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SOIL MANAGEMENT

Yield Parameters as Affected by Introduction or Discontinuation of Catch Crop Use

^a Dep. of Crop Physiology and Soil Science, Tjele, Denmark
^b Dep. of Agricultural Systems, Biometry Research Unit, Danish Institute of Agricultural Sciences (DIAS), Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark

elly.m.hansen{at}agrsci.dk

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
A 24-yr-old permanent field trial on coarse sand (Orthic Haplohumod) under temperate coastal climate conditions was used to determine (i) the effect of introducing perennial ryegrass (Lolium perenne L.) as a catch crop on plots with a history of low input of organic matter, and (ii) the residual effect of long-term use of ryegrass as a catch crop on main crop yield and N uptake. The catch crop (8–10 kg ha^-1) was undersown in spring wheat (Triticum aestivum L.). From 1993 to 1996, four treatments were included: catch crop since 1968, catch crop since 1993, no catch crop, and catch crop until 1993. Each treatment was conducted at two previously established N rates (60 and 120 kg N ha^-1 yr^-1), which were subdivided into four new N rates (0, 60, 90, and 120 kg N ha^-1 yr^-1). Two years after introduction of the catch crop, yields were no longer different from yields with long-term previous catch crop use. The residual effect of long-term catch crop use on yield persisted for more than 4 yr. With previous long-term use of a catch crop compared with no previous use, N fertilization could be reduced by 15 or 27 kg N ha^-1 yr^-1 at the 60 or 120 kg N ha^-1 yr^-1 rate, respectively, without yield reductions. The experiment shows that the use of ryegrass as a catch crop has the potential to benefit main crop yield and soil fertility.

Abbreviations: P_A-+: autumn-plowed, catch crop since 1993 • P_A++: autumn-plowed, catch crop since 1968 • P_S+-: spring-plowed, catch crop until 1993 • P_S--: spring-plowed, no catch crop

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
A MAJOR AGRICULTURAL RESEARCH PRIORITY TODAY is to sustain soil fertility. Under continuous cereal production where straw is removed for fodder or solid fuel, little organic matter is returned to the soil. In the long term, this may lead to soil structure degradation (Schjønning, 1989; Breland, 1995) and loss of soil fertility. Introducing a catch crop may prevent this by increasing organic matter inputs to soil. On a loamy soil, the use of Italian ryegrass (Lolium multiflorum Lam.) as a catch crop provided rapid structure improvements (Breland, 1995), but similar information is not known to be available for coarse sandy soils. Soil organic matter contributes to soil fertility in several ways, which may be difficult to quantify separately. Therefore, it may be better to "look for any benefits to yield, for the crop integrates the various effects of the physical environment in which it lives" (Johnston, 1991).

Repeated use of catch crops may affect the amount of mineralizable N, as seen with long-term straw incorporation (Powlson et al., 1987). If mineralization is synchronized with crop N uptake, N application rates may be reduced while yield levels are maintained. Long-term use of a catch crop showed that N fertilization could be reduced by 11 to 23 kg N ha^-1 yr^-1 without yield reduction compared with no catch crop use (Hansen and Djurhuus, 1997a). However, no information is available on the extent of residual N effects after discontinuation of catch crop use.

To optimize the use of catch crops with continuous cereal production as well as with crop rotations, it is important that the above-mentioned issues be further investigated. A long-term field experiment suitable for such investigations was available on a coarse sandy soil. When the present experiment started, plots with or without ryegrass as a catch crop had existed for 24 yr. By changing the treatments in 1993, the effects of catch crop use could be further investigated. The aim of the experiment was to determine (i) the effect of introducing a catch crop on plots with a history of low input of organic matter, and (ii) the residual effect of long-term use of a catch crop on main crop yield, N uptake and nitrate leaching. This paper reports on the yield parameters; nitrate leaching is reported by Hansen et al. (2000).

