Photosynthetic response and nitrogen use efficiency of sugarcane under drought stress conditions with different nitrogen application levels

Drought stress which often occurs during early growth stage is one constraint in sugarcane production. In this study, the response of sugarcane to drought and nitrogen application for physiological and agronomical characteristics was investigated. Two water regimes (well-watered and drought stress from 60 to 120 day after transplanting) and four nitrogen levels (0, 4.4, 8.8 and 13.2 g pot^?1 equivalent to 0, 90, 180 and 270 kg ha^?1, respectively) were assigned in a Split-plot design with three replications. The results showed that photosynthetic responses to light intensity and intercellular CO₂ concentrations of sugarcane were different between fertilized and non-fertilized treatments. Photosynthetic rates of 180 and 270 N treatments, normally, were significantly higher than that of 90 N, but not significant at drought conditions. Photosynthetic rates of 0 N treatment were the lowest under both conditions. Higher nitrogen application supported higher photosynthetic rate, stomatal conductance, and chlorophyll content because of higher nitrogen concentration accumulated into the leaf. Drought significantly reduced the potential photosynthetic rate, stomatal conductance, SPAD, leaf area, and biomass production. Higher nitrogen applications with larger root system could support higher photosynthetic activities to accumulate more dry mass. Strong positive coefficient between photosynthetic and biomass nitrogen use efficiency and drought tolerance index may suggest that higher nitrogen use efficiency could help plants have higher ability to tolerate drought stress.     

Effect of fertilization on crop responses and solute transport for rice crop in a sub-humid and sub-tropical region

In order to increase the efficacy of water and control the losses of fertilizer, it is necessary to assess the influence of level of fertilization on crop responses, movement and balance of water and solutes from fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization on crop responses and fertilizer solute transport in rice crop field in a sub-humid and sub-tropical region. Field experiment was conducted on rice crop (cultivar IR 36) during the years 2003, 2004, and 2005. The experiment included four fertilizer treatments comprising different levels of fertilizer application. The fertilizer treatments during the experiment were: F₁ = control with N:P₂O₅:K₂O as 0:0:0 kg ha^?1; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha^?1; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha^?1 and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha^?1. The results of the investigation revealed that the magnitudes of crop parameters such as grain yield, straw yield, and maximum leaf area index increased with increase in fertilizer application rate. The levels of fertilization had very little effect on water loss via deep percolation and water use by the crop. The levels of fertilization had considerable effect on N leaching loss and uptake of N whereas it had no significant impact on leaching loss of water-soluble phosphorus. This indicated that PO₄-P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. The results also revealed that increase in level of fertilization increased water use efficiency considerably by increased crop yield. From the observed data of nutrient use efficiency, crop yield and environmental pollution, the fertilization rate of N:P₂O₅:K₂O as 80:40:40 kg ha^?1 (F₂) was the most suitable fertilizer treatment for rice crop among studied treatments.     

The efficiency of nitrogen in cattle manures when applied to a double‐annual forage cropping system

The use of cattle manure (CM) for fertilization presents challenges for optimizing nitrogen (N) use. Our work aimed to assess N efficiencies, in a 6‐year experiment with three biennial rotations of four crops: oat–sorghum (first year) and ryegrass–maize (second year) in a rainfed humid Mediterranean area of Spain. Fertilization treatments included the following: control (no N), 250 kg mineral N ha^?1 year^?1 (250MN), three CM rates (supplying 170, 250 and 500 kg N ha^?1 year^?1) and four treatments where the two lowest CM rates were complemented with either 80 or 160 kg mineral N ha^?1 year^?1. Treatments were distributed randomly in each of three blocks. Maximum dry‐matter yield (~44–49 t ha^?1 rotation^?1) was achieved in the third rotation, and only the control and the 170CM yielded significantly less. Within the limitations of the EU Nitrate Directive, the N steady state supply of 170CM always requires a complement of mineral N (80 kg N ha^?1) to maximize N agronomic efficiency. The maximum N‐fertilizer replacement value (250CM vs. 250MN) was 0·67, without significant differences between the two treatments in other N‐related efficiency indexes, which indicates that plants took advantage of residual‐N effects. Nitrogen losses by leaching in the 250CM treatment were around 5–7% of the N applied. This reinforces the sustainability of manure recycling in long cropping seasons.     

