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a Dep. of Agron. and Plant Genet., 1991 Buford Circle, Univ. of Minnesota, St. Paul, MN 55108-6026
b USDA-ARS, 233 Johnson Hall, Pullman, WA 99164-6421
c Dep. of Crop and Soil Sci., Washington State Univ., Pullman, WA 99164-6420
d Southwest Res. and Outreach Cent., Lamberton, MN 56152
e College of Biol. and Agric., Brigham Young Univ., 301 WIDB, PO Box 25250, Provo, UT 84602-5250
* Corresponding author (pporter{at}umn.edu)
Received for publication October 2, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Abbreviations: HI, high purchased input(s) • LI, low purchased input(s) • OI, organic input(s) • SCN, soybean cyst nematode • ZI, zero input(s)
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Agricultural productivity gains since the 1950s resulted from the development of farming systems that rely heavily on external inputs of energy and chemicals to replace management and on-farm resources (Oberle, 1994). Continuous rotation of corn and soybean cannot be sustained without substantial additions of fertilizer and pesticides (Heichel, 1978; Pimentel et al., 1978). A number of research studies have been conducted comparing conventional corn–soybean production systems with low-input and organic production systems, including those by Chase and Duffy (1991) and Karlen et al. (1995) in Iowa, Munn et al. (1998) in Ohio, Liebhardt et al. (1989) in Pennsylvania, Smolik and Dobbs (1991) and Smolik et al. (1995) in South Dakota, and Posner et al. (1995) and Mallory et al. (1998) in Wisconsin. The economics of organic grain and soybean production from several studies conducted by researchers at numerous midwestern U.S. land-grant universities was reported by Welsh (1999). In summary, these studies reported a range of responses to low-input and organic production systems, from lower yields and economic returns to comparable yields and greater returns.
In 1989, two trials, titled the Variable Input Crop Management Systems (VICMS) trials, were initiated in Minnesota (Perillo et al., 1996). Each trial evaluated two rotation lengths and four management strategies. Rotation lengths included a 2-yr corn–soybean rotation and a 4-yr corn–soybean–oat/alfalfa–alfalfa rotation. The four management strategies compared were conventional production, low purchased inputs, organic production, and a system where fertility levels were not maintained. One trial (V1) began on land with a history of no fertilizer or pesticide application and where soil fertility levels, specifically P, had been depleted over time. The other trial (V2) began on land with a history of conventional fertilizer and pesticide application and where soil fertility levels had been built up over time.
Our objectives in this paper were to document how rotation length and management strategies influenced productivity after the initial four establishment years of the trials. The economics and risks associated with the rotation lengths and management strategies are presented by Mahoney (2001).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Experimental Setup
The treatments were finalized following lengthy discussions with organic farmers and researchers from several land-grant universities and the Rodale Institute. Two crop rotations and four management strategies were established in the late 1980s. The two crop rotations included a 2-yr corn–soybean rotation and a 4-yr corn–soybean–oat/alfalfa–alfalfa rotation. The trials began in the spring of 1989 except for the 4-yr rotation in V2, which began in the spring of 1990. Each crop of each rotation was grown each year, constituting six main plots for each of the three replicates, which were arranged in a randomized complete block design. The four management strategies, arranged as subplots of the crop rotation main plots, were ZI, LI, HI, and OI. Thus, when referring to yields, for both corn and soybean, there were eight treatments (two crop rotation lengths, each involving four management strategies), whereas for both oat and alfalfa, there were four treatments (four management strategies).
Subplot size was 54.9 m long by 30.5 m wide for V1 and 19.8 m long by 9.1 m wide for V2. A bare-fallow or grass border of 10 m surrounded each main plot, allowing for movement of farming equipment onto subplot experimental units. Row spacings were 0.76 m wide for corn and soybean (allowing for 40 and 12 rows per subplot in V1 and V2, respectively) and 0.19 m for oat. Alfalfa seed was broadcast.
