Conservation Tillage Benefits in a Cotton Centered Crop Rotation System

Conservation Tillage Benefits in a Cotton Centered Crop Rotation System

Summary

Tillage used to grow a barley-cotton double-crop was reduced by eliminating tillage prior to planting cotton, eliminating cultivations for weed control in cotton, and especially by eliminating tillage following cotton. Small grain residues increased water infiltration into course textured soils (but not on clay loams) and reduced irrigation advance times sometimes increasing the amount of water used to produce cotton. Weed-sensing, automatic spot-spray technology reduced the amount of spray volume and herbicide used for cotton weed control. Conservation tillage and cotton-small grain double crop rotations were economically competitive with winter-fallow, conventional cotton production using extensive tillage.

Objectives/Performance Targets

1. Evaluate the planting of cotton into cover-crop residues or into small grain crop stubble without preseason tillage.

   Test a weed sensing sprayer and a post-emergence herbicide weed control program in minimum-till cotton.

   Measure changes in soil properties such as organic matter content, crusting, water infiltration and associated changes in fertility and irrigation practices.

   Collect and compare operational, agronomic (i.e., plant growth), and cost data for minimum-till and conventional production systems.

   Disseminate information on alternative production practices.

Accomplishments/Milestones

The feasibility of reducing tillage in irrigated, small grain-cotton double crop rotations in Arizona was studied in experiments conducted on three commercial farms (Fast Track farms, Coolidge; A Tumbling T Ranch, Goodyear; and John Thude Farms Partnership’s Paradise Ranch) and at two University of Arizona experiment stations (Marana and Maricopa Agricultural Centers). Our experiments during the period from fall 2001 to winter 2004 showed that it is possible to substantially reduce the amount of tillage that Arizona’s farmers use to produce these crops. Reductions in tillage are possible in the late-spring transition between small grains and cotton; during the cotton season when tillage for weed control can be eliminated; and in the fall transition from cotton to small grains. We successfully demonstrated the equipment and weed management practices necessary to reduce tillage and have started promoting and demonstrating these practices on commercial farms. The suite of reduced tillage practices we investigated can be adopted separately or in various combinations by growers wishing to reduce tillage and its associated costs thereby facilitating adoption.
Cotton was successfully planted on beds directly into barley cover crop residues and grain crop stubble using standard John Deere MaxEmerge planters equipped with Yetter Farm Equipment 2976 residue manager/coulter assemblies at Coolidge, Maricopa and Marana. The Yetter 2976 residue managers did an excellent job of moving crop residues and cutting a seed line with a fluted coulter resulting in good cotton seed placement in the dry beds at all locations despite the wide range in the amount of residues on the soil surface. At Marana and Maricopa, 200 lb or 100 lb per row unit, respectively, had to be added to the 4-row planters to achieve good operation of the residue managers and soil penetration of the coulter and planter units. In the coarse textured soils at the Coolidge site, good soil penetration of the planter units was obtained without adding extra weight to the grower’s 6-row planter. In general, our results indicated that no-till cotton planting methods did not reduce cotton seedling emergence compared to conventional tillage/planting methods. The Yetter 2967 residue manager/coulters easily shattered and moved the old shredded cotton stalks remaining from previous cotton seasons along with moving small grain crop stubble and residues. Thus, our experiments successfully demonstrated the feasibility of planting cotton into small grain stubble and crop residues without the use of tillage between the grain and cotton crops.