Phyto-purification of livestock-derived organic waste by forage rice under subtropical climate

Soil and water pollution caused by organic waste is a concern for livestock-breeding areas. Nitrogen balance in a paddy-field water-purifying system in which cattle feces were applied was studied for 4 years to assess the suitability of the system for a subtropical area, Japan. Three successive harvestings using ratoon of forage rice following one rice transplanting were conducted with chemical fertilizer and high and low rates of cattle-feces application. Nitrogen load was 81.3–495.0 kg N ha^?1 year^?1, while nitrogen uptake was highly dependent on the yield of the first harvesting. Annual variation of forage rice yields was large, ranging from 15.5 to 26.8 Mg ha^?1 owing to fluctuation in the yield at second and later harvestings. On average, nitrogen was lost by leaching at a rate of 2.3–3.4 kg N ha^?1 year^?1. The nitrogen content in soil at a depth of 0–5 cm increased up to 12.2 kg N ha^?1 over the 4-year period compared with that before the field experiment. However, continuous application of cattle feces could slightly increase the nitrogen content in soil at a depth greater than 35 cm. Our results showed the ability of flooded forage rice to remove nitrogen at up to 320.1 kg ha^?1 year^?1 for a field to which cattle feces were applied. Further investigation is needed to produce a high and stable yield at second harvesting each year, to prevent the accumulation of soil nitrogen, and to assess gaseous nitrogen loss.     

Grain yield responses of lowland rice varieties to increased amount of nitrogen fertilizer under tropical highland conditions in central Kenya

Tropical highland conditions in Mwea Kenya, ensure the high radiation and the large day–night temperature differences. Such conditions are generally believed to promote rice growth and yield, but the current grain yield is lower than the expectation. In the current standard N fertilizer practice in Mwea, 75 kg nitrogen (N) ha^?1 is applied in three splits at fixed timing. The effects of increases in N fertilizer amount (125, 175, and 225 kg N ha^?1) on rice growth and yield were evaluated to test the hypothesis that unachieved high rice grain yield in Mwea is due to insufficient amount of N fertilizer. Two popular lowland varieties in Mwea (Basmati 370 and BW196) and two varieties reported as high yielding in other countries (Takanari and IR72) were used. Shoot dry weight (DW) increased with increases in the amount of N fertilizer applied in three splits at fixed timing, irrespective of variety. It reached approximately 20 t ha^?1 under increased N conditions (>75 kg N ha^?1) in several cases, indicating that high biomass production could be achieved by increasing N application rate. However, the increased biomass did not increase grain yield, due to decreased grain filling under high N conditions in all varieties. Thus, N amounts above 75 kg ha^?1 were ineffective for increasing grain yields in Mwea, where N fertilizer was applied in three splits at fixed timing. Increasing influence of low temperature under high N conditions may be one of the reasons for the decreased grain filling in Mwea.     

Effects of Nitrogen Fertilizer Application Time on Dry Matter Accumulation and Yield of Chinese Potato Variety KX 13

