Runoff capture through vegetative barriers and planting methodologies to reduce erosion,and improve soil moisture,fertility and crop productivity in southern Orissa,India

Use of perennial grasses as vegetative barriers to reduce soil erosion from farm and non-farm lands is increasing world-over. A number of perennial grasses have been identified for their soil conserving properties, but their effectiveness varies with location and method of planting. Installing vegetative barriers in combination with suitable mechanical measures, like bunds or trenches or both, on the appropriately spaced contours may enhance their conservation potential. Hence, the effect of vegetative barriers, viz., sambuta (Saccharum spp.)—a local grass, vetiver (Vetiveria zizanioides) and lemongrass (Cymbopogon citratus) planted in combination with trench-cum-bund, on runoff, soil loss, nutrient loss, soil fertility, moisture retention and crop yield in the rainfed uplands, was studied in Kokriguda watershed in southern Orissa, India through 2001–2005. However, runoff, soil and nutrient losses were studied for 2002, 2003 and 2004 only. Analysis of the experimental data revealed that on a 5% slope, the lowest average runoff (8.1%) and soil loss (4.0 Mg ha⁻¹) were observed in the sambuta + trench-cum-bund treatment followed by vetiver + trench-cum-bund (runoff 9.8%, soil loss 5.5 Mg ha⁻¹). Lemongrass permitted the highest runoff and soil loss. Further, the conservation effect of grass barriers was greater under bund planting than berm planting. Minimum organic C (50.02 kg ha⁻¹), available N (2.49 kg ha⁻¹) and available K (1.56 kg ha⁻¹) loss was observed under sambuta with bund planting. The next best arrester of the soil nutrients was vetiver planted on bund. Significantly better conservation of nutrients under sambuta and vetiver resulted in the soil fertility build-up. Soil moisture content was also higher in the sambuta and vetiver than lemongrass treated plots. Increase in the yield of associated finger millet (Eleusine coracana (L.) Gaertn.) due to vegetative barriers ranged from 18.04% for lemongrass to 33.67% for sambuta. Further, the sambuta and vetiver treated plots produced 13.23 and 11.86% higher yield, respectively, compared to the plots having lemongrass barrier (1.17 Mg ha⁻¹). Considering the conservation potential, and crop yield and soil fertility improvements, the sambuta barrier with trench-cum-bund is the best conservation technology for treating the cultivated land vulnerable to water erosion. Farmers also showed greater acceptance for the sambuta barrier as it is erect growing and available locally. Vetiver with-trench-cum bund can be the second best option.     

Evaluation of Mustard Meal as Organic Fertiliser on Tef (<Emphasis Type="Italic">Eragrostis tef</Emphasis> (Zucc) Trotter) under Field and Greenhouse Conditions

Experiments were conducted to evaluate the potential use of mustard meal as organic fertiliser on tef (Eragrostis tef (Zucc) Trotter). Mustard meal is a high quality nutrient source with 6.35% lignin, 2.1% total extractable polyphenol, C to N ratio of 14 and lignin to N ratio of 1.1. Under field conditions the effect of tef on Nitosol was studied in a split plot design with three replications. Grain yield increases due to increased mustard meal N rate varied from 2 to 116% over the control. The agronomic efficiency was 3.0, 8.3 and 13.5 kg when N was applied at 15, 23 and 31 kg ha⁻¹, respectively. The mustard meal N use efficiency was 7.6, 20.6 and 33.7% for the above-indicated N rates. Application of mustard meal in powder form was more effective than granular. In the greenhouse, the effect of mustard meal and urea N mixed in different quantity was studied with ¹⁵N technique. The N derived from fertiliser was lowest (3.5%) when 20 mg pot⁻¹ from urea was combined with 100 mg pot⁻¹ from mustard meal and highest (11%) when 67 and 33 mg pot⁻¹ as urea and mustard meal were combined, respectively. The N derived from mustard meal was lowest (3.3%) when mustard meal and urea N were combined at 50 mg N pot ⁻¹ each, and highest (8.9%) when combined at 20 and 100 mg N pot⁻¹, respectively. The urea and mustard meal N yields significantly varied between the treatments. The N use efficiency from urea (FNUE) varied from 38.4 to 43%. Combining urea and mustard meal N at 50 mg N pot⁻¹ each has decreased FNUE to 4.4% compared to the urea N applied alone at 50 mg N pot⁻¹. N use efficiency (NUE) from mustard meal was highest (38.4%) when mustard meal and urea N were combined at 33 and 67 mg N pot⁻¹, respectively, and lowest when it was combined at 67 and 33 mg N pot⁻¹.     