Cotton growth was assessed by harvesting the experiments and comparing cotton lint yields between treatments. At Coolidge in 2002, the minimum tillage treatments with either an oat (1007 lb/A) or barley (1089 lb/A) cover crop substantially out-yielded the conventional tillage system (880 lb/A) in terms of lint production by 14.4% and 23.8%, respectively, due to the greater amount of irrigation water used in these treatments. The reverse was true in 2003 when the minimum tillage treatment yielded 24% less than the conventional tillage treatment yield of 1539 lb/A. At Marana, the no-till and conventionally tilled cotton yields were not statistically different although there was a numerical trend of lower yield in the no-till cotton treatments. At Maricopa, the early-planted no-till cotton yielded less than the early-planted conventionally tilled cotton (956 versus 1141 lb/A) and there was a similar but not statistically significant trend in the late-planted cotton treatments. Similar results were obtained in 2004 at Coolidge, Marana and Maricopa. It appears that in some situations no-till cotton may yield less than conventionally tilled cotton. Possible reasons for this trend of lower yield in no-till cotton are changes in fertilizer and weed control practices and the development of hydraulic hard-pans in the soil. Additional research is required address the possible yield decline in no-till cotton using “strip tillage” techniques to rip the seed-line prior to planting cotton. Limited funding from the Cotton Incorporated (Core and State funds) was obtained for the 2005 season to address the yield issues.

A study was conducted at Maricopa in 2003 and 2004 to assess various straw management strategies during grain harvest prior to no-till cotton planting. Treatments included conventional tillage (winter fallow), two cover crop treatments (beardless barley and Cayuse oats) and several Solum barley treatments harvested for grain but cut at different heights (5, 10, and 18 inches) leaving different amounts of stubble in the field. The cereal biomass prior to harvest was determined in each cover crop or grain crop treatment along with grain yields; there were no significant differences between treatments in any of the measured parameters. In both 2003 and 2004, cotton plant establishment after no-till planting, cotton plant height and HNR, and cotton lint yields were similar in all of the treatments. In addition the 2004 data showed that the treatments did not affect the node at which the first fruiting branch occurred or the node (i.e., fruiting branch) of the first retained boll. These results indicate that the methods we are using for planting no-till cotton are not very sensitive to differences in straw biomass or the height of the standing stubble following grain harvest. Thus, growers that use the Yetter attachments and no-till plant cotton on beds do not have to pay particular attention to straw management.

In the fall transition from cotton to grain, we found that John Deere 1560 & 1590 no-till grain drills were capable of planting a fall small grain crop on beds despite the presence of shredded cotton stalks. The coulter/disk opener assemblies on these grain drills were able to slice through the stalks and place grain seed in the ground even when a grain drill seed-line coincided with an old cotton seed-line and shredded stalks. The hydraulic downward pressure these drills can exert and the weight of the drills make it possible to plant into dry, hard ground. A significant challenge in using no-till grain drills is that they are designed to plant on flat ground making it difficult to obtain an adequate plant population in the drill-lines in the bottom of the furrow. Steel spacers were inserted between the rotating tool bars and the disk opener arms to extend the disk openers in the bottom of the furrow. The use of spacers only marginally improved plant populations and, in general, low plant populations reduced grain yields in our experiments compared to standard commercial grain fields. An alternative approach was tried in fall 2004 with funding from the Arizona Grain Council. A pair of custom rear wheels were manufactured that allowed the John Deere 1590 no-till grain drill to run level and track directly behind the tractor on 36, 38 and 40” rows (i.e., the custom wheels tracked near the bottom of the furrows). In addition, the drill lines in the furrow bottoms (generally two per furrow) were blocked and normal plant populations were planted (i.e., concentrated) in the remaining drill lines on the beds following cotton in the fall of 2004. Results from these demonstrations are pending.

Arizona cotton “plow down” regulations are designed to facilitate pink bollworm control and, as an alternative to extensive tillage, allow growers to plant a small-grain crop following cotton provided it is irrigated in December. (This option is based on data showing that the combination of cold winter temperatures and December irrigation eliminate pink bollworm emergence from the cotton stalks in the spring.) Due to our successful small grain planting demonstrations, several growers expressed interest in no-till planting grain crops following cotton in order to avoid significant tillage costs. Avoiding fall tillage after cotton also has the benefit reducing PM10 dust emissions, which are a significant problem in parts of Arizona. This grower interest led to a small grant from the Arizona Grain Council to start several on-farm demonstrations in fall 2004 to test an alternate planting configuration and allow more farmers to try the John Deere 1590 no-till grain drill that we purchased with non-Federal matching funds.

