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Published in Agron J 100:591-599 (2008)
DOI: 10.2134/agronj2007.0190
© 2008 American Society of Agronomy
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CROPPING SYSTEMS

Transition from Intensive Tillage to No-Tillage and Organic Diversified Annual Cropping Systems

Perry R. Millera,*, David E. Buschenab, Clain A. Jonesa and Jeffrey A. Holmesa

a Dep. Land Resources and Environ. Sci., Montana State Univ., 334 Leon Johnson Hall, Bozeman, MT 59717-3120
b Dep. Agric. Econ. and Econ., Montana State Univ., 306 Linfield Hall, Bozeman, MT 59717-2920

* Corresponding author (pmiller{at}montana.edu).


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Transition to no-till (NT) and organic (ORG) farming systems may enhance sustainability. Our objectives were to compare transitional crop productivity and soil nutrient status among diversified NT and ORG cropping systems in Montana. Three NT systems were designed as 4-yr rotations, including a pulse (lentil [Lens culinaris Medik.] or pea [Pisum sativum L.]), an oilseed (canola [Brassica napus L.] or sunflower [Helianthus annuus L.]) and two cereal crops (corn [Zea mays L.], proso millet [Panicum miliaceum L.], or wheat [Triticum aestivum L.]). No-till continuous wheat was also included. The ORG system included a green manure (pea), wheat, lentil, and barley (Hordeum vulgare L.) and received no inputs. Winter wheat in the ORG system yielded equal or greater than in the NT systems, and had superior grain quality, even though 117 kg N ha–1 was applied to the NT winter wheat. After 4 yr, soil nitrate-N and Olsen-P were 41 and 14% lower in the ORG system, whereas potentially mineralizable N was 23% higher in the ORG system. After 4 yr, total economic net returns were equal between NT and ORG systems on a per-ha basis. Studying simultaneous transition to diversified NT and ORG cropping systems was instructive for increased sustainability.

Abbreviations: NT, no-till • NTS, system that emphasized only cool-season spring crops • NTW, system that emphasized winter crops • NTD, system that was highly diversified • NTCW, continuous wheat system alternating annually between spring wheat and winter wheat • ORG, organic • PMN, potentially mineralizable N • SOM, soil organic matter


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication June 3, 2007.
   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
IN THE NORTHERN GREAT PLAINS, two farming systems purport increased sustainability compared with tilled wheat-based systems: NT and ORG. No-till is defined here as (i) the absence of any tillage other than a single pass of the seeder at seeding, and (ii) using commercially available fertilizers and pesticides at generally recommended levels. The ORG system uses tillage and is defined by the absence of synthetic fertilizer and pesticide applications in compliance with the USDA National Organic Program standards (National Organic Program, 2007). No-till systems promote efficient water and nutrient use, enhance soil quality, and use crop diversity to manage pests (Blevins and Frye, 1993; Zentner et al., 2002; Stubbs et al., 2004; Lafond, 2005; Dumanski et al., 2006). Organic systems increase self-reliance, may also enhance soil quality, and use crop diversity to manage pest and nutrient cycles (Drinkwater et al., 1998; Gliessman, 1998, p. 299–314; Mader et al., 2002). Only rarely have ORG and NT systems been studied simultaneously within a single experimental context.

A dryland cropping study begun in 1995 at Scott, SK, includes ORG and low and high input NT management systems, managed with three levels of crop diversity, forming a matrix of nine cropping systems (Thomas and Brandt, 2001). Their diversified annual grain level of diversity is most relevant to the study reported here. During the first 6-yr cycle (1995–2000), ORG management resulted in mean crop yields that were about half that for high-input NT management within diversified annual grain systems, under average or drier than average conditions (Brandt and Ulrich, 2001). Reduced yields under ORG management were attributed to greater weed competition, less available soil N, and the inclusion of a lentil green manure crop (i.e., forgone harvested grain during that year). In the diversified annual grain system, net returns for ORG management ranged from $31 ha–1 less (assuming 50% of crops eligible for certified ORG price premiums), to $36 ha–1 greater (assuming 100% of crops eligible for certified ORG price premiums), than under high-input NT management (Zentner et al., 2001). Entz (2006) compared ORG and high-input tillage-based annual cropping systems on a clay soil in subhumid southern Manitoba and found that net returns were $30 ha–1 greater for the ORG system.

