Effect of NPK levels on yield and yield components of cabbage ( brassica oleracea L . Var . Capitata )

Effect of NPK levels on yield and yield components of cabbage was studied at Horticulture Ornamental Nursery, The University of Agriculture, Peshawar. The experiment was laid out in Randomized Complete Block (RCB) Design with three replications. A total of sixteen treatments were replicated thrice, row-row and plant-plant distance were kept 60cm and 45cm respectively. Nitrogen was applied at the rate of 0, 50, 60 and 70kg ha, while phosphorus and potassium was applied at the rate of 90 and 60kg ha respectively. The fertilizer level (70-90-60kg NPK ha) gave significant results with regard to curd weight plant (976g), curd diameter plant (13.67cm), yield plot (5.87kg), total yield ha (36.85 ton ha), while minimum values for these parameters were recorded in control. Significant values for the number of leaves plant (24) and leaves weight plant(751g) was recorded at fertilizer level (70-90-60kg NPK ha). However plant height and survival percentage remain unaffected with the application of fertilizer. Thus among various levels used, nitrogen at the rate of 70kg hawith phosphorus and potassium @90 and 60 kg hais recommended for cabbage growers in Peshawar.


Introduction
Cabbage (Brassica oleracea L. var.Capitata.) is a member of cruciferae family and a useful vegetable.It belongs to the genus Brassica.Cabbage is dicotyledonous crop with fibrous and branched roots.Cabbage has originated from the wild, leafy, non-heading types, which were found growing in Europe.Headed cabbage are usually consumed as cooked vegetable, or eaten fresh as an ingredient of mixed salads.It can be grown throughout the year in most parts of Africa [1].Cabbage is easily grown under wide range of conditions and is adaptable to most areas of Africa [2].Cabbage has less quantity of calories and protein, but has a large amount of potassium, sulpher, calcium, vitamin A, C, B1 and B2 [2, 3].The green outer leaves of cabbage are richer in vitamin A, calcium and iron than the white inner leaves.Cabbage starts its reproductive growth with the changes in temperature, it is a cool season crop and produces flowers in the areas of mild winter.Temperature above 24 o C is not suitable for cabbage production [4].It can be grown by direct seeding method as well as by transplantation.By direct seeding method, plant will have more balanced roots, stem and leaf.While in transplants root setting in a new environment will be a challenging task, but transplants are best for higher and early yield [5].Cabbage is a bulky crop and requires high amount of nitrogen and potassium.Optimally cabbage requires 60-85 kg N ha -1 , 60-80 kg P2O5 ha - 1 , and 30-90kg K2O ha

Materials and methods
An experiment entitled '' Effect of NPK levels on yield and yield components of cabbage '' was carried out at Horticulture Ornamental Nursery, University of Agriculture, Peshawar.Cabbage cv.Golden Acre's seeds were sown in the pots on 3 rd November 2011.Soil samples were taken randomly from experimental area and analyzed for different nutrients.Ridges were raised 15 cm from the soil surface to provide drainage for the removal of surplus irrigation or excess rain water.When seedlings attained a height of 10-15cm then these were transplanted in the field at 1 st December.Healthy seedlings of uniform size were selected for transplantation.Experimental design was Randomized Complete Block (RCB) Design.A total of sixteen treatments were replicated thrice.Four different levels of nitrogen (0, 50, 60, 70kg ha -1 ) with basal doses of phosphorus (90kg ha -1 ) and potassium (60kg ha -1 ) were applied in experimental plot.Different parameters such as, curd weight (g), curd diameter (cm), yield plot -1 (kg), total yield (tons ha -1 ) and number of leaves plant -1 .ANOVA and LSD techniques were used in order to see any difference among the various fertilizer levels.

Curd weight plant -1 (g)
The statistical data containing curd weight per plant is given in (Table 1), Statistical analysis indicates that different NPK levels had significant effect on curd weight per plant.According to the (Table 1) highest curd weight plant -1 (976.67g) was recorded at a fertilizer level 70-90-60kg NPK ha -1 followed by (866g) and (836g) curd weight plant -1 with fertilizer level 70-90-0kg NPK ha -1 and 60-90-60kg NPK ha -1 respectively.The minimum curd weight plant -1 (493g) was recorded in control treatment.Application of N, P and K increased the average curd weight plant -1 over the control treatment.The application of nitrogen with constant doses of P and K increased the carbohydrate and protein content of the curd, which possibly increased the curd weight.Fertilizer level 70-90-0kg NPK ha -1 gave better results it might be because of the fact that plant is getting appropriate amount of nitrogen and phosphorus.Yield at this application is near to highest yield but because of lack of potassium plant is unable to give the highest yield because once CO2 is converted in to sugar it have to be transported to the organs of plant for storage.The plant transportation system requires energy in the form of ATP which needs potassium for its synthesis.On the other hand fertilizer level 60-90-60kg NPK ha -1 , despite of all basic nutrients cannot give highest yield.It is because of the low dose of nitrogen.As curd of the cabbage is made of the leaves and nitrogen is responsible for vegetative growth.That's why the combination of 70 kg ha -1 N, 90 kg ha -1 P2O5 and 60kg ha -1 K2O showed best results.While the minimum head weight per plant may be due to the insufficient availability of NPK.These results are in agreement with [15-19], who have reported an increase in cabbage head weight with increased level of nitrogen.

