Field peas and chickpeas are pulse crops often grown as a fallow replacement in western Nebraska dryland cropping systems (wheat-fallow or wheat-corn-fallow). Although the most dominant cropping system is no-till, several farmers observed that tillage prior to planting produced better field pea yields. Possible reasons for increased yields using tillage are earlier and more uniform emergence and canopy development, better weed suppression, extended flowering (reproductive) periods, and uniform maturity and dry down at harvest. 

The objective of this field study was to evaluate effects of tillage on germination patterns and grain yield of three pulse crop/varieties including Frontier (chickpea), Orion (chickpea) and Durwood (yellow field pea). The secondary objective was to develop a predictive emergence model based on the accumulation of heat units or growing degree days (GDD) above a minimum base threshold value. This model could then be used to predict emergence in other areas of Nebraska where field peas and chickpeas are grown. 

Trial Summary

The study was conducted at Henry J. Stumpf International Wheat Research Center at Grant. The predominant soil type in the study area was Kuma silt loam and the previous crop in rotation was corn. The whole study area was sprayed with Spartan Elite on March 11 and the tillage blocks were disked on March 14 using a heavy disk. Prior to planting, chickpea seed was treated with a seed fungicide (Obvious®) and both field pea and chickpea seed were inoculated with full rates of liquid and peat inoculants (Cell-Tech®).

The field pea variety Durwood was planted on March 14 at 350,000 live seeds/ac using a 20 ft. Crustbuster® no-till box drill with 7.5-inch row spacing. The chickpea varieties Frontier and Orion were planted on March 23 at 220,000 live seeds/ac in 15-inch rows using two passes with an eight-row John Deere® planter. Durwood field pea was harvested on July 20. The chickpeas were desiccated using a generic paraquat product on August 10 and harvested on August 17.

Germination

Overall germination of both field peas and chickpeas was slow in 2018, which can be attributed to early planting (mid-late March) in combination with one of the coolest and wettest springs on record (Figure 1). The research area received precipitation from two snowstorms in April and planted crops did not start germinating until late April to early May (36-46 days after planting; Figure 2, Table 1).

Tillage had a positive impact on germination. The germination started, progressed, and finished earlier in tillage treatments, regardless of the pulse crop variety (Table 1; Figure 2). For example, 10%, 50%, and 90% germination for Durwood yellow field pea happened 46, 49, and 54 days after planting, respectively; this was four, two, and three days earlier than 10%, 50%, and 90% germination in the no-till blocks, respectively (Table 1). Two chickpea varieties showed similar trends in germination. Frontier and Orion chickpea finished germinating (90% germination) six and three days later in no-till treatments (Table 1). Frontier under no-till was the last one to germinate on May 10 (Table 1).

Earlier germination in tillage treatments can be attributed to warmer soil conditions as suggested by differences in GDD accumulation (Table 1). The GDD base temperatures varied between pulse crop varieties and were 41°F, 43°F, and 32°F for Orion (chickpea), Frontier (chickpea), and Durwood (yellow field pea), respectively. These predictive models suggest that field peas and chickpeas started to germinate at lower soil temperatures than previously thought (chickpeas at 45°F, field peas at 40°F).

Grain Yield

Tillage increased the crop yield in pulse crop varieties during the 2018 growing season at Grant. Although yields were not significantly different between tillage treatments, Frontier and Orion chickpea yielded 32 and 40 bu/ac in tillage versus 23 and 33 bu/ac in no-till treatment, respectively (Figure 3). Durwood yellow field peas yielded 40 bu/ac under tillage which was a 12 bu/ac yield increase over the no-till treatment that yielded 28 bu/ac (Figure 3).

Recommendations

Spring tillage prior to planting caused faster germination and better yield of field peas and chickpeas as compared to no-till in a field experiment conducted at Grant during the above-average wet and cool 2018 growing conditions. We would caution farmers to carefully examine this practice on their fields, especially when pulse crops are grown on lighter soils and in dryer conditions.

We were able to gather some baseline information on GDD models to predict emergence of pulse crops in terms of base temperatures and GDD accumulation in different tillage treatments. These predictive models need to be validated over more years and locations.

Acknowledgment

Partial funding for this research was provided by the Nebraska Environmental Trust.