Our study implicitly compared NT and ORG systems under an over-arching goal of seeking synergistic knowledge for increased sustainability of both systems during simultaneous transition from an intensively tilled cropping system. Therefore, both the NT and ORG systems used tactical crop diversification, constraining herbicide use in the NT system, and constraining tillage in the ORG system. Our specific objective was to compare agronomic and economic productivity and soil nutrient status among diversified NT and ORG cropping systems that varied the inclusion of cool-season winter and spring crops and warm-season crops.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Site Description
This study was conducted at the Montana State University A.H. Post Research Farm 10 km west of Bozeman, MT (45°40' N, 111° 90' W) from 2000 to 2003. The soil type is a well-drained Amsterdam silt loam (fine-silty, mixed, superactive, frigid Typic Haplustolls), with a soil ORG matter (SOM) concentration of 25 g kg–1, and pH of 7.2 to 7.7 in the surface 0.15-m soil layer. The field site had a tillage history spanning more than 30 yr. During this time, one or more soil-inverting tillage operations were usually performed annually using either a multi-bottom moldboard plow or a heavy-duty offset disk before shallower tillage with a chisel plow and/or field cultivator. Thus, the tillage history could be considered to be more intensive than is typical of the semiarid northern Great Plains during that time. Immediately before this study, spring cereal crops were grown in 1997 and 1998. Following spring wheat harvest in 1998, a deep tillage mulcher was used that consisted of a front gang of heavy offset disks and a rear gang of spikes drawn 0.2 to 0.25 m deep, followed separately by a chisel plow operated approximately 0.1 m deep. In 1999, before spring seeding, the field site received a commercial application of glyphosate herbicide (rate unknown) and no tillage. In 1999, an experimental design including only NT systems was sown to several types of spring broadleaf crops and wheat. In 2000, this design was revised to include the ORG cropping system along with the NT systems in the present study, and they are described below. Monthly total rainfall and average temperature values during 2000 to 2003 are reported in Table 1 .


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  		Table 1. Monthly precipitation and mean temperature values during the crop-year (Sept.–Aug.) at Bozeman, MT, 2000 to 2003.

 
Experimental Design
Five cropping systems were compared; all but the continuous wheat system consisted of four phases, with two phases assigned to cereal crops and two assigned to broadleaf crops (Table 2 ). One NT system included only cool-season spring crops (NTS) while another NT system emphasized winter crops (NTW), intended as a counterpart to the NTS system. One NT system was highly diversified (NTD). It included two cool-season crops (spring pea and winter wheat) and two warm-season crops (sunflower and corn or proso millet). A continuous wheat NT system (NTCW) was included as a control treatment; alternating annually between spring wheat and winter wheat, with only a single phase present each year. The ORG system included two annual legumes (winter pea green manure and spring lentil) and two cereal crops (winter wheat and spring barley). A pigmented spring pea (cv. Arvika), mistaken for Austrian winter pea, was sown in September 1999 in the NTW1 and ORG1 phases and did not survive the winter. Also in the NTW1 phase, winter lentil did not survive adequately in 2001, nor winter pea in 2003. Consequently, NTW1 was sown to the spring counterpart identical to NTS1 in 3 of 4 yr, as footnoted in Table 2. In 2000, the ORG1 phase was reseeded to AC Greenfix chickling-vetch (Lathyrus sativus L.), a spring green manure legume popular with ORG farmers in the northern Great Plains. All phases of all cropping systems were present each year, except for the NTCW system, which alternated between spring wheat and winter wheat. The experimental design was a randomized complete block with four replicates, and cropping systems phases were randomized to plots (experimental units) within each block. Plot size was 7.3 by 14.6 m.


