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

This project was initiated to estimate the magnitude and variation in K-supplying capacity of a range of soils with varying soil properties in Bangladesh using a plant-based assay. Soil samples were collected from Dinajpur, Rangpur, Bagura, Rajshahi, Nawabganj, Sirajganj, Tangail, Faridpur, Jhinaidah, Sathkhira, and Comilla districts of Bangladesh, representing diverse mineralogy and properties related to soil K supplying capacity. Pot experiments with rice and maize were conducted in 18 different soils with two treatments (zero K and 100 mg K/ kg soil) in four replications. Other limiting nutrients were applied at a fixed rate in all treatments. The 5th to 7th crop cycles for both rice and maize were grown in 2013. The rice crop was grown up to the booting stage, while the maize crop was allowed to grow up to the V10 stage.

Maize growing in K-fertilized soil produced 64, 50 and 57% more dry matter than unfertilized soil pots in the 5th, 6th and 7th maize crop cycles, respectively. Similarly, K-fertilized soils produced 50, 37 and 31% more dry matter than unfertilized K pots in the, 5th, 6th and 7th rice crop cycles, respectively. On-farm trials for rabi maize were conducted during 2012-13 at 12 farmers’ field in Rangpur, Rajshahi and Comilla districts. Five levels of K (0, 40, 80, 120, and 160 kg K/ha) and two additional treatments based on K recommendations from Nutrient Expert® (NE) and Nutrient Manager (NM) tools were assessed. The benefits of N and P fertilizers were assessed using NE recommendations. The on-farm research trials with rabi maize showed that all K-fertilized plots produced higher yields than the unfertilized K plots across all sites and districts. The NM plot in Rangpur (11 t/ha), NE plot in Rajshahi (9 t/ha), and K160 plot in Comilla (7.4 t/ha) produced the highest grain yields among all treatments.

On-farm research trials with boro rice were also conducted during 2012-13 at 12 farm fields in Rangpur, Rajshahi and Comilla districts. Five application rates of K fertilizer (0, 30, 60, 90, or 120 kg K/ha) and two additional treatments using K recommendations obtained using the NM tool 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 yields compared to unfertilized K plots across all sites and districts. The recommendation of BRRI in Rangpur (5.7 t/ha), K120 in Rajshahi (4.6 t/ha) and K60 in Comilla (4.9 t/ha) produced highest grain yields among the different treatments used in the experiment.