Unfertilized Control Plots Research Articles

Soil Nitrate Concentrations under Corn as Affected by Tillage, Manure, and Fertilizer Applications

AbstractA 3‐yr study was conducted to examine combination effects of tillage (no‐till, conventional‐till), manure, and inorganic fertilizer (ammonium nitrate) on leaching of nitrates from the root zone of corn (Zea mays L.). Soil cores were collected every spring to a depth of 210 cm and analyzed for NO3‐N. Leaching of NO3‐N significantly increased as fertilizer N rates increased, especially when rates exceeded the crop's potential to assimilate N. The concentration of soil nitrate (averaged over depth and tillage) in Year 3 of the study under the unfertilized control plots was 2.5 mg NO3‐N kg−1, whereas the concentration under plots fertilized with 260 kg N ha−1 was 8.7 mg NO3‐N kg−1. Soil nitrate concentrations were consistently lower under no‐tillage when compared with conventional‐tillage. Tillage differences were greatest when high rates of N were added to soil. These results indicate that the use of no‐tillage cultivation may reduce the leaching of nitrates beyond the crop root zone.

Nutrient limitation of hardstem bulrush (Scirpus acutus Muhl.) in a Manitoba Interlake region marsh

Nitrogen and phosphorus fertilizer were added to a hardstem bulrush (Scirpus acutus Muhl.) marsh in the Interlake region of south-central Manitoba to assess nutrient limitation. Neither N nor P increased biomass when applied alone, but N+P increased aboveground biomass to nearly double the control, indicating that both N and P were near limiting. Fertilization had no effect on belowground biomass. Nitrogen fertilization raised the N content of aboveground plant tissues from 0.8% to 1.3%, and P fertilization raised the P content from 0.07% to 0.23% and indicated that added fertilizer was taken up by the plants. Biomass in unfertilized control plots varied substantially between years from 690 g·m−2·y−1 in 1986 to 395 g·m−2·y−1 in 1987. A contrast between this Interlake marsh and the Delta Marsh in central Manitoba, in which emergent vegetation is N limited, provides a clear example that marshes within the same northern prairie region can differ in the limiting nutrient, and potentially in their response to anthropogenic nutrient enrichment.

Effects of Spacing and Nitrogen Fertilizer on ‘Pusa Sawani’ Okra (Abelmoschus esculentus) in Nepal

SummaryA two year study on ‘Pusa Sawani’ okra grown during the summer in Rampur, Nepal (228 m OD; 27° 37′ N) has shown that spacing did not affect days to first harvest or pod length but that pod number plant−1 was affected significantly. Although individual plant yields at each harvest were maximum viith plants spaced 45 cm apart (a population of about 50,000 plants ha−1) pod yields ha−1 were maximum with plants spaced only 15 cm apart (about 150,000 ha−1). Applications of nitrogen fertilizer hastened the first harvest by 4–6 days compared to the unfertilized control plots. The greatest pod yield (9.3 t ha−1) was obtained from plots given 60 kg N ha−1.

Tiller Length vs. Tiller Weight: Applications to Plant Growth Studies

Tiller Length vs. Tiller Weight: Applications to Plant Growth Studies

Growth, Reproduction and Residency in a Declining Population of Microtus agrestis

SUMMARY (1) The population dynamics of Microtus agrestis (L.) inhabiting a young larch plantation in south-west Britain were studied from spring 1967 to spring 1969. As the larch trees grew they shaded out the ground layer vegetation and there was a resultant decline in vole density from 97/ha to 6/ha during the 2 main years of study. By the summer of 1972, this species had disappeared altogether. (2) Vole growth rates were significantly correlated with an index reflecting the abundance and rate of growth of the grasses which formed their main source of food. (3) Despite a good start to the breeding season in 1968, conditions deteriorated rapidly as a result of shading, and there was a considerable rise in perinatal mortality. (4) Rates of residency (minimum survival) were lowest during two main periods of the year. The first, in spring, involved mainly males, and coincided with the onset of sexual activity. The second, in summer, involved mainly females, and coincided with the replacement of overwinter residents by animals of the year. (5) Decreases in the rates of residency were correlated with increases in the distances moved between consecutive captures by male voles, reflecting a concomitant increase in the size of their home ranges. (6) Previously published records of male spring body weights from several parts of Britain were found to be significantly correlated with the standing crop of a meadow at Moor House Experimental Station and with the hay yields of the unfertilized control plots in the Rothamsted Park Grass Experiment. These correlations suggest a link between vole population fluctuations and climate. The effects of the quality or quantity of the spring food supply upon vole growth and reproduction could play an important part in this link.

Urea Fertilizer Effects on Dissolved Nutrient Concentrations in Some Forest Soils

AbstractNutrient concentrations in soil solutions near the surface and below the root zone were measured for 8 months after fall application of urea (448 kg N/ha) to four soils under second‐growth forest in southwestern British Columbia. Surface soil solution pH increased due to ureolysis within a few days, while concentrations of some cations were reduced, with Ca and Mg decreasing more than K and Na. Nitrate concentrations peaked at least 3 months after fertilization. With pH decline accompanying nitrification in fertilized plots, concentrations of Ca and Mg increased substantially over concentrations in unfertilized control plots whereas K and Na showed smaller increases. Effects on Ca, Mg, K, and Na are consistent with interpretations based on pH‐dependent cation exchange capacity and Donnan equilibria. Maximum total N, NO3‐N, and Ca concentrations below the root zone were 11.2, 11.0, and 10.0 mg/liter, respectively, and occurred with a recently afforested, coarse‐textured soil which was low in incorporated organic matter and lacked a forest floor.

The effect of different sowing densities and nutrient levels on leaf area index, production and distribution of dry matter in maize (zea mays l.)

The course of biological curves of accumulation of total (Ybiol), vegetative (Yveg) and grain dry matter (Ygr) in maize(Zea mays L.)was investigated in a field experiment. The different population densities from 27 777 to 121 418 plants per ha were tested in interaction with increasing fertilizer rates (NPK) ranging from zero to 780 kg of pure nutrients per ha. The grain yield (Fgr) plotted against the population density shows a parabolic trend with a maximum at densities from 64 000 to 79 000 plants per ha. An asymptotic trend was obtained for the curve of biological yield (Fbiol) in relation to the population density. The optimum densities for Ygr and Fbiol were identical in the unfertilized control plot. At optimum and higher population levels the application of optimum rate of pure nutrients was 260 kg per ha. Leaf area index(L) was rising with the increasing stand density. Its value was also increased by increasing mineral nutrition but only at plant densities higher than 64 000 plants per ha. The proportion of Ygr/ Ybiol showed an optimum atL value within 2.03 and 2.68. Its value declined with further increase of both, stand densities and levels of NPK. The optimumL estimated for Ygr was within 2.65 and 3.87 and that for Yol in the control variant was 2.65. Tn fertilized plots even the highestL values (5.17) did not influence neither the biological nor the vegetative dry matter yields. Relative photosynthetic potential for dry matter formation (RPP gr) was decreasing with the increasing stand density.