Aboveground nitrogen in relation to estimated total plant uptake in maize and bean

The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments. Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m⁻² 30 day⁻¹) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N that was taken up by the plant daily varied more in maize (about 0.03–0.12 day⁻¹) than in bean (about 0.05–0.08 day⁻¹). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize depending on period within season, whereas for bean it was more constant and smaller (about 40%).     

Recycling of legume residues for nitrogen economy and higher productivity in maize (<Emphasis Type="Italic">Zea mays</Emphasis>)–wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) cropping system

Contribution of legumes towards N economy in cereal-based cropping systems is well-known but there has been a gradual decline in the cultivation of grain legumes, threatening sustainability of maize (Zea mays)–wheat (Triticum aestivum) cropping system in north-western India. A study was made to evaluate and quantify the effect of different grain legumes on productivity, profitability, N economy and soil fertility in maize–wheat cropping system at New Delhi during 2002–2004. Five legumes, viz. blackgram (Vigna mungo), greengram (Vigna radiata), cowpea (Vigna unguiculata), groundnut (Arachis hypogaea) and soybean (Glycine max) were either intercropped with maize or grown in sole cropping, and their residues were incorporated before the following crop of wheat, which was grown with varying rates of N, viz. 0, 40, 80 and 120 kg N ha⁻¹. Maize-equivalent productivity was significantly more with intercropped greengram (16.1–29.9%), cowpea (24.8%) and groundnut (11.1–16.6%) than in sole maize. Land equivalent ratio and other competitive functions were favourably influenced with intercropped maize + greengram and maize + cowpea. Addition of N through legume residues varied from 11.5–38.5 kg ha⁻¹ in intercropped system and 17.5–83.5 kg ha⁻¹ in sole cropping, which improved productivity of following wheat to a variable extent. Nitrogen economy in wheat was 21 kg ha⁻¹ due to residue incorporation of intercropped greengram, cowpea and groundnut; and 49–56 kg N ha⁻¹ of sole cropped greengram and groundnut. Residual soil fertility in terms of organic C and KMnO₄-N showed an improvement under maize-based intercropping systems followed by wheat, and the beneficial effect was more pronounced with sole cropping of legumes due to greater addition of residues. Apparent N balance as well as actual change in KMnO₄-N at the end of study was positive in most intercropped legumes as well as sole cropping systems, with greater improvement noticed under groundnut, soybean and greengram. Net returns were marginal with maize-based intercropping or sole cropping of legumes, but improved considerably with wheat, particularly when greengram, cowpea and groundnut were grown in the previous season. The studies suggested that inclusion of grain legumes, particularly greengram, cowpea and groundnut was beneficial for improving productivity, profitability, N economy and soil fertility in maize–wheat cropping system.     

Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems

Sustainable soil fertility management depends on long-term integrated strategies that build and maintain soil organic matter and mineralizable soil N levels. These strategies increase the portion of crop N needs met by soil N and reduce dependence on external N inputs required for crop production. To better understand the impact of management on soil N dynamics, we conducted field and laboratory research on five diverse management systems at a long-term study in Maryland, the USDA- Agricultural Research Service Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no-till corn (Zea mays L.)–soybean (Glycine max L.)–wheat (Triticum aestivum L.)/double-crop soybean rotation (NT), a conventional chisel-till corn–soybean–wheat/soybean rotation (CT), a 2 year organic corn–soybean rotation (Org2), a 3 year organic corn–soybean–wheat rotation (Org3), and a 6 year organic corn–soybean–wheat–alfalfa (Medicago sativa L.) (3 years) rotation (Org6). We found that total potentially mineralizable N in organic systems (average 315 kg N ha⁻¹) was significantly greater than the conventional systems (average 235 kg N ha⁻¹). Particulate organic matter (POM)–C and –N also tended to be greater in organic than conventional cropping systems. Average corn yield and N uptake from unamended (minus N) field microplots were 40 and 48%, respectively, greater in organic than conventional grain cropping systems. Among the three organic systems, all measures of N availability tended to increase with increasing frequency of manure application and crop rotation length (Org2 < Org3 ≤ Org6) while most measures were similar between NT and CT. Our results demonstrate that organic soil fertility management increases soil N availability by increasing labile soil organic matter. Relatively high levels of mineralizable soil N must be considered when developing soil fertility management plans for organic systems.     