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Experimental Area, Design, and Analyses
The experiment was a 4-yr study (1993 to 1996) conducted on a 24-yr-old field trial site with continuous production of spring-sown crops on an Orthic Haplohumod, coarse sand, siliceous, mesic soil at Jyndevad in southern Jutland, Denmark (54°54' N, 09°07' E, 16 m above sea level). Autumn and spring plowing were continued, while in some treatments the catch crop use was changed as shown in Fig. 1 . Until 1972 the spring-plowed treatments (P_S+- and P_S--) were direct-drilled, and between 1973 and 1986 they were rotovated to a depth of 3 to 5 cm. From 1968 to 1986, the N rates were 70 and 150 kg N ha^-1 yr^-1; from 1987 to 1992, they were 60 and 120 kg N ha^-1 yr^-1. The catch crop used until 1987 was Italian ryegrass, and from 1987 on a medium-late or late perennial ryegrass was undersown in spring with a seed rate of 8 to 10 kg ha^-1. For further details about the management history, see Hansen and Djurhuus (1997a).

View larger version (61K): [in this window] [in a new window]   Fig. 1 Experimental plan and field layout, 1993 to 1997

The catch crop was undersown each spring. After harvest, straw was removed from the plots. No stubble cultivation was practiced after harvest, but plots without a catch crop were sprayed with glyphosate in autumn when needed to kill volunteers and weeds. To control couch grass [Elytrigia repens (L.) Desv. ex Nevski], plots with a catch crop were sprayed with glyphosate in November 9 to 20 d before plowing. Phosphorus and K fertilizer was applied in basal dressings each year. The average dates for management operations were as follows: spring-plowing, 24 March; sowing, 4 April; N fertilization, 1 May; harvest, 27 August; and autumn-plowing, 20 November. The experiment was irrigated at an estimated water deficit of 30 mm. From 1993 to 1996, the irrigations were 95, 60, 60, and 61 mm for each year, respectively.

Each plot was harvested for grain and straw yield with a plot combine. Samples were oven-dried and the amount of Kjeldahl-extracted N in grain and straw was determined using a Kjeltec 1030 Analyzer (Tecator, Höganäs, Sweden). Yield of grain and straw are given as yields of dry matter.

Statistical Methods
The trial consisted of four blocks (Fig. 1). The four combinations of time of plowing and use of catch crop before 1993 were randomized in strips separately for each block. The eight combinations of previous and present N rates were randomized in two steps. First, the levels of previous N rates were randomized in strips (perpendicular to the strips of plowing and catch crop) and across pairs of blocks. Next, the levels of present N rate were randomized within each level of previous N rate. This means that each combination of plowing time and use of catch crop had four replicates, whereas each combination of previous and present N rate had two replicates.

The variables were analyzed by general linear mixed models (see, for example, Searle, 1971; Searle et al., 1992), assuming that the errors of each stratum were distributed according to a normal distribution with mean zero and constant variance. The random effects of the model were set up so that they took into account the special layout of the design (Table 1) .

Some of the variables analyzed were log-transformed before the analyses were conducted in order to obtain the simplest possible effect. For variables where log-transformed values were analyzed, the test of interaction applies to the transformed scale. After fitting and testing, the model was reduced in order to leave only the important and significant effects in the model.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Yield of grain was log-transformed for the statistical analysis, but after the analysis the values were retransformed to the original units for the purpose of describing and discussing the effects. Only the effects that are essential for the purpose of this paper will be discussed in detail (e.g., effects related to catch crop use before 1993 and years after change of the experiment). Each interaction is discussed along with the main effect most relevant for that interaction.

An overview of the results from the statistical analyses is given in Table 1. Since the interactions including time of plowing, use of catch crop before 1993, and present N rate were small, the main effects of catch crop before 1993, and present N rate are also shown (Table 2) . Throughout the paper, mentioned differences between treatments are significant at P < 0.05.

To get an overall picture of the effect of catch crop use before 1993, averages of different treatments are compared in Table 2. Treatments with and without a catch crop before 1993 both include equal numbers of plots with autumn and spring plowing and with and without present catch crop use. In Table 3 , each of the four treatments is compared two by two.

