Amino acids have been reported to improve turfgrass growth compared with mineral nutrition; however, amino acid catabolism in plants has not been well studied. A number of turfgrass fertilizers contain amino acids; however, some amino acids may be more effective additives in fertilizers than others. Three amino acids that could be effective nitrogen sources for plant growth are the branched-chain amino acids (BCAAs). The BCAA leucine (L), isoleucine (IL), and valine (V) could be effective additives because they are nonpolar and hydrophobic, which can promote plant uptake of these compounds. Although the effect of exogenously applied BCAA on plant growth is not well known, BCAAs have been reported to increase protein synthesis in humans, and that rate of increase is related to the intake ratio of L to IL and V. The objective of this study was to evaluate the use of L, IL, and V as a nitrogen sources on creeping bentgrass (Agrostis stolonifera) and to investigate the effect of BCAAs on plant growth when all three are applied as a combination. Using specially made rooting tubes, L, IL, and V were applied in a complete factorial and compared with equal urea nitrogen at four rates, as well as an untreated control. Where all three BCAAs were applied in combination, the application ratios of 2:1:1 and 4:1:1 (L:IL:V) were tested. At 63 days after seeding, there were no differences in root length, root weight, or shoot weight; however, BCAA 2:1:1 and 4:1:1 increased creeping bentgrass shoot density by 24% and 32%, respectively, compared with equal urea nitrogen. Where shoot density was increased, nitrogen application rate had no effect. On the basis of these results, BCAAs applied in a complete combination using ratios of 2:1:1 or 4:1:1 (3.03 lb/acre N) will provide a greater creeping bentgrass shoot density compared with equal urea nitrogen.

The Shockwave (Imants) offers the potential to minimally disrupt the playing surface, relieve soil compaction, and potentially lower surface hardness. However, data are lacking on how the Shockwave compares to traditional aerification. The effects of hollow-tine (HT), solid-tine (ST), and Shockwave with a single pass (SW1) and perpendicular passes (SW2) were investigated and compared to an untreated control (C) for surface hardness, surface stability, soil moisture, water infiltration, percent green cover, and bulk density on established cultivar Rush Kentucky bluegrass (Poa pratensis L.) turf growing on native soil. Treatments were applied June-August with SW1 and SW2 receiving an additional treatment in September of each year. A modified Baldree traffic simulator was used to simulate 28 traffic events in the fall of each year. Data were analyzed using an exponential decay model, and the slope indicating cover loss event-1 was used to compare treatments. In both years of the study, the HT (-0.031 in 2017 and-0.085 in 2018) treatment had the least green cover loss per event. The SW2 (-0.051) had the greatest cover loss event-1 in 2017, while the C (-0.102) treatments experienced the largest cover loss event-1 in 2018. In 2017 after 20 simulated traffic events, surface hardness on SW2 treatments were 30% lower than the highest surface hardness. After simulated traffic in 2018, SW1 treatments resulted in 10% lower surface hardness compared to the hardest surface, indicating the Shockwave can reduce surface hardness. This research indicates that the Shockwave could replace ST in maintaining athletic fields.

ADDITIONAL INDEX WORDS. Agrostis stolonifera, fertilizer, golf, percent cover, turfgrass SUMMARY. The branched-chain amino acids (BCAA) leucine (L), isoleucine (IL), and valine (V) are synthesized in plants and are essential to growth in most organisms. These compounds can be absorbed by the plant when foliarly applied, but plant catabolism of BCAA is not completely understood. A recent study observed that BCAA applied in a 2:1:1 or 4:1:1 ratio (L:IL:V) increased creeping bentgrass (Agrostis stolonifera) shoot density compared with applications of equal urea nitrogen (N) at 3.03 lb/acre N. The present study investigated whether those increases could translate to a quicker establishment rate of creeping bentgrass grown from seed in standard greenhouse pots. The BCAA applications were compared with equal N applications using urea and a commercially available amino acid product. All N treatments were applied at 3.03 lb/acre N, per application and applied a total of four times on a 14-day interval starting 14 days after seeding. Measurements included final shoot density counts and root and shoot weights, as well as digital image analysis of percent green cover for each greenhouse pot every 7 days. No differences were observed after 70 days in shoot weight, or percent green cover between BCAA treatments and urea; however, BCAA 2:1:1 and 4:1:1 increased shoot density 21% and 30%, respectively, compared with urea, and were equal to the commercially available amino acid product. Applications of BCAA 4:1:1 also increased creeping bentgrass rooting weight by a factor of 7 compared with urea N.

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Amino acid‐based products have been used as alternative fertilizer nitrogen (N) sources to improve turfgrass performance, especially where there is a strong reliance on synthetic N sources. However, the physiological mechanisms underlying improvements in turfgrass performance are not well documented. The objective of this research was to determine whether applications of a tryptophan‐containing organic byproduct (TRP‐B) or tryptophan (TRP) + urea improve creeping bentgrass (Agrostis stolonifera L.) performance compared with standalone applications of urea, a commonly used synthetic N source. At two separate universities, mature ‘A‐4’ creeping bentgrass plugs were transplanted into containers and allowed to re‐establish in growth chambers before being treated. Treatments included TRP‐B, urea, and TRP + urea applied every 14 d at three different N rates: 2.5, 12.25, and 24.5 kg N ha−1. At the trial's end, TRP‐B and TRP + urea increased leaf indole‐3‐acetic acid (IAA) by 227 and 255%, respectively, relative to urea at the high N rate, as measured at day 42 of the study. Applications of TRP‐B and TRP + urea also increased root biomass by 22 and 20%, respectively, when compared with urea only at the high N rate. The TRP‐B and TRP + urea treatments did not impact leaf total amino acids or photochemical efficiency when compared with urea only. Overall, results indicate that application of TRP‐B or TRP + urea at 24.5 kg N ha−1 every 2 wk may improve leaf and root IAA content, root biomass, and subsequent creeping bentgrass quality relative to applications of urea only.