4. Conclusions
The application of PS as a fertilizer (45 m3 ha1) in a sprinklerirrigated
maize crop did not improve yields compared to plots
treated with mineral fertilizer containing a similar dose of N
(300 kg ha1). A better strategy is therefore required to maximize
the benefits of PS in the Ebro Valley, e.g. novel application methods
such as immediate ploughing to prevent volatilization of the N
content. The positive effects of organic fertilizers may take several
years to realize, possibly because the nutrients are initially immobilized
(as organic compounds and microbial biomass) but are later
released causing the soil quality to improve. The application of PS
resulted in marginally higher soil quality parameters in both test
years, but the most significant impact was on earthworm abundance,
a key soil quality indicator that is linked to other parameters
such as soil moisture and resistance to penetration. The most
important findings were that the repeated application of PS to soil
under irrigated semiarid conditions has a beneficial impact on the
soil quality without increasing maize yields, and that earthworm
abundance is an inexpensive and early indicator of soil quality.