Seasonal dynamics of carbon and nitrogen pools and fluxes under continuous arable and ley-arable rotations in a temperate environment

Improved understanding of the seasonal dynamics of C and N cycling in soils, and the main controls on these fluctuations, is needed to improve management strategies and to better match soil N supply to crop N demand. Although the C and N cycles in soil are usually considered to be closely linked, few data exist where both C and N pools and gross N fluxes have been measured seasonally. Here we present measurements of inorganic N, extracted soluble organic N, microbial biomass C and N, gross N fluxes and CO₂ production from soil collected under wheat in a ley‐arable and continuous arable rotation within a long‐term experiment. The amounts of inorganic N and extracted soluble organic N were similar (range 5–35 kg N ha⁻¹; 0–23 cm) but had different seasonal patterns: whilst inorganic N declined during wheat growth, extracted soluble organic N peaked after cultivation and also during maximal stem elongation. The microbial biomass was significantly larger in the ley‐arable (964 kg C ha⁻¹; 0–23 cm) than the continuous arable rotation (518 kg C ha⁻¹; 0–23 cm) but with no clear seasonal pattern. In contrast, CO₂ produced from soil and gross N mineralization showed strong seasonality linked to soil temperature and moisture content. Normalization of soil CO₂ production and gross N mineralization with respect to these environmental regulators enabled us to study the underlying influence of the incorporation of fresh plant material into soil on these processes. The average normalized gross rates of N mineralized during the growing season were 1.74 and 2.55 kg N ha⁻¹ nday⁻¹ in continuous arable and ley‐arable rotations respectively. Production rates (gross N mineralization, gross nitrification) were similar in both land uses and matched rates of NH₄⁺ and NO₃⁻ consumption, resulting in periods of net N mineralization and immobilization. There was no simple relationship between soil CO₂ production and gross N mineralization, which we attributed to changes in the C : N ratio of the mineralizing pool(s).     

Using farmer knowledge to combat low productive spots in rice fields of a Sahelian irrigation scheme

In the oldest sections of Burkina Faso's largest irrigation scheme in the Sourou Valley (13° 10′ N, 03° 30′W) rice (Oryza sativa L.) yields dropped from about 5 to 6 t ha⁻¹ in the early 1990s, shortly after establishment of the scheme, to 2 to 4 t ha⁻¹ from 1995 onwards. Farmers blamed this yield decline on the appearance of 2 to 20 m diameter low productive spots. According to farmers and field measurements, the low productive spots decreased yields by 25–50 per cent. The low productive spots are caused by Zn deficiency. Low Zn availability is related to the very low DTPA‐extractable Zn content of the soil (0·08–0·46 mg kg⁻¹), the alkaline‐calcareous character of the soil, the non‐application of Zn fertilizers, and a relatively large P fertilizer dose (21 kg P ha⁻¹). Farmers were correct in relating the calcareous nature of the soil to the presence of the low productive spots. They were instrumental in identifying application of decomposed organic resources (e.g. rice straw at 5 t ha⁻¹) as a short‐term solution that increases yields by 1·5 to 2·0 t ha⁻¹. Application of Zn fertilizer (10 kg Zn ha⁻¹) in 29 farmer fields in the 2001 dry season eradicated the low productive spots and increased yields from 3·4 to 6·0 t ha⁻¹. Although application of Zn fertilizer is strongly recommended, it is not yet available in Burkina Faso. Based on a comparison of fertilizer prices on the world market and the local market, we expect that the use of Zn fertilizers will be highly profitable (cost/value ratio ≫ 2). Despite the relatively recent introduction of irrigated rice cropping, most farmers showed a good understanding of cropping constraints and possible solutions. Both farmers and researchers mutually benefited from each other's knowledge and observations. Copyright © 2004 John Wiley & Sons, Ltd.     