The log-transformed grain yield showed an interaction between use of a catch crop before 1993 and present N rate (Table 1), with the greatest effect of the catch crop before 1993 at the lowest present N rate. The mean residual long-term effect of a catch crop on N requirement was estimated by fitting a quadratic model to the mean grain yield as a function of present N rates. The interaction between use of a catch crop before 1993 and present N rate was significant on the log scale (Table 1), but nonsignificant on the original scale. Therefore, parallel curves for use of a catch crop before 1993 and no catch crop before 1993 were used (Fig. 2a) . As an average of the two treatments with previous long-term use of a catch crop, N fertilization could be reduced by 27 kg N ha^-1 yr^-1 at the 120 kg N ha^-1 yr^-1 rate and by 15 kg N ha^-1 yr^-1 at the 60 kg N ha^-1 yr^-1 rate without yield reduction.

View larger version (20K): [in this window] [in a new window]   Fig. 2 (a) Grain yield and (b) N concentration in grain as function of present N rate (average of years, previous N rates, and mentioned treatments). Symbols for grain yield represent means of log-transformed measured values retransformed to the original unit. In the expression of estimated values, N is the N rate

The effect of the present N rates was significant for all yield parameters (Table 1). The interaction between year and present N for grain yield was found to be partly systematic. The following submodel could describe the systematic part of this interaction:

where is 0.00094, T is time after the change in the experiment (0, 1, 2, or 3 yr) and N is N application rate (0, 60, 90, or 120 kg N ha^-1 yr^-1). The submodel means that the effect of increasing the present N rate rose linearly with time during the experimental period.

In 1993 grain yield was relatively low in the autumn-plowed treatment where ryegrass as a catch crop was introduced for the first time (Fig. 3) . From 1994 on, yield increased compared with the other treatments.

View larger version (23K): [in this window] [in a new window]   Fig. 3 Grain yields as function of year (average of previous and present N rates). Symbols represent means of log-transformed measured values retransformed to the original unit. Lines represent estimated values

In 1993 and 1994, the difference in grain yield between P_A++ and P_A-+ was significantly different from zero (Fig. 3 and Table 3). This means that yield in the autumn-plowed treatment with no history of catch crop use (P_A-+) was less than in the autumn-plowed treatment with previous catch crop use (P_A++). From 1995 on, no differences between the two treatments were found. For total N uptake, the difference between P_A++ and P_A-+ was different from zero only in 1993 (Table 3).

Development over time is shown by comparing the differences between P_A++ and P_A-+ from year to year. The observed decreases in the differences in grain yield from 1993 to 1994 and in N uptake from 1993 to 1995 were significant (Table 3 and Fig. 3). This means that introducing a catch crop after 25 yr of removal of all plant residues except stubble and roots (P_A-+) produced a relative yield increase when compared with continuous catch crop use (P_A++). The effect of the ryegrass catch crop on yield was visible after only 2 yr of catch crop growing. This result supports the hypothesis that even soils managed over the long term with minimal organic inputs have a high potential to respond to new organic inputs (Fauci and Dick, 1994). This is in agreement with Breland (1995), who found that a single incorporation of a catch crop of Italian ryegrass gave structure improvement on a loamy soil. The enmeshment into the soil of a dense web of fine ryegrass roots (Tisdall and Oades, 1979; Carter and Kunelius, 1993; Breland, 1995) and presumably an increase in biological activity (Dick, 1992) thus seemed to have an effect on coarse sandy soil as well when compared with a treatment with minimal return of organic matter. Janzen and Schaalje (1992) pointed out that soils low in fertility may respond more favorably to organic matter additions than more fertile soils. In the present experiment, this may have been the case, because soil sampling in spring 1991 showed that organic C content was less with minimal organic input than with long-term catch crop use (Hansen et al., 2000). Furthermore, in 1993, the first year of the experiment, the relationships between grain yield and N uptake in grain and straw in the two autumn-plowed treatments were different from each other (Fig. 4) . Even though both treatments were fertilized with up to 120 kg N ha^-1, the crop in treatment P_A-+ did not manage to take up more than approximately 80 kg N ha^-1. Apparently, there was some benefit other than N that affected the efficiency with which fertilizer N was used. This suggests a nonnutritional yield response in the treatment with previous catch crop use compared with the treatment with no history of catch crop use as described by Janzen and Schaalje (1992). From 1994 to 1996, there was no difference in the relationship between dry matter yield and N uptake (data not shown), which again implies a rapid effect of the ryegrass catch crop introduced into the treatment with no previous use of catch crop. Such response is of agronomic significance if coarse sandy soils with long-term minimal organic input are to gain some of their lost fertility.