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  		Table 2. Planned phase sequence of four no-till (NT) cropping systems and one organic cropping system at Bozeman, MT, 2000 to 2003.{dagger}

 
Crop Management
Crop-specific management for cultivar, seeding date and rate, and fertilizer N application (excluding ORG system) within all cropping systems is detailed in Table 3 . Complete detail for pesticide and tillage use was too cumbersome to include. Briefly, NT systems generally used fungicidal seed treatments while canola and sunflower seed treatments also had insecticidal activity. Weeds were managed in NT systems via a combination of preseed and postharvest glyphosate application (at rates of 420–560 g a.i. ha–1) and in-crop application of various selective herbicides for broadleaf and/or grassy weed control. Herbicides designed to selectively control grassy weeds in wheat were not used in the diversified NT systems, reflecting the over-arching goal of reducing herbicide inputs in NT systems. It was also a goal of this study to operate the ORG system with reduced tillage. This was accomplished by avoiding postharvest fall tillage unless necessary for late-season weed control and by eliminating tillage between phases ORG4 and ORG1 (i.e., legume green manure was sown directly into standing barley stubble) after 2000. A sparse preexisting infestation of Canada thistle (Cirsium arvense L.) required hand removal of shoots at the bud to flower stage in some ORG cropping system plots to prevent contamination of neighboring plots by wind-blown pappus. Hand-weeding in this manner was effective at preventing spread by seed to neighboring plots, yet ineffective at controlling Canada thistle within the ORG system plots since it increased in extent and severity in those plots from 2000 to 2003. However, during 2000 to 2003 Canada thistle was judged to exert only a minor influence on measured crop yield in the ORG system.


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  		Table 3. Crop management variables used in cropping systems at Bozeman, MT, 2000 to 2003.{dagger}

 
Fertilizer was applied to the NT cropping systems only. The study site has historically proven unresponsive to fertilizer P–K–S application and so these nutrients were applied modestly. Thus, P application rates varied from 5 to 16 kg ha–1, K from 16 to 29 kg ha–1, and S from 6 to 12 kg ha–1, depending on the crop and year. Wheat yields were based on local agronomic knowledge for yield expectations in this environment, corn was presumed to yield similarly to barley, and seed yield expectation for oilseed crops was based on expert opinion from limited research in Montana (Grant Jackson, personal communication, 2000) and extension information in southern Alberta (Doug Moisey, personal communication, 2000). Thus, grain yield targets for canola, corn, sunflower, spring wheat, and winter wheat in the NT systems were set at 2.2, 5.0, 2.2, 4.0, and 4.7 Mg ha–1, respectively. The associated soil nitrate N rates chosen for these crops were 71, 28, 55, 42, and 42 kg ha–1 per megagram of grain yield, respectively. These may represent modest N rates for wheat production in Montana since recommendations currently vary from 44 to 50 kg ha–1 per megagram of targeted winter wheat grain yield, and from 55 to 58 kg ha–1 per megagram of targeted spring wheat grain yield (Jacobsen et al., 2003; G. Jackson, personal communication, 2005). It was our desire to maintain equal N availability between spring and winter wheat to avoid biasing yield potential so we prescribed N as per winter wheat. Despite equal yield targets for canola and sunflower, the N requirement for sunflower was set lower than canola because it was presumed that the deeper rooting system of sunflower would scavenge leached soil nitrate N inaccessible to canola. Estimates of soil available nitrate N were based on soil samples to a 0.6-m depth in cereal and oilseed stubbles from this or adjacent studies managed similarly. After 2000, an additional N credit of 10 kg N ha–1 was attributed to pea or lentil stubbles (Walley et al., 2007). Application rates of N fertilizer were reduced by amounts corresponding to measured soil nitrate N and additional pulse stubble credits. During 2002 to 2003, fertilizer N application to cereal and oilseed crops was split in an attempt to improve N-use-efficiency. Twenty to 30 kg N ha–1 was applied at seeding and the majority was broadcast postemergence preceding forecasted rainfall events (e.g., Zadoks 3.1 in wheat).

