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CHAPTER 2 Perennial Grasses in Cotton and Peanut Rotations in Virginia: Soil Quality Parameters and Crop Growth
Michael Weeks, Jr. and Pat M. Phipps, Tidewater Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Suffolk, VA 23437; Joel C. Faircloth, Dow Agrosciences, Collierville, TN 38017; Mark M. Alley, Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061; and Chris Teutsch, Southern Piedmont Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Blackstone, VA 23824. *Corresponding Author (jmweeks@vt.edu).
Abbreviations: AWC, available water content; CI, cone index; DK, damaged kernel; ELK, extra large kernel; NSA, non-stable aggregates; OK, other kernel; SMK, sound mature kernel; SOM, soil organic matter; TM, total meat; WAE, weeks after emergence; WSA, water stable aggregates
ABSTRACT
Several studies in the southeastern United States have demonstrated benefits of including multiple years of perennial grass in cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) rotations. There has been little research in the Virginia cotton and peanut growing region to examine this effect. The objective of this study was to examine the effects of multiple years of tall fescue (Shedonorus phoenix Scop.) or orchardgrass (Dactylis glomerata L.) in rotation with cotton and peanut on soil quality and annual crop growth. In 2003, eight crop rotations were established with each rotation in peanut the first year. Beginning in 2004, the rotation sequences were continuous cotton, cotton-corn-cotton-peanut, cotton-peanut-cotton-peanut, tall fescue-tall fescue-cotton-peanut, orchardgrass-orchardgrass-cotton-peanut, tall fescue-tall fescue-tall fescue-peanut, orchardgrass-orchardgrass-orchardgrass-peanut, and soybean-cotton-cotton-peanut. Evaluations of soil quality and crop growth were limited to 2006 and 2007 when most of the rotations were in cotton or peanut and crop response could be directly compared between rotations. In 2006, cone index measurements, saturated water infiltration, available water holding content, and carbon and nitrogen content showed few differences between rotations. Cotton following 2 years of perennial grass in 2006 had greater plant height, total nodes, monopodial bolls, and total bolls compared to rotations with only annual crops. Cotton yield was 28% higher following 2 years of either perennial grass compared to all other rotations in cotton in 2006. In 2007, percent water stable soil aggregates was found to be greater following 3 years of either perennial grass compared to any other rotation. In situ moisture content measured during August and September 2007 in selected rotations was higher following 3 years of tall fescue. Based on the addition of nodes, peanut in 2007 displayed greater growth rates following 3 years of perennial grass compared to any other rotation in peanut. Peanut yield in the 3-year perennial grass rotations was higher relative to other rotations and lower where peanut had been grown in the highest frequency over the duration of the crop rotation. The greatest effect on soil quality that may have contributed to yield increases was greater available soil moisture for crop use where the annual crop directly followed a perennial grass crop.
LITERATURE REVIEW
Crop rotation is a beneficial cultural practice for achieving economic and environmentally sustainable agricultural production (Bullock, 1992). An extended interval between the planting of the same annual crop maintains soil quality, decreases input costs, and maintains breaks to prevent soil-borne disease buildup. Common crop rotations in the Southeast region of the United States often include corn (Zea mays L.), soybean [Glycine max (L.) Merr.], wheat (Triticum aestivum L.), cotton (Gossypium hirsutum L.), and peanut (Arachis hypogaea L.) (Franzluebbers, 2007). In the 2007 growing season producers in North Carolina and Virginia planted 668,000 ha of corn, 778,000 ha of soybean, 348,000 ha of wheat, 227,000 ha of cotton, and 45,000 ha of peanut (NASS, 2007).
