The effect of cutting, mulching and applications of farmyard manure on nitrogen fixation in a red clover/grass sward

In organic farming, maximising the amount of nitrogen (N) which is fixed and retained within the soil is of paramount importance for the yield of the following crop. The aim of this study was to establish the extent to which increased soil fertility, farmyard manure (FYM) applications and/or mulching, could adversely affect fixation. At two sites, situated in the South West (SW) and North East (NE) of England, N(2) fixation was estimated in 'organically' managed red clover/grass plots, both with and without green manure (i.e. surface mulched) and/or the addition of FYM. The FYM was incorporated into the seedbeds at both sites in autumn 2002 at the rate of 170 kg total Nha(-1), as either well-composted (SW site), or not actively-composted (NE site) manures. The same FYM application rate was repeated as top-dressings to both sites in autumn 2003. The plots were cut three or four times each year over two growing seasons. In the first harvest year (2003), incorporation of FYM had beneficial effects of increasing dry matter and N yields significantly at the first cut, but there were no significant differences in subsequent cuts. The same pattern was found in the second harvest year (2004) after the top dressings of FYM, suggesting that most of the N in both types of FYM was in recalcitrant forms. Over the two growing seasons, mulching did not affect red clover/grass dry matter or N yields, but did reduce the proportion of N(2) fixed, by up to 60 kg Nha(-1) when compared with plots from which the clover/grass herbage was cut and removed. Thus, the gain in N from FYM or green manure tended to be offset by a similar reduction in N(2) fixation. These results demonstrate the close association between the availability of soil N and the feed-back system which operates on N(2) fixation by red clover.     

Response of irrigated wheat to residual and fertilizer nitrogen

Summary A cotton and a wheat experiment were conducted in sequence to evaluate the effect of residual and fertilizer N on wheat with a water table fluctuating between 65 and 125 cm. Cotton treatments, replicated four times, consisted of 3 irrigation treatments as main plots and 6 N levels as subplots (0, 25, 50, 75, 100, 125 kg N/ha). After cotton the plots were planted to wheat and each subplot was divided into two equal sub-subplots. One received N at a rate similar to that previously applied to cotton and the other sub-subplot was left without N application for evaluating the residual effect. Determination of N forms in the soil before wheat indicated that NO₃-N content of the top 25 cm increased from 4.4 to 16.3 ppm as N applied to cotton increased from 0 to 125 kg/ha. On the other hand, mineralizable-N was greater in the control than in the fertilized treatments, suggesting a priming effect on the mineralization of soil N. The residual effect on wheat was related to mineralizable-N rather than to NO₃-N as grain yield was higher for the control than for the residual fertilizer N treatments. The yield was also higher for the more frequent than for the less frequent irrigation treatments, which may be attributed to increase in mineralization with soil water content. Wheat response to N application was significant. But high N levels accompanied by frequent irrigation enhanced lodging with subsequent reduction in yield. Measuring N uptake by grain and straw indicated 37% recovery of fertilizer N. It was concluded that under the prevailing conditions of high water table wheat response was largely dependent on the applied fertilizer due to insignificant residual N availability.     