Green leaf manuring with prunings of Leucaena leucocephala for nitrogen economy and improved productivity of maize (Zea mays)–wheat (Triticum aestivum) cropping system

Green leaf manuring with prunings of Leucaena leucocephala is regarded as a useful source of N to plants but the actual substitution of N fertilizer, release and recovery of N as well as effects on soil fertility are not adequately studied. The present studies investigated the effect of sole and combined use of Leucaena prunings and urea N fertilizer in different proportions on productivity, profitability, N uptake and balance in maize (Zea mays)–wheat (Triticum aestivum) cropping system at New Delhi during 2002–2003 and 2003–2004. Varying quantities of Leucaena green leaf biomass containing 3.83–4.25% N (18.2–20.5 C:N ratio) were applied to provide 0, 25, 50, 75 and 100% of recommended N (120 kg ha⁻¹) to both maize and wheat before sowing. In general, direct application of urea N increased the productivity of both crops more than Leucaena green leaf manure, but the reverse was true for the residual effect of these sources. The productivity of maize increased progressively with increasing proportions of N through urea fertilizer and was 2.41–2.52 t ha⁻¹ with 60 kg N ha⁻¹ each applied through Leucaena and urea, which was at par with that obtained with 120 kg N ha⁻¹ through urea alone (2.56–2.74 t ha⁻¹). Similarly, wheat yield was also near maximum (4.46–5.11 t ha⁻¹) when equal amounts of N were substituted through Leucaena and urea. Residual effects were obtained on the following crops and were significant when greater quantity of N (>50%) was substituted through Leucaena. Nitrogen uptake and recovery were also maximum with urea N alone, and N recovery was higher in maize (33.4–42.1%) than in wheat (27.3–29.8%). However, recovery of residual N in the following crop was more from Leucaena N alone (8.5–10.3%) than from urea fertilizer (1.7–3.8%). Residual soil fertility in terms of organic C and KMnO₄ oxidizable N showed improvement with addition of Leucaena prunings, which led to a positive N balance at the end of second cropping cycle. Net returns were considerably higher with wheat than with maize, and were comparatively lower with greater proportion of Leucaena because of its higher cost. Nonetheless, it was beneficial to apply Leucaena and urea on equal N basis for higher productivity and sustainability of this cereal-based cropping system.     

Effects of cropping history and phosphorus source on yield and nitrogen fixation in sole and intercropped cowpea–maize systems

Symbiotic N₂-fixation, N uptake efficiency, biomass- and crop production of cowpea and maize as affected by P source, sole- and intercropped, and introduction of break crops were studied on a farmer’s fields in semi-arid Tanzania. Cowpea fixed around 60% of its N from the atmosphere amounting to 70 kg N ha⁻¹ under sole and 36 kg N ha⁻¹ under intercropping as estimated by the ¹⁵N isotope dilution method around peak biomass production. The amount of N₂-fixed was 30–40% higher when P was applied as either TSP or MRP whereas cowpea yield were unaffected. Intercropped maize with 19,000 plant ha⁻¹ accumulated the same amount of N as 38,000 sole cropped maize plants although intercropping reduced the dry matter accumulation by 25%. The N uptake efficiency of the applied ¹⁵N labelled fertiliser was 26%, which equal a total pool of early available plant N of 158 kg N ha⁻¹. Under the N deficient conditions, P application did not increase the grain yield of maize. The LER indicate that sole cropping required 18% more area than intercropping in order to produce the same grain yield, and 35% more land when LER was based on N uptakes. Introduction of break crops in the maize systems, more than doubled accumulation of dry matter and N in the grain compared to continuous maize cropping. During maturation sole crop cowpea shedded leaves containing 41 kg N ha⁻¹. The current findings underline the importance of crop diversity in Sub Saharan Africa agriculture and emphasise the need for including all residues, including shedded leaves, in nutrient balance studies.     

