Assessment of Soil Potassium Supplying Capacity from Soil Nutrient Reserves and Dissemination of Nutrient Management Technologies through Nutrient Manager

The project was initiated to estimate the variability in K-supplying capacity of soils in Dinajpur, Rangpur, Bagura, Rajshahi, Nawabganj, Sirajganj, Tangail, Faridpur, Jhinaidah, Sathkhira, and Comilla Districts of Bangladesh. Pot experiments were conducted for rice and maize using soils collected from 18 locations. Two treatments included 1) zero K and 2) 100 mg K/kg soil. Other limiting nutrients were applied at fixed rates to both the treatments. The rice crop was grown up to the booting stage, while the maize crop was allowed to grow up to the V10 stage in the pot experiments.

Maize growing in fertilized pots produced 50 to 64% additional dry matter than unfertilized pots, while the K-fertilized pots produced 31 to 50% more dry matter in rice than unfertilized K pots. On-farm trials for winter maize were conducted in Rangpur, Rajshahi and Comilla Districts with application rates of K (0, 40, 80, 120, and 160 kg K₂O/ha). Two additional treatments based on K recommendations from the Nutrient Expert^(R) (NE) and Nutrient Manager^(R) (NM) tools were also assessed. The farmers' field trials in winter maize showed that all K fertilized plots produced higher yields than the unfertilized K plots across all sites and districts. The highest maize grain yields of 11, 9 and 7.4 t/ha were obtained in the NM treatment in Rangpur, NE treatment in Rajshahi, and K160 treatment in Comilla.

On-farm trials with summer rice were also conducted in these districts. Five application rates of K fertilizer (0, 30, 60, 90, or 120 kg K₂O/ha), and two additional treatments using K recommendations from NM and Bangladesh Rice Research Institute (BRRI) recommendation were assessed. The N and P fertilizers were applied following the NM recommendation. It was observed that all K fertilized plots consistently resulted in greater rice yields compared to unfertilized K plots across all sites and districts. The highest grain yields of rice in Rangpur (5.7 t/ha), Rajshahi (4.6 t/ha), and Comilla (4.9 t/ha) were achieved in the BRRI recommended treatment, K120 treatment and K60 treatments, respectively.