Information is lacking on the long-term impact of tillage systems on NO3 losses to surface and groundwater. An ll-yr (1982An ll-yr ( -1992 study was conducted to assess NO3 losses to subsurface, tile drainage for corn (Zea mays L.) grown with continuous conventional tillage (CT) and no tillage (NT) on a poorly drained Webster clay loam soil (fine-loamy, mixed, mesic Typic Haplaquoll) at Waseca, MN. Nitrogen was applied at an annual application rate of 200 kg ha-1. Mean annual subsurface drain flow during the ll-yr period was 35 mm higher for NT (315 ram) compared with CT (280 ram). Flow-weighted nitratenitrogen (NO~-N) concentrations increased dramatically in the wet years (1990 and 1991) following the dry period of 1987 to 1989. Flow-weighted NO~-N concentrations during the 11-yr period averaged 13.4 and 12.0 mg L -1 for CT and NT, respectively. Although subsurface drain flow was 12% higher with NT, NO3-N losses were about 5% higher with CT mainly due to higher NO3-N concentrations with CT in the last 2 yr. Corn grain yields and N removal were significantly higher in 6 out of 11 yr with CT compared with NT with no difference between tillage systems in the other 5 yr. Grain yields averaged 8.6 Mg ha -~ with CT and 7.3 Mg ha -~ with NT during the ll-yr period. Multiple regression equations showed that annual flow-weighted NO~-N concentration is best predicted from residual soil NOs in the 0-to 1.2-m profile and spring rainfall while NO3-N flux can be predicted well from May and June rainfall. Results from this long-term study indicate that on this poorly drained soil, CT had a positive effect on corn grain yield and N removal compared with NT, but tillage systems had minimal impact on NO~ losses to subsurface drain flow. Higher drain flow with NT does not necessarily result in higher NO~-N fluxes lost via subsurface drainage.

Land application of dairy (Bos taurus) manure has generated concern regarding the downward movement of nutrients and pathogens from the manure through the soil profile into subsurface drainage water and ultimately to surface waters. The objective of this study was to determine the effect of dairy manure and urea applied at equivalent rates of “available” N on (i) NO3−N, total phosphorus (TP), ortho‐P, NH3−N, and Escherichia coli losses to subsurface tile drainage; (ii) corn (Zea mays L.) production; and (iii) changes in soil test phosphorus (STP) and soil test potassium (STK). Liquid dairy manure and urea fertilizer were broadcast applied at equivalent total “available” N rates ranging from 154 to 224 kg ha−1 yr−1 each fall during 1993–1996. The soil was a poorly drained Webster clay loam (fine loamy, mixed, superactive, Typic Endoaquoll). Nitrate N, TP, and ortho‐P concentrations and NO3−N losses in the subsurface drainage water were not different between the two N sources. Total P exceeded the minimum detection limit in 40 and 52% of the drainage samples from the urea and manured plots, respectively, while only 22 and 35% of the samples had detectable levels of ortho‐P. Losses of TP and ortho‐P were very small and averaged 31 and 10 g ha−1 yr−1, respectively, from the manured plots or <0.02% of the manure‐P applied. Four‐year average corn yields were 0.7 Mg ha−1 greater for the urea treatment compared with dairy manure. Soil test P and STK in the top 20 cm were increased 1 mg kg−1 for every 12 kg P ha−1 and 10 kg K ha−1 applied as manure. We conclude that dairy manure, when applied at optimal rates and incorporated immediately, does not lead to greater losses of N and P in subsurface drainage water on this fine‐textured soil compared with urea.

