Labeled nitrogen fertilizer research with urea in the semi-arid tropics 3. Field studies on alfisol

Field studies with bordered microplots were conducted on an Alfisol in the semiarid tropics of India to determine (1) the fate of15N-labeled urea applied to dryland sorghum in two successive rainy seasons and (2) the effect of method of application on N fertilizer efficiency. Recoveries of15N-labeled fertilizers by above-ground plant parts ranged from 46.7% to 63.6% in 1981 when the rainfall was above the average and from 54.4% to 66.9% in 1980 when the rainfall was near the average. Small (0.014 g) pellets of urea applied twice as postemergent applications in separate 5 cm deep bands were more effective than single preemergent applications either surface applied or incorporated. Both banding and the split applications contributed to overall fertilizer efficiency. Large (1.0 g) pellets of urea (supergranules) placed at a depth of 5 cm were also superior to the incorporated, small-pellet treatment in 1981. The15N-balance data for the soil (0–90 cm in depth)-plant system in 1981 showed that the unaccounted-for fertilizer N ranged from 5.1% to 20.6%. An important finding was that high grain yields, in excess of 6,000 kg/ha, with N fertilizer losses of less than 10% could be obtained through fertilizer management during a very wet season. The data from the Alfisol experiments were compared with data from similar Vertisol experiments; N fertilizer losses resulting from incorporated and surface applications were greater for Vertisols than for Alfisols in the wetter year

Effect of Water Pretreatment on Total Nitrogen Analysis of Soils by the Kjeldahl Method

Effective methods are needed for determining total N when studying the fate of N fertilizer applied to soil. This study was concerned with the pretreatment of samples of a Vertisol (calcareous Typic Pellusterts) with water, 20 and 2 mL for macro- and semimicro-Kjeldahl methods, respectively, prior to digestion. The need for such a modification with certain clay soils was originally recommended in 1925, but its requirement in conjunction with modern Kjeldahl methods is rarely reported. The macro- and semimicro-Kjeldahl methods used involved digestion of soil with a H2SO4-K2SO4-CuSO4 5H2O-Se mixture. Both techniques yielded digestion residues with dark-colored granules and low recoveries of N with soil samples ground to pass through a sieve with 0.8-mm openings (20 mesh), unless the soil was initially treated with water. For instance, N recovery from a surface Vertisol was increased by 29% as a result of a 30-min water soaking prior to a macro-Kjeldahl digestion. Extension of the digestion period up to 5 h after initial clearing did not eliminate the need for the water pretreatment. The requirement for the water pretreatment for semimicro-Kjeldahl methods was greatly reduced when the soil was ground to pass through a sieve with 0.16-mm openings (100 mesh). Increase in soil N due to water pretreatment was reduced from 35 to 6% by grinding the coarser soil to such fineness. A salicylic acid pretreatment, involving water addition after the nitration reaction, permitted satisfactory digestion. The water pretreatment effect appeared to be associated with incomplete digestion of organic N, not with the recovery of fixed NH4+, and was found with both surface and subsoils. Water pretreatment of samples from several horizons of an Alfisol (Udic Rhodustalfs) had little effect on recovery of soil N. A water pretreatment is probably not needed to obtain maximum recoveries of N if the nonmodified Kjeldahl method results in a postdigestion soil residue without dense, darkish granules. However, the water soaking was found to reduce bumping during digestion of many soils and is recommended for routine us

Labeled nitrogen fertilizer research with urea in the semi-arid tropics II. Field studies on a Vertisol

Field studies were conducted on Indian Vertisol to determine the fate of15N-labeled fertilizers applied to dryland sorghum in two successive rainy seasons. In the 1981 season, a split-band (SB) urea application of 74 kg N/ha, half amounts placed 5 cm deep and 8 cm from opposite sides of plant rows at 4 and 19 days after emergence, was superior to preemergent applications of either surface-applied (S) or incorporated (I) applications at the same rate; 907 mm of rainfall fell during the sorghum growing period. Percentages of applied N recovered in the soil-plant system after the sorghum harvest were 94%, 74%, and 72%, respectively, for the SB, I, and S application methods. Substantial quantities, 39%, 45%, and 42% of the added N for the SB, I, and S tretments, respectively, remained in the soil after the final harvest. Plant utilization of added urea-N was greater in 1980 when rainfall during the growing season was 212 mm less than in 1981. S or I applications of urea at 74 kg N/ha, with above-ground plant15N recoveries of 48.0% and 48.6%, respectively, were also equally as efficient during 1980. Residual soil N derived from fertilizer was of little value for a sorghum crop in the following rainy season and for a safflower crop in the post-rainy season in a double-cropping system

The persistent shadow of the supermassive black hole of M 87

In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3−3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5 × 109 M⊙. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet

Zinc Deficiency of Flax in North Dakota

This article address the cause of "chlorotic dieback" and the influences of zinc, phosphorus and iron fertilizers, levels of soil-extractable zinc and soil temperature on this disease

The Use of Anhydrous Ammonia in North Dakota

In 1978, the importance of anhydrous ammonia usage in the state of North Dakota exceeded the national average. Economics drove the usage of ammonia in North Dakota as it is the most highly concentrated form of nitrogen fertilizer available. It was less expensive as well. It can be incorporated in it's application while the farmer tills the land. Their was a worry at this time that foreign sources of ammonia would flood the US marketplace. The physical properties of ammonia are discussed. The equipment used to to apply ammonia rated well with North Dakota farmers in it's application of the quantity required of ammonia. Problems with lateral distribution of ammonia among injection outlets was discussed