Fertilization effects on yield sustainability and soil properties under irrigated wheat–soybean rotation of an Indian Himalayan upper valley

To date, the sustainability of wheat (Triticum aestivum)–soybean (Glycine max) cropping systems has not been well assessed, especially under Indian Himalayas. Research was conducted in 1995–1996 to 2004 at Hawalbagh, India to study the effects of fertilization on yield sustainability of irrigated wheat–soybean system and on selected soil properties. The mean wheat yield under NPK + FYM (farmyard manure) treated plots was ~27% higher than NPK (2.4 Mg ha⁻¹). The residual effect of NPK + FYM caused ~14% increase in soybean yield over NPK (2.18 Mg ha⁻¹). Sustainable yield index values of wheat and the wheat–soybean system were greater with annual fertilizer N or NPK plots 10 Mg ha⁻¹ FYM than NPK alone. However, benefit:cost ratio of fertilization, agronomic efficiency and partial factor productivity of applied nutrients were higher with NPK + FYM than NPK, if FYM nutrients were not considered. Soils under NPK + FYM contained higher soil organic C (SOC), total soil N, total P and Olsen-P by ~10, 42, 52 and 71%, respectively, in the 0–30 cm soil layers, compared with NPK. Non-exchangeable K decreased with time under all treatments except NPK. Total SOC in the 0–30 cm soil layer increased in all fertilized plots. Application of NPK + FYM also improved selected soil physical properties over NPK. The NPK + FYM application had better soil productivity than NPK but was not as economical as NPK if farmers had to purchase manure.     

Nutrient Uptake and Balance of Cotton + Pigeonpea Strip Intercropping on Rainfed Vertisols of Central India

Nutrient uptake and balance of the cotton (Gossypium hirsutum L.) + pigeonpea (Cajanus cajan(L.) Millsp.), a traditional strip intercropping system practiced on the rainfed Vertisols of central India is not known to us. On-farm participatory trials were conducted on 10 farmer fields, five each on medium deep (MDS) and deep soils (DS) of Nagpur, central India to determine the effect of technological interventions on N, P and K uptake of cotton and pigeonpea. The nutrient balance was also quantified as a difference of nutrient inputs and removal. Nutrients accumulated by the crops (grain, stalk and leaves) and weeds removed off the field by hand weeding were considered as nutrient removal, while fertilizer was considered as nutrient input. The interventions included application of recommended dose of fertilizer (RDF), RDF + conservation tillage with in situ green manure (CT₁) and CT₁ + application of ZnSO₄ (CT₂) and compared with farmers’ practice (FP). Nutrient uptake, in general, was higher on DS than on MDS. Among the interventions, N, P and K uptake of cotton and pigeonpea followed the order: CT₂ > CT₁ > RDF > FP. Mean N and P balance was positive in all the treatments. The balance may become negative if nutrient losses are accounted. A negative K balance was observed in all the treatments and the magnitude was the greatest for the FP plots (−39.4 kg ha⁻¹ y⁻¹). In spite of fertilizer-K application in the intervention plots, K balance was negative (−14.4 to −19.5 kg ha⁻¹ y⁻¹). By way of leaf and fruit drop, cotton and pigeonpea litter recycled 12.2 kg N, 1.7 kg P and 6.7 kg K ha⁻¹ y⁻¹     

Phosphorus transformation in a soybean-cropping system in Andosol: effects of winter cover cropping and compost application

Understanding phosphorus (P) transformation is necessary to develop sustainable P management practices on Andosol with large P-fixing capacity. This study was conducted during 2005–2007 in northeastern Japan to determine how the amounts of inorganic P (P_i) and organic P (P_o) fractions change in a Silandic Andosol under soybean production [Glycine max (L.)]. Two treatments were examined: application of composted cattle manure (0 (P0), 61 (P1), and 122 or 183 (P2) kg P ha⁻¹ year⁻¹) and winter cover cropping (no cover crop, rapeseed [Brassica napus], and cereal rye [Secale cereale L.]). Compost was applied before soybean seeding; cover crops were seeded after soybean harvest without further fertilization. Soil P was extracted sequentially with anion exchange resin (P_i), 0.5M NaHCO₃ (P_i, P_o), 0.1M NaOH (P_i, P_o), and 0.5M H₂SO₄ (P_i). Soybean removed 42.3 and 48.5 kg P ha⁻¹ (only 23 and 10% of the added P), respectively, in P1 and P2. In the P2 soil, 64% of excess P was distributed into P_i fractions, mainly resin-P_i and NaOH–P_i (29 and 19%, respectively). In P0, despite no P addition, soybean removed 41.5 kg P ha⁻¹ concurrently with a decrease in NaOH–P_i, suggesting its potential contribution to soybean P uptake. Neither of cover crops had significant effect on soil P fractions during the 3 year period.     