Crop Rotations and Management Strategies
Detailed descriptions of the management strategies are summarized in Table 1 and reported in more detail by Perillo et al. (1996). Each of the four strategies was managed independently of the other. In general, the ZI strategy involved no purchased inputs other than seed: There were no fertilizers or pesticides of any kind applied in this strategy throughout the course of the trials. Fertilizer or manure was applied to the remaining three strategies according to recommendations of the University of Minnesota Soil Testing Service (e.g., Rehm et al., 1993) to achieve moderate corn and soybean yield goals. The HI strategy assumed a 10% higher yield goal than the LI strategy, and fertilizer rates were adjusted accordingly. These recommendations provided for fertilizer application based on soil organic matter, cropping history, crop to be grown, and yield potential for the crop. Average fertilizer application rates are listed in Table 2. The LI and HI strategies involved the use of commercially available fertilizers and pesticides. Whereas the LI strategy relied principally on banded applications, inputs were broadcast in the HI strategy. Details of the pesticide applications were reported by Kurle and Pfleger (1994). The OI strategy involved practices commonly acceptable for organic certification: the use of manure for fertilization, no synthetic pesticides, and use of untreated seed. For the OI strategy, solid beef manure was fall-applied before corn in the 4-yr rotation and liquid swine manure was spring-applied before corn in the 2-yr rotation. The use of the two manure sources reflects the presence of alfalfa in many dairy and beef operations but not in most swine operations. The N, P2O5, and K2O composition of the solid beef manure averaged 12.2, 5.4, and 13.3 g kg-1, respectively, compared with 8.0, 5.3, and 3.3 g kg-1, respectively, for the liquid swine manure. Under current organic certification guidelines, the 2-yr OI strategy would not be certifiable due to the requirement of a broader crop rotation (USDA–AMS, 2000). Nonetheless, an evaluation of the 2-yr OI strategy with other management strategies (the 2-yr LI and HI strategies in particular) could demonstrate the results of lowering synthetic inputs for conventional growers.
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Planting and Harvest Operations
Corn and soybean planting date depended on management strategy. To better manage weeds without herbicides, corn in the ZI and OI management strategies was usually planted in mid- to late May, approximately 10 to 14 d later than corn in the LI and HI management strategies. Soybean planting usually occurred in late May for the ZI and OI management strategies and 7 to 10 d later than for the LI and HI management strategies. Oat and alfalfa were planted on the same date for all management strategies, typically in mid- to late April. Each year, crop cultivars were the same for all rotations and management strategies in V1 and V2. In the early years, the cultivars included ‘Pioneer Brand 3585’, ‘Hardin’, ‘Don’, and ‘Pioneer Brand 5262’ for corn, soybean, oat, and alfalfa, respectively, whereas in the later years, the cultivars included ‘Pioneer Brand 3730’, ‘IA2021’, ‘Dane’, and ‘Pioneer Brand 5262’ for corn, soybean, oat, and alfalfa, respectively. Seeding rate was approximately 64 000 to 80 000 seeds ha-1 for corn, 370 000 to 400 000 seeds ha-1 for soybean, 81 kg ha-1 for oat, and 12 kg ha-1 for alfalfa over the duration of the trial.
Corn and soybean grain was harvested with a two-row (1.5 m) header on a plot combine from a minimum of 60 m2 in V1 and 20 m2 in V2. Seed yields were adjusted to moisture contents of 155 g kg-1 for corn and 130 g kg-1 for soybean. Oat was harvested by hand, taking four to six 1-m2 quadrants in each subplot. A field-scale combine harvested the remaining plot area after yield estimates had been obtained. The oat straw was baled and removed from the plot area, except in 1989 in V1 when oat was green-chopped and no grain yields were obtained. Alfalfa yields were estimated from an area of no less than 24 m2 in V1 and 12 m2 in V2 after cutting with a forage plot harvester and determining water content from a subsample. A field-scale harvester removed the alfalfa from remaining plot area. Alfalfa harvest did not occur in the year it was underseeded in oat, but in the following year, harvest occurred on at least three dates throughout the growing season, depending on weather conditions and suitability for harvest. Alfalfa forage yield and oat grain yield were converted to a dry weight basis.