Soil nutrient dynamics,growth and yield of green maize and vegetable cowpea with organic-based fertilization

The growth and yield performance of green maize (Zea mays), followed by a late-season vegetable cowpea (Vigna unguiculata), was assessed with two rates of three different types of organic-based fertilizers (OBFs) fortified with an inorganic nutrient source. There was also an inorganic fertilizer treatment of NPK 20–10–10 applied at 300 kg ha^?1 and a no-fertilizer control treatment. Maize growth was affected by fertilizer type and rate. Organic fertilizer, applied at 5 t ha^?1, 3 weeks before maize released enough nutrients to have comparable growth as inorganic fertilizer. Applying the OBF at 2.5 t ha^?1 was inadequate to give comparable growth. Application of fortified OBF with total nitrogen content higher than 2.4% N at 5.0 t ha^?1 gave maize grain yields comparable with NPK fertilizer. Cowpea yields following early-season maize were highest with DPW + NPK. They were significantly lower with 2.5 t ha^?1 of the OBFs. Application of the IAR&T-OBF (OBF made by Institute of Agricultural Research and Training) and decomposed poultry waste (DPW) + NPK at 5.0 t ha^?1 gave comparable seed yields significantly higher than OYO-OBF (OBF made by Oyo State Government of Nigeria). NPK fertilizer application supported early-season maize cultivation, but it was not adequate to support the following cowpea. OBF should have nitrogen content up to 2.4% and applied at 5.0 t ha^?1 to support an early-season maize cultivation with a late-season cowpea.     

C and N accumulation in arable soils of West Germany and its influence on the environment — Developments 1970 to 1998

During the last three decades, large amounts of soil organic matter (SOM) and associated nutrients have been accumulated in arable soils of Western Germany (former FRG) due to deepening of the plough layers (from < 25 to > 35 cm) and to fertilizer application rates which have exceeded the amounts of nutrients removed in harvested crops. Organic carbon and total nitrogen balances (1970—1998) on 120 plots from 16 farms in southern Lower Saxony yielded a cumulative increase of up to 16 t C ha⁻¹ and 1 t N ha⁻¹ in loess soils used for cash crop production and up to 26 t C ha⁻¹ and 2.4 t N ha⁻¹ in sandy soils under livestock production. The buffering capacity for reactive compounds, particularly of C, N, S and P and of other (organic or inorganic) pollutants will reach its limits in the near future, after organic matter ”︁equilibria” have been re‐established. An immediate adaptation of the current fertilizer application rates to the nutrient export by field crops is therefore urgently needed.     

Long-term fertilizer trials on loam soil at M⊘ystad,south-eastern Norway: Crop yields,nutrient balances and soil chemical analyses from 1983 to 2003

Abstract

Factorial combinations of N, P and K fertilizer have been compared with the use of farmyard manure at M?ystad since 1922 in a seven-year crop rotation (3 ley, oat, potato, wheat, barley). Until 1982, low inputs of N fertilizer (22 kg ha^?1) were used. In 1983, they were brought into line with current farming practice. This paper presents the results of three subsequent rotations. Yields without any fertilizer were on average 48% of those with 100 kg N ha^?1 in compound fertilizer, whilst those with 20, 40 and 60 Mg ha^?1 farmyard manure were 81, 87 and 90%, respectively. Yields with other combinations of N, P and K declined in the order NP, NK, N, PK and K. When NPK fertilizer was used, apparent recoveries of applied fertilizer were close to 50% for N and K, and around 40% for P. Much lower values were found for nutrients applied singly. Balance between N supply and removal was indicated at rates of about 60 kg N fertilizer ha^?1 in potatoes, 75 kg ha^?1 in cereals and 90 kg ha^?1 in leys. A surplus of P was found in all crops at all N levels, and of K in cereals and potatoes. In leys, K balance was achieved with an N supply of 90 kg N ha^?1. Nutrient balance was indicated at a little below 20 Mg ha^?1 yr^?1 farmyard manure. Larger manure applications gave large nutrient surpluses, particularly of N. Soil reaction remained close to neutral with the use of calcium nitrate and manure, but declined with the use of ammonium nitrate. Manure use gave the highest amounts of available P, K and Mg in soil. Similar increases in total inorganic P were found with manure use as with fertilizer use, but amounts of organic P and total K were little affected.     

