Quantifying turfgrass-available N from returned clippings using anion-exchange membranes

Returning clippings can provide N to turf, but the amount of plant-available N derived from clippings is not easy to quantify. An accurate estimate of N released by clippings would be useful in guiding turf N fertilizer recommendations. The objective of this study was to determine if anion-exchange membranes (AEMs) could be used to quantify plant-available soil N when clippings are returned. A greenhouse and two field experiments were set out in randomized block designs using a factorial arrangement of 2 clipping practices [removed (CRM) and returned (CRT)] and 4 rates of N fertilization (0 to 392 kg N ha-1 yr-1) on a cool-season lawn turf. Cumulative N uptake in the clippings was determined and correlated to AEM desorbed NO3-N. Returning clippings resulted in greater overall N uptake and AEM desorbed NO3-N. However, the response of N uptake to AEM desorbed NO3-N was not the same for CRM and CRT treatments. Uptake was greater for CRT than CRM at any given AEM desorbed NO3-N level past the minimum values. This suggests that, in addition to NO3-N, other N forms (most likely NH4-N) are being released from the clippings and taken up by the turf. Anion-exchange membranes alone are not adequate to quantify the plant-available N provided by returned clippings. To accurately assess the total pool of plant-available N to turf when clippings are returned with ion-exchange technology, cation- and anion-exchange resins are needed to quantify the total plant-available N pool derived from clippings