Irrigation and Trinexapac‐Ethyl Effects on Seed Yield in First‐ and Second‐Year Red Clover Stands

Abstract

Irrigation and trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐hydroxymethylene)‐3, 5‐dioxo‐cyclohexanecarboxylic acid ethylester] plant growth regulator (PGR) have been reported to enhance seed yield in red clover (Trifolium pratense L.). This study examined the interaction of irrigation and TE on seed productivity in first‐and second‐year stands in western Oregon (OR). Two field trials were established and followed over a 2‐yr period (2012–2013, 2013–2014). Treatments consisted of an untreated control, and 140, 280, 420, 560, and 700 g a.i. ha−1 TE PGR applied at BBCH growth stages 32 and 51, and in split applications at BBCH 32 + 51. A single irrigation (100 mm) applied at BBCH 55 increased seed yield and weight in first‐and second‐year stands by 13 and 5%, respectively. Seeds m−2 increased nearly 10% with irrigation in both first‐and second‐year stands in 2013 but not in 2014. Application of TE at BBCH 32 increased seed yield by 13.8% in second‐year stands, except at the 700 g a.i. ha−1 rate, and had no effect or reduced seed yield in first‐year stands. Seed weight was reduced by TE at all timings and reductions were proportional to the rate of application. Seeds m−2 increased in first‐year stands with TE rates ≥280 g a.i. ha−1 and ≥420 g a.i. ha−1 in 2012 and 2013, respectively, and with all rates in second‐year stands. There was no interaction between irrigation and TE in any year. First‐ and second‐year stands will likely benefit from irrigation; however, TE only increased seed yield in second‐year stands.Core Ideas Irrigation and trinexapac‐ethyl independently increase red clover seed yield but there is no interaction between the two. Red clover seed yield is enhanced by increasing seed weight with irrigation whereas seed weight is reduced with trinexapac‐ethyl. Irrigation increases seed yield in first‐and second‐year stands but trinexapac‐ethyl only increases seed yield in second year stands.

Factors Underlying Seed Yield in Red Clover: Review of Current Knowledge and Perspectives

“…Management practices that can impact seed yield are, for example, fertilization with phosphorus and potassium (depending on the soil nutrient level and exploitation of the crop) [2], fertilization with boron in B-deficient soils [38], irrigation in arid areas [39,40], and adequate weed and pest control [19]. Clover seed weevils (Apion trifolii and Apion apricans) and the lesser clover leaf weevil (Hypera nigrirostris) can cause heavy seed losses in some years and some locations [41].…”

“…A recently optimized practice is to apply plant growth regulators (PGRs) such as Trinexapac-ethyl-commercially registered as Palisade ® EC or Moddus ® -which inhibit gibberellic acid biosynthesis, resulting in shorter plants, firmer and more upraised stems, more intensive flowering (26-62% more flowers per square m) and easier harvesting [39]. When applied at stem elongation (BBCH 32), increases in seed yield of 9-21% have been reported [39,45,46]. Unfortunately, the effectiveness of Trinexapac-ethyl heavily depends on the accurate timing of the application, the weather conditions after application, and the crops' stress level [45].…”

Trinexapac‐ethyl Affects Seed Production in Crimson Clover

“…Seed set was not affected by TE application rate and timings in crimson clover seed crops in 2015 and 2016 (Table 2). Seed set ranged from 4.4 to 9.2% in 2015 and 2016 and was considered to be low in comparison with results from red clover studies where seed set ranged from 35 to 75% (Anderson et al, 2016).…”

“…The efficiency of dry matter partitioning to seed yield in relation to crop biomass is measured by harvest index (HI). Plant growth regulators have been used in red clover seed crops to increase HI by promoting partitioning to seed in relation to vegetative biomass and to reduce lodging (Anderson et al, 2015, 2016; Silberstein et al, 1996).…”

“…Anderson et al (2015) reported a 9 to 16% seed yield increase in red clover across New Zealand and Oregon environments when TE was applied at Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie (BBCH) 32. Red clover seed yield was increased when TE was applied at BBCH 32 in second‐year stands but not in first‐year stands (Anderson et al, 2016). No studies have investigated the effects of TE on canopy characteristics and seed yield in crimson clover.…”