Studies have reported potential for using perennial grass crops, typically bahiagrass (Paspalum notatum Flueggē), and perennial grass and legume mixes to improve soil quality. Soil quality parameters which may be influenced by perennial grass crops include greater organic carbon (C) sequestration, less soil disturbance, alleviation of soil compaction, increased water stable aggregates (WSA), and increased water infiltration (Wright et al., 2002). Research in the Midwest comparing continuous corn, corn and soybean, oat (Avena sativa L.) and legume meadows, and mixed legume meadow, has shown no significant differences for soil cone index (CI) values to a depth of 15 cm; however, bulk density was 7% higher in annual crop rotations compared to meadow rotations combined (Karlen et al., 2006). In replicated experiments at multiple sites, the latter research also found higher total organic C, total microbial C, and percent WSA in meadow rotations compared to annual crop rotations. Similar results were reported for smooth bromegrass (Bromus inermis Leyss) and switchgrass (Panicum virgatum L.) rotations when compared to corn, soybean, and alfalfa (Medicago sativa L.) rotations in the Midwest where organic C was higher in the 0 – 15 cm and 15 – 30 cm depth following either grass compared to annual crops (Al-Kaisi et al., 2005). Total nitrogen (N) was higher following smooth bromegrass compared to the annual crop rotation. In Uruguay, research utilizing tall fescue (Shedonorus phoenix Scop.), white clover (Trifolium repens L.), and birdsfoot trefoil (Lotus corniculatus L.) rotations showed 2.5 times higher particulate organic C at a depth of 20 –60 cm compared to rotations including sorghum (Sorghum bicolor L.), barley (Hordeum vulgare L.), flax (Linum perenne L.), sunflower (Helianthus annuus L.), and wheat (Gentile et al., 2005).
However, after 38 years of rotation there were no differences in total organic C comparing the pasture rotation to continuous cropping rotations. In another extended cropping systems research project in Uruguay, researchers demonstrated a trend of decreasing soil C content over a 26-year period while annual crops were continuously produced (Prechac et al., 2002). This is in contrast to a production system where 4 years of pasture was followed by 4 years of continuous annual cropping. Soil C content in the Ap horizon in this cropping system showed a pattern of decreasing C over the annual cropping period and then a return to a C content of approximately 4% by the final year of pasture.
In the Virginia cotton and peanut growing region, irrigation is rare and producers typically rely on rainfall and stored soil moisture between rainfall events (J.C. Faircloth, personal communication, 2007). Soil organic matter (SOM) can often have dramatic effects on plant available water or available water content (AWC). In a review of published data on SOM and AWC, it was found that increasing SOM content from 1 to 3% by mass results in a doubling of AWC, particularly where soils were dominated by the sand fraction with a low water holding capacity (Hudson, 1994). Olness and Archer (2005) found a 2.5 to 5% increase in available water content (AWC) with every 1% increase of SOM by mass in soils with less than 40% clay. They conclude that the effects of SOM on AWC are dependent on the adhesion of organic matter onto clay particles creating stronger aggregates, enhanced structure, and stable pores. Increased structure results in not only greater AWC water but also increased infiltration of surface water and resistance to compaction (Hudson, 1994). Infiltration and resistance to compaction is also aided by the extensive soil coverage provided by perennial grasses which reduces the impact of rain-drops, protects soil aggregates, and prevents the sealing of soil pores (Ghadiri and Payne, 1977; Romkens et al., 2001; Kinell, 2005). Crop rotation research in Florida showed higher rates of saturated infiltration for 2 years at the surface and 1 year in the compacted zone in soils under cotton following 2 years of bahiagrass compared to cotton and peanut rotations (Katsvairo et al., 2007a). Further, perennial grasses have the potential to grow deep roots over several seasons, pushing through restrictive plow layers when soil moisture is adequate, which creates channels in compacted zones for roots of row crops to reach moisture below compacted zones (Prechac et al., 2002). According to Elkins et al. (1977), by increasing the rooting depth in sandy coastal plains soils from approximately 15 to 61 cm, days without drought following a saturating rainfall can be increased from 3 to 12 days.
Perennial grasses grown in relatively long rotations (i.e., at least 3 to 4 years of grass) have been observed to be beneficial to plant growth in several crops in the United States, Europe, South America, and Australia including peanut, cotton, sugarcane (Saccharum spp. L.), potatoes (Solanum tuberosum L.), and grain crops (Eltun el al., 2002; Prechac et al., 2002; Wright et al., 2002; Pankhurst et al., 2005; Katsvairo et al., 2006). Early research in Florida examining bahiagrass in peanut rotations reported increases in peanut yields of 684 kg ha-1 following 1 year of bahiagrass compared to peanut following corn (Norden et al., 1977). When peanut followed 4 years of bahiagrass in the latter study, yields were increased by 881 kg ha-1 compared to peanut following corn. In recent research in Florida and Alabama, peanut preceded by 2 years of bahiagrass had higher yields in both irrigated and non-irrigated systems in 2 of the 4 years of the study (Katsvairo et al., 2007b). Differences in cotton yield were only observed in 1 of the 4 years of the latter study where yields were higher following bahiagrass compared to cotton and peanut rotations. Lack of differences was thought to be due to rank cotton growth following bahiagrass. In a related study, cotton following 2 years of bahiagrass had higher total root biomass, area, length, and crown root diameter compared to cotton following peanut; however, yields were similar (Katsvairo et al., 2007a).
