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Results from MSPB-Funded Project 66-2016/17

As stated in a previous blog, one of the objectives of the MSPB is to support the training of agricultural practitioners by providing funds that support graduate research assistants that are affiliated with funded projects. A list of theses and dissertations that have resulted from this effort, along with the names of degree recipients, can be found here.

One such product from this support effort is a thesis titled “Evaluation of narrow row production and twin-row planter errors for furrow irrigated soybean in Mississippi” that was authored by Mr. Richard Smith as part of Project 66-2016/17 under the direction of Dr. John Orlowski, former Soybean Specialist at the MSU-DREC. Results from Chapters I and II of this thesis are summarized below.

Chapter I: Development of a narrow row production system for furrow irrigated soybean in Mississippi

•   Irrigated field-scale experiments were conducted in Hollandale and Stoneville, Miss. in 2016 and 2017 and in Stoneville in 2017. The predominant soil series at both sites was Sharkey clay. Planting dates were Apr. 9 at Stoneville and May 10 at Hollandale in 2016, and Apr. 8 at Stoneville in 2017.

•   At each location, a MG IV soybean variety was planted at a rate of 100, 140, and 180 thousand seeds/acre in a single row on a 40-in.-wide bed (wide), in twin rows spaced 8 in. apart on a 40-in.-wide bed, and in four rows spaced 20 in. apart (narrow) on an 80-in.-wide bed.

•   Canopy closure was measured weekly from early vegetative growth to 95% canopy closure in all treatments, and seed yield was determined at the end of the season. A partial budget analysis was calculated for each treatment combination each year to determine whether or not it would be economical to purchase new planting equipment in order to switch from one row spacing system to another.

•   Row spacing affected canopy closure at all site-years. From 41 to 78 days after planting (DAP), plants in narrow rows formed a quicker canopy than those in wide rows. Plants in twin rows in the early-April plantings at Stoneville had canopy closure patterns similar to plants in the wide rows, whereas plants in the twin rows in the early-May planting at Hollandale had canopy closure patterns similar to plants in the narrow rows. Plants in wide rows never formed a complete canopy at any of the sites.

•   At all three site-years, narrow-row seed yields (87.0, 70.4, and 73.7 bu/acre) exceeded yields from wide rows (75.8, 65.0, and 68.2 bu/acre, respectively). Yields from twin rows were always intermediate to those from narrow and wide rows; they were similar to those from wide and narrow rows in two site-years each.

•   The recommended seeding rate of 140,000/acre resulted in the greatest seed yield in all row spacings. Thus, planting more than 140 thousand seeds/acre in these irrigated plantings would have resulted in lower net returns to seeding rate.

•   The economic analysis indicates that it would be beneficial for Mississippi soybean producers to switch to a narrow row system for soybean production.

Chapter I Take Home Message

The above summary points from these irrigated studies support the following conclusions.

•   Narrow rows should be used to achieve maximum yields from soybean plantings in Mississippi.

•   Using a seeding rate greater than 140 thousand/acre will not result in increased yield and will likely lower net return. This is also the finding from a separate Mississippi study reported here.

•   The magnitude of yield differences found between narrow and wide rows in these experiments, coupled with the economic analyses that determined potential revenue advantages when purchasing a narrow-row planter, indicate that it is economically advantageous to switch to narrow row equipment for Mississippi soybean plantings.

•   These findings are likely specific to soybeans grown and irrigated on the cracking clay soils that will facilitate movement of irrigation water across the 80-in.-wide beds used for the narrow row plantings in these experiments.

Chapter II: Evaluation of planter errors associated with twin row production

•   Irrigated experiments were conducted in 2016 and 2017 at two locations: MSU-DREC at Stoneville, Miss. (Sharkey clay soil), and Monsanto Learning Center, Scott, Miss. (Commerce very fine sandy loam soil). Seeds of four soybean varieties ranging in maturity from MG 4.2 to 5.4 were planted in a twin row arrangement on 40-in.-wide raised beds at 140 thousand seed/acre.

•   Four potential planter error treatments were imposed: NONE–full intended stand with two normal twin rows on adjacent beds; SINGLE–One row of a twin pair missing on the same bed; SEPARATE–one row of a twin pair missing on adjacent beds; WHOLE–both rows of a twin pair missing on the same bed.

•   Canopy closure was determined weekly from emergence to 95% canopy closure. Seed yield was determined in all treatments. A partial budget analysis was conducted to aid with replant decisions when a twin-row planter error occurred. Seed yield losses associated with the above simulated planter errors were compared to replanting costs to determine the feasibility of replanting vs. keeping the affected stand. Expected revenue loss due to the reduced seed yield in each of the above planter errors was compared to the cost of stand termination and replanting.

•    MG affected seed yield in every year in the order of 4.7 > 4.2 > 4.9 > 5.4, and did not interact with planter error treatment.

•   As expected, canopy closure in the NONE treatment was quicker and more complete than that in the WHOLE treatment regardless of soil type. On the clay soil site, canopy closure of the NONE and SINGLE treatments were similar, and closure in the SEPARATE treatment was below that in the NONE and SINGLE treatments and above that in WHOLE. On the sandy loam site, closure in the SINGLE and SEPARATE treatments was below that in the NONE treatment and above that in the WHOLE treatment. As expected, canopy closure by plants growing on the sandy loam site was quicker than canopy closure by plants growing on the clay site.

•   In all of the site-years, seed yield from the NONE and SINGLE treatments were similar and above the yields from the WHOLE treatment. Yields from the SEPARATE treatment were below those from the NONE treatment in three of the four site years.

•   Results from this study indicate that a replant is only warranted when both rows on a single bed are missing, and then only at high soybean prices.

Chapter II Take Home Message

•   On both loam and clay soils, there should be no yield loss if only a single row in a set of twin rows is missing. The plants in the remaining twin row were able to compensate for the missing row. They also provided sufficient canopy development to prevent weed growth.

•   On both loam and clay soils, there will be yield loss if both rows in a set of twin rows on the same bed are missing. Also, the loss of canopy because of the loss of both rows in a twin set will allow weed escapes that will need attention.

•   It is unlikely that the planter errors depicted in this study will occur on a widespread basis in a given field planted in twin rows. Therefore, these results should be applied only to the depicted situation that is widespread in a given field since it is unlikely that a few missing rows in a large field can be replanted easily. That being said, the worst case scenario depicted above (WHOLE) will likely reduce whole-field yield if it occurs on a widespread basis in that field.

•   Modern planters with seed-drop monitors should alert the operator to the above-depicted planter errors before they affect a large planted acreage. If these errors are not corrected as soon as possible, then the above results do indicate that yield loss is likely to occur if more than a single row within a twin-row set is missing.

Composed by Larry G. Heatherly, Aug. 2018, larryheatherly@bellsouth.net