*3.2.5 Soil P2O5 and K2O contents*

The soil P2O5 content indicates the capacity of a soil to supply P for crop growth and it is affected by P fertilizer application. It was increased during 1958–1983, because of inadequate N fertilizer rates during 1958–1980 (**Table 2**) and low yielding potato from 1973 to 1982 resulted in an accumulation of P fertilizer in the soil. Increased crop yield after 1982 due to increased N fertilizer rate and cultivating nematode resistance variety caused a decreasing trend of soil P2O5 during 1984–1996 compared to the highest soil P2O5 content recorded in1977 and 1982. Integrating FYM with P fertilizer increased soil P2O5 content to the 'very high' level. FYM only and FYM plus N or NK fertilizers increased soil P2O5 to the 'high' level compared to the initial soil P2O5 measured in 1958 (**Figure 15**).

Integrated nutrition and application of FYM only increased soil K2O during 1958–1980 compared to the initial soil K2O content (**Figure 16**), it was caused by low crop yield resulting in an accumulation of residual fertilizer K in the soil. The decreasing trend of soil K2O after 1980 was caused by a combined effect of increased K removal from the soil through high crop yields (**Figure 10**) and K loss by K leaching

*Effect of Balanced and Integrated Crop Nutrition on Sustainable Crop Production in a Classical… DOI: http://dx.doi.org/10.5772/intechopen.102682*

#### **Figure 15.** *Effect of integrated nutrition and FYM on soil P content in 0–30 cm depth.*

**Figure 16.**

*Effect of integrated nutrition and FYM on soil K content in 0–30 cm depth.*

on sandy soil. FYM combined with K fertilizer generally maintained soil K2O content, but FYM only and FYM plus N or NP fertilizers depleted soil K2O to the 'low' level after 1982 (**Figure 16**). The negative input–output balance caused a K-mining of the soil of 5 kg K per ha and year at FYM alone, and 41, and 30 kg K per ha per year, respectively at FYM plus N, and FYM plus NP fertilizers and decreased soil K2O content. FYM plus PK fertilizer resulted in the highest soil K2O content (**Figure 16**) due to low crop yield (**Figure 10**) and inefficient use of K fertilizer (**Figure 14**). Analysis of soil K2O in 30–90 cm in 1987, 2008, and 2018 showed residual K fertilizer movement below 30 cm depth. The soil K2O content increased by 37% in 30–60 cm and 22% in 60–90 cm depth at FYM plus PK fertilizer compared to the FYM plus NPK fertilizer (data not shown).
