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Skip Row Planting

Sunday, April 15, 2007
filed under: Hybrid Selection/Planting

Skip-row planting of crops is not a new concept; but it is receiving renewed evaluation at the Central Great Plains Research Station near Akron, Colo. Motivated by the region’s multi-year drought, USDA-ARS and Colorado State University researchers at the station have undertaken investigations of dryland skip-row corn, sorghum and, most recently, sunflower.

The sunflower evaluation, which began in 2006, is led by ARS soil scientist Francisco Calderon and CSU regional water resource specialist Joel Schneekloth. Schneekloth says the sunflower inquiry was prompted by the promising results of the skip-row corn investigation, which began in 2004 and is headed by Akron ARS research leader and soil scientist Merle Vigil. That work has suggested that a skip-row planting arrangement, as compared to conventional corn rows, has potential for greater yields in drier areas and/or in dry years where corn yields run less than 70 bushels per acre.

Schneekloth explains that a number of dryland producers in the Central Great Plains have moved away from both corn and sunflower in recent years due to the drought. “But with skip row, some are looking at that as a possible way to get back into corn,” he adds. Thus the logical question: How about skip-row sunflower as a vehicle for increasing this crop’s viability under drought conditions?

What is the definition of skip-row planting? It’s a configuration in which one or more rows are omitted in between planted rows, Three approaches have been followed in the corn plots at Akron: (1) plant two rows, skip two rows; (2) plant one, skip one; and (3) plant two and skip one. Variable plant populations were also used in combination with the alternate planting arrangements, since any yield benefits with skip rows can be limited if per-acre populations are too low.

“Moisture utilization” lies at the heart of how skip rows can benefit sunflower and other crops under dry conditions. “As the plant roots down, it will also root out away,” Schneekloth points out. “If we have a larger space for the plant to root away from the row, we can utilize moisture at a later date when it’s critical — like during the reproductive stage.

“Whereas if you have planted in standard 30-inch rows, once those rows meet, that’s the end of the moisture between the rows. So all the plant can do is go down; and if there’s no moisture left going down, it’s ‘out of gas.’ ”

The objectives of the Akron skip-row sunflower study are as follows: (1) Determine sunflower yields for different planting configurations and nitrogen fertilizer combinations. (2) Determine water use by sunflower under the different skip-row treatments. (3) Measure soil and canopy temperatures throughout the late stages of sunflower growth under the various configurations. (4) Test the theory that added N fertilizer will result in the exhaustion of soil moisture prior to seed production (due to more vegetative growth) — which in turn would reduce seed yield and oil content.

The 2006 sunflower planting encompassed three configurations: conventional 30-inch row spacing; plant one/skip one (P1S1) and plant two/skip two (P2S2). The skip-row treatments were combined with two nitrogen rates: low (30 lbs N added) and high (60 lbs N added). The sunflower plots were planted in early June into good wheat stubble.

A population of approximately 14,000 plants per acre was used in all treatments. For the skip-row plots, that came out to an in-row population spacing of about 24,000, or a plant every six to seven inches.

The researchers measured soil moisture weekly during the growing season, utilizing neutron tubes placed in the rows and also between rows, down to a six-foot depth. Data loggers measured temperatures both in the soil and at the plant canopy. The tubes allowed Calderon and Schneekloth to observe the impact of row spacing on moisture extraction in two dimensions. In the conventional plots, 15 inches was the furthest distance a neutron tube was located from the plant row; in the P2S2 plots, tubes were as far as 45 inches away from the nearest row.

From January 1 through early August 2006, Akron received a total of six inches of moisture. Half of that came in July, however — which was great timing for the sunflower plots. That was it until early September, when a heavy rain and runoff saturated the soil profile and resulted in many plants toppling over, particularly in the more top-heavy skip-row sunflower. The toppling was very localized, though, so sufficient plants were left standing for adequate data collection.

At harvest, the highest sunflower yields (Figure 1) came on the conventional sunflower with the lower nitrogen rate. “All skip-row treatments had higher yields than the conventional high-N treatment,” Calderon and Schneekloth report. The best yielding skip-row treatment was the P1SI low-N one, which ended up slightly below the conventional low-N treatment. However, yields between treatments were not significantly different.

Oil content was highest in the conventional ’flowers (Table 2), followed by the skip-row treatments. Added nitrogen rate did not have a clear effect on oil levels.

In an interesting related evaluation, the Akron scientists also decided to measure yield and oil from the “buffer” rows surrounding the study plots. The buffer area was seeded in a plant one/ skip one configuration, but with a lower in-row population similar to that of the conventional treatment plots. “These buffers became interesting because they had obviously large ’flower heads and thick stalks,” note Calderon and Schneekloth. Seed yield on the buffer rows actually ended up being the highest of any treatment (Figure 1). The researchers believe that was due to the added nitrogen actually causing a yield reduction in the conventional and P1SI plots during the hot and dry 2006 season.

The findings on moisture usage, as revealed through the neutron tubes, were quite illuminating. “One of the important questions that we had before starting with this project was whether the sunflower was capable of exhausting the soil water towards the middle of the skip treatments in the P2S2, which had the widest spacing between rows,” the investigators state. As shown in Figure 2, the answer seems to be “yes.” Besides having “a vigorous downward root growth via the taproot,” the sunflower plants were also able to “send roots laterally out to the middle of the P2S2 skips, down to more than five feet deep, before maturity,” they report.

Another dimension was also measured: the amount of biomass at physiological maturity. Calderon and Schneekloth found that the conventional ’flowers had more biomass (Table 1) than the skip-row treatments. However, since the conventional ’flowers had twice the number of rows, the in-row biomass of the conventionals “was actually lower than that of the skip treatments,” as had been expected. The high-N fertilizer did not result in higher biomass in the conventional sunflower; and, in fact, seemed to reduce it.

“We can preliminarily say that our hypothesis that N fertilizer reduces the sunflower yields by causing soil moisture depletion through excessive vegetative growth is not supported by our results,” the Akron researchers indicate, “because our data show that the high-N fertilizer sunflower did not have higher biomass at maturity than the non-fertilized plants.

“It is important to note,” they continue, “that the sudden increase in soil moisture near maturity might have minimized any skip-row or N treatment differences; so more years of data will be needed to elucidate the effects of skip-row versus conventional planting.”

Schneekloth emphasizes that no hard conclusions should be drawn from this single year’s data — especially given the high rainfall event that occurred shortly before crop maturity. He and Calderon plan to conduct at least two more years of skip-row sunflower evaluation before developing firm conclusions and recommendations.

They’re also hoping to utilize findings from the skip-row corn and sorghum research at Akron and elsewhere in order to develop whole-rotation recommendations — for instance, following corn by planting sunflower within the skip-row areas; then perhaps planting sorghum in the skip areas following the sunflower crop. — Don Lilleboe

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