 percent higher than the improved varieties. Land races could prove higher yielders if the extra biomass production is directed towards seed filling.


Introduction
In soybean [Glycine max (L.) Merrill] grain yield is the product of dry matter accumulation and partitioning.Greater total dry matter results in greater seed yield Seeds were sowed at four planting dates.Planting dates were allotted to main while varieties were allotted to sub plots.Each treatment was replicated four times in randomized complete block design with split plot arrangement.Twenty seedlings per meter row were maintained with 5cm space between the plants and 50 cm apart rows.As the field was already under soybean last year, therefore a starter dose of 25 kg N and 64 kg P2O5 ha -1 as DAP was applied at the time of sowing.

Data collection
In each subplot two central rows were harvested to determine biomass yield.The harvested material was dried in oven at 70 0 C for 24 hours till constant weight.The dry biomass yield thus obtained was converted into Kg ha -1 .The stage when most of the leaves turned yellow, desiccated, and 95 percent of the pods lost green colour and attained mature pod colour, as full maturity (R8).Plant height data was recorded by measuring height of ten randomly selected plants in each subplot from the base to the top of the main stem at maturity.

Statistical analysis
The data was subject to analysis of variance technique appropriate for randomized complete block design with split plot treatment arrangement.When the F value was significant, means were compared using LSD test at 0.05 level of probability   Statistically, the biological yield produced by May and June planting was greater and similar, which could be attributed to higher plant height, leaf area and crop growth rate (CGR).The lowest biological yield from July planting may be due to low plant height, leaf area and particularly low crop growth rate.Biological yield from April planting inspite of similar plant height, and greater leaf area was relatively less than May and June planting.
The only reason could be the lower crop growth rate due to low temperatures in the month of April (Fig. 1).The higher biomass production of land races was because of greater plant height, leaf area, CGR and RGR as compared with improved varieties.

Conclusion
It is concluded that delaying planting dates from April to July decreased days to maturity, plant height and biological yield.Land races took maximum days to maturity, biological yield, and plant height as compared to improved varieties.During second year of soybean cultivation crop mature earlier but short plants and minimum biological yield as compared to first year of cultivation.
[1].Overproduction of vegetative dry matter does not always reduce seed yields, but improve partitioning of dry weight could result in higher seed yields [2, 3].Planting date, the most critically important environmental factor influencing soybean development and production [4].Several workers have reported substantial reduction in days to maturity with delayed planting [5, 6].Similar reduction in plant height with late planting [7-9].Long duration soybeans were high biomass producers than short duration soybeans [6].When planting was delayed from optimum time, substantial reduction in biomass yield was observed [10, 11].Based on the hypothesis of the above workers, it was considered essential to explore and compare.The biomass production potential of land races and improved verities of soybean under different planting dates.Materials and method Plant materials and experimental design Research was conducted on maturity, plant height and biomass production of three land races (Kulat brown, Kulat White, Mothi) and two improved varieties (NARC-II, Swat-84) of soybean at New Developmental Farm, The University Agricultural Peshawar, Pakistan, during 2004 and 2005.

Planting dates Biological yield (kg ha -1 ) Kulat brown Kulat white Mothi NARC-II Swat-84 Kulat brown Kulat white Mothi NARC-II Swat-84 Figure 3. Biological yield (kg ha -1 ) of soybean varieties as affected by planting dates
Means of the same category followed by the different letters are significantly different from one another using LSD test (P≤0.05)

Table 1 . Two years means for days to maturity (R8), plant height (cm) and biological yield (kg ha -1 ) of soybean land races vs improved varieties as affected by planting dates ble 2. Table 2. Two years means for days to maturity (R8), plant height (cm) and biological yield (kg ha -1 ) of soybean land races vs improved varieties as affected by planting dates
D.F. Full maturity Plant height (cm) Biological yield (kg ha -1 )