Application time of nitrogen (N) fertilizer can significantly influence the yield and quality of potato tubers. The objective of this experiment was to assess the effects of N application time on dry matter accumulation in foliage and tubers, as well as on marketable tuber ratio, dry matter concentration, and specific gravity of the Chinese cultivar KX 13. The four treatments were as follows: all the 150 kg?N?ha^?1 applied at planting (T1); 100 kg N ha^?1 applied at planting and 50 kg N ha^?1 applied 1 week before tuber initiation (20 days after emergence, DAE) (T2); 100 kg N ha^?1 applied at planting and 50 kg N ha^?1 applied 1 week before tuber bulking stage (35 DAE) (T3); and 100 kg?N?ha^?1 applied at emergence and 50 kg N ha^?1 applied 1 week before tuber bulking stage (35 DAE) (T4). For all treatments, 90 kg P₂O₅ ha^?1 ((NH₄)₂HPO₄) and 150 kg K₂O ha^?1 (K₂SO₄) were applied at planting. Thirty tons per hectare of marketable tuber yield was achieved with T3, while 23 t ha^?1 marketable yield was achieved by applying all 150 kg N ha^?1 at planting (T1). Relative to treatment T1, T3 also significantly increased harvest index (HI) from 0.76 to 0.86 and marketable tuber ratio from 64.8% to 79.2%. Applying N at planting in conjunction with dressing at 20 DAE (T2) gave a high marketable tuber ratio (74%) and HI (0.86), but the lower total tuber yield led to a lower marketable tuber yield. Without N application at planting (T4), N dressing did not increase the yield and HI. Treatments with N dressing had no significant effect on specific gravity or dry matter concentration of tubers.     

Influence of rice varieties,nitrogen management and planting methods on methane emission and water productivity

A field experiment was conducted during rainy seasons of 2009 and 2010 at New Delhi, India to study the influence of varieties and integrated nitrogen management (INM) on methane (CH₄) emission and water productivity under flooded transplanted (FT) and aerobic rice (AR) cultivation. The treatments included two rice (‘PB 1’ and ‘PB 1121’) varieties and eight INM practices including N control, recommended dose of N through urea, different combinations of urea with farmyard manure (FYM), green manure (GM), biofertilizer (BF) and vermicompost (VC). The results showed 91.6–92.5 % lower cumulative CH₄ emission in AR compared to FT rice. In aerobic conditions, highest cumulative CH₄ emission (6.9–7.0 kg ha^?1) was recorded with the application of 100 % N by organic sources (FYM+GM+BF+VC). Global warming potential (GWP) was significantly lower in aerobic rice (105.0–107.5 kg CO₂ ha^?1) compared to FT rice (1242.5–1447.5 kg CO₂ ha^?1). Significantly higher amount of water was used in FT rice than aerobic rice by both the rice varieties, and a water saving between 59.5 and 63 % were recorded. Under aerobic conditions, both rice varieties had a water productivity of 8.50–14.69 kg ha^?1, whereas in FT rice, it was 3.81–6.00 kg ha^?1. In FT rice, a quantity of 1529.2–1725.2 mm water and in aerobic rice 929.2–1225.2 mm water was used to produce one kg rice. Thus, there was a saving of 28.4–39.6 % total water in both the rice varieties under AR cultivation.     

Effect of nitrogen root zone fertilization on rice yield,uptake and utilization of macronutrient in lower reaches of Yangtze River,China

Improper application of nitrogen (N) has led to high N losses and low N use efficiency in the lower reaches of Yangtze River in China. An effective method to solve such problems is the deep fertilized N in root zone (RZF). Limited information is available on the effect of RZF on the uptake of macronutrients (N, P and K) and rice yield. Field experiments, conducted from 2014 to 2015, compared the farmer fertilizer practice (FFP, with 225 kg ha^?1 of N, split into three doses) and RZF using the same rate but placing N 5 cm away from rice roots in holes 10 cm deep (RZF10) or 5 cm deep (RZF5) as a single application. The highest mean yield (10.0 t ha^?1) was obtained in RZF10, which was 19.5% more than that in FFP. Root zone fertilization of urea (whether 10 cm deep or 5 cm deep) resulted in greater accumulation of N, P and K in stem, leaf sheaths, leaf blades and grains compared to that in FFP in sandy and in loam soils. The uptake of N, P and K was the highest in RZF10 (average at 176.7, 66.2 and 179.1 kg ha^?1, respectively), higher than that in FFP by 45.0, 17.0 and 22.6%, respectively. N apparent recovery efficiency was markedly higher in RZF10 (53.1%) than in FFP (27.5%). RZF10 significantly increased the N, P, K uptake compared with FFP under different N rates in both sandy and loam soils. These results suggest that the N, P and K input amount should be re-determined under RZF.     

