Maize Culture in Reed Canarygrass Sod to Renovate Municipal Wastewater Effluent1

Abstract

AbstractField conditions that accompany conventional maize (Zea mays L.) culture may not permit adequate infiltration of wastewater effluent needed for optimum yields. Two experiments with randomized complete block designs were conducted over a 3‐year period on effluenttreated soils to assess the effects of suppressing reed canarygrass (Phalaris arundenacea L.) with several types and rates of herbicides on (a) yields of interplanted maize grain and fodder; (b) total crop yields and N removal by maize‐reed canarygrass combinations; (c) feed quality of interplanted maize; (d) water infiltration capacity of the Typic Hapludoll soil; and (e) the N concentration in the soil water at the bottom of the root zone (just above the water table).Herbicidal suppression of 60% of the reed canarygrass was necessary to obtain maximum grain and fodder yields of the interplanted maize. This degree of suppression was achieved consistently by glyphosate (N‐(phosphonomethy1) glycine) applied at 0.56 kg AI/ha. This treatment holds most promise for use in the type of culture system outlined because: 1) This was the only treatment that suppressed at least 60y0 of the reed canarygrass without completely killing it, 2) The soil under this treatment was capable of sustained infiltration rates of 1.7 cm/hr to prevent the ponding that occurred in killed grass sods, 3) One application of glyphosate was effective over a 2‐year penod. Annually‐applied paraquat (1,l'‐dimethyl‐ 4,4'‐bipyridinium dichloride) at 0.56 kg AI/ha also provided satisfactory (but sometimes lower) yields of maize interplanted in reed canarygrass.Total N removal by maize‐reed canarygrass combinations was maximum when the grass was not suppressed by herbicides. This was due to the superior capacity of reed canarygrass compared to maize to remove N from effluent‐treated soils. The N concentration in the soil water also reflected N removal by the combined crops, in that minimum soil water N occurred when N removal by the crops was maximum. An effluent‐renovation croping system in which maize is interplanted in herbicide unsuppressed reed canarygrass will remove more N but could lead to much lower maize yields than a system where the grass is suppressed.Feed quality of maize ears or fodder was not influenced by degree of reed canarygrass suppression, except for two occasions where the crude protein concentration of fodder and/or ears was reduced, and one occasion where the fodder digestibility was increased, when the grass herbicide‐suppressed or was partly suppressed.