View larger version (19K): [in this window] [in a new window]   Fig. 4 Grain yield as function of N uptake in grain and straw in 1993 in autumn-plowed treatments. Symbols represent measured values of two previous N rates. In the expression of estimated values, N is the N uptake in grain and straw

Comparing the differences between P_S+- and P_S-- from year to year showed no decrease in grain yield and total N uptake (Table 3 and Fig. 3). This means that suspending 25 yr of catch crop use did not cause any immediate reduction in yield. Hence, the residual effect of the long-term catch crop use on yield was more persistent than the 4-yr course of the present experiment. Davies et al. (1996) and Rasmussen et al. (1998) indicated that organic N added through recent crop management practices was more available than the "background" soil N, and Shen et al. (1989) showed that recently added organic residues in soil were about seven times more mineralizable than native soil organic matter. Other results have shown that N retained in organic forms after the first growing season following the addition of green manure is released relatively slowly (Ladd et al., 1981; Janzen et al., 1990). However, in the long run, small increases in the quantity of mineralizable N in the soil may add up to be of agronomic significance.

The previously mentioned nonnutritional effects found in the autumn-plowed treatments in 1993 (Fig. 4) did not appear in the spring-plowed treatments (data not shown). The reason may be that spring plowing, which previously has shown trends toward higher grain yields and N uptake than autumn plowing (Hansen and Djurhuus, 1997a), has blurred the ability to identify an eventual nonnutritional effect of the long-term use of ryegrass as a catch crop. However, an eventual nonnutritional effect in the spring-plowed treatment might have been small or nonexistent due to a higher soil organic C content in the spring-plowed treatment without previous catch crop use than in the corresponding autumn-plowed treatment (Hansen et al., 2000).

	Conclusions

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
The introduction of ryegrass as a catch crop after 25 yr of removal of all residues except stubble and roots caused a rapid yield increase in spring wheat. After 2 yr, yields were no longer significantly different from yields achieved with long-term previous catch crop use.

The use of ryegrass as a catch crop in continuous spring barley production from 1968 to 1992 gave on average 0.39 Mg ha^-1 yr^-1 higher yields of grain and 10 kg N ha^-1 yr^-1 higher total N uptake from 1993 to 1996 than with no previous catch crop use.

With previous long-term use of a catch crop, N fertilization could be reduced by 27 kg N ha^-1 yr^-1 at the 120 kg N ha^-1 yr^-1 rate and by 15 kg N ha^-1 yr^-1 at the 60 kg N ha^-1 yr^-1 rate without yield reduction.

Suspending 25 yr of catch crop use did not cause any immediate reduction in yield of spring wheat. After 4 yr, yields were still higher than yields with minimal organic inputs. Hence, the residual effect of long-term catch crop use on yield was more persistent than the 4-yr course of the present experiment.

The experiment shows that the use of ryegrass as a catch crop in spring grain production has a potential benefit on the main crop yield and on soil fertility.

Received for publication May 6, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Hansen, E. M. Articles by Djurhuus, J. Search for Related Content PubMed Articles by Hansen, E. M. Articles by Djurhuus, J. Agricola Articles by Hansen, E. M. Articles by Djurhuus, J. Related Collections Soil Fertility and Productivity Other Soil Management