Clipping Management and Nitrogen Fertilization of Turfgrass: Growth, Nitrogen Utilization, and Quality

The effect of returning grass clippings on turfgrass growth and quality has not been thoroughly examined. The objective of this research was to determine the effects of returning grass clippings in combination with varying N rates on growth, N utilization, and quality of turfgrass managed as a residential lawn. Two field experiments using a cool-season turfgrass mixture were arranged as a 2 x 4 factorial in a randomized complete block design with three replicates. Treatments included two clipping management practices (returned or removed) and four N rates (equivalent to 0, 98, 196, and 392 kg N ha(-1)). Soils at the two sites were a Paxton fine sandy loam (coarse-loamy, mixed, active, mesic Oxyaquic Dystrudepts) and a variant of a Hinckley gravelly sandy loam (sandy-skeletal, mixed, mesic Typic Udorthents). Returning clippings was found to increase clipping dry matter yields (DMYs) from 30 to 72%, total N uptake (NUP) from 48 to 60%, N recovery by 62%, and N use efficiency (NUE) from 52 to 71%. Returning grass clippings did not decrease turfgrass quality, and improved it in some plots. We found that N fertilization rates could be reduced 50% or more without decreasing turfgrass quality when clippings were returned. Overall, returning grass clippings was found to improve growth and quality of turfgrass while reducing N fertilization needs.

Relationship of Turfgrass Growth and Quality to Soil Nitrate Desorbed from Anion Exchange Membranes

Anion exchange membranes (AEMs) are a potential method for determining the plant available N status of soils; however, their capacity for use with turfgrass has not been researched extensively. The main objective of this experiment was to determine the relationship between soil nitrate desorbed from AEMs and growth response and quality of turfgrass managed as a residential lawn. Two field experiments were conducted with a bluegrass-ryegrass-fescue mixture receiving four rates of N fertilizer (0, 98, 196, and 392 kg N ha(-1) yr(-1)) with clippings returned or removed. The soils at the two sites were a Paxton fine sandy loam (coarse-loamy, mixed, active, mesic Oxyaquic Dystrudepts) and a variant of a Hinckley gravelly sandy loam (sandy-skeletal, mixed, mesic Typic Udorthents). Anion exchange membranes were inserted into plots and exchanged weekly during the growing seasons of 1998 and 1999. Nitrate-N was desorbed from AEMs and quantified. As N fertilization rates increased, desorbed NO3-N increased. The relationship of desorbed NO3-N from AEMs to clipping yield and turfgrass quality was characterized using quadratic response plateau (QRP) and Cate-Nelson models (C-Ns). Critical levels of desorbed NO3-N ranged from 0.86 to 8.0 microgram cm(-2) d(-1) for relative dry matter yield (DMY) and from 2.3 to 12 microgram cm(-2) d(-1) for turfgrass quality depending upon experimental treatment. Anion exchange membranes show promise of indicating the critical levels of soil NO3-N desorbed from AEMs necessary to achieve maximum turfgrass quality and yield without overapplication of N.

Kentucky Bluegrass Response to Potassium and Nitrogen Fertilization

The response of Kentucky bluegrass (Poa pratensis L.) to potassium (K) fertilization has been inconsistent. The objective of this research was to determine the effects of K fertilization across varying nitrogen (N) rates and clipping management on Kentucky bluegrass clipping yields, quality, tissue K concentrations, apparent N recovery, and N use efficiency. A 2 x 4 x 4 factorial was arranged in a splitplot design and repeated across two years. Main plots were clipping treatments (returned vs. removed) and subplots were N rates (0, 98, 196, and 294 kg ha(-1) yr(-1)) in combination with K rates (0, 81, 162, and 243 kg ha(-1) yr(-1)). There was no positive effect of K on clipping yields and quality even though soil extractable K levels tested low. Higher K rates, however, increased N recovery and use efficiency for all but the highest N rate. Tissue K response to K fertilization was nonlinear. Yield and quality responses were not correlated to tissue K concentration. Nonexchangeable K levels were high in the native soil, and may have provided an additional source of K for bluegrass. The results suggest that extractable K values alone may not adequately predict available K to Kentucky bluegrass in this sandy loam soil.