Different seeders were used throughout this study according to availability and suitability for NT and ORG cropping systems. In 2000, a locally constructed seeder was used to seed NT plots, with 25-mm-wide knife openers and all dry fertilizer was dribble-banded on top of the seed row from 38-mm-diameter hoses attached to two Gandy applicators mounted on either side of the seeder. After 2000, a commercial custom-fabricated NT plot seeder was used, with disk openers for seed (rear rank) and fertilizer (front rank) application. Fertilizer P-K-S (formulated using various mixtures of different commercial fertilizers) was applied with the seed but most often fertilizer N (urea) was banded 25 mm beside and 25 mm below the seed row to prevent seedling injury. In 2000, a double-disk drill was used to sow tilled ORG system plots, and to sow ORG lentil (ORG3) in 2001. Otherwise, the NT disk plot seeder described above was used to sow the ORG systems. Seeding depth was generally 25 mm below the top of the moist soil to a maximum depth of 50 mm, except for small-seeded canola, which had a targeted seed depth of 13 to 19 mm below the soil surface. Row spacing varied among cropping system phases and years. Generally, a row spacing of 0.26 m was used, with the following exceptions. In 2001, lentil in the ORG cropping system (ORG3) was sown at 0.15-m row spacing due to a desire to increase crop competition by using narrow row spacing. For the same reason, in 2002 and 2003, all ORG cropping system phases used a 0.13-m row spacing. Beginning in 2002, the NT corn (NTD3) and sunflower (NTD4) used a 0.46-m row spacing to promote equidistant plant populations within and between rows. The stand densities for corn (present after 2001) and sunflower were attained by seeding at supra-optimal rates and hand-thinned to desired population densities approximately 1 mo after emergence; 62,000 plants ha–1 for sunflower in 2000 and 2001, and 48,000 plants ha–1 for both crops in 2002 and 2003.

Crop Data
The 7.3-m-wide plots were sown with four passes of a 1.8-m-wide plot seeder but only the central two seeder passes were used for data collection to avoid edge effects from neighboring plots. Shoot biomass was measured by clipping crop plants at the soil surface, with a predetermined number of rows of approximately 1 m in width and 1 m in length, repeated at the front and rear of each plot. Thus, the total sampling area was approximately 2 m2 for each plot to measure shoot biomass. Shoot biomass samples were dried for 72 h (50°C) and dry matter weight obtained. Grain yield was determined by combining an area approximately 1.5 by 14.6 m and calculating the exact area from the number and measured length of harvested crop rows. If necessary, grain samples were dried at 50°C for 72 h. Dry grain samples were cleaned and the dry weight determined by measuring the grain moisture content in a representative subset of samples for each crop. Seed weight was determined by counting and weighing 250 seeds and adjusting for grain moisture content. Grain density was measured by obtaining the net weight of grain held in a standard 0.946-L (1 U.S. quart) container. Grain N content was measured with a LECO CNS analyzer. A conversion factors of 5.7 was used to convert from grain N to protein in all cereal crops (Jones, 1941). Grain N yield was obtained by multiplying the dry weight of the grain by the grain N concentration.

Soil Data
Each plot was divided into four equal rectangles (quadrants). A 0.6-m soil sample was collected from the center of each quadrant of each plot using a 38-mm-diameter soil core 23–29 Mar. 2004 (before spring seeding). The cores were separated into 0- to 0.15-, 0.15- to 0.3-, and 0.3- to 0.6-m sections, and sections from each of the four quadrants were composited. Soil was dried (40°C) and submitted to a laboratory for analysis of Olsen P (Olsen and Sommers, 1982), exchangeable K with inductively coupled plasma–atomic emission spectroscopy (Thomas, 1982), total Kjeldahl N (TKN; Stevenson, 1996), SOM (LECO combustion, Bricklemyer et al., 2005), and DTPA-TEA Zn (Reed and Martens, 1996) in the upper 0.15 m, nitrate N (1 M KCl) with Cd reduction flow injection (Willis, 1980) at all depths, and ammonium N (field moist, 1 M KCl) with phenate flow injection (Mulvaney, 1996), sulfate-S (0.5 M NH4Ac/0.25 M HAc [Tabatabai, 1996]), and potentially mineralizable N (PMN) from the 0- to 0.6-m depth. The PMN analysis blended 5 g of field-moist soil with 12.5 mL of deionized water in a 42-mL centrifuge tube, purged with N2(g), and incubated at 40°C for 7 d (Bundy and Meisinger, 1994). After incubation, 12.5 mL of 2 M KCl was added to the slurry so that the final solution was 1 M KCl. The resulting slurry was shaken for 30 min., filtered (glass fiber, 1.5-µ), and the filtrate analyzed for ammonium N. To calculate PMN, the ammonium N concentration from nonincubated soil was subtracted from the ammonium N concentration from incubated soil.