Soil nitrate-N levels required for high yield maize production in the North China Plain

High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize (Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458 no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha⁻¹) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season. Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake was 180 and 186 kg N ha⁻¹, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting soil nitrate-N content (r ² = 0.894), and 1 kg soil nitrate-N ha⁻¹ was equivalent to 1.23 kg fertilizer-N ha⁻¹ for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer rate (P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha⁻¹ with a range from 66 to 118 kg N ha⁻¹. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha⁻¹ for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize growing season.     

Nitrogen in soils,plants, surface water and shallow groundwater in a bahiagrass pasture of Southern Florida,USA

Despite substantial measurements using both laboratory and field techniques, little is known about the spatial and temporal variability of nitrogen (N) dynamics across the landscapes, especially in agricultural landscapes with cow–calf operations. This study was conducted to assess the comparative levels of total inorganic nitrogen, TIN (NO₃–N + NH₄–N) among soils, forage, surface water and shallow groundwater (SGW) in bahiagrass (Paspalum notatum, Flueggé) pastures. Soil samples were collected at 0–20, 20–40, 40–60, and 60–100 cm across the pasture’s landscape (top slope, TS; middle slope, MS; and bottom slope, BS) in the spring and fall of 2004, 2005 and 2006, respectively. Bi-weekly (2004–2006) groundwater and surface water samples were taken from wells located at TS, MS, and BS and from the run-off/seepage area (SA). Concentrations of NH₄–N, NO₃–N, and TIN in SGW did not vary with landscape position (LP). However, concentrations of NH₄–N, NO₃–N, and TIN in water samples collected from the seep area were significantly (P ≤ 0.05) higher when compared to their average concentrations in water samples collected from the different LP. Average concentrations of NO₃–N (0.4–0.9 mg l⁻¹) among the different LP were well below the maximum, of 10 mg l⁻¹, set for drinking water. The maximum NO₃–N concentrations (averaged across LP) in SGW for 2004, 2005 and 2006 were also below the drinking water standards for NO₃–N. Concentration of TIN in soils varied significantly (P ≤ 0.05) with LP and soil depth. Top slope and surface soil (0–20 cm) had the greatest concentrations of TIN. The greatest forage availability of 2,963 ± 798 kg ha⁻¹ and the highest N uptake of 56 ± 12 kg N ha⁻¹ were observed from the TS in 2005. Both forage availability and N uptake of bahiagrass at the BS were consistently the lowest when averaged across LP and years. These results can be attributed to the grazing activities as animals tend to graze more at the BS. The average low soil test value of TN (across LP and soil depth) in our soils of 10.9 mg kg⁻¹ (5.5 kg N ha⁻¹) would indicate that current pasture management including cattle rotation in terms of grazing days and current fertilizer application (inorganic + feces + urine) for bahiagrass pastures may not have negative impact on the environment.     

Nutrient evolution in soil and cereal yield under different fertilization type in dryland

Under semiarid conditions the response of crops to synthetic fertilizers is often reduced. Organic fertilizers can be used to provide a continuous source of nutrients for the crops. The soil nitrogen and crop yield in a rotation of durum wheat (Triticum durum)–fallow-barley (Hordeum vulgare)–vetch (Vicia sativa) were studied during 4 years when synthetic fertilizer (chemical), compost (organic) or no fertilizer (control) were applied in a field with high initial contents of soil NO₃–N (> 400 kg N ha⁻¹), phosphorus (22 mg kg⁻¹) and potassium (> 300 mg kg⁻¹). Changes in soil organic matter, phosphorus and potassium were also measured. During the crop period, chemical fertilization significantly increased the content of soil NO₃–N in the first 0.30 m of soil with respect to organic fertilization and the control. The yield of wheat and barley was not increased after applying chemical or organic fertilizer with respect to the unfertilized plots. The estimated losses of nitrogen were similar for the three types of fertilization, as well as the uptake of nitrogen for the total biomass produced. The initial levels of organic matter and phosphorus were maintained, even in the plots that were not fertilized, while the potassium decreased slightly. Thus, the rotation and burying of crop residues were enough to maintain the crop yield and the initial content of nutrients.     