Production and nutritional value of sorghum and black oat forages under nitrogen fertilization

The effect of nitrogen (N) fertilization on the dry‐matter (DM) yield and nutritional value of sorghum (Sorghum sp., cv. Jumbo) and black oat (Avena strigosa cv., IPR 61) was investigated in the context of forage and livestock production in southern Brazil. Sorghum was cultivated with 0, 37·5, 75, 150, 225, 300 and 375 kg N ha^?1 during the summer crop seasons of 2010/11 and 2011/12. Black oat received 0, 40, 80, 120, 160, 200 and 240 kg N ha^?1 in the winter of 2011. According to the adjusted polynomial regression, sorghum DM yield increased in response to N up to 288 (12·9 t ha^?1) and 264 kg ha^?1 (5·6 t ha^?1) in 2010/11 and 2011/12 respectively. Crude protein (CP) content of sorghum was highest at 349 and 328 kg N ha^?1, but in vitro dry‐matter digestibility (IVDMD) was highest at 212–207 kg N ha^?1 in 2010/11 and 2011/12 respectively. Sorghum neutral detergent fibre (NDF) and acid detergent fibre (ADF) were not affected by N fertilization. In black oat, the maximum DM yield (6·0 t ha^?1) was obtained with 187 kg N ha^?1; the IVDMD, NDF and ADF were not affected by N fertilization, but the CP content increased up to 220 kg N ha^?1. It is concluded that these forage species can improve the year‐to‐year amount and quality of forage produced but high rates of N fertilizer are required to achieve high yields. Fertilizer N rates of 210–280 kg N ha^?1 in sorghum and 180 kg N ha^?1 in black oat in the crop rotation provide the greatest responses in DM yield consistent with good nutritional quality for livestock production.     

Economic Optimum Nitrogen Fertilization Rates and Nitrogen Fertilization Rate Effects on Tuber Characteristics of Potato Cultivars

The objective of the research was to determine the economic optimum nitrogen (N) fertilization rates and to determine the effects of N fertilization rates on tuber characteristics and fresh mass loss after storage under cold and ambient conditions of four potato cultivars, Ágata, Asterix, Atlantic, and Monalisa. The experiments were, simultaneously, conducted in the same area and similar experimental conditions during the fall/winter period in Viçosa, Minas Gerais State, Brazil. In each experiment, five N fertilization rates (0, 50, 100, 200, 300 kg ha^?1) were evaluated in a randomized complete block design. For all cultivars, increasing N fertilization rate increased total and marketable yields and tuber dry matter yield up to a maximum following a quadratic model. Increasing N fertilization rate linearly increased the tuber protein concentration of Atlantic and Monalisa and had no effect on tuber pH. N fertilization rate effects on tuber mass, tuber titratable acidity, and fresh mass loss during storage were cultivar-dependent. N use efficiency (tuber yield divided by N fertilization rate) decreased with increase in N fertilization rate. The economic optimum N fertilization rates ranged from 147 to 201 kg ha^?1 depending upon cultivar and relative prices of N and potato tubers. Depending on the cultivar, under favorable price conditions (low N price and high tuber price), the economic optimum N fertilization rates to be applied by potato growers were 92–95% of the estimated N fertilization rate for obtaining the maximum potato yield, whereas under unfavorable conditions (high N price and low potato tuber price) the economic optimum N fertilization rates to be applied should be decreased to 86–92% of the rates for maximum yield.     