Time‐dependent effects of fertilization on plant biomass in floating fens

Abstract. A cross‐over fertilization experiment was carried out in Dutch floating fens to investigate effects on biomass production in the same and the following years. In total 16 fertilizer treatments were applied, combining four treatments in 1999 with four treatments in 2000 (addition of 20 g.m^?2 N, 5 g.m^?2 P, both elements and unfertilized control). The above‐ground biomass production of vascular plants was co‐limited by N and P in both years. However, in plots that were only fertilized in 1999 the effects of individual nutrients differed between the two years: N‐fertilization slightly increased the amount of biomass produced in the same year (1999), whereas P‐fertilization did so in the following year (2000). Fertilizer applied in 1999 also influenced the effects of fertilizer applied in 2000. One year after N‐fertilization vascular plant growth was still co‐limited by N and P, but one year after P‐fertilization, vascular plant growth was only limited by N. Bryophyte biomass responded weakly to fertilization. Nutrient concentrations in plant biomass, nutrient standing crops and measurements of N and P availability in the soil indicated that one year after fertilization, the N‐fertilizer had mostly ‘disappeared’ from N‐fertilized plots, whereas the availability of P remained markedly enhanced in P‐fertilized plots. In addition, P‐fertilization enhanced the uptake of N by plants the following year. The time‐dependence of fertilizer effects was probably caused by (1) higher addition of P than of N relative to the requirements of plants; (2) longer retention of P than of N in the system; (3) positive effect of P‐fertilization on the availability of N; (4) contrasting effects of N‐ and P‐fertilization on nutrient losses by plants and/or on their responses to subsequent nutrient addition; (5) changing interactions between vascular plants and mosses (mainly Sphagnum spp.); (6) nutrient export through the repeated harvest of above‐ground biomass. To determine which nutrient limits plant growth fertilization experiments should be short, avoiding that indirect effects of a non‐limiting nutrient influence results. To indicate how changed nutrient supply will affect an ecosystem longer‐term experiments are needed, so that indirect effects have time to develop and be detected.     

Basal fertiliser application method, tuber initiation nitrogen, foliar NPK and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The effects of broadcast granular, placed liquid and foliar fertilisers on the tolerance of potatoes to infection by potato cyst nematodes were investigated. The tolerance of the potato cv. Pentland Dell was not significantly improved by fertiliser application type but placed liquid fertiliser, with or without foliar applications, increased the concentrations of N, P and K measured in whole plant dry matter of PCN infected plants. The tolerance of the potato cv. Sante was not statistically improved by altering the balance of fertiliser nitrogen applications between planting and tuber initiation or by applying foliar nitrogen. Nitrogen applications of 120 kg N ha^-1 at planting and a further 120 kg N ha^-1 at tuber initiation supplemented with foliar N, however, achieved a larger tuber yield than the same nitrogen programme without foliar N and gave a significantly greater yield than the application of 240 kg N ha^-1 at planting plus foliar N. The emergence of both cultivars was delayed in the absence of oxamyl. N, P and K concentrations within whole plant dry matter were significantly higher in plants from oxamyl treated plots and both N and K concentrations were significantly increased by increasing the quantity of N at planting, at 56 DAP. Splitting the fertiliser N between planting and tuber initiation appears to be important in maintaining the availability of this nutrient to PCN infected plants throughout the season.     

Impact of long-term additions of chemical fertilizers and farm yard manure on carbon and nitrogen sequestration under rice-cowpea cropping system in semi-arid tropics

Restoration of soil organic carbon (SOC) in arable lands represents potential sink for atmospheric CO₂. The strategies for restoration of SOC include the appropriate land use management, cropping sequence, fertilizer and organic manures application. To achieve this goal, the dynamics of SOC and nitrogen (N) in soils needs to be better understood for which the long-term experiments are an important tool. A study was thus conducted to determine SOC and nitrogen dynamics in a long-term experiment in relation to inorganic, integrated and organic fertilizer application in rice-cowpea system on a sandy loam soil (Typic Rhodualf). The fertilizer treatments during rice included (i) 100% N (@ 100 kg N ha^?1), (ii) 100% NP (100 kg N and 50 kg P₂O₅ ha^?1), (iii) 100% NPK (100 kg N, 50 kg P₂O₅ and 50 kg K₂O ha^?1) as inorganic fertilizers, (iv) 50% NPK + 50% farm yard manure (FYM) (@ 5 t ha^?1) and (v) FYM alone @ 10 t ha^?1 compared with (vi) control treatment i.e. without any fertilization. The N alone or N and P did not have any significant effect on soil carbon and nitrogen. The light fraction carbon was 53% higher in NPK + FYM plots and 56% higher in FYM plots than in control plots, in comparison to 30% increase with inorganic fertilizers alone. The microbial biomass carbon and water-soluble carbon were relatively higher both in FYM or NPK + FYM plots. The clay fraction had highest concentration of C and N followed by silt, fine sand and coarse sand fractions in both surface (0–15 cm) and subsurface soil layers (15–30 cm). The C:N ratio was lowest in the clay fraction and increased with increase in particle size. The C and N enrichment ratio was highest for the clay fraction followed by silt and both the sand fractions. Relative decrease in enrichment ratio of clay in treatments receiving NPK and or FYM indicates comparatively greater accumulation of C and N in soil fractions other than clay.     

