Monitoring of the content of mobile forms of phosphorus and potassium in arable soils of the Belgorod region
We analyzed the dynamics of the content of mobile forms of phosphorus and potassium in arable soils of the Belgorod region and assessed the current state of soils by these indicators of fertility according to the results of a continuous agrochemical soil survey conducted by the agrochemical service of the Belgorod region in 1964-2018. In the soil cover of arable land in the Belgorod region typical chernozems (44.8% of all arable soils), leached chernozems (25.7%), and ordinary chernozems (13.0%) prevailed. According to the results of background monitoring, typical virgin chernozem (the Yamskaya steppe conservation area, Belgorod Region) contained 0.2% of total phosphorus and 1.64% of potassium in the upper part of the humus-accumulative horizon (10-20 cm); the content of mobile forms of phosphorus and potassium amounted to 28 mg/ kg and 101 mg/kg, respectively. That is, according to the rating scale used in the agrochemical service, the content of mobile forms of phosphorus was low; the content of mobile forms of potassium was increased. During the observation period, the weighted average content of mobile forms of phosphorus in arable soils increased by 91 mg/kg to 146 mg/kg; the weighted average content of mobile forms of potassium increased by 67 mg/kg to 172 mg/kg. According to the results of the tenth survey cycle (2015-2018), the proportion of soils with a very high content of mobile phosphorus (more than 200 mg/kg) increased to 17.6%; the proportion of soils with a very high content of mobile potassium (more than 180 mg/kg) increased to 33.8%. At the same time, the proportion of soils with very low (less than 20 mg/kg) and low (21-50 mg/kg) phosphorus provision decreased to 0.1% and 2.2%, respectively. Arable soils with a very low provision of mobile forms of potassium (less than 20 mg/kg) were not identified, whereas the proportion of arable soils with a low provision of mobile forms of potassium (21-40 mg/kg) was only 0.2%. In the tenth cycle of the survey, the removal of phosphorus and potassium with the crop was compensated by the entry of these elements with organic and mineral fertilizers. As a result, their content increased by 151.5% and 256.1%, respectively.