Effects of sowing date and nitrogen fertilizer on forage yield,nitrogen‐ and water‐use efficiency and nutritive value of an annual triple‐crop complementary forage rotation

Complementary forage rotation (CFR) systems based on non‐limiting inputs of fertilizer nitrogen (N) (～600 kg N ha^?1) are perceived as uneconomic. An experiment was carried out in Australia to investigate the effects of rates and timing of N fertilizer and sowing date on yield, nutrient‐use efficiency and nutritive value of a triple‐crop (maize, forage rape, field peas) CFR system. Treatments were early‐ and late‐sown maize grown with 0 or 135 kg fertilizer N ha^?1 pre‐sowing (N1) and 0, 79 or 158 kg N ha^?1 post‐sowing (N2). Forage rape was sown with 0 or 230 kg N ha^?1 (N3) and field peas without N. Application of fertilizer N at N1, N2 and N3 increased CFR yield from 28·5 to 48·8 t dry matter (DM) ha^?1 and irrigation water‐use efficiency (IWUE) from 3·4 to 6·1 t DM per megalitre. Increase in yield and IWUE of CFR occurs at the expense of nitrogen‐use efficiency (NUE) as applications of N at N1, N2 and N3 decreased NUE of CFR from 524 to 91 kg DM kg^?1 N. Nutritive value, particularly metabolizable energy content of all forages, was similar among N treatments, and interactions between treatments were minimal. Results indicate that increase in NUE of CFR may occur at the expense of reduced yield, but increased IWUE need not compromise the yield of this CFR system.     

The effect of sowing date and nitrogen on the dry‐matter yield and nitrogen content of forage rape (Brassica napus L.) and stubble turnips (Brassica rapa L.) in Ireland

Two field experiments were conducted at Teagasc, Moorepark, Ireland, to determine the effect of sowing date and nitrogen application on the dry‐matter (DM) yield and crude protein (CP) content of forage rape and stubble turnips. The first experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) on forage rape DM yields. The second experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) over two soil sites (fertile or nitrogen depleted) on forage rape and stubble turnip DM yields. A delay in sowing from 1 to 31 August characterized a 74·5% decrease in forage rape DM yield, while stubble turnip DM yield decreased by 55·5%. Forage rape DM yields increased positively up to 120 kg N ha^?1 at the first two sowing dates over both sites. In contrast, stubble turnips showed less response beyond 40 kg N ha^?1 on site 1 in the first two sowing dates, while DM yield increased positively up to 120 kg N ha^?1 on the less fertile site. The results indicate that the optimal sowing time for forage rape and a stubble turnip in Ireland was early August.     

Plant and soil responses to nitrogen and phosphorus fertilization of bromegrass‐dominated haylands in Saskatchewan,Canada

Field experiments were conducted at three different sites in Saskatchewan, Canada (Colonsay, Vanscoy and Rosthern) over two years (2005 and 2006) to determine the effects of dribble‐banded and coulter‐injected liquid fertilizer applied in the spring of 2005 at 56, 112 and 224 kg N ha^?1 with and without P at 28 kg P₂O₅ ha^?1. The three sites were unfertilized, 7‐ to 8‐year old stands of mainly meadow bromegrass (Bromus riparius)‐dominated haylands. All fertilization treatments produced significantly (P ≤ 0·05) higher dry matter yield than the control in the year of application at the three Saskatchewan sites. There was no significant difference between the two application methods (surface dribble band vs. coulter injected) for any fertilizer treatments. The addition of 28 kg P₂O₅ ha^?1 P fertilizer along with the N fertilizer did not have a significant effect on yield in most cases. In the year of application, increasing N rates above 56 kg N ha^?1 did not significantly increase yield over the 56 kg N ha^?1 rate in most cases, but did increase N concentration, N uptake and protein concentration. A significant residual effect was found in the high N‐rate treatments in 2006, with significantly higher yield and N uptake. In 2005, the forage N and P uptake in the fertilized treatments were significantly higher than the control in all cases. The N uptake at the three Saskatchewan sites increased with increasing N rate up to the high rate of 224 kg N ha^?1, although the percent recovery of applied N decreased with increasing rate. The P fertilization with 28 kg P₂O₅ ha^?1 also increased P uptake. Overall, rates of fertilizer of approximately 56 kg N ha^?1 appear to be sufficient to produce nearly maximum forage yield and protein concentration of the grass in the year of application.     