Recovery of mineral fertiliser N and slurry N in continuous silage maize using the <Superscript>15</Superscript>N and difference methods

The stable isotope technique and the difference method are common approaches for estimating fertiliser N uptake efficiency. Both methods, however, have limitations and their suitability may depend on N management and environmental conditions. A field experiment was conducted on a humus sandy soil in northern Germany to estimate fertiliser N uptake efficiency of silage maize in the year of application (Zea mays L.) by the stable isotope and the difference method as influenced by the type of N fertiliser (mineral vs. cattle slurry), the application mode (separate or combined application), and N rate. Seven N treatments were included (0, 50, 100 and 150 kg mineral N ha⁻¹; 20, 40 m3 cattle slurry ha⁻¹; 50 kg mineral N ha⁻¹ plus 40 m3 slurry ha⁻¹), where either mineral N or slurry N was labelled, and mineral N was split into two dressings. In addition, 4.1 kg ha⁻¹ labelled mineral N was incorporated into otherwise unlabelled treatments (0, 20, 40 m3 ha⁻¹, and 50 kg mineral N ha⁻¹ plus 40 m3 ha⁻¹) to estimate N uptake from the upper soil layer. Uptake of ¹⁵N was followed in leaves, stalk, ear, and the whole crop. Fertiliser N uptake efficiency (FNUE_15N) of mineral fertiliser N obtained by the isotope technique ranged between 51 and 61%. Recovered fertiliser N was mainly found in the ear, while less labelled N remained in leaves and the stalk. The nitrogen rate tended to increase the amount of recovered N, but the effect was not consistent among plant parts and the whole crop. Plant N uptake from non-fertiliser N was found to increase N input up to 100 kg N ha⁻¹. Nitrogen recoveries of the two mineral N dressings were similar for the different plant parts as well as for the whole crop. Fertiliser N uptake efficiency (FNUE_diff) of mineral N estimated by the difference method resulted in substantially higher values compared to FNUE_15N, varying between 56 and 98%. More N was taken up from the upper soil layer with increasing N supply, which is regarded as a major error source of the difference method. Slurry N was taken up less efficient in the year of application than mineral fertiliser N as indicated by recovery rates of 21–22% (FNUE_15N) and 39–62% (FNUE_diff), respectively. When mineral N and slurry were applied together, the difference method estimated significantly lower N uptake efficiencies for both mineral and slurry N compared to a single application, while values obtained by the isotope method were not affected.     

Soil nitrogen conservation with continuous no-till management

Tillage management is an important regulator of organic matter decomposition and N mineralization in agroecosystems. Tillage has resulted in the loss of considerable organic N from surface soils. There is potential to rebuild and conserve substantial amounts of soil N where no-till management is implemented in crop production systems. The objectives of our research were to measure N conservation rate with continuous no-till management of grain cropping systems and evaluate its impact on mineralizable and inorganic soil N. Samples were collected from 63 sites in production fields using a rotation of corn (Zea mays L.)—wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.)—double-crop soybean (Glysine max L.) across three soil series [Bojac (Coarse-loamy, mixed, semiactive, thermic Typic Hapludults), Altavista (Fine-loamy, mixed semiactive, thermic Aquic Hapludults), and Kempsville (Fine-loamy, siliceous, subactive, thermic Typic Hapludults)] with a history of continuous no-till that ranged from 0 to 14 yrs. Thirty-two of the sites had a history of biosolids application. Soil cores were collected at each site from 0–2.5, 2.5–7.5 and 7.5–15 cm and analyzed for total N, Illinois soil N test-N (ISNT-N), and [NH₄ + NO₃]-N. A history of biosolids application increased the concentration of total soil N by 154 ± 66.8 mg N kg⁻¹ (310 ± 140 kg N ha⁻¹) but did not increase ISNT-N in the surface 0 – 15 cm. Continuous no-till increased the concentration of total soil N by 9.98 mg N kg⁻¹ year⁻¹ (22.2 ± 21.2 kg N ha⁻¹ year⁻¹) and ISNT-N by 1.68 mg N kg⁻¹ year⁻¹ in the surface 0–15 cm. The implementation of continuous no-till management in this cropping system has resulted in conservation of soil N.