A weed-sensing, automatic spot sprayer and post-emergence herbicide weed control programs were evaluated during three no-till cotton seasons (2002 to 2004). A 6-row hooded sprayer equipped with Redball model 410 conservation spray-hoods was modified by installing three WeedSeeker automatic spot sprayer units (each with one spray nozzle) from NTech Industries, Inc. in two of the 28 inch wide hoods. Thus, in each pass through the field, the weed-sensing, automatic spot spray system could be compared to conventional continuous spray technology. Roundup Ready cotton varieties were planted at all experiment sites. A proposed preemergence Prowl (pendimethalin) application was not made at any of the study sites because the large amounts of barley residues and stubble present in the conservation tillage plots was thought to be sufficient to bind and inactivate the herbicide before it reached the soil surface. Thus, weed control in all conservation tillage treatments was obtained using postemergence and layby herbicide applications.

WeedSeeker spray units under the Redball 410 hoods were compared to conventional continuous spray nozzles in other 410 spray hoods in terms of the spray volume applied and weed control. The data collected in 2002 to 2004 in Coolidge, Marana and Maricopa showed that the weed-sensing automatic spot spray system could reduce the amount of spray volume and herbicide used by 36 to 63%. The data from Maricopa in 2003 indicated the savings could be much greater (e.g., in the treatment with thick Solum cover crop residues) or much less if volunteer grain germinates after grain harvest. At Maricopa in 2004, the presence of large volunteer cotton in the treatment with Solum barley cover crop residues reduced the savings in spray volume and herbicide used relative to the savings in 2003. In general the weed control data comparing spray systems collected in 2003 and 2004 in Marana and Maricopa indicated that the weed-sensing, automated spot-spray system provided commercially acceptable weed control comparable to that obtained with conventional continuous spray systems for most weed species. However, the data also indicate that for some weed species such as annual sowthistle, morningglory and sprangletop at Marana and watergrass and sprangletop at Maricopa, the automated system did not perform quite as well as conventional continuous spray technology with the postemergence herbicides that we applied. The Coolidge weed control data comparing conventional continuous spray technology with the weed sensing, automatic spot spray systems indicated that under some conditions, the weed-sensing sprayer did not perform adequately.

Factors affecting the performance of the WeedSeeker units included setting of the sensitivity level of the computer controller, the size of the weeds sprayed (and therefore the timeliness of herbicide applications) and the presence of barley cover crop residues that partially cover weed seedlings. A larger calibration spray volume (GPA) and higher pressure may solve some of these problems by improving weed foliage spray coverage. Cumulative weed control evaluations made later in the season at Coolidge, Marana and Maricopa after multiple herbicide applications suggest that it is possible to obtain commercially acceptable weed control in conservation or reduced tillage cotton production systems. However,the weed control data also indicates that controlling weeds in conservation tillage systems remains a challenge and that additional research is needed to develop improved weed control strategies. The registrations of two new herbicides, trifloxysulfuron and flumioxazin, and the introduction of Roundup Ready Flex Cotton will undoubtedly help in this regard.

Soil samples were collected at each site in each plot from the top 6 inches of the soil profile at the start of the experiments in the fall of 2001 to evaluate changes soil properties. Additional soil samples were collected each fall after cotton harvest and in the spring after grain harvest or cover crop termination in conservation tillage treatments to monitor soil organic matter content. As the experiments were modified or new experiments were established, additional soil samples were collected. Separate sets of soil samples were collected at each site and analyzed for textural properties as part of the irrigation studies. It was anticipated that there would be changes in the experiments over time and that laboratory soil analysis results would vary slightly with each laboratory, thus, the soil samples were stored so samples could be analyzed simultaneously to determine changes in soil organic matter over time. The analysis of the soil samples is pending and will be completed in a couple of months.