Soil and Weed Sampling
Soil samples were taken before the initiation of the trials and from every subplot in the falls of 1992 and 1998. Samples were obtained from the surface 0.3 m of soil. Samples were analyzed by the University of Minnesota soils laboratory for pH, Bray-P1, and K in 1992 and pH, Bray-P1, K, and organic matter in 1998 using standard recommended procedures (Brown, 1998). Every fall, soil samples were taken to a depth of 1.5 m from the subplots going into corn the following year. These samples were analyzed for NO3–N to determine the N fertilization rate.
In 1998, soil samples from the surface 0.2 m were evaluated for the presence of soybean cyst nematode [Heterodera glycines Ichinohe] (SCN). Twenty cores per subplot were complied and analyzed for SCN as described by Chen et al. (2001).
Weed counts of the broadleaf and grass species were determined annually from four to six 0.5- to 1-m2 quadrants within all subplots. In some years, these measurements were taken before the first alfalfa cutting, whereas in other years, they were taken just before corn and soybean harvest. This varied due to available personnel and labor constraints. Analysis of weed data will be reported in a separate publication (Dyck, personal communication, 2002); however, some general trends are presented here to aid in interpretation of results.
Data Analysis
The analysis of yield data across years began in 1993, after the first complete cycle of the 4-yr rotation had occurred. Yield data from each year and across 7 yr (1993–1999) were subjected to analysis of variance (SAS Inst., 1992), and means were separated using Fisher's protected least significant difference (LSD) test at the P = 0.05 level (Kempthorne, 1952). For each crop in V1 and V2, residual plots were checked, and no pattern of increasing variance was detected, indicating homogeneity of variances. For corn and soybean, yields of the 2-yr HI strategy were used as the basis of comparison because the 2-yr HI strategy most closely resembles the practices of the vast majority of producers in the region. For oat and alfalfa, which were grown only in the 4-yr rotation, yields of the HI strategy were compared with yields of the other three management strategies.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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At the beginning of the trials, the soil K level was high enough ( >140 mg kg-1) in both V1 and V2 to be considered nonlimiting for crop production. By 1998, this was still the case, even in the ZI strategy where no K fertilizer was applied (Table 3). In both V1 and V2, soil K levels were greatest in the OI strategies, especially in the 4-yr rotation. The differences observed between the 4- and 2-yr OI strategies with respect to soil P and K levels were most likely due to the differences in manure type. For the 4-yr OI strategy, the manure source was solid beef manure while for the 2-yr OI strategy, the manure source was liquid swine manure. The liquid swine manure had less K relative to P compared with the solid beef manure (Table 2).
By 1998, a decade after the trials began, rotation length and management strategy had no effect on soil organic matter (Table 3). The soil organic matter averaged 44 and 42 g kg-1 in V1 and V2, respectively. Similar values were observed at the start of the trials. A manuscript describing soil quality differences due to rotation length and management strategies is in preparation.
Crop Yields
Corn, soybean, oat, and alfalfa yields in V1 and V2 for each of the two rotation lengths and four management strategies were influenced by year-to-year variability in climatic conditions (Fig. 1–4
, respectively). This is seen in the analysis of variance for corn and soybean, which when averaged across 7 yr from 1993 through 1999, showed significant three-way interactions among year, rotation length, and management strategy (Tables 4 and 5). Because our interests are in overall trends, yield data were summarized across years to better understand trends associated with crop response to rotation length and management strategy over time in spite of these interactions. For corn, the three-way interaction is due in part to a difference in magnitude of response of the ZI strategy relative to the other strategies (Fig. 1). For soybean, the three-way interaction is due in part to a difference in direction of response of the 4-yr OI strategy in 1996 and 1997 (Fig. 2). Analysis of variance for each crop each year highlighted fairly consistent patterns with respect to crop, rotation length, and management strategy (Table 6). Every year, in both V1 and V2, management strategy had a significant (P < 0.05) effect on corn yields and soybean yields, and rotation length had a significant effect on corn yields more often than on soybean yields.