Phosphorus and K fertilization during the last 30 to 40 yr has led to increased levels of soil test P (STP) and K (STK). Soil test incline rates with continued fertilizer application, decline rates in the absence of fertilizer application, and the critical soil test level for yield response have to be known for long‐term economically and environmentally sound crop production. A 20‐yr study was conducted at two sites to determine: (i) the incline rates of STP and STK during a 12‐yr application period, (ii) the decline rate of STP during an 8‐yr residual period and during a 20‐ yr period on unfertilized plots, and (iii) the critical soil test value corresponding to no yield response to broadcast P or K. Initial Bray P, and exchangeable K soil tests were 22 and 150 ppm, respectively, for a Webster clay loam (fine‐loamy, mixed, superactive, mesic Qpic Endoaquolls) located at Waseca, MN, and 10 and 228 ppm, respectively, for an Aastad clay loam (fine‐loamy, mixed, superactive Pachic Udic Haploboroll) located at Morris, MN. Phosphorus and K were broadcast annually for 12 yr at rates of 0, 50, and 100 lb P2O5/acre and 0,50, and 100 lb K2O/acre. For the Webster soil, STP increased by 0.42 and 1.92 ppm/yr with the 50‐ and 100‐lb P2O5 rates, respectively, and by 0.69 and 2.49 ppm/yr for the Aastad sol Decline rates of STP ranged from as high as 3.3 pp/yr at an initial STP of 40 ppm to 0.4 ppdyr at initial STP of ≤10 ppm. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr,] yields were not increased by broadcast applications of P when STP was >13 ppm on the Webster soil and >19 ppm on the Aastad soil. Year‐to‐year STK variability was very high and precluded calculation of incline or decline rates or the critical STK concentration. These 20‐yr results suggest that crop producers with very high STP levels could refrain from applying P and should use periodic soil testing to monitor the draw‐down of STP. Soil test P can be maintained at 18 to 20 ppm for optimum profitability by applications of 40 to 50 lb P2O5/acre per yr. Research Question Soil test P (STP) and K (STK) have been increasing in Minnesota during the last 30 yr due to P and K fertilization in excess of crop requirements. For longterm profitable and environmentally sound crop production, soil test incline rates with fertilization and decline rates due to crop uptake in the absence of fertilization must be known. The objectives of this study were to determine: (i) the incline and decline rates of STP and STK during a 20‐yr period and (ii) the critical STP and STK concentrations when a corn or soybean yield response to broadcast P or K does not occur. Literature Summary Previous research has indicated that incline and decline rates of STP and STK are a hction of the initial soil test level and the P and K application rates. Subsoil nutrient resources, soil type, the dominant mineral type, and crop uptake also can affect these incline and decline rates. Decline rates are greater as initial soil test levels increase while incline rates tend to be greater at lower s...

Nitrogen placement options for improved N efficiency are limited in ridge‐tillage systems where primary and secondary tillage for fertilizer incorporation is absent. Studies were conducted for 3 yr on a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) in southern Minnesota to determine the effect of placement and time of N application on corn (Zea mays L.) production and postharvest residual soil nitrate (RSN) and to evaluate the spoke‐wheel injector for precise placement of urea‐ammonium nitrate solution (UAN, 28‐0‐0) for corn after soybean [Glycine max (L.) Merr.] in a ridge‐tillage system. Nitrogen as UAN was either band‐applied on the ridge, broadcast, or point injected into the ridge (PINJ‐R) or valley (PINJ‐V) and was compared with anhydrous ammonia (AA) injected into the valley (INJ‐V). Single preplant and pre‐emergence applications were compared with split applications where 30 to 40% was applied preemergence and 60 to 70% was applied at the V7 and V16 growth stages. Leaf N concentration at the Rl stage and whole plant dry matter and N concentration at the R2 stage were generally enhanced by single preemergence applications compared with split applications and by PINJ‐R compared with the PINJ‐V treatment. Grain yield, total N uptake, and net economic return were generally optimized by point injecting UAN and the injection of preplant AA compared with band and broadcast applications of UAN. Split applications did not produce higher yields, N uptake, or net economic return than single preemergence injected applications of N. However, RSN was highest with the V16 application of UAN under these nonirrigated conditions. Three‐year average grain yield and net economic return were highest with the preemergence PINJ‐R treatment. These results suggest that a single preemergence spoke‐wheel application of UAN into the ridge or preplant AA in the valleys can be successfully used to optimize N management and corn production following soybean in a ridge‐tillage system. Nitrogen efficiency will be enhanced and ammonia volatilization will be reduced with these application methods. Research Question Economically profitable and environmentally sound corn production in conservation tillage systems requires excellent N management. Placement options are often limited, however, if no primary or secondary tillage is conducted. The objectives of this study were to: (i) determine the effect of placement and time of N application on corn production and residual soil nitrate (RSN) levels, (ii) evaluate band vs. broadcast and single vs. split applications of N, and (iii) evaluate the spoke‐wheel injector as a tool for precise placement of urea‐ammonium nitrate (UAN) solution for corn following soybean in a ridge‐tillage system. Literature Summary Many studies have cited reduced corn yields and significant volatilization losses of ammonia when urea containing fertilizers, e.g. UAN, are applied to the soil surface and not incorporated in conservation tillage systems. These negative effects are most prevalent in no‐till c...

