Soil mineral-N and N-fertilizer requirements of spring cereals in two long-term tillage trials on loam soil in southeast Norway
Introduction
Reduced tillage leads to changes in many of the soil's physical properties, several of which may be expected to be of importance for the turnover of nitrogen. Soil bulk density often increases in the 10–20 cm soil horizon in the absence of ploughing. This leads to reduced air-filled pore space and higher water contents and may alter the soil's thermal properties. Increased volumetric heat capacity may result in lower diurnal temperature amplitude and the presence of crop residues on the surface reduces soil temperatures markedly in the early part of the growing season due to greater reflectivity and insulation (Børresen and Njøs, 1990). It is reasonable to assume that lower nitrogen mineralisation may result from such changes (Nyborg and Mahli, 1990; Iragavarapu and Randall, 1995).
In Germany, it was suggested that deep tillage caused an excessive level of nitrogen mineralization for cereals, with resulting lodging, and that reduced tillage was a means of avoiding this (Kahnt, 1976). More recently, it has been shown that increasing plough depth actually causes considerable amounts of nitrogen to become immobilised (Nieder et al., 1995). Conservation tillage is also thought to increase net immobilisation and lower net mineralisation, leading to lower nitrate concentrations in the soil solution (Ehlers and Claupein, 1994). This suggests that N-fertilizer requirements may actually increase with reduced tillage, at least initially. Some investigations have indeed shown yield decreases with reduced tillage at low levels of N-input (Blevins et al., 1977; Meisinger et al., 1985). However, the question is complicated by the fact that growth retardation, caused for example by unfavourable seedbed conditions or increased weed competition, may be partly offset by higher fertilization, even though such factors have little to do with nitrogen availability.
Other factors may lead to increased nitrogen availability. The accumulation of organic matter in the upper soil layers of untilled soil represents an increase in nitrogen reserves, which may eventually become available to plants. Rice et al. (1986)found that nitrogen availability improved after a number of years without tillage in maize. Ehlers and Claupein (1994)suggest that the period of N-accumulation will end after about 10 years of reduced tillage, whereafter the supply of soilborne N and fertilizer efficiency will be similar to that experienced with conventional tillage. Furthermore, the omission of autumn ploughing prevents the stimulation of mineralisation at a time when there is a high risk of nutrient leaching. Several investigations have demonstrated reduced nitrogen leaching in winter in the absence of autumn ploughing (Dowdell et al., 1987; Goss et al., 1988a, Goss et al., 1993b; Møller Hansen and Djuurhuus, 1997). Reduced leaching has also been found in spring, as a result of greater surface runoff from unploughed land during the snow-melt period (Eltun, 1995).
Norwegian tillage trials have in several cases given results that indicate reduced tillage affects the crop's nitrogen supply, but we know little about the mechanisms involved. Significant increases in cereal lodging have been found after only a few years with reduced tillage (Marti, 1984; Riley, 1985). Pronounced changes related to tillage have also been found in the development pattern and nitrogen concentrations of potatoes (Ekeberg and Riley, 1996). An explanation for both these findings may be an increase in the release and uptake of nitrogen during the latter part of the growing season.
Studies of nitrogen levels in soil and plants were performed over the period 1991–1996 in two long-term tillage trials started in 1980, in which yields with reduced tillage have for many years been maintained at a level similar to those obtained with conventional tillage. The aim of theses studies was to compare cereal crop nitrogen requirements under contrasting tillage systems, and to measure residual nitrogen levels in the soil.
Section snippets
Field trials
Both trials were on moderately well-drained morainic loam soil at Apelsvoll Research Centre, Division Kise (60°46′N, 10°49′E). They included two tillage treatments (reduced vs. conventional tillage) on plots of approximately 100 m2 (Trial I) and 200 m2 (Trial II). There were four replicate blocks in each trial. Reduced tillage comprised in the years 1991–1993 the use of a machine (fertilizer harrow) with spring tine coulters for fertilizer and seed placement, in two separate passes, followed by
Soil physical conditions
Bulk density at a depth of 0–20 cm was slightly higher and total porosity slightly lower under reduced tillage than under conventional plough tillage. At 23–27 cm depth, there was no difference due to tillage. Air capacities and air permeability were, as a result, severely reduced in the upper horizons (Table 1). Air permeability was significantly reduced also in the lowest horizon sampled, even though the total porosity was unchanged. There were slight increases in the soil's volume percent
Discussion
Both the trials were started in 1980, so for the period reported there were treatments which had not been ploughed for 12–17 years. The changes recorded in soil physical conditions were typical of those found in other tillage studies in Scandinavia (Riley et al., 1994), but not dramatic. Problems with perennial and annual weed grass were combatted as necessary by spraying with glyphosate herbicide either in autumn or in spring before seeding. Excessive traffic on the plots under wet conditions
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2016, Industrial Crops and ProductsCitation Excerpt :Similarly, a lower yield of durum wheat under reduced tillage has been reported when no N fertilizer was applied, whereas application of 50 to 100 kg N ha−1 alleviated the deleterious effect of reduced tillage on crop yield (De Giorgio et al., 2004). In some other studies, identical responses of crops to N fertilizer rate have been documented, regardless of the tillage method (Riley, 1998). In addition to the rate of N, source of N also plays an important role in N management.
Effects of over-winter green cover on soil solution nitrate concentrations beneath tillage land
2014, Science of the Total EnvironmentCitation Excerpt :There was no overall significant effect of tillage practices on the mean NO3−-N concentrations across three over-winter seasons: the effect of Tillage (F1,2357, p = 0.101) and the interaction of Tillage by Cover (F2,2357, p = 0.115) were not significant. Contradictory evidence can be found in the literature in regard to the effects of different tillage practices (including direct drilling) on nitrate losses (Dowdell and Cannell, 1975; Goss et al., 1993; Riley, 1998). Although the overall effect of tillage practices across three over-winter sampling seasons was not significant in this study on a leaching susceptible soil, it should not be neglected that under RT the NR treatment significantly reduced NO3−-N concentrations compared to M and NC (see Section 3.2).