播期对内蒙古西部荒漠区棉花产量、品质及养分吸收利用的影响

于2014—2015年在内蒙古自治区阿拉善盟阿拉善左旗内蒙古棉花综合实验站设置大田试验,以‘中棉所50’为材料,采用“一膜三管六行”机采棉配套栽培技术种植,研究播期(4月20日、4月30日和5月10日)对棉花产量、品质及养分吸收的影响.结果表明: 随着播期推迟,棉花生育时期推迟,生育期缩短,铃期日均温降低,收获密度增加;播期显著影响棉株干物质累积、养分吸收与分配,以及产量和品质形成,4月30日播种条件下,棉株干物质和养分在经济器官中的分配比例、养分总积累量及养分的皮棉生产效率较高,籽棉和皮棉产量最高,达6505.9和2660.9 kg·hm^-2,且纤维品质较优;4月20日播期下,收获密度、生物量和养分累积量最低,虽然生物量和养分经济系数最高,但最终籽棉和皮棉产量仍较4月30日播期降低10.9%～14.0%和11.1%～14.2%;5月10日播期,虽然可以避开种子萌发期低温冷害,但棉铃发育期日均温偏低,尽管生物量和养分累积量最高,但是生物量和养分经济系数、养分的皮棉生产效率最低,最终籽棉和皮棉产量较4月30日播期降低32.5%～34.7%和35.9%～36.2%,且纤维品质最差.综合分析, 4月30日左右为内蒙古西部荒漠旱区棉花种植的最佳播期.     

Effect of inorganic fertilizer and farmyard manure on soil physical properties, root distribution, and water-use efficiency of soybean in Vertisols of central India

A field experiment was conducted on a Vertisol for three consecutive years (1998-2000) to study the effects of combined use of inorganic fertilizer (NPK) and organic manure (farmyard manure) on soil physical properties, water-use efficiency, root growth and yield of soybean [Glycine max (L.) Merr.] in a soybean-mustard cropping system. Application of 10 Mg farmyard manure and recommended NPK (NPK+FYM) to soybean for three consecutive years improved the organic carbon content of the surface (0-15 cm) soil from an initial value of 4.4 g kg(-1) to 6.2 g kg(-1) and also increased seed yield and water-use efficiency by 103% and 76%, respectively, over the control. The surface (0-15 cm) soil of the plots receiving both farmyard manure and recommended NPK had larger mean weight diameter (0.50 mm) and a higher percentage of water stable aggregates (55%) than both the inorganically fertilized (NPK) (0.44 mm and 49%) and unfertilized control plots (0.41 mm and 45.4%). The saturated hydraulic conductivity (13.32 x 10(-6) m s(-1)) of the NPK+FYM treatment of the 0-7.5 cm depth was also significantly greater than that of the NPK (10.53 x 10(-6) m s(-1)) and control (8.61 x 10(-6) m s(-1)) treatments. The lowest bulk density (1.18 Mg m(-3)) in the 0-7.5 cm layer was recorded in NPK+FYM whereas it was highest in the control plots (1.30 Mg m(-3)). However, at sub-surface (22.5-30 cm) layer, fertilizer and manure application had little effect on bulk density and saturated hydraulic conductivity. Root length density (RLD) up to the 30 cm depth was highest in the NPK+FYM plots and it was 31.9% and 70.5% more than NPK and control plots. The RLD showed a significant and negative correlation (r=-0.88( * *)) with the penetration resistance.     