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Corn yield in V2 since 1993 for the 2-yr HI strategy averaged 8.72 Mg ha-1 (Fig. 1). In V2, as in V1, the 4-yr rotations yielded more than the 2-yr rotations in all management strategies except HI. Compared with the 2-yr HI strategy, the 4-yr HI strategy yielded the same, the 2- and 4-yr LI strategy 92 and 98%, the 2- and 4-yr OI strategy 62 and 93%, and the 2- and 4-yr ZI strategy 43 and 88%, respectively.
While corn in the 4-yr OI strategy yielded 91% of the 2-yr HI strategy across the 7 yr in V1, in certain years, yields were comparable (1993, 1995, and 1999), whereas in other years, yields were reduced 10% or more (1994, 1996, and 1997). In V2 across the 7 yr, corn in the 4-yr OI strategy yielded 93% of the 2-yr HI strategy, with yields of the 2-yr HI strategy comparable in certain years (1994, 1995, and 1999), while in other years, yields were reduced 10% or more (1993, 1996, and 1998) compared with the 2-yr HI strategy (Fig. 1).
The treatments with the lowest corn yields in V2 since 1993 were the 2-yr ZI and OI strategies (Fig. 1 and Table 4). Phosphorous levels in V2 were adequate to support relatively high corn yields in the ZI strategies (Table 3). Yield in the 2-yr ZI strategy was hampered by lack of adequate N, whereas low yield in the 2-yr OI strategy was due to difficulties in adequately controlling weed competition. As previously mentioned, weed control was more problematic in the 2-yr OI strategy compared with the 4-yr OI strategy (Table 7).
Soybean
In both V1 and V2 across the 7-yr period from 1993 through 1999, soybean yields in the 4-yr rotations were greater than those in the 2-yr rotations in all management strategies. In V1, yield for the 2-yr HI strategy averaged 2.90 Mg ha-1 (Fig. 2). Compared with the 2-yr HI strategy, the 4-yr HI strategy yielded 103%, the 2- and 4-yr LI strategy 90 and 99%, the 2- and 4-yr OI strategy 80 and 81%, and the 2- and 4-yr ZI strategy 70 and 76%, respectively. In V2, yield for the 2-yr HI strategy averaged 2.74 Mg ha-1 (Fig. 2). Compared with the 2-yr HI strategy, the 4-yr HI strategy yielded 106%, the 2- and 4-yr LI strategy 85 and 103%, the 2- and 4-yr OI strategy 59 and 84%, and the 2- and 4-yr ZI strategy 73 and 85%, respectively.
In both V1 and V2, across the 7-yr period from 1993 through 1999, soybean in the 2- and 4-yr HI strategies consistently yielded as well as or better than the other six treatments (Table 5 and Fig. 2). Although significant differences in any one year between the 2- and 4-yr HI strategies were rarely detected, when averaged across all years, the 4-yr rotation resulted in greater soybean yield than the 2-yr rotation. These differences could not be explained by the presence of SCN, which in 1998, was found in fewer than one-third of the subplots in both trials at levels well below those thought to negatively impact yield. The SCN was detected in 7 and 23 of 72 subplots in V1 and V2, respectively. The highest population density in any one subplot was 238 and 1225 eggs 100 cm-3 soil in V1 and V2, respectively. The presence of the nematode was not associated with either rotation length or management system. In V1, SCN was detected in 3 of 48 subplots in the 4-yr rotation and 4 of 24 subplots in the 2-yr rotation. In V2, SCN was detected in 13 of 48 subplots in the 4-yr rotation and 9 of 24 subplots in the 2-yr rotation. In V1, of the 16 subplots associated with each management strategy, the ZI, LI, HI, and OI strategies had 5, 0, 0, and 2 subplots with SCN, respectively. In V2, of the 16 subplots associated with each management strategy, the ZI, LI, HI, and OI strategies had 4, 4, 5, and 9 subplots with SCN, respectively. Diseases associated with soybean may have been more of a problem in the 2-yr rotation than in the 4-yr rotation, resulting in some of the observed yield differences between the two rotation lengths. Unfortunately, disease incidence and severity were not monitored on an individual subplot basis.