Water infiltration and irrigation advance times were measured each cotton season to assess the impact of conservation tillage on irrigation practices. Minimum tillage practices were expected to increase infiltration by leaving old root channels and soil cracks intact, allowing the water to flow deeper through the soil vadose. Also, surface organic residues usually slow the advance of the water front resulting in increased opportunity time for infiltration. In some surface irrigation situations, increased infiltration may actually hinder the movement of water down the field, resulting in excessive water use and reduced irrigation efficiency. At Coolidge, Marana and Maricopa, which were furrow irrigated fields, a furrow infiltrometer was used for infiltration assessment; at Goodyear, a double-ring infiltrometer was used. In Coolidge (sandy clay loam soil type), the reduced tillage plots averaged just over 10 inches of water infiltrated in a 4-hr period compared to the conventional plots that infiltrated 4 to 7 inches in the same time period. In Marana where the soil was a clay, the reduced tillage plots infiltrated about the same amount of water as in the conventional tillage plots. In Goodyear where the soil was a silty clay, an average of 1.5 inches of water infiltrated the reduced tillage treatment while 1 inch of water infiltrated the conventional tillage treatment, with both tillage systems approaching steady state within the 4-hr infiltration measurement period. At Maricopa (sandy clay loam), the reduced tillage plots infiltrated 2.4 inches more water then the conventional tillage plots during the 4-hour measurement period. These results indicate that on coarse textured soils, conservation tillage practices did appear to increase infiltration as expected but on a clay soil there was little change in water infiltration rates in response to changing tillage practices.

Field slopes and irrigation advance times were also measured each cotton season. In Coolidge, the average slope for the plots in 2003 was 0.04%, slightly less than the slope measured in 2002. Advance time measurements were difficult to obtain due to continuous leakage into adjacent furrows. However, some data were collected for both treatments in both the wheel and non-wheel furrows allowing for limited comparisons. For example, at the 800 ft. distance in the conventional-tillage, tractor wheel furrow, the water front had arrived in just over 1 hour while the advance of the water front in the conservation or minimum tillage wheel furrow took almost 3.5 hours to reach the same distance. At Maricopa, the field had a slope of 0.00007% indicating that it was basically a level field. The advance times recorded mostly followed the expected pattern with the conventional tillage wheel furrows having the fastest advance times, followed by the conventional tillage non-wheel furrow, conservation tillage wheel furrow and finally the conservation tillage non-wheel furrow that had the longest advance times. In Marana, the 2003 elevation data showed the fields to average about 0.05% slope, slightly lower than the 0.08% measured in 2002. This change in slope may have occurred because of erosion of the top end of the field and movement of soil particles down the furrows. The advance time results were each year with the conventional tillage wheel row having the fastest advance time, followed by the reduced tillage wheel furrow, the reduced tillage non-wheel furrow and the conventional non-wheel furrow. Deep ripping and tillage during the winter might have increased the infiltration and advance times in conventional tillage, non-wheel furrows where the soil was not compacted. Our experience in the fall of 2003 irrigating the field at Marana suggests that number of small grain-cotton double-crop cycles that can be grown will depend on maintaining irrigation efficiency and addressing the potential decline in cotton yields. At Marana after two annual barley-cotton cycles, the head end of the field (i.e., next to the irrigation ditch) was eroded away and was lower than the rest of the field making irrigation difficult. Conversations with growers suggest that at this point they would finish the third barley planting as a grain crop (or plant wheat) and then till and laser-level the field. The amount of slope in furrow-irrigated fields as a function of soil type required to maximize the number of grain-cotton double crop cycles needs to be further investigated.

At the Coolidge, Marana, and Maricopa sites, conservation tillage plots received more water than the conventional plots. At Goodyear, both tillage systems received the same amount of water. Thus, as expected, minimum or conservation tillage practices increased irrigation advance times and the amount of water applied to the cotton crop except that the greater field slope at Goodyear appeared to minimize the effect of tillage practices on irrigation advance times and the amount of water applied. At Coolidge in 2003, the low slope and low flow rate on a sandy soil led to increased water use although the difference was not as great as in the 2002 season. The long set times resulted in an additional 12.5 inches of water being applied in 2003 compared to an additional 21 inches in 2002. At Marana, high clay content and additional crop residues in the conservation tillage plots did not impact irrigation management. At Goodyear, the presence of grain crop residues in the no-till plots helped to slow down the water front, an effect similar to the construction of in-field borders in the conventional tillage plots. The data collected showed that the amounts of irrigation water applied in the conservation tillage and conventional tillage treatments were similar at Marana and Maricopa. This was probably due to the short length of the fields (i.e., irrigation runs) compared to the longer field at Coolidge.

