European Journal of Agronomy 12 2000 251 – 268
A survey on actual agricultural practices and their effects on the mineral nitrogen concentration of the soil solution
Carlo Grignani , Laura Zavattaro
Dipartimento di Agronomia, Sel6icoltura e Gestione del Territorio, Uni6ersita` di Torino, 6ia Leonardo da Vinci,
44
,
10095
Grugliasco, Italy Received 19 April 1999; received in revised form 1 October 1999; accepted 4 February 2000
Abstract
In intensive integrated crop-livestock farming systems, the surplus of N at the farm scale may be large and reflects on the N balance at the field scale. A study was conducted to assess the N fertilizer efficiency in four private farms
in intensively cropped areas of NW Italy, and to monitor the effects of agricultural practices on the mineral N concentration of the soil solution, sampled every 2 weeks for 2 years and considered as an indicator of potential
leaching. Two cultivation systems were compared in each farm, one involving continuous maize rotation, the other assuring a continuous soil cover permanent meadow or winter cereal-maize double cropping system. The fertiliza-
tion level in the arable crops was high 369 – 509 kg N ha
− 1
year
− 1
compared to the crop removals, and resulted in a low efficiency, as indicated by the four examined efficiency indexes calculated N surplus, N removal-fertilizer ratio,
N apparent recovery, N use efficiency. The soil-water-nitrate concentration showed large temporal variations in the range of 1 – 150 mg l
− 1
for five out of the eight cropping situations, while concentrations smaller than 10 mg l
− 1
were always recorded in the meadows and in one of the four soils Aeric epiaquept. The fertilizer management that
characterized each cropping system affected the soil-mineral-nitrate content in shallow arable soils. The longer soil cover duration in double-cropping systems did not result in a reduction of soil N compared to maize as a single crop,
not even in winter the bare-soil intercropping period in maize-based systems. However, the temporal oscillations of the concentration were buffered by the crop cover duration and by the presence of a shallow water table 1 m deep
in the soil profile. The average nitrate content of the soil could be predicted by the N uptake of the crop, the N removal – fertilizer ratio, the soil pH and sand content, however no simple explanatory relationship was found with
the experimental factors. Hence, in farm conditions, in the absence of sufficient data for a deterministic model approach, the target of reducing the risk of leaching should be achieved by maximizing the fertilizer efficiency. © 2000
Elsevier Science B.V. All rights reserved.
Keywords
:
Cultivation systems; Fertilizer efficiency; Nitrogen leaching; Soil nitrate content www.elsevier.comlocateeuragr
1. Introduction
Environmental sustainability of intensive inte- grated crop-livestock farming systems lies primar-
Corresponding author. Tel.: + 39-11-6708777; fax: + 39- 11-6708798.
E-mail address
:
grignaniagraria.unito.it C. Grignani 1161-030100 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 1 1 6 1 - 0 3 0 1 0 0 0 0 0 4 9 - 6
ily in the efficiency of the use of nutrients, above all nitrogen Schepers and Fox, 1989. A study on
different kinds of breeding farms in Piemonte Grignani, 1996 showed a general imbalance be-
tween farm global inputs and outputs, with a nitrogen surplus of 300 kg ha
− 1
year
− 1
, on aver- age. The nitrogen inputs were mainly concentrates
and fertilizers, but only 30 of the total input was found in farm outgoing products meat, milk and
grain. Consequently, most of the nitrogen input was leached with drainage water, lost in volatile
compounds or accumulated in the farm system, such as in soil organic pools. These and similar
results obtained in other countries Jarvis, 1993; Simon et al., 1994; Weissbach and Ernst, 1994;
Cuttle, 1997 have often led policy makers to ascribe high nitrate leaching losses to intensive
livestock farming systems.
Although several studies of nitrogen leaching have been undertaken over many decades in vari-
ous environments Juergens-Gschwind, 1989, the general understanding of the effects of agricul-
tural practices on N leaching remains fragmen- tary. Assessment of N leaching is in particular
greatly influenced by the method used to measure leachable mineral N such as soil-core extractions,
ceramic cups, lysimeters, tile drainage, plot or farm balance, as well as by the scale at which N
leaching quantification is undertaken such as soil profile, experimental plot, farm or catchment;
Armstrong and Burt, 1993.
Most studies have been conducted at the point measurement scale, focusing on the soil mineral N
concentration Cavazza et al., 1986; Patruno, 1987; Verte´s and Decau, 1992; Benoit, 1994; Par-
dini et al., 1995; Grignani et al., 1996. At this scale, a theoretical deterministic description of the
vertical water and solutes movement is available, obtained from several decades of laboratory ex-
periments Jury and Flu¨hler, 1992. Two-dimen- sional field studies have been conducted, mainly
using tile drains Decau and Le Corre, 1992; Scholefield et al., 1993; Lewan, 1994; Drury et al.,
1996; Borin, 1997, while three-dimensional stud- ies on catchments and model applications coupled
to GIS systems are becoming extremely popular Shaffer et al., 1996; David et al., 1997; Richter et
al., 1998 among others. A further difficulty encountered in N leaching
research is that of the representativeness of exper- imental treatments in comparison to the agricul-
tural practices
adopted by
farmers. Crop
management is often conditioned to a great extent by farm organization systems, in particular in
forage systems oriented to livestock production, where both the forage yield in terms of fodder
quality, rather than DM production and the organic fertilizer supply are connected to animal
husbandry. Hence, choices on the crop, rotational system, time, amount and type of fertilizer appli-
cations, tillage, irrigation, etc., are not indepen- dent, and an evaluation of the real effects of the
cultivation system can be carried out through an analysis of real situations, in real farms. Some
authors have therefore tried to work in situations where agricultural practices were a variable rather
than a factor Benoit et al., 1995; Vereijken, 1997, although this may imply a higher degree of
uncertainty, as not all variables can be measured with the same precision as in experimental plots.
The objective of this study was to assess the response of the mineral nitrogen concentration of
the soil solution to various aspects of forage system management crop and crop rotation, kind
of fertilizer supplied, time and amount of supply in real conditions, after monitoring the effectively
adopted agricultural practices. The analysis was conducted in four private farms, two dairy cow-
breeding farms and two pig breeding farms, com- paring two fields cultivated with different crops.
2. Materials and methods
