**Author details**

variation (%), CT = 34, MF = 23, BS1 = 16, BS2 = 16]. In the case of AE, the BS1 treatment was significantly greater than the corresponding BS2 treatment, which indicates that a direct relationship does not exist between the contribution of N and grain production. This tendency is confirmed when we analyse the regressions for the distinct production indices and different doses of N, which are not correlated. As observed in **Table 9**, the values of r2 are low, and a statistically significant relationship between the coefficients and the constants was not observed in any case. [23, 24] find that an excessive N fertilization results in low-use efficiency, without any yield benefits and long-term environmental consequences, soil acidification, Nleaching… [25] does not find any relationship between grain yield and N application rates (r = 0.26). Similar pattern was obtained to P addition and yield index, but, for example [26] find

a positive relationship between P addition and corn yield response.

= 0.016 α1 = 0.16 α2 = 0.01

= 0.044 α1 = 0.02 α2 = 0.01

= 0.215 α1 = 0.69 α2 = 0.13

= 0.239 α1 = 0.68 α2 = 0.03

**Table 9.** Regression values for corn yield (Y) (kg ha−1) and harvest rate (HR) in relationship with N and P applied.

The application of the Verdiberia-ASP-NP (Plateau-ASP-ActiSolids©) biosolid, which origi‐ nates from the sludge of urban treatment plants, was demonstrated to be suitable for maize production (*Zea mays* L., Automat-Advanta variety). This suitability can significantly increase

This product does not present a risk of increasing the heavy metal concentration; considering the elemental concentration of the biosolid in total quantities (kg ha−1), the resulting values

From the analysis of temporal variation, the values measured for the C/N, C/P and N/P ratios during the evaluation time period indicate that sludge rapidly incorporated into the soil with

α1, α2 = Significance value for N, P and constant coefficients.

284 Organic Fertilizers - From Basic Concepts to Applied Outcomes

the yield compared with equivalent mineral fertiliser.

were substantially lower than the established normative limits.

**Y = N × 1.27 + 9932.5**

Y = P × 4.2 + 10464.8

HR = P × 8.5 × 10−5 + 0.84

**4. Conclusions**

a high rate of mineralisation.

HR = N × 4.8 × 10−5 + 0.84

r2

r2

r2

r2

Emilio Carral\* , Adolfo López-Fabal, Socorro Seoane, Teresa Rodríguez, Carlos Caaveiro and Elvira López-Mosquera

\*Address all correspondence to: emilio.carral@usc.es

Higher Polytechnic School, University of Santiago de Compostela, Lugo-Galiza, Spain