Potassium content in soil,uptake in plants and the potassium balance in three European long-term field experiments

This study quantitatively assesses the fate of K derived from mineral fertilizers and organic manures and the effective K balance in three long-term field experiments at Rothamsted (UK), Bad Lauchstaedt (Germany) and Skierniewice (Poland). Plant availability, uptake and the overall utilization of K over the last 30 years (1965–1996) are discussed and related to soil K Availability Indices determined by the standard methods used in each of the three countries. In addition, to provide a standard comparison of the three sites, Exchangeable K (1 M NH₄OAc) and Non-exchangeable K (K extracted by boiling with 1 M HNO₃) were measured on one recent (1995) set of soil samples. Plant availability and utilization of K was partly related to clay content, but more closely to the cation exchange surfaces associated with both mineral and organic constituents and also, at Rothamsted, to the capacity of clay minerals to fix K. The recovery rate of K from mineral fertilizer by crops did not exceed 62%. Fertilizers were least effective in the most strongly K fixing soil at Rothamsted (44% maximum) and most effective in the soil with the highest cation exchange capacity (CEC) at Bad Lauchstaedt (62%), where the greater quantity of exchange sites appear to be associated with humic material. Recoveries of K from farmyard manure (FYM) varied from 22–117% (values of >100% indicating subsoil uptake or the release of reserves). Deficiencies of N, P and Mg in some treatments decreased the effectiveness of applied K and may have caused increased leaching of K from the plough layer. FYM was generally more effective than mineral fertilizer where mineral N and P were not applied because these nutrients were effectively supplied in the manure. But the effectiveness of mineral K fertilizer decreased when applied in combination with FYM because FYM was the preferred source of K. Where FYM application increased the CEC of soils, this also improved K utilization but only where K was not extensively leached or fixed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of experimental season of prescribed fire and nutrient addition on structure and function of previously grazed grassland

Aims Understanding the drivers of grassland structure and function following livestock removal will inform grassland restoration and management. Here, we investigated the effects of fire and nutrient addition on structure and function in a subtropical semi-native grassland recently released from grazing in south-central Florida. We examined responses of soil nutrients, plant tissue nutrients, biomass of live, standing dead and litter, and plant species composition to experimental annual prescribed fire applied during different seasons (wet season vs. dry season), and nutrient additions (N, P and N + P) over 9 years.Methods Experimental plots were set up in a randomized block split-plot design, with season of prescribed fire as the main treatment and nutrient addition as the subplot treatment. Species cover data were collected annually from 2002 to 2011 and plant tissue and plant biomass data were collected in 2002–2006 and 2011. Soil nutrients were analyzed in 2004, 2006 and 2011.Important findings Soil total phosphorus (P) levels increased substantially with P addition but were not influenced by prescribed fire. Addition of P and N led to increased P and N concentrations in live plant tissues, but prescribed fire reduced N in live tissue. Levels of tissue N were higher in all plots at the beginning of the experiment, an effect that was likely due to grazing activity prior to removal of livestock. Plant tissue N steadily declined over time in all plots, with annually burned plots declining faster than unburned plots. Prescribed fire was an important driver of standing dead and litter biomass and was important for maintaining grass biomass and percent cover. Nutrient addition was also important: the addition of both N and P was associated with greater live biomass and woody forbs. Removal of grazing, lack of prescribed fire, and addition of N + P led to a reduction of grass biomass and a large increase in biomass of a woody forb. Annual prescribed fire promoted N loss from the system by reducing standing dead and litter, but maintained desirable biomass of grasses.     

