MSc

A field experiment was conducted in the wet lands of the College of Agriculture, Vellayani campus during the second crop season of 1988 to study the effect of top dressing paddy with phosphorus in the form of ammophos and superphosphate in addition to a basal application on the yield of grain and straw.
The experiment was carried out in a simple randomised block design with thirteen treatments. Factomphos and superphosphate were applied at different times viz., full basal, full top dress at AT, ½ basal + ½ at AT, ½ basal + ½ at AT + ¼ at PI. A control treatment without any phosphorus was also included. The Package recommendation of 90:45:45 kg ha-1 of N:P:K was given uniformly to all plots except in the control which received N and K only. The variety used was Jyothi. A destructive row for collection of plant samples was also maintained. Soil and plant samples were withdrawn from each plot at different stages viz. prior to and 15 days after top dressing at AT, 10 days after top dressing at PI and at harvest and analysed for available P in the soil and the phosphorus content of the plant. The growth, yield and yield characters were also studied.
Increased plant height and tiller count could be observed during the active tillering and maximum tillering stages when factomphos was applied half as basal and half top dressesd at AT. The two-split treatments of factomphos recorded highest tiller count at harvest.
Among the yield characters, increase in the productive tiller count alone was significant under the influence of split application of P either as superphosphate or factomphos.
The application of P in two splits of half basal and half top dress at AT resulted in increased grain yield which was significant over the control, three splits and the single top dressed treatments. The two-split treatments and the full basal treatment were similar in their influence. Between superphosphate and factomphos used for top dressing, no significant differences could be noticed. In general, the full top dressed P and the three – split treatments were similar and both were inferior.
With regard to straw yield, the phosphorus applied in two splits showed better performance when compared to the others. However, among the different treatments, there was no significant difference. Control was significantly inferior. Between superphosphate and factomphos used in the two – split treatments, the latter was found better. The full top dressed and the three – split treatments were similar and gave lower straw yield.
Studies on the phosphorus absorption by rice plant made during three sampling stages indicated that increased absorption of phosphorus was during the period between the first and second sampling stages, which nearly coincided with the active tillering and maximum tillering stages respectively of the crop, with peak absorption at the second stage and thereafter it decreased gradually. In this regard the two - split P treatments recorded higher values among which factomphos application resulted in the highest plant P content of the harvest stage which was significant.
The uptake of phosphorus studied in the various stages was also found to be higher in the two – split P treatments of factomphos. Maximum available phosphorus in the soil could be noticed in the treatments where P application was made in two – splits, which was however on par with full basal P treatments.
In general the nitrogen content of grain and straw were higher in the two – split P treatments with a maximum content in the factomphos top dressed treatment. However, no treatmental difference could be seen in the case of potassium content of grain or straw.
Correlation studies revealed that the available P in the soil and the phosphorus content of the plant estimated at various stages were positively and significantly correlated with yield.
The result indicated that peak phosphorus absorption by rice occurs at maximum tillering stage and that the phosphate application at or after PI is not likely to be helpful in bringing about the desired yield increase in rice.