Increasing emphasis on environmentally sound nutrient management requires an improved understanding of fertilizer P and K needs for profitable crop production. A 20‐yr study was conducted on two glacial till soils to determine: (i) the effect of various P and K rates on corn (Zea mays L.) and soybean (Glycine max (L.) Merr.] yields and profitability during a 12‐yr application phase and an 8‐yr residual phase, and (ii) whether triennial applications of P and K produce crop yields equal to those from annual applications. Initial Bray P1 and exchangeable K soil tests were 22 and 150 ppm, respectively, for the Webster clay loam (tine‐loamy, mixed, superactive, mesic mic Endoaquolls) and 10 and 228 ppm, respectively, for the Aastad clay loam (fine‐loamy, mixed Pachic Udic Haploboroll). Phosphorus and K were applied annually for 12 yr at rates of 0, 50, and 100 lb P2O5/acre and 0, 50, and 100 lb K2O/acre while rates of 150 lb P2O5/acre and 150 lb K2O/acre were applied every third year. Yields were improved by the 50‐ lb P2O5 rate in 6 of 12 yr when the soil test P (STP) was <22 ppm for the Webster soil and in 8 of 12 yr when the STP was ≤10 ppm for the Aastad soil. Yields were not improved further by the 100‐lb P2O5 rate on either soil. Yields from triennial P application were similar to those from annual P application in 23 of 24 siteyr. Annual application of fertilizer K increased yield only in 3 of 24 site‐yr. During the 8‐yr residual period, yields were increased above the control in all 15 site‐yr by carryover from the 541b P2O5 rate. Corn yields were optimized at leaf K concentrations ranging from 1.14 to 2.29%, indicating the importance of knowing nutrient uptake characteristics of hybrids when assessing the K status of corn. Economic return was generally highest with the 150‐lb P2O5 rate applied every third year. Results from this study indicate that most profitable long‐term returns can be obtained with broadcast applications of 150 lb P2O5/acre on a triennial basis and by monitoring STP and soil test K (STK) to take advantage of residual availability. Research Question Economically profitable and environmentally sound crop production requires a better understanding of long‐term fertilizer P and K applications for improved nutrient management. The objectives of this study were to determine the effects of P and K fertilizer rates on corn and soybean yields and profitability during a 12‐yr application phase and a subsequent 8‐yr period to measure the residual effect, and to compare triennial applications of P and K with annual applications of the same total quantity of nutrients. Literature Summary Soil testing lab summaries indicate that soil test P (STP) and K (STK) frequently have been built to High and Very High levels by fertilization during the past 30 to 40 yr. Studies reported during the past 10 yr, however, indicate little, if any, yield response by corn or soybean to fertilizer P and K applications when STP or STK are in the Mediuim or higher range. Some studies have recommended that profits could be i...