Economic and environmental optimization of nitrogen fertilizer recommendations for cereals in Norway

Abstract

Results of 240 annual N fertilizer trials in 1991–2007 in spring and winter cereals are presented. On average, spring barley and oat yields increased little beyond 120 kg N ha^?1 in fertilizer. Somewhat higher figures were found for spring and winter wheat. Regression equations for yield and N uptakes in grain and straw were derived, related to N fertilizer input and the yield level in individual trials (indicator of yield expectancy). These equations accounted for 90% of the variation in yield and 80% of that in N uptake. Quadratic N responses were significant in all cases, as were interactions between N responses and yield level. They were verified with data from 27 separate trials performed in 2008–2010. The yield equations were used to calculate economically optimum N fertilizer levels with varying ratios of product price to fertilizer cost at contrasting levels of yield. The optimum N fertilizer level for barley and oats was found to increase by 8.3 kg N ha^?1 per Mg increase in expected yield. The equivalent figure in wheat was 16.3 kg N ha^?1. Optimum N fertilizer levels decreased by 4.1 and 6.7 kg N ha^?1, for barley/oats and wheat respectively, per unit increase in the cost/price ratio. The equations for N uptake were used to calculate simple N balances between fertilizer input and removal in crop products. Large N surpluses were indicated at low levels of yield expectancy, but the surplus declined markedly with increasing yield level, despite greater N fertilizer inputs at high yield. Calculations made for national average yield levels in recent years showed N surpluses of 50–60 kg N ha^?1 when only grain is removed and 25–40 kg N ha^?1 when straw is removed also. Limiting N input to obtain zero balance reduces yields considerably at average levels of yield expectancy.     

Effect of straw biochar application on soil carbon,greenhouse gas emissions and nitrogen leaching: A vegetable crop rotation field experiment

Intensive vegetable crop systems are rapidly developing, with consequences for greenhouse gas (GHGs) emissions, nitrogen leaching and soil carbon. We undertook a field trial to explore the effect of biochar application (0, 10, 20 and 40 t ha⁻¹) on these factors in lettuce, water spinach and ice plant rotation. Our results show that the 20 and 40 t ha⁻¹ soil treatments resulted in the SOC content being 26.3% and 29.8% higher than the control (0 t ha⁻¹), respectively, with significant differences among all treatments (p < .05). Biochar application caused N₂O emissions to decrease during the lettuce and water spinach seasons, by 1.5%–33.6% and 12.4%–40.5%, respectively, compared the control, with the 20 t ha⁻¹ application rate resulting in the lowest N₂O emissions. Biochar also decreased the dissolved nitrogen (DN) concentration in leachate by 9.8%–36.2%, following a 7.3%–19.9% reduction in dissolved nitrogen in the soil. Similarly, biochar decreased the nitrate (NO₃⁻) concentrations in leachate by 3.9%–30.2%, following a 3.8%–16.7% reduction in the soil nitrate level. Overall, straw biochar applied at rate of 20 t ha⁻¹ produced the lowest N₂O emissions and N leaching, while, increasing soil carbon.     

Winter legumes as a nitrogen source for no-tillage cotton

Winter legumes can serve dual purposes in no-tillage cropping systems. They can provide a no-tillage mulch, and supply a considerable quantity of N for thesummer crops. Cotton (Gossypium hirsutum L.) was no-tillage planted into crimson clover (Trifolium incarnatum L.), common vetch (Vicia sativa L.), and fallowed soil for two years to determine the effects of winter legume mulches on growth, yield, and N fertilizer requirements. The legumes were allowed to mature and reseed prior to planting cotton. The winter legumes produced no measurable changes in soil organic matter, N, or bulk density, but water infiltration was more rapid in the legume plots than in the fallowed soil. In the fallow system, 34 kg ha^?1 N fertilizer was required for near maximum yields. In the clover plots, yields without N fertilizer were higher than when N (34 and 68 kg ha^?1) was applied. In the vetch plots, cotton yields were highest without N fertilizer the first year, but yields were increased with 34 kg ha^?1 N the second year because of a poor vetch seed crop and a subsequently poor legume stand. In the clover plots, a 20–30% cotton seedling mortality occurred in one year, but this stand reduction apparently did not affect cotton yields. Winter legume mulches can provide the N needs for no-tillage cotton without causing an excessive and detrimental quantity of N in sandy soils naturally low in soil N (0.04%). Unless the reseeding legume systems are maintained for at least 3 years, the legumes do not, however, provide an economical N source for cotton when N fertilizer requirementsare low (34 kg ha^?1 in this study). A possible disadvantage of the system for reseeding legumes is that cotton planting is delayed 4–6 weeks beyond the normal planting date, which can reduce yields in some years.     