In both V1 and V2, the 4-yr OI strategy yielded well from 1993 through 1996 but poorly from 1997 through 1999 relative to yield of the HI strategies (Fig. 2). While soybean in the 4-yr OI strategy yielded 81% of the 2-yr HI strategy across the 7 yr in V1, in certain years, yields were comparable (1994, 1995, and 1996), whereas in other years, yields were reduced 15% or more (1997, 1998, and 1999). In V2 across the 7 yr, soybean in the 4-yr OI strategy yielded 84% of the 2-yr HI strategy, with yields of the 2-yr HI strategy comparable in certain years (1993 and 1994), while in other years, yields were reduced 15% or more (1997, 1998, and 1999) compared with the 2-yr HI strategy (Fig. 2). From 1993 through 1996, yield in the 4-yr OI strategy was 99 and 96% of the 2-yr HI strategy in V1 and V2, respectively. From 1997 through 1999, however, yield in the 4-yr OI strategy was only 58 and 69% of the 2-yr HI strategy in V1 and V2, respectively. Weed control, particularly in soybean, was especially problematic from 1997 through 1999 in the OI strategies, partly because in 1997, there were continual wet field conditions in June and early July that precluded timely rotary hoeing and cultivation. As in corn, visual observation and weed counts (Huggins et al., 1994) suggested there was more weed pressure in the OI strategies than in the other management strategies (Table 7). Foxtail species, primarily green (Setaria viridis) but also yellow (S. pumila) and giant (S. faberi) foxtail, were the most prevalent weeds. Broadleaf weeds included Canadian thistle [Cirsium arvense (L.) Scop.], smartweed (Polygonum pensylvanicum L.), and milkweed (Asclepias syriaca L.).
Oat
Across the 7-yr period from 1993 through 1999, oat yield in V1 for the 4-yr HI, LI, and OI strategies averaged 1.74 Mg ha-1 (Table 8). Oat yield of the ZI strategy was lower than that of the other management strategies. There was a significant management strategy x year interaction because in 2 yr (1994 and 1998) oat yields were not different between management strategies while in the other years, the 4-yr ZI strategy yielded considerably less than the other management strategies (Table 6 and Fig. 3). Across the same 7-yr time frame in V2, there was no significant difference in oat yield between the four management strategies, which averaged 1.80 Mg ha-1 (Table 8 and Fig. 3).
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Alfalfa
In V1, there was a significant management strategy effect on alfalfa yield in 6 of the 7 yr from 1993 to 1999 (Table 6). Across the 7-yr period, yield in V1 for the 4-yr HI strategy averaged 11.7 Mg ha-1 (Table 8). The LI and OI strategies yielded 93 and 92% of the HI strategy, respectively, with the ZI strategy substantially lower at 54% (as might be expected). In V2, management strategy did not influence alfalfa yield in any year from 1993 to 1999 (Table 6). Across the same time frame, however, yield for the 4-yr HI, LI, and OI strategies averaged 11.3 Mg ha-1 while yield in the ZI strategy was 91% of that in the other three strategies (Table 8).
The apparent large difference in response of alfalfa between V1 and V2 for the ZI strategy relative to the other strategies may be attributable to the lower soil P levels in V1 compared with V2 (Table 3) due to management-induced low fertility at the V1 site before the start of the trial. There was no alfalfa yield difference between the OI strategy and the HI strategy in V2 where, by 1998, soil P levels were not different (Table 3). However, in V1, where the soil P level in the OI strategy was lower than that in the HI strategy, alfalfa yield was reduced. While this difference in soil P level had no effect on oat yield, it apparently negatively influenced alfalfa yield. This is not surprising given that alfalfa has greater P requirements than oat.