Each spring (25 Apr.–6 May) the depth of moist soil was determined using a standard 1.1-m (42-inch) Paul Brown soil moisture probe (Brown, 1959) that was modified to 1.4 m in 2003. The probe was inserted four times per plot and the depth of moist soil recorded in a systematic pattern starting at the front of the plot in the west-central seeder pass and proceeding diagonally at intervals toward the rear of the plot in the east-central seeder pass. These four values were averaged to estimate the depth of wet soil per plot. Plant-available soil water was estimated by assuming 125 mm per meter of moist soil depth in this silt loam soil based on the interaction of soil texture and soil water holding capacity (Henry, 2003, p. 111).

Statistical and Economic Analyses
Statistical analysis was conducted with JMP IN (Sall et al., 2005). Grain or seed yield was analyzed with all phases of all cropping systems present and variance was not constant across crop types, so cereal crops were analyzed separately. Cropping system phase effects were considered fixed, while year and replicate were considered random effects. A P value of 0.10 was used to test for statistical significance unless otherwise stated. In most cases, data from 2001 to 2003 were analyzed to ensure a minimum of 1 yr of planned crop sequence history preceding each cropping system phase. The year x phase interaction was significant for all cereal crop analyses and so was used as the error term to determine significance for the cropping system phase effect on crop productivity and grain quality attributes, or for orthogonal contrasts. For comparisons of soil properties between ORG and NT systems, orthogonal contrasts were used and associated P values reported.

Annual net returns were estimated for each cropping system from data on crop inputs used, the machinery operations conducted (tillage, seeding, harvesting, etc.), crop yields and quality, and representative crop prices. The machinery complement assumed was a producer-scale set of equipment representative of large-scale commercial farms in Montana, rather than the experimental plot-scale equipment actually used. The returns for the ORG cropping system were calculated assuming that USDA certification was completed after the required 36-mo transition period, in time for the 2003 harvest (46–47 mo in this study); thus, price premiums were not available between 2000 and 2002 in this study. There is a shortage of available data for ORG price premiums of sufficient detail to reflect relevant prices for grains and oilseeds. Organic prices reflecting regional levels were constructed using a fixed premium over conventional prices for 2003 (the year after certification was achieved). These premiums were obtained from multiple sources, including conversations with ORG producers and buyers (both groups requested anonymity), and with consideration of published sources (Streff and Dobbs, 2004). The ORG premiums above conventional prices were set at 75% for hard red winter wheat, 25% for barley, and 100% for lentils. The ORG barley was judged to not be of sufficient quality to have satisfied malting requirements. Costs and returns were based on updates from published work reflecting surveys of Montana producers (Johnson et al., 1998), on a current spreadsheet-based rotational cost estimation tool (Griffith, 2006), and on a series of interviews with NT, ORG, and tillage-based producers undertaken as part of a related project. Crop prices were updated to relevant levels from sources such as Montana Agricultural Statistics Service (2006), the U.S. Dry Pea and Lentil Association (USA Dry Pea & Lentil Council 2006), the Saskatchewan Department of Agriculture (2006), and private sources. Input prices, particularly for fuel and fertilizer, were updated based on USDA indices published in U.S. Agricultural Statistics (National Agricultural Statistics Service, 2006) and on conversations with several input suppliers in the region. Representative costs for all cropping systems were based on quantities used for all purchased inputs (seed, fertilizer, fuel, a representative machinery repair cost, and herbicide). These costs exclude returns to labor, management, the machinery complement, and land. The net returns are therefore the per-ha funds available to the producer for family living, any hired labor, machinery reinvestment, and a return to land. For simplicity, costs excluded any crop insurance premiums or crop insurance revenues and returns excluded government payments (direct payments, disaster payments, or loan deficiency payments).


