Elsevier

Soil and Tillage Research

Volume 48, Issue 4, 27 October 1998, Pages 265-274
Soil and Tillage Research

Soil mineral-N and N-fertilizer requirements of spring cereals in two long-term tillage trials on loam soil in southeast Norway

https://doi.org/10.1016/S0167-1987(98)00165-2Get rights and content

Abstract

Much uncertainty exists among growers concerning the need to adjust N-fertilizer application to cereals when reduced tillage is adopted. Studies in long-term trials are required to give an adequate answer to this question, which is of both economic and environmental interest. N-fertilizer requirements of spring cereals and of soil mineral nitrogen contents at different times of the year were measured over the period 1991–1996 in two long-term tillage trials established in 1980 at Kise (60°46′N, 10°49′E) on morainic loam soil. Tillage treatments comprised conventional tillage with autumn ploughing and reduced tillage without ploughing and with harrowing in spring kept to the minimum necessary for seeding. Four levels of N-fertilizer (0, 60, 90 and 120 kg N/ha) were compared in 1991–1995 in barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), and their residual effect was measured in 1996. Levels of soil mineral nitrogen before fertilization in spring were on an average 8% lower with reduced tillage than with conventional tillage. Plant development was delayed with reduced tillage, but this was compensated for later in the season. A two-year incubation study under covered plots in the field did not reveal any effect of tillage on net nitrogen mineralisation. There was a tendency to higher straw yield with reduced tillage, but no overall effect on grain yield. Responses to N-fertilizer were almost identical with both the tillage systems, and yields increased up to the highest level of application. Crop nitrogen contents were monitored, but only minor differences were found between tillage systems in total uptakes and apparent N-fertilizer recoveries. On the basis of these results it is concluded that long-term reduced tillage does not affect the N-fertilizer requirements of spring cereals on loam soils under cool climatic conditions.

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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