Bahiagrass (Paspalum notatum Flugge) management combining nitrogen fertilizer rate and defoliation frequency to enhance forage production efficiency

Bahiagrass (Paspalum notatum Flugge) pastures are widespread in warm climates worldwide and respond to nitrogen (N) fertilizer. Nitrogen fertilization has recently decreased because of increased cost and concerns regarding excessive N in the environment. Responses of bahiagrass to treatments representing three alternative levels of pasture management were assessed. Treatments, each including 56 kg N ha^?1 applied for each growth period, were as follows: (i) six harvests with a total of 336 kg N ha^?1 annually (referred to as intensive management), (ii) three harvests with 168 kg N ha^?1 annually (intermediate management) and (iii) two harvests with 112 kg N ha^?1 annually (extensive management). The intensive management produced the most forage with the highest nutritive value. Intermediate management, with only half the amount of N fertilizer, produced at least 80% of the forage yield each year as the intensive management treatment (4‐year average of 8236 vs. 9122 kg ha^?1 for the intermediate and intensive management treatments respectively) with forage of acceptable nutritive value for some classes of livestock. Limited forage production from the last harvest each year restricts autumn management opportunities, even though crude protein concentration was usually sufficient for some classes of livestock. Extended growth periods, as those that occur with the less‐intensive management treatments, provide opportunities to accumulate forage for late‐season grazing. Matching livestock enterprises to the forage produced, particularly in terms of nutritive value, can contribute to favourable livestock production responses from a range of bahiagrass pasture management approaches.     

Performance of white clover/perennial ryegrass mixtures under cutting

Clover persistence in mixtures of two varieties of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover (Trifolium repens) varieties differing in leaf sizes was evaluated at two cutting frequencies. An experiment was sown in 1991 on a clay soil. The plots received no nitrogen fertilizer. In 1992, 1993 and 1994, mixtures containing the large-leaved clover cv. Alice yielded significantly more herbage dry matter (DM) and had a higher clover content than mixtures containing cvs Gwenda and Retor. Companion grass variety did not consistently affect yield or botanical composition. Cutting at 2 t DM ha^?1 resulted in slightly higher total annual yields than cutting at 1.2 t DM ha^?1, but did not affect clover content. In 1992 the mixtures yielded, depending on cutting frequency and variety, 10·6–14·6 t DM ha^?1 and 446–599 kg ha^?1 N, whereas grass monocultures yielded only 1·2–2·0 t DM ha^?1 and 25–46 kg ha^?1 N. From 1992 to 1994 the annual mean total herbage yield of DM in the mixtures declined from 12·2 to 10·5 to 8·7 t ha^?1, the white clover yield declined from 8·7 to 6·5 to 4·1 t ha^?1 and the average clover content during the growing season declined from 71% to 61% to 46%, whereas the grass yield increased from 3·4 to 4·0 to 4·5 t ha^?1. The N yield decreased from 507 to 406 to 265 kg N ha^?1 and the apparent N fixation from 470 to 380 to 238 kg N ha^?1. Nitrate leaching losses during the winters of 1992–93 and 1994–95 were highest under mixtures with cv. Alice, but did not exceed 10 kg N ha^?1. The in vitro digestible organic matter (IVDOM) was generally higher in clover than in grass, particularly in the summer months. No differences in IVDOM were found among clover or grass varieties. The experiment will be continued to study clover persistence and the mechanisms that affect the grass/clover balance.     