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
The climate during this study was drier and warmer than 30-yr average values for Bozeman, MT. Precipitation in each of the four crop-years (Sept.–Aug) ranged from 76 to 97 mm less than the 30-yr average annual precipitation of 421 mm (Table 1). Further, July was warmer than average all 4 yr (average difference was 2.2°C), and August was warmer than average in 3 of 4 yr, including 2 yr with differences greater than 3°C. Thus, these research results need be considered in a climatic context that is drier and warmer than normal at Bozeman. However, annual precipitation for the majority of Montana cropland averages 300 to 350 mm (Padbury et al., 2002) and so this dry context may fortuitously enhance regional applicability.

Crop Production and Quality
Average shoot biomass, grain yield, harvest index, grain density, grain protein concentration, and grain N yield values for cereal phases of all cropping systems were summarized for 2001 to 2003 (Table 4 ). Winter wheat was the only crop common to both NT and ORG systems. A visual qualitative assessment showed that greenness intensity of the winter wheat vegetation was much greater for NT than the ORG winter wheat at heading each year (Miller, unpublished data, 2001–2003). However, the mean shoot biomass and grain yield for winter wheat in the ORG system (ORG2) equaled or exceeded that in the three diversified NT system phases (NTD2, NTW2, and NTW4) (Table 4), despite the fact that winter wheat in the NT systems received an average of 117 kg ha–1 of fertilizer N during 2001 to 2003. Soil water appeared to be the chief limiting factor to winter wheat productivity during these 3 yr. The depth of moist soil measured in ORG2 following the winter pea green manure did not differ from the depth of moist soil under pea or lentil stubble in NTW2, but was greater than NTD2 (pea or lentil stubble preceded by sunflower) or NTW4 (canola stubble) (Table 5 ). Mean harvest indices and grain density (i.e., test weight) were greatest for ORG2, lower for NTW2, and lower yet for NTD2 and NTW4 (Table 4). Low harvest indices and grain densities are an indication that insufficient water was available to the crop to sustain growth to maturity. Even when water equal to ORG2 was available to the crop, such as was the case for NTW2, it appears that summer drought limited yield more strongly than in the ORG system. Thus, it appeared that the visually slower rate of biomass accumulation for winter wheat in the ORG system metered soil water use efficiently under this climatic context, likely due to spring soil nitrate N concentrations that were lower than the fertilized NT systems. Reduced soil nitrate N concentration associated with ORG cropping systems was previously reported by Brandt and Ulrich (2001) at Scott, SK. However, Entz et al. (2001) reported that soil N status was generally adequate on 14 ORG farms in the northern Great Plains.


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  		Table 4. Phase means for productivity and grain quality parameters for cereal crops grown in four no-till (NT) and one organic (ORG) cropping systems at Bozeman, MT, 2001 to 2003.{dagger}

 

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  		Table 5. Depth (m) of moist soil measured in spring with a Brown soil probe following various crops in different phases of no-till (NT) and organic (ORG) cropping systems, Bozeman, MT, 2001–2003.{dagger}

 
Average grain densities (i.e., test weight) in the three winter wheat NT system phases were less than the standard for U.S. No. 1 winter wheat (773 g L–1), averaging 734 g L–1 when preceded by canola, or by sunflower 2 yr previous, and 752 g L–1 when preceded by pea. Thus, grade reduction due to low grain density would have partially offset the value associated with high grain protein for winter wheat in the NT systems. Grain density consistently exceeded this standard in the ORG system. During 2000 to 2003, a simple regression analysis of grain protein in the ORG2 winter wheat showed an apparent decline from 143 to 123 g kg–1 (r2 = 0.15; P = 0.10). However, grain N yield, an integrative measure of soil N uptake, did not trend significantly (r2 < 0.01; P = 0.44) over these 4 yr. Regardless, winter wheat grain protein in the ORG system was at market-acceptable levels (M. Lund, personal communication, 2005). Grain N yield for ORG2 equaled two of three NT system phases where winter wheat was grown, despite adequate N fertilizer application in the NT systems. This suggests that one winter pea green manure crop and one lentil crop harvested for grain in the ORG system was sufficient to offset the average annual N application of 117 kg ha–1 in the NT systems. Straw N yield did not differ between ORG2 and NT winter wheat system phases in 2001, but was 20 to 58 kg N ha–1 higher in the NT system phases in 2002 (P < 0.01; data not shown). Straw N was not measured in 2003. There was approximately 52 mm less precipitation in June 2002 than in June 2001, apparently preventing N translocation from straw to grain in the fertilized NT system. Conversely, ORG winter wheat straw averaged 50% less N than NT winter wheat straw, suggesting that low levels of nitrate in spring, combined with higher levels of mineralizable N (discussed below), may increase grain N-use-efficiency.