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SUMMARY |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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By 1998, the 4-yr OI strategy had no effect on soil organic matter content relative to the 2-yr HI strategy. The 4-yr OI strategy did result in a slight increase of approximately 0.2 pH units compared with the 2-yr HI strategy. Since the trials began, soil P levels in the OI strategies increased at the site with initially very low P fertility (V1) but declined at the other site with initially high P fertility (V2). Soil P levels were positively influenced to a greater extent with the 2-yr OI strategy compared with the 4-yr OI strategy, primarily due to the fertilizer manure source. Soil K levels in the OI strategies increased in both V1 and V2 in response to the manure application.
Averaged across the 7-yr time frame from 1993 through 1999, corn yields in the 4-yr OI strategy were 91 and 93% of the 2-yr HI strategy for V1 and V2, respectively. Soybean yields in the 4-yr OI strategy across that same time frame were 81 and 84% of the 2-yr HI strategy for V1 and V2, respectively. These data show a larger reduction in yield from organically produced soybean relative to organically produced corn in a 4-yr corn–soybean–oat/alfalfa–alfalfa rotation compared with yield in a conventional 2-yr corn–soybean rotation. We suspect this may have been due in part to decreased weed seed production in the OI strategy during the oat/alfalfa–alfalfa phase of the cropping sequence in the 4-yr rotation followed by increased weed pressure during the corn phase. Because soybean followed corn in the rotation, soybean was subjected to a greater weed pressure than the corn.
Corn yield in the 4-yr OI strategy compared with the 2-yr OI strategy was 29% greater in V1 and 50% greater in V2. Corn yield in the 4-yr ZI strategy compared with the 2-yr ZI strategy was greater by 41% in V1 and 106% in V2. Soybean yield in the 4-yr OI strategy compared with the 2-yr OI strategy was not different in V1 and greater by 42% in V2. Soybean yield in the 4-yr ZI strategy compared with the 2-yr ZI strategy was greater by 10% in V1 and 17% in V2. These results indicate external inputs of fertilizer and pesticides mask the true value of crop rotation. One potential way of reducing the amount of external inputs (and associated costs) in a cropping system is to expand the crop rotation into a more diversified crop sequence pattern, thereby taking full advantage of the benefits of crop rotation.
Averaged across the 7-yr time frame, corn yield in V1 for the 4-yr HI strategy was 96% of the 2-yr HI strategy while in V2, corn yields for the 4- and 2-yr HI strategy were the same. Soybean yields for the 4-yr HI strategy were 103 and 106% of the 2-yr strategy for V1 and V2, respectively. These results suggest soybean was more responsive than corn to the expanded rotation length in the HI strategy. Although not examined, it is suspected that soybean diseases may have played a role in the observed soybean yield decline in the 2-yr rotation compared with the 4-yr rotation.
Averaged across the 7-yr time frame, oat yields were similar when produced in the 4-yr OI strategy and the 4-yr HI strategy in both V1 and V2. Alfalfa yield in the 4-yr OI strategy was 92% of that of the 4-yr HI strategy in V1, whereas in V2, the yields were the same. We suspect the reason alfalfa yield in the 4-yr OI strategy was lower than that of the 4-yr HI strategy in V1 was related to the lower soil P levels in V1 relative to V2.
This research documented long-term corn and soybean yield response when grown under OI and HI management strategies. While there was a reduction in both corn and soybean yields in the 4-yr OI strategy compared with the 2-yr HI strategy, the OI strategy had lower production costs than the HI strategy; consequently, net returns, without taking into account organic price premiums, for the two strategies were equivalent (Mahoney, 2001; Welsh, 1999). These results are consistent with those of several other studies conducted at land-grant universities in the Midwest and suggest that organic production systems can be competitive with conventional production systems.
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