Effect of mineral nitrogen fertilizer forms on N2O emissions from arable soils in winter wheat production

Nitrogen fertilizers are supposed to be a major source of nitrous oxide (N₂O) emissions from arable soils. The objective of this study was to compare the effect of N forms on N₂O emissions from arable fields cropped with winter wheat (Triticum aestivum L.). In three field trials in North‐West Germany (two trials in 2011/2012, one trial in 2012/2013), direct N₂O emissions during a one‐year measurement period, starting after application of either urea, ammonium sulfate (AS) or calcium ammonium nitrate (CAN), were compared at an application rate of 220 kg N ha^?1. During the growth season (March to August) of winter wheat, N₂O emission rates were significantly higher in all three field experiments and in all treatments receiving N fertilizer than from the non‐fertilized treatments (control). At two of the three sites, cumulative N₂O emissions from N fertilizer decreased in the order of urea > AS > CAN, with emissions ranging from 522–617 g N ha^?1 (0.24–0.28% of applied fertilizer) for urea, 368–554 g N ha^?1 (0.17–0.25%) for AS, and 242–264 g N ha^?1 (0.11–0.12%) for CAN during March to August. These results suggest that mineral nitrogen forms can differ in N₂O emissions during the growth period of winter wheat. Strong variations in the seasonal dynamics of N₂O emissions between sites were observed which could partly be related to weather events (e.g., precipitation). Between harvest and the following spring (post‐harvest period) no significant differences in N₂O emissions between fertilized and non‐fertilized treatments were detected on two of three fields. Only on one site post‐harvest emissions from the AS treatment were significantly higher than all other fertilizer forms as well as compared to the control treatment. The cumulative one‐year emissions varied depending on fertilizer form across the three field sites from 0.05% to 0.51% with one exception at one field site (AS: 0.94%). The calculated overall fertilizer induced emission averaged for the three fields was 0.38% which was only about 1/3 of the IPCC default value of 1.0%.     

保护地蔬菜轮作体系中两种不同复合肥对产量的影响及其氮素动态特征

Yield and N uptake of tomato (Lycopersicum esculentum Mill.) and pepper (Capsicum annuum L.) crops in five successive rotations receiving two compound fertilizers (12-12-17 and 21-8-11 N-P₂O₅-K₂O) were studied to determine 1) crop responses, 2) dynamics of NO₃-N and NH₄-N in different soil layers, 3) N balance and 4) system-level N efficiencies. Five treatments (2 fertilizers, 2 fertilizer rates and a control), each with three replicates, were arranged in the study. The higher N fertilizer rate, 300 kg N ha^-1 (versus 150 kg N ha^-1), returned higher vegetable fruit yields and total aboveground N uptake with the largest crop responses occurring for the low-N fertilizer (12-12-17) applied at 300 kg N ha^-1 rather than with the high-N fertilizer (21-8-11). Ammonium-N in the top 90 cm of the soil profile declined during the experiment, while nitrate-N remained at a similar level throughout the experiment with the lower rate of fertilizer N. At the higher rate of N fertilizer there was a continuous NO₃-N accumulation of over 800 kg N ha^-1. About 200 kg N ha^-1 was applied with irrigation to each crop using NO₃-contaminated groundwater. In general, about 50% of the total N input was recovered from all treatments. Pepper, relative to tomato, used N more efficiently with smaller N losses, but the crops utilized less than 29% of the fertilizer N over the two and a half-year period. Local agricultural practices maintained high residual soil nutrient status. Thus, optimization of irrigation is required to minimize nitrate leaching and maximize crop N recovery.     