Soil Nutrient Concentrations
The ORG system had lower nitrate N (–41%), Olsen P (–14%), exchangeable K (–6%), and sulfate-S (–18%) concentrations (P < 0.1) than in the NT cropping systems (Table 6 ). This was likely due to the lack of fertilization in the ORG cropping system during the previous 4 yr. Greater nitrate N (+58 kg ha–1) in the NT systems reflects N fertilizer practice. This difference in nitrate concentrations likely resulted in lower grain protein concentration in the ORG winter wheat than in the NT winter wheat. Average concentrations of Olsen P, exchangeable K, sulfate-S, and DTPA-TEA Zn were all above critical levels for this location; therefore, these nutrients likely did not affect crop yields. However, it is logical to assume that continued export of nutrients from these plots will eventually impact ORG crop productivity unless replaced with acceptable ORG nutrient sources. In a German study, unfertilized 30-yr-old ORG soil showed two- to three-fold increases in red clover biomass, and subsequent oat productivity, from various P fertilizer treatments in a controlled environment (Romer and Lehne, 2004). That P response was associated both directly with plant nutrition and indirectly with biological N2 fixation in the red clover. This is consistent with a Montana greenhouse study on a 19-yr-old ORG soil that had never been fertilized, where spring wheat shoot biomass was 28% higher (P < 0.05) in soils fertilized with 10 to 30 kg P ha–1 than in the nonfertilized control (Jones, unpublished data). These combined results strongly suggest that ORG systems will require inputs to maintain soil fertility in the long term, and may require the reintroduction of livestock.


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  		Table 6. Mean soil nutrient concentrations for four no-till (NT) systems and one organic (ORG) system after 4 yr at Bozeman, MT, 23–29 Mar. 2004.

 
After 4 yr, the PMN concentration was greater in the ORG than in the NT cropping systems (Table 6). This difference is likely due to both the incorporation of green legume biomass in the ORG soils and increased surface area of both soil ORG aggregates and residue caused by tillage in the ORG system (used for weed control in 3 of 4 yr). Greater PMN concentration in the ORG than in the NT cropping systems would have somewhat offset the lower soil nitrate N concentrations in the ORG cropping system, providing greater release of available N throughout the growing season. It is expected that PMN in the NT systems will increase in the future as SOM accumulates, based on previous reports in the northern Great Plains (McConkey et al., 2002; Lafond, 2005).

Economic Returns
The average net returns per ha for the ORG cropping system were similar to those for the NT systems after 4 yr (Fig. 1 ). Annual net return to specific crops within each cropping system is given in Table 7 . Readers are cautioned that the returns to the entire system are more important to consider than the phase-specific returns to any single crop because each crop has differential benefits and costs to subsequent crops in the system (Ikerd, 2006). In this study, the key dimensions of these costs and benefits in this case are water and N, but may also be related to pest management. For example, sunflower in the NTD system extracted soil water to the greatest soil depth in this study (1.8 m compared with 1.2 m for spring wheat, data not shown) and reduced subsequent pea or lentil yields by 25% compared with that following wheat, and winter wheat yields 2 yr later by 18% compared with that 2 yr after wheat (data not shown). Subsequent crop yield loss following deep-rooted sunflower has been documented previously in the Great Plains (Anderson et al., 1999; Nielsen et al., 1999; Bowman et al., 2000). Conversely, limited soil water extraction and enhanced N cycling by pea or lentil can increase subsequent wheat yields (Miller et al., 2002, 2003; Miller and Holmes, 2005). Readers should also note that comparative net returns among these cropping systems necessarily reflect different sets of crop enterprises.


