The development of sustainable N management systems requires a better understanding of the contribution of on‐farm resources to the active N pool size and its mineralization. This study explores the effect of substrate diversity on improving N supply through mineralization. A “diverse system”, consisting of a corn (Zea mays L.)‐corn–soybean (Glycine max L.)‐wheat (Triticum aestivum L.) rotation with cover crops and fertilized with composted manure was compared with a corn monoculture with conventional fertilizers. Nitrogen mineralization was measured in situ and in laboratory incubations as was the ability of each soil to mineralize added compost and red clover (Trifolium pratense) residue in the 6th and 7th yr of rotation. Net mineralized N in the diverse system was 90 and 40% higher than that in the monoculture at 70 and 150 d of laboratory incubations respectively. Comparable response was found in situ where a 70% higher net mineralization was observed in the diverse system at 70 d. The 70‐ and 150‐d mineralizable N pools increased over time, but the ability of soil organisms to break down additional substrate did not change as a result of system diversity. At 150 d of laboratory incubation, a synergistic effect was observed when 5 Mg ha−1 of compost plus 5 Mgha−1 of clover was added to either soil. The combination of the two organic materials mineralized more N than the sum of their individual mineralization results. A more diverse cropping system may increase the soil's capacity to supply N to a growing crop while maintaining desirable levels of soil organic matter. This is essential for the overall long‐term productivity and sustainability of agricultural systems.

properties (Arshad and Coen, 1992;Yakovchenko et al., 1998). Increasing soil C, the basic constituent of In this study, we investigated the impact of cropping system mansoil organic matter, is an important objective for the agement on C and N pools, crop yield, and N leaching in a long-term sustainable use of soil resources (Lal and Kimble, 1997) agronomic experiment in Southwest Michigan. Four management types, conventional (CO), integrated fertilizer (IF), integrated com-and may have cash value to farmers if a viable system post (IC), and transitional organic (TO) were applied to two crop of CO 2 credits is established. The management of orsequences, a corn (Zea mays L.)-corn-soybean [Glycine max (L.) ganic N is equally important. Mineralization is the pri-Merr.]-wheat (Triticum aestivum L.) rotation and continuous corn, mary source of N in most production systems (Paul and which were grown with and without cover crops in the IF, IC, and Clark, 1996), and a failure to account for the soil's ability TO managements. Using compost as a fertility source and reducing the to mineralize N during the growing season can result use of herbicides and other chemicals resulted in long-term changes in in dramatic overfertilization, N loss, and groundwater soil organic matter pools such TO Ն IC Ͼ IF Ն CO for total C and contamination (Keeney, 1989). A sustainable cropping N and for the labile C and N measured through aerobic incubations system should provide adequate fertility for N-demanding at 70 and 150 d. Mineralizable N varied within the rotation, tending crops while preventing the accumulation of excess soil to increase after soybean and decrease after corn production in all nitrates when leaching is likely to occur. systems. Corn yield was closely associated with 70-d N mineralization potential, being greatest for first-year corn with cover and least for MATERIALS AND METHODS Ecol. Lab., Colorado State Univ., Fort Collins, CO 80523. Received

No abstract

Designing and implementing more productive, nutrient-efficient, and environmentally sound orchard management systems requires a better understanding of plant and soil responses to more biologically driven management practices. This study explored the effect of orchard floor and N management on soil organic C and N, populations of nematodes, NO3 leaching, and yields in tart cherry (Prunus cerasus L. `Montmorency') production. A baseline conventional orchard system consisting of an herbicide-treated tree row and a full rate of N fertilizer was compared to two modified-conventional and ten alternative orchard floor and N management systems. Living ground cover and the use of mulch with or without composted manure increased total C and the active C and N pools in the soil. For instance, supplemental mulch or mulch applied using a side-delivery mower increased soil C by >20% above the conventional baseline. The size of the active C pool increased 45% and 60% with the use of the species mix 2 ground cover and compost, respectively. Increases in the active N pool ranged from a low of 25% in the soils using mulch or a ground cover mix to a high of 60% when compost was used. As a result, the ability of these soils to provide N to growing plants was enhanced. Total soil N increased in the treatment using natural weeds as ground cover and the full rate of N fertilizer. It is likely that weeds were able to convert significant amounts of fertilizer N into organic forms. Increasing the active C and N pools stimulates microbial activity, and may favor populations of nonplant parasitic nematodes over plant parasitic species. Using a trunk-to-trunk cover crop mix under the cherry trees reduced NO3 leaching by >90% compared to a conventional, herbicide treated soil, even when N fertilizer was used at full rate. Nitrate leaching also dramatically diminished when N fertilizer was fertigated at a reduced rate or when compost was used as N source. Alternative orchard floor and N management did not reduce yields when compared to the baseline conventional treatment.