Changes in soil carbon and crop yield over 60 years in the Zurich Organic Fertilization Experiment,following land‐use change from grassland to cropland

Changes in land‐use and agricultural management affect soil organic C (SOC) storage and soil fertility. Grassland to cropland conversion is often accompanied by SOC losses. However, fertilization, crop rotation, and crop residue management can offset some SOC losses or even convert arable soils into C sinks. This paper presents the first assessment of changes in SOC stocks and crop yields in a 60‐year field trial, the Zurich Organic Fertilization Experiment A493 (ZOFE) in Switzerland. The experiment comprises 12 treatments with different organic, inorganic and combined fertilization regimes. Since conversion to arable land use in 1949, all treatments have lost SOC at annual rates of 0.10–0.25 t C ha^?1, with estimated mean annual C inputs from organic fertilizers and aboveground and belowground plant residues of 0.6–2.4 t C ha^?1. In all treatments, SOC losses are still in progress, indicating that a new equilibrium has not yet been reached. Crop yields have responded sensitively to advances in plant breeding and in fertilization. However, in ZOFE high yields can only be ensured when mineral fertilizer is applied at rates typical for modern agriculture, with yields of main crops (winter wheat, maize, potatoes, clover‐grass ley) decreasing by 25–50% when manure without additional mineral fertilizer is applied. ZOFE shows that land‐use change from non‐intensively managed grassland to cropland leads to soil C losses of 15–40%, even in rotations including legumes and intercrops, improved agricultural management and organic fertilizer application.     

A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on shallow soil overlying Chalk: crop uptake and leaching losses

The objective of this work was to determine the fate of fertilizer nitrogen (labelled with nitrogen-15) applied to an undisturbed shallow soil overlying Chalk contained in 10 lysimeters (80 cm diameter, 135 cm deep). Measurements are reported of the nitrogen uptake by four spring barley crops and the rate and extent of leaching of nitrate beyond the roots. The crops were fertilized with 0, 80 or 120 kg N ha^?1 in each of four years, but only the first application in 1977 was labelled with nitrogen ?15. Rainfall and irrigation approximated to the long-term average, but in two treatments dry or wet spring conditions were imposed for the 10 weeks after sowing the first crop in 1977. The dry matter and grain yields of the spring barley crops varied from year to year in the ranges 8.7–14.0 t ha^?1 and 3.5–6.1 t ha^?1 respectively. The total nitrogen harvested in the crop approximated to the amount of nitrogen applied in each year with an apparent recovery of fertilizer in the range 38–76%. The recovery of nitrogen derived from fertilizer (labelled with nitrogen-15) was 46–54% in the first crop and after 2 years rapidly declined to below 1%. The total amount of nitrogen-15 labelled fertilizer recovered in four barley crops was 49–57% of that applied. Mean annual nitrate concentrations in water draining from the base of the lysimeters were in the range 11.8–26.7 mg N 1^?1 and did not differ significantly between nitrogen fertilizer treatments (0, 80 and 120 kg N ha^?1 a^?1). In all treatments nitrate concentrations varied considerably within each growing season, with a cycle of peaks and troughs. Annual losses of nitrate were in the range 39–128 kg N ha^?1, and the mean annual losses over the 4 years varied between lysimeters from 65 to 83 kg N ha^?1. Nitrogen-15 labelled nitrate was detected in the first drainage water collected in autumn following its spring application, 5 months earlier. Recovery of fertilizer-derived nitrogen in drainage water was greatest during the winter following the second barley crop, and was 3.4–3.7% of the nitrogen-15 applied. Over the 4 years of the experiment 6.3–6.6% of labelled fertilizer was accounted for in drainage water, representing 2–3% of the total nitrogen lost by leaching.     

