A simple and precise procedure for estimating total N in plant tissue is described; a modification is also described for analysis of samples containing high nitrate concentrations. Plant tissue samples are placed in pyrex Folin‐Wu tubes and digested with a salt‐catalyst‐sulfuric acid mixture by heating the tubes in an aluminum block. Samples are digested at the boiling point of the mixture for 60 min after initial clearing of the digests. Analyses of diverse plant materials, containing from 0.006 to 0.3% NO3‐N3 indicated that the proposed and standard AOAC procedures yielded essentially the same total N values. The coefficient of variation for the proposed methods varied from 0.87 to 1.10%. The tube digestion procedures described allows digestion of 60 plant samples simultaneously and thus greatly improve the efficiency of total N determinations.
High rates of N loss have been observed from N fertilizers applied directly on the surface in no‐till corn (Zea mays L.) production systems. Field experiments were conducted at four locations over a three‐year period to determine what effects N source and N placement had on N losses in both no‐till and conventional till corn production systems. Soils used were: Stoy loam, an Aquic Hapludalf; Clermont silt loam, a Typic Ochraqualf; Avonberg silt loam, an Aeric Fragiaqualf; Chalmers silty clay loam, a Typic Argiaquoll; and Lyles fine sandy loam, a Typic Haplaquoll. Nitrogen sources used were anhydrous ammonia (NH3), urea‐ammonium nitrate solutions (UAN), solid urea and solid ammonium nitrate (NH4NO3). Placement variables used were injection of NH3 and UAN 20 cm below the soil surface and broadcasting UAN, urea and NH4NO3 on the soil surface with no incorporation. Nitrogen rates used were 0 and 165 kg N/ha. Injecting NH3, or UAN below the surface resulted in consistently higher corn grain yields than applying UAN, NH4NO3 or urea directly on the soil‐residue surface. Percent N in leaf and grain also reflected an increase in N use efficiency with subsurface N placement. Percent N in leaf was significantly higher where NH3 or UAN were injected as compared to UAN or urea surface applied.
A 6‐yr field experiment was conducted to determine the effects of liquid and solid dairy (Bos taurus) manure applications on a Crosby silt loam (Aerie Ochraqualfs) soil cropped to corn (Zea mays L.). Liquid manure at rates of 112, 224, and 336 Mg ha−1 and solid manure at rates of 34, 67, and 101 Mg ha−1 were spread annually for 5 yr. No manure was applied the 6th yr, but the soil was cropped to determine residual nutrient effects. Check and inorganic fertilizer treatments were also included in the study. Manure addition increased corn yields when compared to the check (no fertilizer). There were variable weather conditions and nutrient concentrations of the manure sources, and the manure application rates were relatively high. Corn yields were as great or greater from plots supplied with manure and manure slurries as those supplied with commercial fertilizer. Over the 5 yr of manure application, the 224 Mg ha−1 rate of liquid manure and the 67 Mg ha− rate of solid manure results in maximum corn yields that were 1% higher than commercial fertilizer. Accumulations of nutrients in the soil from high liquid manure application rates (224 and 336 Mg ha−1) increased corn yields during the residual cropping year. Corn leaf N and P concentrations tended to reflect N and P rates applied with the manures and the fertilizer treatment compared to the check, but not consistently each year. Source of manure had little affect on corn leaf composition. Soil P, K, and Na increased with each additional year of manure application and tended to increase with higher application rates. Extractable P accumulated in the upper profile of soil, whereas exchangeable K and Na increased at lower depths in the soil profile, especially with the highest manure application rates. Based on this study, both solid and liquid dairy manures are valuable sources of nutrients for corn production; however, they are less efficient than commercial fertilizers when comparing equivalent nutrient levels and when they are applied to the soil surface. Excessive application of either manure source causes potential for considerable groundwater pollution.
Randomized complete block design field experiments were conducted to determine the effects of rates and methods of liquid swine manure application on volatile NH3‐N losses from cropland. In addition, a greenhouse study was conducted to determine the effect of wind on the rate of NH3‐N volatilization from soil and the accuracy of NH3‐N loss measurements under field conditions. A partially closed system was utilized to directly collect volatilized NH3‐N from microplots.The NH3‐N collection system did not accurately estimate volatile N losses when windy conditions existed as often encountered in the field. Using direct measurement of NH4+‐N in waste before and after exposure to the atmosphere to correct for the low estimates of NH3‐N loss under field conditions, an average of 48.1% of the volatilized N was collected under greenhouse conditions with relatively constant temperature and wind.The rate of NH3‐N loss from manure increased with increasing temperature and air movement. The proportions of the applied NH4+‐N lost as NH3‐N during a 3.5‐day sampling period in the spring from swine manure (pH 6.4) applied to soil (pH 6.4) and corrected for the effect of wind were: 14.0%, 12.2%, and 11.2% for the 90, 135 and 180 metric ton/ha, respectively, of surface applied liquid swine manure; 2.5% for both the 90 and 180 metric ton rates, respectively, of injected liquid swine manure; 14.7% for surface applied urea fertilizer (168 kg N/ha); and 65.8% of the applied NH4+‐N from swine manure surface applied (90 metric tons/ha) on a plastic liner. Fresh swine manure (pH 7.8) surface applied at the rate of 135 metric tons/ha on greenhouse loam soil (pH 7.0) lost 82.5% of the applied NH4+‐N in an 8‐day sampling period.
A 2‐year field experiment was conducted to study the effects of salt (0.2 and 0.5%) in swine rations, liquid waste handling systems (aerobic and anaerobic), and application rates on the recycling of swine wastes to Fox silt loam and Chalmers silt loam soils cropped to corn (Zea mays L.).Liquid swine waste (1.8 to 3.0% dry matter) was applied annually at rates of 45, 90, and 134 metric tons/ha. The high rate provided an average of 378 kg N, 113 kg P, 163 kg K, and 42 kg Na per ha. Check and inorganic fertilizer (168 kg N/ha, 56 kg P/ha, 112 kg K/ha) treatments were included.Soil Na, nitrate N, and extractable P concentrations increased with increasing waste application rates. Soil electrical conductivity was not affected by waste application rate. The effects of dietary salt levels and waste handling systems on the chemical composition of the soils were inconsistent.There was evidence for downward movement of Na, K, and NO3− in the soil profile of plots receiving waste and fertilizer. Downward movement of NO3− was observed to a greater extent in fertilizer‐treated plots than in waste‐treated plots. Under climatic conditions prevailing in this study, 2 years of waste application had no detrimental effects on the chemical composition of the two silt loam soils.Soil application of waste resulting from different dietary salt levels and waste handling systems resulted in similar corn yields and leaf chemical composition. Yields were higher from plots treated with waste and inorganic fertilizer compared to the check plot. Corn yields increased with increasing rates of waste application up to the 90‐metric tons/ha rate, then leveled off. Nitrogen, P, and K concentrations in corn ear leaf tissue increased with increasing waste applications.
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