Drip fertigation with slurry as a promising tool to reduce nitrogen losses under organic maize

Abstract

The European Union (EU) actively promotes the adoption of organic farming, in which crop N requirements are satisfied via organic fertilizers, such as slurry. Maize (Zea mays L.) is a key crop for both feed and food production with high N uptake. In this short-term study, we tested fertigation with microfiltered slurry liquid faction for maize fertilization as viable strategy to enhance nitrogen use efficiency (NUE) under organic farming while reducing N losses, via ammonia (NH₃), nitrous oxide (N₂O), and nitrate leaching (NO₃^-). We compared three strategies (i) slurry application through surface broadcast of the liquid fraction before sowing as reference fertilization ("Ante" treatment, or "A"), (ii) slurry application through both pre-sowing broadcast of the liquid fraction and fertigation as side-dressing with the microfiltered liquid fraction ("Ante + Post" treatment, or "A + P"), and (iii) slurry microfiltered liquid fraction application as side dressing via fertigation ("Post" treatment, or "P"). Compared to "A", cumulative N losses were reduced by 38% under "A + P" and 58% under "P". Furthermore, NH₃ volatilization decreased by 43% and 71% under "A + P" and "P", respectively. These treatments also reduced N₂O emissions by 30% and 37%. Nitrate leaching was reduced by 56% in the "P" treatment. Overall, the "P" strategy was the most effective in reducing N losses, while "A + P" tended to increase grain production (12.6 Mg ha^-1) and NUE (38.1 kg grain kg^-1 N supply) compared to "P" (11.0 Mg ha^-1 and 35.5 kg grain kg^-1 N supply). These results were primarily attributed to the improved synchronization between N supply and maize N requirements, emphasizing the risk associated with slurry application before sowing. Although conducted over a short experimental period, our study suggests that drip fertigation with slurries can overcome the potential yield losses of organic systems for crops with high N demand such as maize, while reducing N losses, fulfilling the environmental principles of organic farming and current requirements from EU policies.

Keywords: Cattle slurry; Drip fertigation; Nitrogen Use Efficiency; Organic maize.

Fig. 1

Schematic representation of the experimental field depicting the placement of sampling devices for N₂O emissions, NO₃^--leaching and NH₃ volatilization. Roman letters stand for pseudo-replicates within each treatment (i.e., “Ante” [A], “Ante + Post” [A + P], “Post” [P], and control).

Fig. 2

Weather conditions during the field experiment and slurry application events.

Fig. 3

Development of soil Water Filled Pore Space (a), ammoniacal (b) and nitric-N (c) content through the monitoring period at 0.3 m depth for the three treatments: Ante, “A”; Ante + Post, “A + P” and Post, “P”. Filled triangles represent fertigations on both “A + P” and “P”, while empty ones represent fertigations only for “P” treatment.

Fig. 4

Development of N₂O-N emissions from soil surface, through the monitoring period for the three treatments: Ante, “A”; Ante + Post, “A + P” and Post, “P”; and control. Filled triangles represent fertigations on both “A + P” and “P”, while empty ones represent fertigations only for “P” treatment.

Fig. 5

Development of NH₃-N volatilisation after surface broadcast of liquid-separated slurry on “A” treatment (first event), and after fertigation events on Ante + Post, “A + P” and Post, “P” treatments. Filled triangles represent fertigations on both “A + P” and “P”, while empty ones represent fertigations only for “P” treatment.

Fig. 6

Development of soil drainage-water NO₃^--N concentration (a), and NO₃^--N leaching losses (b) through the monitoring period at 0.45 m depth for the three treatments: Ante, “A”; Ante + Post, “A + P” and Post, “P”. Filled triangles represent fertigations on both “A + P” and “P”, while empty ones represent fertigations only for “P” treatment. The dashed line indicates a long period without measurements.

Fig. 7

Biplot of Principal Component Analysis for main variables (Nitrogen Use Efficiency [NUE]; Grain yield [Grain]; maize vegetative biomass production [Biomass]; mean soil NO₃^--N content at 0.3 m depth [soil_NO3]; mean soil NH₄⁺-N content at 0.3 m depth [soil_NH4]; mean soil Water Filled Pore Space content at 0.3 m depth [WFPS]; cumulative N₂O emissions [N2O]; cumulative NH₃ volatilisation [NH3] and cumulative NO₃^--N leaching losses [NO3_leaching]) as arrows, and clustered treatments (“Ante” [A], blue; “Ante + Post” [A + P], orange and “Post” [P], grey).