Radiation‐use efficiency for forage kale crops grown under different nitrogen application rates

Crop growth is related to radiation‐use efficiency (RUE), which is influenced by the nitrogen (N) status of the crop, expressed at canopy level as specific leaf N (SLN) or at plant level as N nutrition index (NNI). To determine the mechanisms through which N affects dry‐matter (DM) production of forage kale, results from two experiments (N treatment range 0–500 kg ha^?1) were analysed for fractional radiation interception (RI), accumulated radiation (R_acc), RUE, N uptake, critical N concentration (N_c), NNI and SLN. The measured variables (DM, RI and SLN) and the calculated variables (NNI, R_acc and RUE) increased with N supply. RUE increased from 0·74 and 0·89 g MJ^?1 IPAR for the control treatments to 1·50 and 1·95 g MJ^?1 IPAR under adequate N and water in both experiments. This represented an increase in RUE of 52–146% for the range of N treatments used in both experiments, whilst R_acc increased by 9–17%, compared with the control treatments. Subsequently, the total DM yield of kale increased from 6·7 and 8 t DM ha^?1 for the control treatments to ≥ 19 t DM ha^?1 when ≥150 kg N ha^?1 was applied. The DM yields for the 500 kg N ha^?1 treatments were 25·5 and 27·6 t DM ha^?1 for the two experiments. RUE increased linearly with SLN, at an average rate of 0·38 g DM MJ^?1 IPAR per each additional 1 g N m^?2 leaf until a maximum RUE of 1·90 g MJ^?1 IPAR was reached in both experiments. There were no changes in RUE with SLN of > 2·6 g m^?2 and NNI >1, implying luxury N uptake. RUE was the most dominant driver of forage kale DM yield increases in response to SLN and NNI.     

Performance and environmental effects of forage production on sandy soils. I. Impact of defoliation system and nitrogen input on performance and N balance of grassland

Grassland and its management is central to the productivity of and nitrogen (N) losses from dairy farms in north‐west Europe. Botanical composition, production and N surplus of grassland were assessed during five consecutive years. The experiment consisted of all combinations of five defoliation systems: cutting‐only (CO), rotational grazing (GO), grazing + one (MSI) or two silage cuts (MSII) and simulated grazing (SG). Four mineral N fertilization rates (0–300 kg N ha^?1 year^?1) and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1) were applied. Fertilizer N was more efficient in producing net energy (NEL) in grazing‐dominated, low white clover systems (GO and MSI systems: 70 and 88 MJ NEL kg^?1 N) than in white clover‐rich systems (MSII, CO and SG systems: ≤60 MJ NEL kg^?1 N). While sward productivity in system MSI was similar to that in system GO, system MSII benefited from increased N₂ fixation at low N rates. There were small differences in NEL concentrations of the herbage between defoliation systems. Crude protein concentration of the herbage increased with increasing N supply from fertilizer, excreta and N₂ fixation. N surpluses (?63 to +369 kg N ha^?1 year^?1) increased with increasing grazing intensity and increasing N fertilization rate. The average response in N surplus applied was 0·81, 0·59, 0·40, 0·33 and 0·24 kg N ha^?1 in systems GO, MSI, MSII, CO and SG respectively.     

Effects of alternate wetting and drying irrigation on percolation and nitrogen leaching in paddy fields

