Pig slurry fertilization in a double-annual cropping forage system under sub-humid mediterranean conditions

Abstract

In areas of Southern Europe with very intensive pig production, most of the pig slurry (PS) is applied asfertilizer. However, in the European Union, no more than 170 kg N ha−1year−1can be applied in nitratevulnerable zones (NVZs) from livestock manures. In this context, a six-year trial was conducted for amaize-triticale double-annual forage cropping rotation under rainfed conditions. Four different N rateswere applied (0, 170, 250 and 330 kg N ha−1year−1), to evaluate their effect on crop yield, N uptake, unre-covered N and soil nitrate content. The corresponding PS rates were defined as zero (PS 0), low (PSL)medium (PSM) and high (PSH). The annual average dry matter (DM) yields (maize + triticale) for the PSfertilization treatments PS0, PSL, PSM and PSH were 12.6, 17.7, 20.2 and 22.0 Mg DM ha−1, respectively.Maize DM yield was influenced mainly by weather conditions, and triticale DM yield was clearly influ-enced by initial soil NO3−-N and PS fertilization rates. Unrecovered N was affected by PS fertilizationrate and initial soil NO3−-N content. A residual effect of the PS when applied to maize had an importanteffect on soil NO3−-N and subsequent triticale DM yield. Moreover, total annual average unrecoveredN, considering the sum of both crops (maize + triticale), were 91, 144, and 222 kg N ha−1in PSL, PSMand PSH, respectively. In order to avoid part of this unrecovered N, mainly by lixiviation of nitrates, PSfertilization in triticale should be applied as side dressing at tillering. The application of N, in the formof PS, at rates higher than the legally permitted maximum of 170 kg N ha−1year−1, may result in betteryields. However, high rates of PS fertilization may originate in significantly lower N use efficiency anda higher potential environmental impact in double-cropping systems, practiced in rainfed sub-humidMediterranean conditions.