A soil test for estimating mineralizable N in soil is needed to improve fertilizer use efficiency. Our objectives were to: (i) test the effectiveness of two chemical indices in estimating potentially mineralizable N (N0) in soils, and (ii) determine if these indices could be used to differentiate the impact of cultural practices on the N‐supplying capacity of soils. We collected samples from the 0‐ to 0.15‐m depth of 42 soils representing all agroecological regions in Saskatchewan, Canada. We determined (i) N mineralized (Nmin), N0, and the rate constant (k) by aerobic incubation at 35°C for 24 wk, and (ii) the NH4‐N extracted by (a) 2 M KCl heated at 100°C for 4 h, and (b) a steam‐distilled phosphate‐borate solution buffered at pH 11.2. The association between N0 and the hot 2 M KCl extracted NH4‐N was close (r2 = 0.78, significant at P < 0.001); the relationship between N0 and the phosphate‐borate NH4‐N was slightly less precise (r2 = 0.73, P < 0.001). When NH4‐N extracted with cold 2 M KCl was subtracted from the NH4‐N extracted with hot extractants, the association with Nmin was weaker (r2 ≤ 0.50). The value of k for the 42 soils was generally constant (avg. 0.067 ± Sxt 0.05 = 0.040 wk−1). In a second experiment, we compared the two chemical extractants vs. the N mineralized in a 24‐wk incubation regarding their effectiveness in differentiating the effects of eight 37‐yr crop rotation treatments on N‐supplying capacity. These three indices performed effectively in this regard. For example, the 2 M KCl NH4‐N was closely associated with N mineralized in 24 wk (r2 = 0.92), as was phosphate‐borate NH4‐N (r2 = 0.88; both significant at P < 0.001). We concluded that the chemical extractants may provide a quick test for assessing N‐supplying capacity of the soil.

Electrical conductivity of saturation extracts was related to that of 1:1 and 1:2 (soil:H2O) suspensions and extracts for a wide range of Saskatchewan soils. The conductivity of 1:1 extracts was 1.75 times greater than for 1:1 suspensions and the conductivity of 1:2 extracts was 1.38 times greater than that of 1:1 suspensions. The conductivity of the saturation extract was closely related to all of 1:1 extract or suspension; 1:2 extract or suspension (r = 0.96–0.98). The regression coefficient relating the conductivity of 1:1 and 1:2 extracts and suspensions to that of the saturated paste extract decreased in going from coarse to medium to fine soil textures. The concentrations of Na+, Ca2+ + Mg2+ and Cl− in 1:1 and 1:2 (soil:H2O) extracts were highly correlated with the amounts in the saturation extract (r = 0.93 to 0.99). Key words: Soil salinity, 1:1 and 1:2 suspension and extract, saturated paste

. 1997. Nitrogen contribution of field pea in annual cropping systems. 2. Total nitrogen benefit. Can. J. Plant Sci. 77: 323-331. The total nitrogen (N) benefit of field pea (Pisum sativum ) to a succeeding non-legume crop was measured in a small plot experiment at Scott, Saskatchewan in the moist Dark Brown soil climatic zone, and in a small plot and landscape experiment near Melfort, Saskatchewan in the moist Black soil climatic zone from 1993 to 1995. The total N benefit was calculated as the difference in net N mineralized from soil plus N in the above-and below-ground crop residue between field pea and non-legume stubble-cropped plots over the growing season. Landscape slope position did not affect the total N benefit of field pea to a succeeding wheat crop, and preseeding tillage had an inconsistent effect on the total N benefit between years. The direct N benefit of field pea aboveground residue available to the succeeding crop in the landscape experiment was a minor component of the total N benefit, which averaged 25 kg N ha -1 . The total N benefit was equivalent to the N residual effect, defined as the amount of fertilizer N required for a non-legume crop grown on non-legume stubble to achieve the same yield as that of the non-legume crop on field pea stubble. This confirms that the N residual effect of field pea to the succeeding non-legume crop was due to the N contribution; any non-N contribution to the N residual effect was effectively excluded. Key words: Pisum sativum, Triticum aestivum, Hordeum vulgare, Brassica rapa, Linum usitatissimum, total nitrogen benefitBeckie, H. J., Brandt, S. A., Schoenau, J. J., Campbell, C. A., Henry, J. L. et Janzen, H. H. 1997. Apport d'azote par le pois de grande culture à la sole suivante. 2. Gain total de N. Can. J. Plant Sci. 77: 323-331. Le gain total de N laissé par une culture de pois sec (Pisum sativum) pour une culture non-légumineuse suivante a été mesuré de 1993 à 1995. L'expérience était réalisée en petites parcelles à Scott (Saskatchewan) dans la zone semi-aride à sols brun foncé et en petites parcelles ainsi et en grandes parcelles paysagères près de Melfort, dans la zone subhumide à sols noirs. Le gain total de N correspond à la différence entre le N minéralisé par le sol plus N contenu dans les restes de cultures laissés pour la culture suivante par une sole de légumineuse, et celui laissé par une culture non-légumineuse. L'emplacement sur la pente n'avait pas d'effet sur le gain total de N dû au pois de grande culture pour la culture de blé suivante, tandis que l'effet de la préparation culturale du lit de semence variait d'un an à l'autre. Les avantages directs du N contenu dans les restes de cultures laissés en surface pour la culture suivante dans l'expérience en parcelles grandeur réelle n'était qu'un composant mineur du gain total de N, lequel se montait en moyenne à 25 kg N ha -1 . Le gain total de N était équivalent à l'arrière-effet de N, lequel est la quantité d'engrais N requise pour une culture non-légumineuse pour produire autant après ...

