*3.1.3 Sustainable yield index (SYI) and green water use efficiency (WUE)*

SYI indicates the stability of crop yields in the long run. The high index shows the low variation of yield increase over years. Application of mineral fertilizers N + P + K + Mg increased SYI and WUE of crop. Omitting nutrient and application

**Figure 4.** *Effect of balanced nutrition, omitting nutrient, and FYM on the trend of average yield.*

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

of only FYM decreased SYI and WUE compared to the balanced nutrition. The WUE was reduced by 63%, 34%, and 7–59%, respectively at without any fertilizer, application of only FYM, and omitting nutrients compared to the N + P + K + Mg treatment (**Figure 6**). The reduction of WUE is directly related to the decline in crop yield because of nutrient omission and application of only FYM.

#### *3.1.4 Nutrient use efficiency*

Nitrogen use efficiency (NUE) at the balanced nutrition (N + P + K + Mg) treatment was 77%. Any lack of nutrients reduced the NUE to 49% - 73% (**Figure 7**). P use efficiency (PUE) at the balanced nutrition was 49%. Omitting Mg, K + Mg, and N + Mg resulted, respectively 46%, 42%, and 25% PUE compared to the N + P + K + Mg treatment (**Figure 7**). The balanced nutrition resulted in the highest K use efficiency (KUE) of 84% compared to omitting nutrients and application of only FYM. The KUE at omitting Mg, P + Mg, and N + Mg fertilizers and only FYM

**Figure 6.**

*Effect of balanced nutrition, omitting nutrient, and FYM on average WUE and SYI of the crop (n = 62 years).*

application were, respectively 78%, 77%, 37%, and 75% (**Figure 7**). The highest nutrient use efficiencies were achieved in the treatment with the balanced supply of nutrients for crop demand. Application of FYM without mineral fertilizer decreased N and K use efficiencies, because of the lower plant availability of N and K in the FYM. P and K fertilizers application without N resulted in a very low PUE and KUE, because of the very low yield and poor recoveries of P and K.

## *3.1.5 Soil P2O5 and K2O contents*

P and K fertilizers application affects soil P2O5 and K2O content. The balanced nutrition (N + P + K + Mg) increased soil P2O5 and maintained the soil K2O in comparison to the omission of P and K respectively.

The P2O5 content of loamy sand soil on arable land is classified as 'very low' (below 3), 'low' (4–9), 'medium' (10–18), 'high' (19–32), and 'very high' (above 33) mg P2O5 per 100 g soil at 0–30 cm depth [25]. At the start of the trial the soil P content, as well as the K level were therefore classified as medium. P fertilizer application increased soil P2O5 content toward very high during 1958–1983: the inadequate N rate during 1958–1980 (**Table 2**) and the limited potato growth in 1973–1982 caused a low crop yield (**Figure 4**) that resulted in an accumulation of P fertilizer in the soil. Increased crop yield after 1982 due to increased N fertilizer rate and cultivating potato variety resistance to nematodes reduced soil P2O5 content during 1984–1996. P fertilizer application generally increased soil P2O5 content to 'high' level, but omitting P fertilizer reduced the soil P2O5 content compared to the initial measurement in 1958 (**Figure 3**).

The K2O content of loamy sand soil on arable land is classified as 'very low' (below 3), 'low' (4–9), 'medium' (10–18), 'high' (19–32), and 'very high' (above 33) mg K2O per 100 g soil at 0–30 cm depth [25]. Application of K fertilizer-maintained soil K2O content at the 'medium' range, while the omission of K fertilizer decreased soil K2O content to the 'low' level (**Figure 2**). Application of K fertilizer increased the soil K2O content during the early decades, because of low K removal from the soil. The decreasing soil K2O content after 1981 was generally driven by combined effects of increased K removal from the soil with high crop yield and loss of K by leaching on sandy soil.

A low crop yield (**Figure 1**) produced a low PUE and KUE (**Figure 7**), at P + K mineral fertilizers application without N, resulted in the highest soil P2O5 and K2O contents (**Figures 2** and **3**). Soil P2O5 and K2O analysis at 30–90 cm in 1987, 2008, and 2018 showed residual P and K fertilizers movement below 30 cm depth. P + K mineral fertilizers application without N increased the soil P2O5 and K2O contents respectively by 43% and 49% in 30–60 cm and by 48% and 96% in 60–90 cm depth compared to the application of N + P + K mineral fertilizers (data not shown).

#### *3.1.6 Soil organic matter and soil pH*

Improvement of soil organic matter positively influences soil fertility through its impact on the chemical, physical, and biological properties of a soil. The soil organic matter was measured as soil C (carbon) content. The soil organic C decreased in comparison to the initial value of 2.1% measured in 1958, because crop residues were removed from the field during 1958–2009. It was slightly increased with mineral fertilizer and FYM application compared to the treatment without any fertilizer (**Figure 8**). During 1959–1973, the soil organic C was not measured.

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

The soil pH was optimized by lime application to avoid the negative effect of pH on nutrient availability. Lime (CaO) applied every 3 years to the whole field at 1000 kgha−1 increased soil pH compared to the initial pH measured in 1958 (**Figure 9**).