Nitrate leaching and residual soil nitrogen supply following outdoor pig farming

Abstract. Large nitrogen (N) inputs to outdoor pig farms in the UK can lead to high nitrate leaching losses and accumulation of surplus N in soil. We investigated the residual effects of three contrasting outdoor pig systems as compared to an arable control on nitrate leaching and soil N supply for subsequent spring cereal crops grown on a sandy loam soil during 1997/98 and 1998/99 harvest seasons. Previously, the pig systems had been stocked for 2 years from October 1995 and were designated current commercial practice (CCP, 25 sows ha^?1 on stubble), improved management practice (IMP, 18 sows ha^?1 on undersown stubble) and best management practice (BMP, 12 sows ha^?1 on established grass). Estimated soil N surpluses by the end of stocking in September 1997 were 576, 398, 265 and 27 kg ha^?1 N for the CCP, IMP, BMP and continuous arable control, respectively. Nitrate leaching losses in the first winter were 235, 198, 137 and 38 kg ha^?1 N from the former CCP, IMP and BMP systems and the arable control, respectively. These losses from the former pig systems were equivalent to 41–52% of the estimated soil N surpluses. Leaching losses were much smaller in the second winter at 21, 14, 23 and 19 kg ha^?1 N, respectively. Cultivation timing had no effect (P>0.05) on leaching losses in year 1, but cultivation in October compared with December increased nitrate leaching by a mean of 14 kg ha^?1 N across all treatments in year 2. Leaching losses over the two winters were correlated (P<0.001) with autumn soil mineral N (SMN) contents. In both seasons, spring SMN, grain yields and N offtakes at harvest were similar (P>0.05) for the three previous pig systems and the arable control, and cultivation timing had no effect (P>0.05) on grain yields and crop N offtake. This systems study has shown that nitrate leaching losses during the first winter after outdoor pig farming can be large, with no residual available N benefits to following cereal crops unless that first winter is much drier than average.     

Nursery‐Box Total Fertilization Technology (NBTF) Application for Increasing Nitrogen Use Efficiency in Chinese Irrigated Riceland: N–Soil Interactions

High N fertilizer and flooding irrigation applied to rice in anthropogenic‐alluvial soil often result in N leaching and low use efficiency of applied fertilizer N from the rice field in Ningxia irrigation region in the upper reaches of the Yellow River. Sound N management practices need to be established to improve N use efficiency while sustaining high grain yield levels and minimize fertilizer N loss to the environment. We investigated the effects of Nursery Box Total Fertilization technology (NBTF) on N leaching at different rice growing stages, N use efficiency and rice yield in 2010 and 2011. The four fertilizer N treatments were 300 kg N ha⁻¹ (CU, Conventional treatment of urea at 300 kg N ha⁻¹), 120 kg N ha⁻¹ (NBTF120, NBTF treatment of controlled‐release N fertilizer at 120 kg N ha⁻¹), 80 kgN ha⁻¹ (NBTF80, NBTF treatment of controlled‐release N fertilizer at 80 kg N ha⁻¹) and no N fertilizer application treatment (CK). The results showed that the NBTF120 treatment increased N use efficiency, maintained crop yields and substantially reduced N losses to the environment. Under the CU treatment, the rice yield was 9634 and 7098 kg ha⁻¹, the N use efficiency was 31·6% and 34·8% and the leaching losses of TN were 44·51 and 39·89 kg ha⁻¹; NH₄⁺‐N was 5·26 and 5·49 kg ha⁻¹, and NO₃⁻‐N was 27·94 and 26·22 kg ha⁻¹ during the rice whole growing period in 2010 and 2011, respectively. Compared with CU, NBTF120 significantly increased the N use efficiency and decreased the N losses from the paddy field. Under NBTF120, the N use efficiency was 56·3% and 51·4%, which was 24·7% and 16·6% higher than that of CU, and the conventional fertilizer application rate could be reduced by 60% without lowering the rice yield while decreasing the leaching losses of TN by 16·27 and 14·36 kg ha⁻¹, NH₄⁺‐N by 0·90 and 1·84 kg ha⁻¹, NO₃⁻‐N by 110·6 and 10·14 kg ha⁻¹ in 2010 and 2011, respectively. Our results indicate that the CU treatment resulted in relatively high N leaching losses, and that alternative practice of NBTF which synchronized fertilizer application with crop demand substantially reduced these losses. We therefore suggest the NBTF120 be a fertilizer application alternative which leads to high food production but low environmental impact. Copyright © 2014 John Wiley & Sons, Ltd.     

