Subsurface drainage of gravitational water from the soil profile through tiles is a common practice used to improve crop production on poorly drained soils. Previous research has often shown significant concentrations of nitrate‐N (NO3‐N) in drainage water from row‐crop systems, but little drainage research has been conducted under perennial crops such as those used in the Conservation Reserve Program (CRP). Four cropping systems (continuous corn, a corn‐soybean rotation, alfalfa, and CRP) were established in 1988 to determine aboveground biomass yields, N uptake, residual soil N (RSN), soil water content, and NO3 losses to subsurface tile drainage water as influenced by cropping system. Hydrologic‐year rainfall during the 6‐yr study ranged from 23% below normal to 66% above normal. In dry years, yields were limited, RSN accumulated at elevated levels in all crop systems but especially in the row‐crop systems, soil water reserves and RSN were reduced to as deep as 2.7 m in the alfalfa (Medicago sativa L.) and CRP systems, and tile drainage did not occur. Drainage occurred only in the corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] systems in the year of normal rainfall. In years of excess precipitation, drainage from the row‐crop systems exceeded that from the perennial crops by 1.1 to 5.3X. Flow‐weighted average NO3‐N concentrations in the water during the flow period of this study were continuous corn = 32, corn‐soybean rotation = 24, alfalfa = 3 and CRP = 2 mg/L. Nitrate losses in the subsurface drainage water from the continuous corn and corn‐soybean systems were about 37X and 35X higher, respectively, than from the alfalfa and CRP systems due primarily to greater season‐long ET resulting in less drainage and greater uptake and/or immobilization of N by the perennial crops.

No abstract

No abstract

No abstract

This study quantified the effects of tillage (moldboard plowing [MP], ridge tillage [RT]) and nutrient source (manure and commercial fertilizer [urea and triple superphosphate]) on sediment, NH4+ -N, NO3- -N, total P, particulate P, and soluble P losses in surface runoff and subsurface tile drainage from a clay loam soil. Treatment effects were evaluated using simulated rainfall immediately after corn (Zea mays L.) planting, the most vulnerable period for soil erosion and water quality degradation. Sediment, total P, soluble P, and NH4+ -N losses mainly occurred in surface runoff. The NO3- -N losses primarily occurred in subsurface tile drainage. In combined (surface and subsurface) flow, the MP treatment resulted in nearly two times greater sediment loss than RT (P < 0.01). Ridge tillage with urea lost at least 11 times more NH4+ -N than any other treatment (P < 0.01). Ridge tillage with manure also had the most total and soluble P losses of all treatments (P < 0.01). If all water quality parameters were equally important, then moldboard plow with manure would result in least water quality degradation of the combined flow followed by moldboard plow with urea or ridge tillage with urea (equivalent losses) and ridge tillage with manure. Tillage systems that do not incorporate surface residue and amendments appear to be more vulnerable to soluble nutrient losses mainly in surface runoff but also in subsurface drainage (due to macropore flow). Tillage systems that thoroughly mix residue and amendments in surface soil appear to be more prone to sediment and sediment-associated nutrient (particulate P) losses via surface runoff.

No abstract

The development of cropping systems that use N efficiently requires methods that evaluate system differences in N use. A procedure, based conceptually on soil and plant processes that affect N use, was developed to evaluate differences in N use efficiency among cropping systems. The method uses measurements of yield, grain N, aboveground plant N, applied N, and postharvest inorganic soil N to partition cropping system differences in yield and grain N into N efficiency components. The components consist of N supply, available N efficiency, available N uptake efficiency, N utilization efficiency, grain Naccumulation efficiency, and N harvest index. The N efficiency component analysis was demonstrated for a field study with hard red spring wheat (Triticum aestivum L. ‘WB 906R’) where conventional tillage had a greater yield and grain N than no‐tillage. At low N rates, 78% of the difference in yield between the two was attributed to N supply and available N efficiency components. At high levels of applied N, 88% of the yield difference was attributed to the N utilization efficiency component. Differences in grain N were attributed to N supply and available N efficiency components, whereas components of grain N accumulation efficiency, available N uptake efficiency, and N harvest index were nonsignificant. Overall, this new approach transcends empirical analyses and provides insight into underlying mechanisms of cropping system differences in N use.

No abstract