Effects of annual and biennial applications of phosphorus and potassium fertilizer and farmyard manure on yields of potato tubers, on nutrient uptake and on soil properties

Abstract

SummaryA long-term manurial experiment on potatoes was initiated in 1970 on the acidic brown hill soil of Simla to study the effects of fertilizers supplying per hectare: 44 kg P (P44); 44 kg P and 125 K (P44K125) and 88 kg P with 125 kg (P88K125) and of farmyard manure (FYM) supplying 44 kg P/ha applied annually and biennially. The potatoes gave large responses to all the manures. The annual or biennial effects of FYM measured in years of application were as great as that of P and K fertilizer in increasing tuber yield and K uptake by tubers but FYM increased P uptake more than fertilizers did. FYM applied each year gave largest uptake of P. P88 treatment was not better than P44 treatment. The residual effects of the manures on yield were measured in years when the treatments were not applied; the residual effects of FYM were higher than those of fertilizers. Mean residual effects of the treatments on P uptake were 46% and 51% of their annual or biennial effects respectively. About 90% of P added to the soil was not taken up by the crops and was present in the forms of aluminium-bound P, iron-bound P and calcium-bound P in this descending order. The residual effects of the treatments on K uptake were about 84% of their annual or biennial effects. About 60% of K applied to the soil was not taken up by the crops and most was present in exchangeable form. Annual applications of all the manures were better than their biennial applications indicating that residual effects built up from three applications over 6 years were too small to sustain yields.Soil analyses made 6 years after the start of the experiment showed that FYM was a better source of P than single superphosphate in increasing soil available P. FYM also increased soil exchangeable K more than the K fertilizer did. The highest increase in available P and K in soil was from annual applications of manures. Biennial applications of P as superphosphate or FYM resulted in P accumulating in the soil, while biennial K fertilizer dressings did not increase exchangeable K; however, biennial FYM did increase exchangeable K. Using P alone reduced soil available K. FYM increased pH, organic carbon and total N in soils while P and K fertilizer increased only the pH.