Potato tuber yield and quality in response to different nitrogen fertilizer application rates under two split doses in an irrigated sandy loam soil

Abstract

Management strategies to minimize nitrogen (N) losses to the atmosphere and water bodies from potato production fields while maintaining tuber yields and quality relies on good N management. A 2-year (2016–17 and 2017–18) field trial with ‘Symphonia’ potato was completed on a sandy loam soil irrigated with flood irrigation in Punjab, Pakistan to investigate the effect of N fertilizer rate on vegetative, yield and tuber quality parameters. The N fertilizer treatments comprising six N rates from 0 to 300?kg ha^?1 were applied at 50?kg N increments. Number of stems and tubers plant^?1 showed a quadratic response while other parameters revealed cubic trends in response to N fertilizer rates. Applying more than 250?kg ha^?1 of N fertilizer did not increase vegetative growth and yield. In conclusion, the optimal N-application rate of 250?Kg ha^?1 has great potential to improve yield and quality of potato in the sub-tropical region of Punjab, Pakistan. These findings, besides improving productivity can minimize the risk of N fertilizer loss to the atmosphere.     

Diversified nitrogen rates influence nitrogen agronomic efficiency and seed yield response index of sesame (Sesamum Indicum,L.) cultivars

ABSTRACT

Due to elevating costs of N fertilizer and growing apprehensions about nitrate, experiments evaluating nitrogen agronomic efficiency (NAE) is becoming increasingly important in crop production. NAE and seed yield potentiality of three cultivars of sesame (Shandwel–1, Giza–32 and Sohag–1) were evaluated under four N applications (0, 72, 108, and 144 kg N ha^?1) in a field experiment. Results showed that Sohag–1 recorded the highest values of yield and yields traits surpassing the other two cultivars. Sesame plants received 144 or 108 kg N ha^?1 produced the highest seed yield. In plots fertilized by 108 or 144 kg N ha^?1, Sohag–1 was the potent cultivar for recording higher seed yield. N addition more or less than 108 kg N ha^?1 caused suppression in NAE. Sohag–1 was the most effective and responsive cultivar in N use being exceeded the averages of each seed yield at zero N rate and seed yield response index (SYRI).     

Effects of biochar and fertilizer sources on nitrogen uptake by chilli pepper plants under Mediterranean climate

This study determined N uptake by serrano chilli pepper for two years and evaluated the effects of biochar amendment or organic N (org-N) fertilizer on N use under a Mediterranean climate. A field experiment was conducted using microplots from 2016 to 2017 in California, USA. Treatments included biochar amendment rates [0 (control), 10, 30 and 50 tons (t) ha⁻¹] biochar, all with 100% inorganic N fertilizer (165 kg N ha⁻¹), and org-N fertilizer applications at 50%, 75% and 100% of the total available N supply. Pepper yield, vegetative biomass, N uptake, ammonia (NH₃) volatilization and changes in soil organic carbon (SOC), and nitrate were determined. Pepper yield was highest in the 50% org-N and lowest in the 50 t ha⁻¹ biochar treatment during the first year. There were no differences in fruit yield among the organic treatments during the second year, and all were higher than that from the control. The 100% org-N treatment had less NH₃ volatilization than all other treatments during the first year. The two-year results showed that chilli pepper plants sequestered 4.6‒6.1 kg N to produce one ton fresh pepper fruits. During the first year, the 50% org-N treatment resulted in the highest N productivity or yield with lowest projected N fertilizer application requirements as compared to other treatments although there were no differences among all treatments in the second year. Thus, a combination of inorganic and org-N fertilizers can be an effective strategy to improve soil N productivity in long-term management.     