Eastern gamagrass [Tripsacum dactyloides (L.) L.] is a native perennial warm‐season grass with the potential to produce high yields of high quality forage. There is, however, little information on the response of eastern gamagrass to different harvest intervals and N rates. The objective of this research was to evaluate the forage yield, crude protein concentration, and total N removal by eastern gamagrass using different harvest intervals and N rates at two sites in northern Missouri. At Elsberry and Clifton Hill, MO, established stands of ‘PMK‐24’ eastern gamagrass were burned prior to green‐up each spring. Individual plots were randomly assigned either a 4‐ or 6‐wk harvest interval and five N rates (0, 50, 100, 150, or 200 lb N/acre) as ammonium nitrate and were evaluated in each harvest interval. In 1991 and 1992, total N and crude protein concentrations were determined on harvested forage and total N removal was estimated. Total forage yields were greater with the 6‐ than the 4‐wk harvest interval at Elsberry all 3 yr, and in 1 of 3 yr at Clifton Hill. In 1991, total forage yields did not increase with N rate with either harvest interval at Elsberry, nor the 6‐wk harvest interval at Clifton Hill. In 1992 and 1993, total forage yields increased linearly with N rate at Clifton Hill, and curvilinearly with N rate at Elsberry. Forage crude protein concentrations were consistently greater with the 4‐ than the 6wk harvest interval at both sites in 1991 and 1992. In general, forage crude protein concentrations increased linearly with N rate with both harvest intervals. In 1991, up to 200 lb N/acre was removed with the harvested forage at both sites. Total N removal increased linearly with N rate with both harvest intervals in 1991 and 1992 at Clifton Hill, but total N removal was variable at Elsberry. For grazing, a 4‐wk harvest interval will provide animals with higher protein forage. For hay production, a 6‐wk harvest interval may provide greater forage yields with fewer harvests. Research Question Eastern gamagrass is a native perennial warm‐season grass with the potential to produce high yields of high quality forage with multiple harvests during the growing season. Warm‐season grass forage yield and crude protein concentration can be increased by N fertilization. With multiple forage harvests, greater N rates may be needed to maintain high forage yields and crude protein concentrations. There is, however, little information on eastern gamagrass forage yield, protein concentration, or N removal under different harvest intervals and N fertilization rates. The objective of this research was to determine appropriate harvest intervals and N rates for eastern gamagrass in northern Missouri. Literature Summary In southern Illinois, eastern gamagrass forage yields ranged from 6690 to 21 720 lb/acre, and in northwestern Oklahoma, forage yields ranged from 14 020 to 20 290 lb/acre with multiple harvests taken during the growing season. Crude protein content of eastern gamagrass is high for a warm‐season grass ranging fr...

Environmental variation, and the interaction of environment with management practices, can significantly affect perennial forage yields. The objective of this research was to evaluate the importance of environmental main effects and the interaction between environments, N rates, and harvests on eastern gamagrass [Tripsacum dactyloides (L.) L.] forage yields. Established eastern gamagrass stands were fertilized with 0, 168, or 336 kg N ha−1, and harvested three times during the growing season for three consecutive years at two locations in northern Missouri. Year and the year × location interaction were significant environmental sources of variation affecting forage yields. The year main effect had the larger variance component and accounted for 9% of the total variation in forage yields. The harvest main effect and year × harvest interaction had the largest variance components, and together accounted for more than 67% of the total variation in forage yields. Most of the variation between harvests resulted from differences in first‐harvest yields, taken at the reproductive growth stage, compared with regrowth harvest yields which were at vegetative growth stages. Variation in precipitation amounts between harvests significantly influenced regrowth harvest yields, causing a significant year × harvest interaction. Forage yield responses to N rates also varied between years, causing a significant year × N rate interaction. Location was not an important source of variation in eastern gamagrass forage yield in this study, nor was there a significant interaction between N rates and harvests. Resultsuggest that supplemental irrigation and longer rest periods between harvests may help improve forage yields and distribution.