Figure 1
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  		Fig. 1. Annual and average economic net returns per hectare for an organic and four no-till cropping systems at Bozeman, MT, 2000 to 2003. Assumes no organic premiums from 2000 to 2002.

 

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  		Table 7. Annual phase and whole farm average net returns by cropping system and crop phase.{dagger}

 
As illustrated in Fig. 1, the ORG system benefited from lower input cost levels and crop price premiums in 2003; there were no price premiums for crop years 2000 to 2002 consistent with the USDA's 3-yr transition period for ORG certification. During the 3-yr transition period, the net returns to ORG averaged $87 ha–1 less than for the NT systems, highlighting an important temporal economic challenge for ORG farmers. In 2003, net returns for the ORG system averaged $230 ha–1 greater than for the NT systems. It is noteworthy that glyphosate was inadvertently applied in September 1999 to the plots to be converted to ORG management, which prevented the eligibility of price premiums for the 2002 crop by 1 to 2 mo, markedly reducing profitability under the transition scenario for ORG. In a similar transition to ORG production, Zentner et al. (2001) reported net returns that averaged $31 ha–1 lower for ORG compared with high-input NT, assuming half of the ORG crops were eligible for price premiums, in diversified annual grain cropping systems at Scott, SK. Presumably a similar temporal pattern would have occurred in that study, with years not eligible for ORG price premiums incurring much lower economic returns, than in years following the 3-yr transition period when price premiums were available.

In our study, the standard deviation (and the coefficient of variation) for the ORG cropping system returns of 31.9 (0.23) was within the range of those for the NT systems from 19.5 to 42.8 (0.10–0.25), due to the relatively low returns during 2000 to 2002 (before ORG certification). These results are consistent with Zentner et al. (2001), who reported that income was less variable overall for ORG cropping systems than NT cropping systems in their study, but was more variable than high-input NT management within the diversified annual grains system.

In our study, there was an additional important economic tradeoff not immediately evident in Fig. 1. Producer interviews suggest that labor and management requirements are 30 to 40% higher for ORG farming than for conventional tillage-based farming. These labor and management requirement differences are even greater when comparing ORG and NT farms. Much of this difference is due to increased marketing requirements, directly related to the premiums achieved by ORG producers. Thus, the favorable return per ha achieved under ORG farming is typically coupled with fewer hectares farmed. Conversely, the favorable economic data for 2003 suggest that once the transition period is completed, there may be economic benefits to ORG farming in the northern Great Plains.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Under a drier-than-normal environmental context, winter wheat grown in an ORG cropping system had similar or greater grain productivity and superior grain quality compared with well-fertilized wheat within NT cropping systems. The ORG cropping system generated less net return per ha during transition and greater net return per ha after the 3-yr market transition period. After 4 yr of ORG management without supplemental fertilizer, soil macronutrients were less for the ORG cropping system compared with NT systems that received adequate N fertilizer and modest amounts of P-K-S fertilizer. However, PMN, an indicator of soil N supply ability, was greater for the ORG cropping system. This study had a more general goal of reducing chemical inputs in NT systems and reducing tillage in the ORG system. Through crop diversification, we successfully omitted expensive grassy herbicide applications during wheat phases of the NT cropping systems. We were also able to use crop diversity, by successfully deploying a winter pea green manure, to omit tillage between two annual phases of the ORG system. Further, we were able to avoid postharvest tillage in most ORG cropping phases in most years. In summary, a study of simultaneous transition to diversified NT and ORG cropping systems provided valuable insights for increased agricultural sustainability.


   ACKNOWLEDGMENTS
 
This study was funded by the Montana Agric. Exp. Stn., the Montana Wheat and Barley Committee, and the Montana Fertilizer Advisory Committee. We are grateful for the knowledge input from Bob Quinn in assisting with the design and management of the organic system.

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   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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