MEHLICH-3

To evaluate different methods for soil potassium availability, surface soil samples (0-15 cm) were collected from 55 locations in Haryana covering a wider range of dominant textures and management conditions. Each soil sample was then equilibrated with 0, 100, 200 and 400 mg K kg-1 soil for about a week to obtain soils with a wider spectrum of their initial K content. Available potassium in all the samples air-dried at room temperature was determined using 1N ammonium acetate (NH4OAc), Mehlich-3 (M3) and sodium tetraphenylboron (NaBPh4). The results showed that the average percent increase in available K extracted by ammonium acetate, Mehlich-3 and sodium tetraphenyl boron for 100, 200 and 400 ppm treated soils was 34.65%, 31.68%, 26.73%; 57.28%, 60.56%, 53.52% and 22.66%, 23.46% and 26.81%, respectively in comparison to 0 ppm treated soils.  However, higher (2-3 times) available potassium was extracted by using sodium tetraphenyl boron in comparison to ammonium acetate and Mehlich-3 extractants. The regression model showed best fit for sodium tetraphenyl boron.

Total soil P (TP), soil-test P (STP), and the degree of soil P saturation are affected by long-term P application but relationships between these measurements need to be established for grain production cropping systems to improve P management guidelines. This research studied these relationships from samples collected from 11 long-term (4-23 yr) Iowa P trials. Mean soil clay content and pH (0to 15-cm depth) ranged from 171 to 375 g kg 21 and 6.1 to 6.8, respectively, and maximum cumulative P application was 192 to 1098 kg P ha 21. Soil was analyzed for Bray-P 1 (BP), Mehlich-3 P (M3P), Olsen P (OP), TP, P sorption index (PSI), and P saturation by STP/ PSI and Mehlich-3 extractable P, Al, and Fe (M3sat) indices. Soil-test P increased as P applied increased and declined when P was not applied. Total P increased linearly with increasing BP, M3P, and OP (r 5 0.52-0.55), and increases were 1.8, 1.7, and 3.5 mg TP kg 21 per mg STP kg 21 for BP, M3P, and OP, respectively. Usually STP was linearly correlated to M3sat and STP/PSI (r 5 0.80-0.94), and M3sat was linearly correlated to STP/PSI (r 5 0.86-0.92). Results indicate that STP can approximately estimate long-term effects of P application on TP, and soil P saturation for conditions similar to those in this study, but TP estimates are improved by grouping similar soil series. Further research for a wider range of soils and STP would be useful to better describe relationships between these measurements.

Total soil P (TP), soil-test P (STP), and the degree of soil P saturation are affected by long-term P application but relationships between these measurements need to be established for grain production cropping systems to improve P management guidelines. This research studied these relationships from samples collected from 11 long-term (4-23 yr) Iowa P trials. Mean soil clay content and pH (0to 15-cm depth) ranged from 171 to 375 g kg 21 and 6.1 to 6.8, respectively, and maximum cumulative P application was 192 to 1098 kg P ha 21. Soil was analyzed for Bray-P 1 (BP), Mehlich-3 P (M3P), Olsen P (OP), TP, P sorption index (PSI), and P saturation by STP/ PSI and Mehlich-3 extractable P, Al, and Fe (M3sat) indices. Soil-test P increased as P applied increased and declined when P was not applied. Total P increased linearly with increasing BP, M3P, and OP (r 5 0.52-0.55), and increases were 1.8, 1.7, and 3.5 mg TP kg 21 per mg STP kg 21 for BP, M3P, and OP, respectively. Usually STP was linearly correlated to M3sat and STP/PSI (r 5 0.80-0.94), and M3sat was linearly correlated to STP/PSI (r 5 0.86-0.92). Results indicate that STP can approximately estimate long-term effects of P application on TP, and soil P saturation for conditions similar to those in this study, but TP estimates are improved by grouping similar soil series. Further research for a wider range of soils and STP would be useful to better describe relationships between these measurements.

In areas of intensive agriculture continuous applications of mineral and organic fertilizers can lead to an accumulation of phosphorus (P) in the soils and progressive saturation of their sorption capacities, increasing the risk of P losses to aquatic ecosystems. The long-term evolution (44 years) of soil P forms has been studied in a factorial experiment combining three soils (sandy, clay and a peaty) with three types of fertilization (no fertilizer, farmyard manure and mineral fertilizer). The P distribution in the calcium P (P Ca), iron P (P Fe), iron + aluminium P (P Fe+Al) forms, and the effect of treatments on P availability (oxalate extractable-P, Mehlich-3-P, Olsen-P, water extractable-P) were determined. Two sorption P indices and the degree of soil saturation were also calculated. Soil P forms were affected by both quantity and quality of P inputs. Farmyard manure caused a more consistent increase in soil P content, affecting the water soluble and labile P forms (Mehlich-3-P and Olsen-P) in particular. Readily assimilable and potentially mobile P forms were positively correlated with the amount of high molecular weight humic fractions, thus stressing the importance of the type of incorporated materials and their evolution in determining soil P behaviour. Soils treated with farmyard manure, and to a lesser extent with mineral fertilizer, exceeded the threshold values of 20 mg kg −1 for Olsen-P and 150 mg kg −1 for Mehlich-3-P, thus evidencing a potential risk of P loss to water bodies. While in absolute terms the more consistent accumulations were observed in clay and peaty soils, the P content of sandy soils is of particular concern, given their lower P sorption capacity and higher degree of saturation. Among the soil P tests, Mehlich-3-P proved to be the best indicator to assess Italian soil conditions for both agronomic and environmental purposes.

Iowa soil-test interpretations and fertilizer recommendations for phosphorus (P) and potassium (K) were last updated in 1999. The only change from previous recommendations (Voss et al., 1996; Voss and Mallarino, 1996) was to add interpretations for the Mehlich-3 (M3) P and K tests to existing interpretations for the Bray-1 P, Olsen P, and ammonium-acetate K tests (Voss et al., 1999).

An experiment was conducted in subarctic Alaska from 1999 to 2001 to determine the effect of liquid and solid cattle (Bos taurus) manure application rates on smooth bromegrass (Bromus inermis Leyss.) and oat (Avena sativa L.) biomass production, nutrient uptake, and soil properties. One-time manure application of 100 and 200 kg N ha 21 was made in May 1999 in comparison with annual fertilizer application of 50, 100, and 200 kg N ha 21. In the first year, liquid manure at 100 and 200 kg N ha 21 generated 3036 and 4292 kg ha 21 smooth bromegrass biomass, respectively, statistically (p $ 0.05) similar to that of fertilizer application (3654 kg ha 21) at 200 kg N ha 21 but greater (p # 0.05) than control (1572 kg ha 21). Similar results were found with oat. The 200 kg N ha 21 liquid manure application continued to benefit crop growth in the second and third years. Solid manure did not influence biomass production of either crop in most crop/year combinations. Cumulatively, in 3 yr, smooth bromegrass recovered 59% of nitrogen from liquid manure, compared with 37% by oat. Soil Mehlich 3-P accumulation was found in some liquid and solid manure treatments for both crops. High soil exchangeable K was found in 1999 after liquid manure application but declined over time. Our results suggest that 100 kg N ha 21 liquid manure can replace nitrogen fertilizer at a similar rate. Liquid cattle manure was better than solid cattle manure in promoting bromegrass and oat production.

Abstract: Land application of large amounts of manure from confined livestock facilities is an environmental concern often associated to excess phosphorus (P) in soils and potential pollution of water resources. Recovery of P from livestock manure is an attractive ...