Little data exists on the effect of inclusion of cool season perennial grasses in cotton and peanut rotations in Virginia. The objective of this study was to examine changes in soil quality parameters as influenced by crop rotations including perennial grasses compared to crop rotations including only annual crops and if cotton and peanut growth and development expressed any differences observed in soil quality.
MATERIALS AND METHODS
The study was conducted at the Virginia Tech Tidewater Agricultural Research and Extension Center in Suffolk, VA (36° 40’ N, 76° 43’ W). The soil type was Nansemond fine loamy sand (Coarse-Loamy, Siliceous, Subactive, Thermic Aquic Hapludults). Eight crop rotations were arranged in a randomized complete block design with four replications (Table 2.1). Rotations were continuous cotton (Ct-Ct-Ct-Ct), cotton-corn-cotton-peanut (Ct-C-Ct-P), cotton-peanut-cotton-peanut (Ct-P-Ct-P), tall fescue-tall fescue-cotton-peanut (F-F-Ct-P), orchardgrass (Dactylis glomerata L.)-orchardgrass-cotton-peanut (O-O-Ct-P), tall fescue-tall fescue-tall fescue-peanut (F-F-F-P), orchardgrass-orchardgrass-orchardgrass-peanut (O-O-O-P), and soybean-cotton-cotton-peanut (S-Ct-Ct-P). In results and discussion, the underlined letter in rotation abbreviation indicates the crop being grown that season (e.g. F-F-Ct-P for results in 2006 where cotton was the crop grown). Plots were 7.38 m (24 ft) wide by 12.3 m (40 ft) long and soybean, corn, cotton, and peanuts rows were planted on 0.9 m (3 ft) centers. Perennial grasses were planted using a self-propelled walk behind cultapack-type seeder with spacing of approximately 15 cm. Plots transitioning from perennial grass to a row crop were killed with glyphosate in either the proceeding fall or spring. Strip tillage into residue was used prior to planting for rotations transitioning into cotton in 2006 and cotton and peanut in 2007. A ripper – bedder implement was used to create a strip into residue and to make a rip to a depth of approximately 30 cm in one pass prior to planting (Figure 2.1). A second tractor pass was used to plant the annual crop. In 2004, cultivars DP 451 BG/RR, AG 5603 RR, Jessup with the Max-Q endophyte, and WP300 were planted for cotton, soybean, tall fescue, and orchardgrass crops, respectively. In 2005, cultivars DP 451 BG/RR, Pioneer 33M54, and VA 98R were planted for cotton, corn, and peanut crops, respectively. In 2006 the cotton cultivar planted was DP 444 BG/RR. In 2007 cultivars DP 444 BG/RR and variety Perry were planted for cotton and peanut, respectively. Cotton was planted 11 May 2006 and 27 Apr. 2007. Mepiquat Pentaborate (9.6% ai) was applied as a growth regulator in early and late July to all cotton plots at rates of approximately 0.44 L ha-1 (6 oz a-1) to 0.59 L ha-1 (8 oz a-1) depending on extension recommendations (Faircloth et al., 2007b). Peanut was planted 15 May 2007. Fertility, pest, and weed management for cotton and peanut were conducted according to Virginia Cooperative Extension recommendation (Faircloth et al., 2007a; Faircloth et al., 2007b).
Available Water Content and Bulk Density
Available water content and bulk density measurements were made in October 2006 using the methods described by Klute (1986) and Blake and Hartge (1986). Intact soil cores were removed from each plot using 5 cm copper pipe segments with 5 cm diameters, taped end to end to a length of 15 cm. In 2 random locations in each plot, the pipe was driven into the soil using a rubber mallet. Soil cores were then excavated and sliced into 5 cm segments. Measurements of AWC were made on the upper 5 cm segment and lower 5 cm segment of each intact core. Cheese cloth was placed on the bottom of each core to prevent soil from escaping. Cores were placed on a permeable ceramic pressure plate cloth side down. Ceramic plates were selected based on equilibration pressure desired. Cores were saturated for 24 hours by capillary flow from the bottom up and weighed. Available water content was measured using pressure pots equilibrated to 33 kPa (field capacity), 100 kPa, or 1500 kPa (permanent wilting point) in which the pressure plates with cores were placed (Klute, 1986). All cores were subjected to each pressure. After each equilibration period (4 days, 1 week, and 2 weeks, respectively) cores were weighed and re-saturated. After the final equilibration at 1500 kPa, cores were dried and weighed to determine the total water maintained at each pressure as well as bulk density of the soil in each core.
