Long-term effect of continuous manurial practices on grain yield and some soil chemical properties in rice-based cropping system

Rice-rice-pulses (Rice fallow) is the major cropping system in Cauvery Delta of Tamil Nadu. A long-term fertility experiment was initiated in 1992 to study the effect of organics, agro-chemicals and biofertilizers on productivity of a rice-rice system in relation to changes in fertility status of soil. Results of ten years experimentation revealed that the treatment receiving continuous application of NPK at 125: 50: 50 kg ha⁻¹ in kharif (kuruvai) and 150: 60: 60 kg ha⁻¹ in rabi (thaladi) season along with green manure at 6.25 t ha⁻¹ in kharif and 12.5 t ha⁻¹ of FYM in rabi and gypsum at 500 kg ha⁻¹ both in kharif and rabi seasons, respectively recorded significantly higher grain yield in both the seasons consecutively for ten years (1992–2001). At the end of the 20^th rice crop (tenth year), the soil chemical properties like pH, EC, organic C, available N, P and K exhibited significant differences due to various treatments imposed. The values of nutrient uptake by rice crop also showed significant differences among various treatments. The results suggest the need for conjoint use of organic and inorganic nutrient sources for sustaining rice productivity in the heavy soils of Cauvery Delta zone.