Manure and inorganic fertilization impacts on soil nutrients, aggregate stability, and organic carbon and nitrogen in different aggregate fractions

Manure application can enhance soil fertility and crop yield; however, knowledge of optimum application rates of manure is needed to prevent negative impacts on soils and environment. This study was aimed to compare the long-term effects of manure and inorganic fertilizer application at different rates on soil nutrients, aggregate stability, organic carbon, and nitrogen in different aggregate size fractions. The experiment was conducted on a long-term manure site under a randomized complete block design with six treatments: three manure [low manure (LM; application based on phosphorous requirement), medium manure (MM; application based on nitrogen requirement), high manure (HM; two times prescribed nitrogen rate)], two chemical fertilizer [medium fertilizer (MF; suggested inorganic fertilizer rate), high rate of fertilizer (HF)], and control (CK; no manure nor fertilizer). Manure application maintained soil pH, improved nutrient availability and aggregate stability compared to the CK. The HM treatment increased aggregate-associated soil organic carbon (SOC) and total nitrogen (TN) concentration by 40 to 50% in all size fractions as compared to the CK. Further, HM increased particulate organic matter (POM) by 1.2 times as compared to the CK, while inorganic fertilizer application did not alter these parameters compared to the CK.