Resistance to Penetration
Soil resistance to penetration was measured following the methods described by Bradford (1986). A data-logging soil compaction meter (Field Scout SC900 Soil Compaction Meter, Spectrum Technologies, Inc. Plain Field, IL) was used to measure CI values at 6 locations selected arbitrarily per plot with the exception of avoiding ripper streaks in strip tillage or row middles where wheel traffic regularly occurred. The data logging soil compaction meter took CI readings at 2.5 cm increments to a depth of 45 cm in kPa. Samples were taken during the season following saturating rain-fall (5 – 10 cm) then allowing 24 hours for drainage to eliminate differences in soil resistance associated with moisture status. Sampling dates were 20 and 28 June 2006 and 7 June 2007.
Carbon and Nitrogen Content
Changes in soil C and N content were measured in 2006 at depths 0 to 7.5 cm and 7.5 to 15 cm. Samples were taken using aforementioned 5 cm diameter copper rings taped end to end, then air-dried for 24 to 48 hours in a 3 cm layer and sieved through a 2 mm (number 10) sieve and then a 180 µm (number 80) sieve (Fisher Scientific Company, Pittsburgh, PA). Total soil C and N levels were determined in duplicate by dry combustion using a VarioMax CNS macro elemental analyzer (Elementar Americas Inc., Mt. Laurel, NJ). In 2007 similar methodology was employed, except samples were limited to depths 0 – 2.5 cm and 0 – 5 cm to increase the chance of observing differences in C and N by decreasing dilution of the sample with soil from lower depths
Stable Soil Aggregates
Percent WSA were measured from each treatment using methods described by Kemper and Rosenau (1986). Each plot was sampled at 4 arbitrarily selected locations to a depth of 2.5 cm. Each sample was spread out to a 3 mm thickness and then air-dried for 24 hours. Following drying, samples were passed through a 2 mm sieve onto a 1 mm sieve to break out aggregates in the 1 to 2 mm size class. Two, 4 g sub-samples were then taken from each larger sample of aggregates. Sub-samples were placed into 0.76 mm sieves and brought to field capacity using a cold air vaporizer. Time to obtain field capacity was initially found by placing dried soil in the vaporizer for varying durations and continuously weighing to indicate the desired level of moisture. This method showed an average time to reach moisture status of 45 minutes which coincided with color change. Samples were then placed in an oscillator (Five Star Cablegation and Scientific Supply, Kimberly, ID). Samples were oscillated into de-ionized water for 3 minutes at a rate of 34 oscillations min-1. Water and soil in each can for each paired sample were washed into drying tins. Samples were then oscillated for 5 minutes in 100 ml of sodium hydroxide (NaOH) solution (2 g L-1) and a rubber spatula was used to crush remaining stable aggregates. Samples were then oscillated for an additional 3 minutes. This process dispersed any WSA and prevented any large sand particles or particulate organic residue from being measured. Sodium hydroxide solution and dispersed soil was washed into drying tins. All H2O and NaOH soil solutions from each sample were then dried at 105°C for 48 hr.
CHAPTER 1: Literature Review
Benefits of Rotation with Perennial Grasses for Soil Quality
Soil Organic Matter and Carbon
Moisture Conservation
Impact of Cultural Tactics on Disease
Crop Rotation and Reduced Tillage for Cotton and Peanut Pathogen and Pest Suppression
Summary
CHAPTER 2: Perennial Grasses in Cotton and Peanut Rotations in Virginia: Soil Quality Parameters and Crop Growth
Abstract
Literature Review
Materials and Methods
Results and Discussion
Conclusions
CHAPTER 3: Perennial Grass in Cotton and Peanut Rotations: Impact on Soilborne Pathogens
Abstract
Literature Review
Materials and Methods
Results and Discussion
Conclusions
CHAPTER 4: Summary and Conclusions
References
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Perennial Grass Based Crop Rotations in Virginia: Effects on Soil Quality, Disease Incidence, and Cotton and Peanut Growth.