Smallholder farmer management impacts on particulate and labile carbon fractions of granitic sandy soils in Zimbabwe

Crop production in maize-based smallholder farming systems of Southern Africa is hampered by lack of options for efficiently managing limited and different quality organic nutrient resources. This study examined impacts of farmers’ short- and long-term organic resource allocation patterns on sizes and quality of soil organic matter (SOM) fractions. Farmers’ most- (rich) and least- (poor) productive fields were studied for two seasons under low (450–650 mm yr⁻¹) to high (>750 mm yr⁻¹) rainfall areas in Zimbabwe, on Lixisols with ∼6% clay and 88% sand. Rich fields received 0.5–14 Mg C ha⁻¹ compared with <4 Mg C ha⁻¹ for poor fields, and the differences were reflected in soil particulate organic matter (POM) fractions. Organic inputs were consistent with resource endowments, with well-endowed farmers applying at least five times the amounts used by resource-constrained farmers. Rich fields had 100% more macro-POM (250–2,000 μm diameter) and three times more meso-POM (53–250 μm) than poor fields. Application of high quality (>25 mg N kg⁻¹) materials increased labile C (KMnO₄ oxidizable) in top 60 cm of soil profile, with 1.6 Mg C ha⁻¹ of Crotalaria juncea yielding labile C amounts similar to 6 Mg C ha⁻¹ of manure. Labile C was significantly related to mineralizable N in POM fractions, and apparently to maize yields (P < 0.01). Farmers’ preferential allocation of nutrient resources to already productive fields helps to maintain critical levels of labile SOM necessary to sustain high maize yields.     

Deuterium uptake and plasma cholesterol precursor levels correspond as methods for measurement of endogenous cholesterol synthesis in hypercholesterolemic women

To assess the validity of two techniques used to measure human cholesterol synthesis, the rate of uptake of deuterium (D) into plasma free cholesterol (FC), and plasma cholesterol precursor (squalene, lanosterol, desmosterol and lathosterol) levels were compared in 14 women [65–71 yr with low density lipoprotein-cholesterol (LDL-C)≥3.36 mmol·l ⁻¹]. Subjects consumed each of six diets for 5-wk periods according to a randomized crossover design. The experimental diets included a baseline diet (39% energy as fat, 164 mg chol·4.2 MJ⁻¹) and five reduced-fat diets (30% of energy as fat), where two-thirds of the fat was either soybean oil; squeeze, tub or stick margarines; or butter. Fractional and absolute synthesis rates (FSR and ASR) of FC were determined using the deuterium incorporation (DI) method, while cholesterol precursor levels were measured using gas-liquid chromatography. Data were pooled across diets for each variable and correlation coefficients were calculated to determine if associations were present. There was good agreement among levels of the various cholesterol precursors. In addition, FSR in pools/d (p·d⁻¹) and ASR in grams/d (g·d⁻¹) were strongly associated with lathosterol (r=0.72 and 0.71, P=0.0001), desmosterol (r=0.75 and 0.75, P=0.0001), lanosterol (r=0.67 and 0.67), and squalene (r=0.69 and 0.68) when levels of the precursors were expressed as μmol·mmol⁻¹C. Significant but lower correlations were observed between the D uptake and plasma cholesterol precursor levels when the latter were expressed in absolute amounts (μmol·L⁻¹). The wide range of fatty acid profiles of the experimental diets did not influence the degree of association between methods. In conclusion, the DI method and levels of some cholesterol precursors correspond as methods for shortterm measurement of cholesterol synthesis.     

Broiler chicken litter application timing effect on Coastal bermudagrass in southeastern U.S.