Crop nitrogen recovery and soil nitrogen dynamics in a 10‐year field experiment with biowaste compost

When fertilizing with compost, the fate of the nitrogen applied via compost (mineralization, plant uptake, leaching, soil accumulation) is relevant both from a plant‐production and an environmental point of view. In a 10‐year crop‐rotation field experiment with biowaste‐compost application rates of 9, 16, and 23 t ha^–1 y^–1 (f. m.), the N recovery by crops was 7%, 4%, and 3% of the total N applied via compost. Due to the high inherent fertility of the site, N recovery from mineral fertilizer was also low. In the minerally fertilized treatments, which received 25, 40, and 56 kg N ha^–1 y^–1 on average, N recovery from mineral fertilizer was 15%, 13%, and 11%, respectively. Although total N loads in the compost treatments were much higher than the N loads applied with mineral fertilizer (89–225 kg N_tot ha^–1 y^–1 vs. 25–56 kg N_tot ha^–1 y^–1; both on a 10‐year mean) and the N recovery was lower than in the treatments receiving mineral N fertilizer, soil NO ‐N contents measured three times a year (spring, post‐harvest, autumn) showed no higher increase through compost fertilization than through mineral fertilization at the rates applied in the experiment. Soil contents of N_org and C_org in the plowed layer (0–30 cm depth) increased significantly with compost fertilization, while with mineral fertilization, N_org contents were not significantly higher. Taking into account the decrease in soil N_org contents in the unfertilized control during the 10 years of the experiment, 16 t compost (f. m.) ha^–1 y^–1 just sufficed to keep the N_org content of the soil at the initial level.     

Corn Yield and Nitrogen- and Water-Use under No-Tillage Rotations

Increased crop diversity and length of rotation may improve corn (Zea mays L.) yield and water- and nitrogen-use efficiency (WUE and NUE). The objectives of this study were to determine effects of crop rotation on corn yield, water use, and nitrogen (N) use. No-tillage (NT) crop rotations were started in 1997 on a Barnes clay loam (fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, S.D. Rotations were continuous corn (CC), corn–soybean [Glycine max (L.) Merr.] (CS), a 3-year rotation of corn–soybean–oat/pea (Avena sativa L. and Pisum sativum L.) hay (CSH), a 3-year rotation of corn–soybean–spring wheat (Triticum aestivum L.) (CSW), and a 5-year rotation of corn–soybean–oat/pea hay companion seeded with alfalfa (Medicago sativa L.)–alfalfa–alfalfa (CSHAA). Fertilizer N was applied to corn on all rotations at planting (16 kg N ha^?1) and side-dressed (64 kg N ha^?1). Average corn grain yields (1998–2007) were greatest under CSW (7.38 Mg ha^?1) and least under CC (4.66 Mg ha^?1). Yields were not different among CSH, CSW, and CSHAA rotations. Water-use efficiency of rotation was ordered as CSW > CSH > CSHAA > CS > CC. Nitrogen-use efficiency was greatest under CSW and least under CC. There were no differences in yield advantage (YA) among crop rotations during years with plentiful early-season rainfall (May 1–July 31). In years with low spring rainfall, YA was greatest under CSW (54%) and least under CSHAA (33%). Corn yields under extended rotations (CSH, CSW, and CSHAA) were greater than under CC and CS, but lack of rainfall may result in reduced yields under CSHAA.     

Leaf chlorophyll readings as an indicator of nitrogen status and yield of spinach (Spinacia oleracea L.) grown in soils amended with Luecaena leucocephala prunings

A field study was conducted to evaluate the nitrogen status and yield of spinach grown in soils amended with prunings of Leucaena leucocephala, (applied at a rate of 3, 5, 7 or 11 t ha^?1). A ‘no fertilizer’ 0 nitrogen (N) and 150 kg N ha^?1 (recommended) were the control treatments. SPAD readings were recorded for the top six leaves. Nitrogen sufficiency indices were used to indicate the N status of plants. Application of L. leucocephala prunings increased spinach yields (8.98–13.86 t DM ha^?1) relative to the 0N treatment (1.35 t DM ha^?1) and yields increased with increasing rate of pruning application. SPAD readings showed a linear increase with the increase in applied prunings. There was preferential distribution of N to upper leaves. The relationship between shoot N concentration and SPAD readings was linear and strongest for the top three leaves (r² = 0.84–0.92). The results indicate the potential of chlorophyll meter readings in assessing N status of leafy vegetables grown on soils amended with different levels of legume tree prunings.