The widely adopted alternate wetting and drying (AWD) irrigation for rice production is increasingly needed to quantify the different water outflows and nitrogen leaching losses. We investigated the effects of AWD on percolation, water productivity, nitrogen leaching losses, and nitrogen productivity through in situ experiments. Results show that AWD reduced irrigation water without a significant impact on grain yields and increased the mean water productivity by 16.9 % compared with continuously flood irrigation (CFI). The mean nitrogen productivity of 135 kg ha^?1 N level was 22.2 % higher than that of 180 kg ha^?1 N level, although grain yields substantially increased because of nitrogen fertilization application. The percolation was also reduced by 15.3 % in 2007 and 8.3 % in 2008 compared to CFI. However, the cumulative percolation of the first 5 days after irrigation in AWD plots is significantly larger than that in CFI plots. The NH₄ ⁺–N and TN leaching losses of AWD and CFI had no significant variations while the NO₃ ^?–N leaching losses were increased caused by AWD. The total NH₄ ⁺–N, NO₃ ^?–N, and TN leaching losses of AWD in the first 3 days after irrigation were higher than that of contemporaneous CFI. The results indicate that the bypass or preferential flow and strengthened nitrification–denitrification nitrogen transformation processes because of alternate wetting and drying potentially decrease the water saving effectiveness and increase the NO₃ ^?–N loading to the groundwater.     

Biomass yield and nutrient content of a tropical mulberry forage bank: effects of season,harvest frequency and fertilization rate

Effects of season (SEAS), organic fertilization with laying hen manure (N) and harvest frequency (FREQ) on forage yield and composition were evaluated in a high‐density mulberry forage bank, established under low‐input tropical farming conditions. The experiment, replicated over two consecutive years, was arranged in 18 treatments resulting from a 3 × 3×2 factorial design which combined three FREQ (60, 90 and 120 d), 3 N rates (100, 300 and 500 kg N ha^?1 year^?1) and the two seasons (RAIN and DRY). Forage yield, leaf‐to‐stem ratio, the edible fraction (EDIB, %), nutrient content and the maturity indexes were monitored. Either forage yield or qualities by plant fraction were strongly affected by SEAS, FREQ, N rate and by their interactions. Effects of FREQ and N were modulated by SEAS. Increasing FREQ during RAIN negatively affected EDIB yield and quality after 90 d, while increasing ligneous fraction. During DRY, longer FREQ allowed higher total forage and EDIB yields. Leaves were more abundant in RAIN, and its yield was increased with fertilization but only during this season. Maturity indexes were higher in DRY than in RAIN. Under the conditions of this experiment, harvesting at 60 and 90 d in RAIN and DRY, respectively, with an N rate of 300 kg N ha^?1 year^?1 seems the best agronomic choice for an optimal compromise between forage yield and nutritive value.     

Determining corn nitrogen rates using multiple prediction models

Weather uncertainty and soil spatial variability impact nitrogen (N) cycling and corn (Zea mays L.) growth, making accurate N predictions a challenge. Field studies were conducted in Lansing, Michigan, to evaluate a computer model (i.e., Adapt-N), a preseason year-based model (i.e., maximum return to N [MRTN]), and a crop sensor model (i.e., active canopy sensor with algorithm) for recommending corn N rates. To determine site-specific economic optimum N rates (EONR), five N rates were also applied (0, 33%, 66%, 133%, and 166% of the suggested MRTN) as starter + sidedress (SD) at V4. In a wet year (i.e., 2015), Adapt-N increased V8 SD N rates 35 kg N ha^?1 relative to the MRTN V4 SD N application. Although the greater rate of N may have provided additional yield protection, no statistical yield differences were observed between the two models. The MRTN model increased partial factor productivity (PFP) 20% relative to Adapt-N. Limited expression of V8 corn N deficiency reduced crop sensor total N rates (21–56 kg N ha^?1) and yield (0.82–1.05 Mg ha^?1) relative to other models. In a drier year (i.e., 2016), N demand was reduced (EONR 64 kg N ha^?1 less than 2015), resulting in similar corn response to all three models. Despite differences in actual corn N rate recommendations, all three models resulted in similar economic net returns across study years.

Abbreviations: EONR, economic optimum nitrogen rate; MRTN, Maximum Return to Nitrogen; NUE, nitrogen-use efficiency; PFP, partial factor productivity; SBNRC, sensor-based nitrogen rate calculator; SD, side-dress