MSc

A field trial to study the relationship of sugarcane yield and nutrient status through foliar diagnosis was carried out at Sugarcane Research Station, Tiruvalla during 1992, with the hybrid variety COTI 88322 (Madhuri). The experiment was laid out in a 33 factorial randomised block design consisting of three levels each of nitrogen (0, 165.0 and 330.0 kg N/ha), phosphorus (0, 82.5 and 165.0 kg P2o5/ha) and potassium (0, 82.5 and 165.0 kg K2o/ha).
In order to standardise the leaf position, the leaf that just began to unroll (spindle like) was taken as the first leaf and the second, third, fourth, fifth and sixth leaves were counted from first leaf below. At the end of germination phase only third, fourth and fifth leaves were collected as no sixth leaf was found at this stage and from the second stage onwards the sixth leaf was included in the study. For standardising the best season suited for the collection of leaf and to predict yield, samples were collected at six different stages of plant growth. The stages of sampling were : (1) germination phase (2) Tillering phase (3) At the beginning of grand growth phase (4) After grand growth phase but before flower formation (5) After flower formation but before maturity phase and (6) At the time of harvest. Attempts were made to find out the direct and indirect contributions of N, P and K in different leaves with and without sheath on yield and to predict yield based on the step-wise regression analysis. Attempt was also made to fine out the influence of leaf nutrient content at different leaf position collected at various stage of sampling on the nutrient uptake of sugarcane. Studies were also made to find out the influence of different levels of N, P and K on cane juice quality and nutrient uptake of sugarcane at harvest stage.
Observations revealed that the N content in the leaf with sheath varied from 0.35 to 1.41 per cent, while it was from 0.53 to 1.58 per cent for leaf without sheath. The N content of leaf with sheath showed a gradual decline with age of crop while the N content in the leaf without sheath increased from first to third stage and there after decreased. The differences in the levels of N applied reflected in N content of leaves at the second and third stage of sampling. The P content in the leaf with sheath varied from 0.056 to 0.166 per cent and the leaf without sheath varied from 0.088 to 0.161 per cent. Phosphorus distribution at different leaves in all the stages were rather inconsistent in both the cases. The response to the different levels of P applied was more pronounced in the second stage of sampling. Potassium per cent in leaf with sheath varies from 0.33 to 1.16 per cent while it was from 0.39 to 1.04 per cent for leaves without sheath. The content of potassium in the leaves without sheath was low in all the stages compared to leaves with sheath. The decrease in K content with age was not conspicuous. The effect of different levels of K was clearly reflected in the fourth stage of sampling.
Results also showed that the extent of role played by the NPK content of leaves with sheath on yield at the first, third and fifth stages of sampling was low while the NPK content of leaves without sheath at the first and fifth stage of sampling had a little influence on final yield of sugarcane. The nitrogen content in the fourth leaf with sheath and third and fourth leaves without sheath collected at the second stage of sampling established a significant influence on the yield of sugarcane. The P and K contents of the fifth leaf with sheath collected at the second stage of sampling established a significant effect on yield of sugarcane.
Observations revealed that among the stages of sampling, the second stage is recommended for N, P and K, Regarding the leaf positions, the third, fourth and fifth leaves without sheath is ideal for diagnostic purpose in relation to N, while the above leaves with sheath is ideal for diagnostic purpose in relation to K. For P, the fifth leaf with sheath is found to be the best.
Stepwise regression model fitted with yield and percentage of nutrients in different leaf positions at various stages of sampling gave a maximum prediction of 73 per cent (R2 = 0.7297) when the nutrient content of the third, fourth and fifth leaves collected at the second stage of sampling was considered.
The nitrogen content at the third and sixth leaves without sheath collected at the second and fifth stages of sampling had a significant correlation with the nutrient uptake of sugarcane at harvest stage. The different treatments of NPK failed to play a significant influence on the brix, pol and CCS per cent of cane juice.