Agronomic data were collected at all experimental sites along with the relevant crop production records from participants and growers. Complete crop production records and other relevant data for the time period from fall 2001 to fall 2003 were sent to our cooperating agricultural economist, Trent Teegerstrom. Project participants have discussed various crop production scenarios to guide Trent in the preparation of crop budgets, and preliminary budgets were prepared in 2004. These crop budgets showed that the barley grain-cotton double crop rotation was economically superior to conventional cotton production but the barley cover crop-cotton double crop system was not economically advantageous for growers. The budgets also showed that tillage costs were reduced but weed control costs were sometimes increased. Record collection through fall 2004 will be completed in the next month and crop budgets will be prepared for dissemination. Partial budgets for the automatic spot spray system will also be produced to allow growers to evaluate the economic factors involved in adopting new spray technology. It is anticipated that these budgets will be published in the University of Arizona College of Agricultural and Life Sciences 2005 Cotton Report. I also anticipate sharing conservation crop budget information with farmers at Extension meetings during 2005.

We have made substantial progress in adapting conservation tillage practices to Arizona conditions and have shared our results with growers at experiment station field days and at Cooperative Extension meetings and workshops for farmers. Specifically field tours were held at the Marana Agricultural Center (2003 & 2004) and at the Maricopa Agricultural center (June and October 2003, October 2004). Our conservation tillage work has also be shared with cotton growers at the Cotton Beltwide Conferences (January 2003, and 2004) and project participants S. Husman and W. McCloskey were invited speakers at the 2004 Western States Conservation Tillage Conference sponsored by the University of California on September 8th & 9th in Five Points, CA. Research reports on our irrigation, crop production and weed management results have been published in the University of Arizona, College of Agriculture and Life Sciences Cotton Report in 2003 and 2004.

Impacts and Contributions/Outcomes

Specific impacts and contributions were due to the publication of two research reports in the University of Arizona, College of Agriculture and Life Sciences 2003 Cotton Report, an additional two publications in the 2004 Cotton Report and the interactions of project participants with Arizona farmers at experiment station field days and Cooperative Extension workshops. The outcomes to date include the continuing enthusiasm of our grower cooperators and the interest of other farmers in conservation tillage practices. The realization that no-till planting of a grain crop following cotton and irrigation in December will meet pink bollworm control regulations prompted one farmer in Marana, Tom Clark, to borrow the John Deere 1560 no-till grain drill and planted a 32-acre field with Solum barley following his 2003 cotton crop. External funding was obtained to purchase a John Deere 1590 no-till grain drill in 2004. External funding was also obtained from the Arizona Grain Council, the Arizona Cotton Growers Association and Cotton Incorporated to continue on farm demonstrations and research with Arizona farmers in 2005. Three farmers used the John Deere 1590 drill to plant grain crops following cotton harvest in fall 2004 with two more growers slated to plant with the drill in January 2005. One farmer purchased a used John Deere 1560 notill grain drill and planted a grain crop in a dead bermudagrass pasture and plans to use it in his cropping systems. Additional farmers seem interested but are still hesitant to adopt new practices and are waiting for us to gather additional data and experience with conservation tillage practices. Discussion of crop budgets for conservation tillage and the associated cost advantages along with the demonstration of better weed control will increase the willingness of farmers to try the system. Without a doubt, we have raised the awareness of Arizona growers regarding conservation tillage practices through our routine contacts with growers, through our grower participants talking to other growers and the more formal activities discussed above. Given the fact that we have been conducting research on conservation tillage practice for only three years, we are encouraged by our progress and look forward to continuing our work another year.

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