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In a significant move to optimize fertilizer usage in the state’s rice-wheat agricultural system, the Punjab Agricultural University (PAU) has emphasized the judicious use of Diammonium Phosphate (DAP) fertilizer. The institution’s soil test-based recommendations are expected to revolutionize farming practices by promoting efficient use of this costly input.

Dr. Satbir Singh Gosal, Vice-Chancellor of PAU, underlined DAP’s role as the costliest fertilizer input in the rice-wheat system, emphasizing the potential for cost savings through soil test-based recommendations. Recent studies by PAU have brought to light a significant phosphorus accumulation in Punjab’s soils due to the continuous overuse of DAP and other phosphatic fertilizers.

Dr. Gosal divulged that excessive DAP usage has resulted in 31% of soils being classified as ‘very high’ and 30% as ‘high’ in crop-available phosphorus, with only 19% falling into the ‘medium category,’ necessitating the recommended dose of this fertilizer. Higher phosphorus categories yield substantial discounts in P fertilizer use for all crops. Additionally, the retention or incorporation of paddy straw contributes to increased soil organic carbon, enhancing phosphorus availability.

Dr. Ajmer Singh Dhatt, Director of Research, emphasized the significance of adhering to soil test results for phosphorus application. For medium phosphorus soils, PAU recommends 55 kg of DAP per acre in wheat (or 65 kg when residue is retained or incorporated), as well as in potato crops, with a 25% dose increase only when the soil tests low in P.

Dr. Dhatt outlined clear and practical guidelines for DAP application in wheat, such as a 25% reduction for soils with high phosphorus levels (9-20 kg/acre) in low organic carbon soils (less than 0.4%) or medium phosphorus (5-9 kg/acre) in soils with moderate organic carbon content (0.4 to 0.6%). He also recommended a 50% reduction in DAP use for soils with high phosphorus (9-20 kg/acre) and medium organic carbon (0.4 to 0.6%) or medium phosphorus in soils with high organic carbon (over 0.6%).

Moreover, Dr. Dhanwinder Singh, Head, Department of Soil Science at PAU, revealed that under certain conditions, wheat requires no DAP application, such as in high phosphorus soils (9-20 kg/acre) with high organic carbon (over 0.6%) or soils with very high phosphorus levels (over 20 kg/acre), regardless of organic carbon content. Integrated nutrient management practices allow a 50% reduction in DAP use for wheat, provided alternative sources like poultry manure or dried gobar gas slurry are applied at 2.5 tonnes/acre in the previous rice crop or by using 4 tonnes/acre of rice husk ash or bagasse ash in wheat. Also in fields, where organic carbon content of soil comes under high category after continuous retention/incorporation of paddy straw, the dose of DAP can be reduced by 50%. In addition, no DAP is necessary in wheat if farmyard manure is applied at a rate of 10 tonnes per acre to the previous potato crop, Dr. Singh explained.

Dr. Singh also cautioned against the excessive use of phosphatic fertilizers, which can lead to zinc deficiency in field crops. In cases where DAP is unavailable, he suggested alternatives like single superphosphate (16% phosphorus) or nitro-phosphate (20% phosphorus) to address the phosphorus requirements of the crops.

The comprehensive recommendations from PAU aim to foster sustainable farming practices, reduce costs, and ensure resource efficiency in Punjab’s agriculture, benefiting both farmers and the environment.

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