Presently, more than 85% of the broiler chicken (Gallus gallus domesticus) litter (BCL) is being applied to pasture lands year-round. This practice results in nutrient losses and potentially unfavorable environmental impacts particularly during the wet winter months. A field plot experiment was initiated in 2001 on a Ruston silt loam in Mize, MS to identify the proper BCL application timing that enhances BCL nutrient uptake by crops while minimizing undesirable nutrient buildup in soil. Seven treatments (BCL application timings) were employed on previously established “Coastal” hybrid bermudagrass [Cynodon dactylon (L.) Pers.] plots. For each treatment, the quantity of broiler chicken litter (a mixture of chicken manure plus bedding materials) needed for each plot was calculated based on the BCL total N content to provide 400 kg N ha⁻¹ for top bermudagrass yield (18 Mg ha⁻¹) and applied either as a single, two-way split, or three-way split at different dates as follow: May; May/June; April/May/June; May/June/July; June/July/August; July/August/September; and August/September/October. Bermudagrass was harvested 5 times each year for dry matter (DM) and nutrient uptake determination. Significant differences in DM yield were observed in each year among application timings. The greatest DM yield was 18.6 Mg ha⁻¹ for the single application in May and lowest at 15.0 Mg ha⁻¹ for Aug/Sep/Oct application dates in 2001 and followed by the same trend in 2002. The N and P uptake by bermudagrass ranged from 270 to 381, and 53 to 63 kg ha⁻¹ respectively, in 2001. Similar trend, but lower values for nutrient uptake were observed in 2002. Significant differences were observed among BCL application timings in regard to soil residual of total carbon (TC), total nitogen (TN), Mehlich 3 extracted P (M3-P), NO₃–N, Cu, and Fe elements at the end of the study. In general, summer and early fall BCL applications resulted in greater buildup of most of these elements. Based on the results of this study, there is a wide window (May–July) for BCL application timing on bermudagrass considering the criteria of producing high yield and low soil residual nutrient. However, the best BCL application timing should be in spring (late April–June) when minimum temperatures exceed those required (24–27°C) for bermudagrass growth.     

Minimizing nitrogen losses from a corn–soybean–winter wheat rotation with best management practices

Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year-round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn (Zea mays L.)-soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation managed under Best Management (BM) compared with conventional practices (CONV). The study was conducted from May 2000 to October 2004 at Elora, Ontario, Canada. Cumulative NO₃ leaching loss was reduced by 51% from 133 kg N ha⁻¹ in CONV to 68 kg N ha⁻¹ in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11–16% to leaching in CONV and <4% in BM. High soil derived N leaching loss in CONV, which occurred mostly (about 80%) during November to April was attributable to 45–69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency (FNUE) was higher in BM (61% of applied) than in CONV (35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV (for corn: 2000 and 2003, wheat: 2002, soybean: 2004) or higher in BM (soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP (no-tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.     

Effects of mulch,N fertilizer,and plant density on wheat yield,wheat nitrogen uptake,and residual soil nitrate in a dryland area of China

Understanding mulching influences on nitrogen (N) activities in soil is important for developing N management strategies in dryland. A 3 year field experiment was conducted in the Loess Plateau of China to investigate the effects of mulching, N fertilizer application rate and plant density on winter wheat yield, N uptake by wheat and residual soil nitrate in a winter wheat-fallow system. The split plot design included four mulching methods (CK, no mulch; SM, straw mulch; FM, plastic film mulch; CM, combined mulch with plastic film and straw) as main plot treatments. Three N fertilizer rates (N0, 0 kg N ha⁻¹; N120, 120 kg N ha⁻¹; N240, 240 kg N ha⁻¹) were sub-plot treatments and two wheat sowing densities (LD, low density, seeding rate = 180 kg ha⁻¹; HD, high density, seeding rate = 225 kg ha⁻¹) were sub-subplot treatments. The results showed that wheat yield, N uptake, and N use efficiency (NUE) were higher for FM and CM compared to CK. However, soil nitrate-N contents in the 0–200 cm soil profile were also higher for FM and CM compared to CK after the 3 year experiment. Wheat grain yields were higher for SM compared to CK only when high levels of nitrogen or high planting density were applied. Mulching did not have a significant effect on wheat yield, nitrogen uptake and NUE when soil water content at planting was much high. Wheat yield, N uptake, and residual nitrate in 0–200 cm were significantly higher for N240 compared to N120 and N0. Wheat yield and N uptake were also significantly higher for HD compared to LD. When 0 or 120 kg N ha⁻¹ was applied, HD had more residual nitrate than LD while the reverse was true when 240 kg N ha⁻¹ was applied. After 3 years, residual nitrate-N in 0–200 cm soil averaged 170 kg ha⁻¹, which was equivalent to ~40% of the total N uptake by wheat in the three growing seasons.