Cool-season turfgrass color and growth calibrated to leaf nitrogen

Tissue N analysis a tool available for N management of turfgrass. However, peer-reviewed calibration studies to determine optimum tissue N values are lacking. A field experiment with a mixed cool-season species lawn and a greenhouse experiment with Kentucky bluegrass (Poa pratensis L.) were conducted across 2 yr, each with randomized complete block design. Treatments were N application rates between 0 and 587 kg N ha-1 yr-1. In the field experiment, clipping samples were taken monthly from May to September, dried, ground, and analyzed for total N. Clippings samples were collected one to two mowings after plots were fertilized. Linear plateau models comparing relative clipping yield, Commission Internationale de l' Eclairage hue, and CM1000 index to leaf N concentrations were developed. In the greenhouse experiment, clipping samples were taken every 2 wk from May to October and composited across sample dates for leaf N analysis. Color and clipping yields were related to leaf N concentrations using linear plateau models. These models indicated small marginal improvements in growth or color when leaf N exceeded 30 g kg-1, suggesting that a leaf N test can separate turf with optimum leaf N concentrations from turf with below optimum leaf N concentrations. Plateaus in leaf N concentrations with increasing N fertilizer rates suggest, however, that this test may be unable to identify sites with excess available soil N when turf has been mowed before tissue sampling.

Extractable Soil Phosphorus Concentrations and Creeping Bentgrass Response on Sand Greens

Few studies have directly related turfgrass growth and quality responses to extractable soil P concentrations in sand greens. A 3-yr field experiment was conducted on a sand-based putting green to determine creeping bentgrass (Agrostis stolonifera L.) growth and quality responses to extractable soil P. Extractable soil P concentrations were obtained by using the modified-Morgan, Mehlich-1, and Bray-1 extractants. Critical extractable P concentrations (above which there is a low probability of response to increasing soil P concentrations) for shoot counts, thatch thickness, relative clipping yields, quality ratings, P deficiency ratings, tissue P concentrations, and root weights were determined using Cate-Nelson (CN) and quadratic response and plateau (QRP) models. Both models fit the data relatively well in most cases (R2 values from 0.12 to 0.89), and critical concentrations for the QRP models were always greater than the CN models. Critical extractable P concentrations were lowest for the modified-Morgan extractant (1.4 to 12.0 mg kg(-1)) and greatest for the Mehlich-1 extractant (14.1 to 63.6 mg kg(-1)). Application of estimated critical extractable P concentrations in this study could be used to substantiate observed responses or explain lack of responses in other previously reported creeping bentgrass P studies. We found better model fits with modified-Morgan extractable P for bentgrass quality ratings, deficiency ratings, and tissue P concentrations than with P extracted by the Mehlich or Bray methods. This suggests that the modified-Morgan extractant may have advantages over stronger-acid extractants when used on sand-based media. The results can be used to revise or update existing P fertilization recommendations for bent-grass grown on sand-based media.

Decomposition Rates and Nitrogen Release of Turf Grass Clippings

Decomposition rates and N release patterns of turfgrass clippings from lawns are not well understood. Litter bags containing clippings were inserted into the thatch layer of a coolseason turf. The experiment was arranged as a 2 × 4 factorial in a randomized complete block design with three replicates. Treatments included four rates of N fertilizer (0, 98, 196, and 392 kg N ha-1 yr-1) and two clipping treatments (returned vs. removed). Litter bags were removed periodically over the growing season and samples were analyzed for biomass, N and C concentrations, and C:N ratio on an ash-free basis. Percentage N loss from the clippings after 16 weeks ranged from 88% to 93% at the 0 and 392 kg N ha-1 rates, respectively, and from 86% to 94% when clippings were removed (CRM) or returned (CRT), respectively. Percentage C loss from the clippings ranged from 94% to 95% at the 0 and 392 kg N ha-1 rates, respectively, and from 92% to 96% with CRM and CRT, respectively. Cumulative N release was similar across N fertilization rates, (ranging from 131 g N kg-1 to 135 g N kg-1 tissue) but was higher for CRT (151 g N kg-1 tissue) than for CRM (128 g N kg-1 tissue). Grass clippings decomposed rapidly and released N quickly when returned to the turf thatch layer. This indicates the potential for reduced N fertilization when clippings are returned. Such rapid decomposition also suggests that the contribution of grass clippings to thatch development is negligible.