Frederick R. Magdoff

A soil test for nitrogen availability in the northeastern United States.

Abstract A soil test for nitrogen availabilty to corn (Zea mays, L) has gained wide acceptance in the northeast region of the United States. The test involves sampling the surface 30 cm of soil during the early part of the growing season. The N03‐N present at that time is correlated with the probability of obtaining a yield increase by using sidedress nitrogen fertilizer. The test has been evaluated in 272 yr‐site N response experiments in Vermont, Pennsylvania, Connecticut, New York, and New Hampshire. The various states in the region that are now offering a N soil test (Vermont, Pennsylvania, Connecticut, and Maine) have different methods of making recommendations based on soil‐test levels. However, 20 to 30 mg NO3‐N/kg soil is about the critical range above which there is a low probability of obtaining yield increases due to sidedress fertilizer N. Therefore, no additional N fertilizer is recommended. A major problem, which is slowing widespread utilization of this test is that the soil must be sampled...

Flow path studies in forested watersheds of headwater tributaries of Brush Brook, Vermont

An investigation was undertaken into how headwater tributaries of Brush Brook, Vermont, could have average pH differences of almost two units (4.75 and 6.7). Sampling along four tributaries revealed that most of one tributary, below an area of seeps, had consistently higher pH, Ca2+, Mg2+, and K+, and lower Al than other sites. Bedrock mapping showed numerous fractures in vicinity of the seeps. A portion of this tributarys watershed and a portion of an acid tributarys watershed were intensively mapped for soil depth. Sampling showed the widespread existence of dense basal till in the watershed of the acid tributary but none in that of the near-neutral stream. Lateral flow, found above the dense till, was chemically similar to that of the acid tributary and to solutions sampled from soil B horizons. There were no differences in the average pH of nonseep soils sampled from either watershed. Flow paths are hypothesized to be through the B horizons in the acid tributaries and from below the soil profile in the near-neutral tributary. The acid catchment should be more sensitive to environmental change.

Field nitrogen dynamics: Implications for assessing N availability

Abstract The amount of organic‐N in a given soil is a result of the cumulative influences of factors affecting additions to and losses from the soil. Many of these factors also influence the rate of N mineralization and, thus, the quantity of available N for plants. Regression techniques were used with data gathered while field testing a soil N availability test for corn (Zea mays L.) to evaluate the influence of various factors on N availability and the rate of N mineralization. Both check plot (no N fertilizer) yields and soil test NO3‐N were related to total Kjeldahl N (TKN), drainage class, and manure application. The estimated rate of N mineralization decreased as TKN increased. Answers to a farmer questionnaire that accompanied samples submitted for soil testing also indicated the importance of soil characteristics and fresh organic residue decomposition to N availability. These findings suggest that soil tests based on TKN or parameters correlated with TKN will not successfully predict N availabili...

Exchangeable cations and the pH-independent distribution of cation exchange capacities in Spodosols of a forested watershed

The cation exchange behavior of acid, high organic matter (OM) forest soils has been little studied. We measured cation exchange capacities (CEC) and exchangeable cations in fresh, field-moist samples from soil horizons of a forested mountain watershed in north central Vermont. CEC, measured by compulsive exchange on 148 horizon samples, ranged between 0.07 and 84.3 cmolc kg−1. Below pH 5.3, the CEC was linearly correlated with OM and was independent of pH. The amount of ‘permanent’ charge associated with the OM was about 30 cmolc kg−1. However, individual horizons exhibited pH-dependent charge behavior if the pH was adjusted during CEC measurement.

Soil nitrogen availability under grassland and cultivated corn

SummaryAdjacent corn and ryegrass plots were fertilized with rates of 0, 50, 100, 150, and 200 kg N as ammonium nitrate/ha. Corn growing on this soil did not respond to fertilizer N while ryegrass responded to rates of up to 200 kg N/ha. The differences in N availability was also reflected in the higher profile NO3−N under corn than under ryegrass. The same general trends occurred on a second soil, where N availability for the hay crop was also less than for corn crop. Compared with corn, hay responded more to N fertilizer and had lower soil NO3−N levels.Grasslands appear to respond to higher N fertilizer rates than cultivated crops on the same soil.

Evaluation of a nitrogen availability test

Abstract To evaluate a N availability test, we plotted corn (Zea mays L.) silage yields and N contents from several sites in Pennsylvania and Vermont against the total estimated available N (TEAN). Field N mineralization was estimated by using an empirical laboratory‐derived relationship between mineralized‐N (Nm) and the NH4‐N released by autoclaving (Ni). TEAN was calculated by summing estimated mineralized‐N of soil samples taken to 15 cm plus added inorganic‐N. By using a statistical procedure, we divided the data into two response populations with the critical value of 13.3 kg TEAN/ton maximum yield. Further field testing of the autoclaving N availability index is needed.