S. Kamaraj and Palaniappan Muthuvel. Tamil Nadu Agricultural Univ, Coimbatore, India
Increased production through intensive cultivation with high inputs especially with inorganic fertilizers is aimed at in several countries to meet the needs of growing population. High input farming without conserving the natural resources, mainly soil fertility, has led to mining of soil nutrients resulting in declined fertilizer productivity. In India use of N fertilizers matches the removal by crops. Phosphatic fertilizer use also shows a positive balance while the K balance, in general, is negative. Hence field experiments were conducted at two locations with Cassava in the North Western Zone soils (Typic Rhodustalfs) of Tamil Nadu, India with a twin objective of optimizing nutrient requirement and developing a balanced fertilizer schedule. Cassava is a major crop in this zone. The soils of the experimental site were sandy clay loam and sandy loam. Besides, the response for major secondary and micronutrients was also studied. The experiment had 16 treatment combinations viz., three levels of N viz., 60, 90 and 120 kg N t ha-1 representing 100, 150 and 200 per cent of state recommendation with 50, 100, 150 and 200 per cent of recommended levels of P and K that is 30, 60, 90 and 120 kg P2O5 and 80, 160, 240 and 320 kg ha-1 K2O respectively with recommended levels of Ca, S, Zn and B applied at rates of 46.6, 40, 5.7 and 1.4 kg ha-1 respectively. Besides these treatment combinations there were also treatments involving major nutrients without Ca, without S, without Zn and without B inorder to study the response of secondary and micronutrients. Randomized block design was followed with three replications. The experiment was conducted in two locations during 2001 and 2002. Soil nutrient status monitored at different growth stages indicated that each successive level of NPK fertilization enhanced availability of NPK in soil. Positive response was there for individual application of Ca or S or Zn along with 150 per cent of the recommended level of NPK on N availability. Uptake of N and K by Cassava was enhanced by each successive level of applied N and K. Increases in P uptake due to increments of added P could be observed upto 150 per cent of the recommended level of P. In one location the yield increase was upto 150 per cent of state recommended NPK level while in the other location the response was upto 200 per cent of recommended P and K with 150 per cent of recommended N. While B addition had no response in tuber yield Ca, S or Zn had positive effect. Protein and starch contents of tuber were increased by fertilizer treatments. From the analysis of NPK optimization it was concluded that the present level of 60:60:160 kg NPK needs to be upwardly revised to 90:90:240 kg NPK besides the addition of recommended Ca, S and Zn.