Effect of various depth methods of fertilizer application on the balance of mobile phosphorus and exchangeable kalium in the cultivation of lupinus angustifolium on the soils of the upper Volga region

The dynamics of mobile phosphorus and exchangeable potassium in the arable layer of a developed sod-podzolic light loamy soil with a leaching type of water regime was studied, depending on the fertilizer systems and methods of their incorporation in narrow-leaved lupine crops in the conditions of the North-Western region of the Non-Chernozem zone. It was found that, on average, over two rotations of a 5-field fruit-and-grain crop rotation, a negative balance of mobile phosphorus was observed in the control variant (-4.56 kg/ha for both methods of incorporation), as well as with the application of calculated doses of NPK for a planned yield of lupine seeds of 1.8 t/ha (-0.89 kg/ha for the background of minimum tillage and -2.85 kg/ha for the background of ploughing). A positive balance of P2O5 was established both with the utilization of liquid wastewater from a pig complex (+12.01 kg/ha for the background of minimum tillage and +10.85 kg/ha for the background of ploughing), and with the application of solid manure (+33.70 and +32.10 kg/ha, respectively). A deficit of exchangeable potassium was detected only in the control variant (-7.59 and -7.65 kg/ha for the methods of tillage), while other fertilizer systems ensured expanded reproduction of K2O for all methods of incorporation. A positive trend was observed in the formation of mobile phosphorus and exchangeable potassium reserves in favor of minimum tillage, which is explained by the increased degree of their fixation in soils with a light loamy granulometric composition compared to ploughing. To ensure expanded reproduction of P2O5 and K2O in developed low-productive sod-podzolic soils, it is recommended to apply 30-35 m3/ha of liquid wastewater or 10-12 t/ha of solid manure annually and incorporate them into the soil using disc implements at a depth of 7–10 cm.