Curd diameter (cm)
The statistical data pertaining to the curd diameter is presented in (Table 1).According to the statistical analysis different NPK levels had significant effect on curd diameter.Table 1 shows that mean highest curd diameter (13.67cm) was recorded with the fertilizer level 70-90-60kg ha -1 NPK followed by (13.33cm) and (13.00cm) curd diameter at 60-90-60kg ha -1 NPK and 70-90-0kg ha -1 NPK respectively.The minimum diameter plant -1 (8cm) was recorded in control treatment.Among various levels of NPK, the difference in curd diameter may be because of increased reserved substances in the leaves, resulting from increased supply of NPK.All of three basic elements work together to attain the best yield.Nitrogen is the building block of chlorophyll, enzymes and hormones.Phosphorus is a major component of ATP and ADP and once CO2 is converted in to sugar it has to be transported to organs of the plant for storage.The plant transportation system requires energy in the form of ATP which needs potassium for its synthesis.That's why the combination of 70 kg ha -1 N, 90 kg ha -1 P2O5 and 60kg ha -1 K2O showed best results.These results are in agreement with [20, 16, 12], who studied the effect of different doses of NPK on cabbage & found that curd diameter was more effected by increased NPK levels.

Yield per plot (kg)
The statistical data relating to the yield per plot is given in (Table 1).The statistical analysis shows that different NPK levels had significant effect on yield per plot.Highest yield plot -1 (5.87kg) was observed with the fertilizer level 70-90-60kg NPK ha -1 , followed by (5.33kg) and (4.97kg) yield plot -1 with 70-90-0kg NPK ha -1 and 60-90-60kg NPK ha -1 respectively.The minimum yield plot -1 (2.86kg) was recorded in control treatment.With the increased level of NPK, possibly curd accumulated more proteins & carbohydrates, so an increase in curd weight ultimately increased yield plot -1 .The plot which got the optimum amount of basic elements gave highest yield because all the processes for optimum growth were continued and plant grows normally.While the plot with fertilizer level 70-90-0kg NPK ha -1 gave better results it might be because of the fact that plant is getting appropriate amount of nitrogen and phosphorus.Yield at this application is near to highest yield but because of lack of potassium plant is unable to give the highest yield.Fertilizer level 60-90-60kg NPK ha -1 , despite of all basic nutrients cannot give highest yield.It might be because of the low dose of nitrogen.These results are in agreement with [21, 18, 16], who found that the application of nitrogen fertilizers increased uniformity among the plots which ultimately increased yield.Total Yield ha -1 (tons) Statistical analysis revealed that different NPK levels had significant effect on total yield ha -1 .According to the (Table 1) highest yield ha -1 (36.85 tons ha -1 ) was observed with the fertilizer level (70-90-60kg ha -1 NPK) followed by (30.86 tons ha - 1 ) and (30.83 tons ha -1 ) yield with 70-90-0kg ha -1 NPK and 60-90-60kg ha -1 NPK respectively.The lowest yield (18.34 tons ha -1 ) was noted in control plot.It is obvious that the application of N, P and K increased the yield ha -1 as compare to the control treatment.Increase or decrease in total yield ton ha -1 entirely depends upon yield per plot and the yield per plot was increased with the application of appropriate NPK level.The addition of nitrogen with phosphorus and potash significantly increased total yield per hectare.Highest yield was obtained from the plots with maximum rates of NPK [22].

Number of leaves plant -1
The data pertaining to the number of leaves per plant is given in (Table 1).According to the means highest number of leaves (24) were recorded with fertilizer level (70-90-0 kg NPK ha -1 ) followed by ( 23) and ( 22.67) number of leaves plant -1 with fertilizer level 70-90-60kg NPK ha -1 and 70-0-0kg NPK ha - 1 respectively.The least number of leaves plant -1 (15) were recorded in control treatment.As nitrogen is responsible for vegetative growth, and phosphorus for leaf expansion and increasing leaves number so there is a possibility of low nitrogen and phosphorus availability to those plants, which had low number of leaves.Results obtained from the fertilizer levels 70-0-0kg NPK ha -1 and70-90kg NPK ha -1 revealed that nitrogen alone and in combination also gave better results for number of leaves so the basic element for leaves formation is nitrogen.The combination of 70 kg ha -1 N, 90 kg ha -1 P2O5 and 0 kg ha -1 K2O showed best results.Similar results were obtained by curd weight (g), Curd diameter plant -1 (cm), Yield per plot (kg), Total Yield ha -1 (tons) and Number of leaves plant -1 as affected by different levels of NPK Treatments N For optimum growth of the cabbage, nutrients must be available in suitable quantity.Soil contains a lot of nutrients, but most of these are in unavailable form.Fertilizers are formulated to supply the nutrients already existing in the soil.The type of fertilizer and quantity depends on soil type, initial nutrient reserves in the soil and yield level.