Supplementary foliar N, P and K, applied individually or in combinations, and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The use of supplementary foliar N, P and K to ameliorate the reduced nutrient uptake of potato plants infected by potato cyst nematode (PCN) were investigated. The potato cv. Pentland Dell achieved yields in plots not treated with oxamyl similar to those found in plots treated with oxamyl when supplementary foliar N or N plus K was applied to plots infested with 13 eggs g^-1 soil of Globodera pallida. Yield improvements from foliar N applications were attributed to increased leaf area index but the reason for yield increases from foliar N plus K applications could not be clarified. In a second experiment, where PCN infestation was 76 eggs g^-l soil, the potato cv. Sante gave yields up to 19% higher than a standard fertiliser practice when supplementary foliar N was applied to plots not treated with oxamyl. Nutrient analysis showed that without oxamyl there were significantly lower concentrations of N, P and K in whole plant dry matter at 58 days after planting (DAP) but higher levels of N in the fourth leaf dry matter at 98 DAP. Emergence was significantly advanced by the use of oxamyl in both experiments. Sante dramatically reduced populations of Globodera rostochiensis from an average of 76 eggs g^-1 soil to 7 eggs g^-1 soil. Foliar application of nutrients is a promising method of ameliorating the effects on potatoes of PCN invasion but the nutrient concentrations and timing of individual sprays need to be more closely matched to crop requirement than was possible in our experiments     

Phosphorus availability to rice (Oriza sativa L.)-wheat (Triticum estivum L.) in a Vertisol after eight years of inorganic and organic fertilizer additions

Integrated use of inorganic fertilizer N and well decomposed cattle manure (CM) or 30-35 days old Parthenium (Parthenium hysterophorus L.), a weed grown off site as green manure (GM) under repeated applications of fertilizer P and urea N for eight years in a rice (Oriza sativa L.)-wheat (Triticum estivum L.) sequence was studied on transformation of fertilizer P applied to soil at the National Research Center for Weed Science, Jabalpur, India. Based on the results, it appeared that, repeated applications of 52 kg super-phosphate P resulted in a marked increase in Olsen P linearly with time. Conjunctive use of urea fertilizer N with organic manure resulted in a larger increase in Olsen P in the Vertisol. Studies further revealed that the greater accumulation of fertilizer P applied in excess to crop removal occurred in inorganic P in the plots receiving only fertilizer N. However, plots receiving fertilizer N along with organic manures led to P accumulation predominantly in organic forms. The study suggests that these two pools of P acted as a sink when fertilizer P was applied in excess to crop removal and are bio-chemically active. The Olsen P status after 8 cycles of rice-wheat crops revealed that the average amount of fertilizer P required after adjusting for crop uptake to increase Olsen P by 1 mg kg(-1) soil was 7.2 kg Pha(-1) in the plots receiving only fertilizer N. Whereas, application of 5t FYM or 6t GM reduced it to 4.6 kg Pha(-1). The plots receiving manure always maintained a greater concentration of Olsen P. The application of CM or GM with fertilizer N enriched short-term inorganic P as well as long-term organic P fertility. After eight years, larger concentrations of organic P in the subsurface layer (16-30 cm), compared to initial values, indicates downward movement of P in organic forms.     

Survival and growth of dominant tree seedlings in seasonally tropical dry forests of Yucatan: site and fertilization effects

Aims Seasonally tropical dry forests of the Yucatan Peninsula are typically found in sites with nutrient-poor soils because of the recent geological origin of the region. The landscape is dominated by extensive karstic plates that shape environments where vegetation regeneration through seed germination may be limited by the availability of suitable microsites. In this study, we documented the survival and growth of seedlings from three dominant tree species (Bursera simaruba, Piscidia piscipula and Lysiloma latisiliquum) in seasonally tropical dry forests in Yucatan. Specifically, we evaluated the effect of nutrient addition (N and P, separately and in combination) on seedling survival and growth across three sites with differing levels of precipitation.Methods We conducted a nutrient addition experiment, whereby we established 12 plots of dimensions 10×10 m (100 m 2) at each site, from which three plots were randomly selected to receive one of four treatments: N addition, P addition, N and P addition and no nutrient addition (controls). Prior to treatment application, in each plot, we planted 10 seedlings of each species in October 2010 and subsequently conducted surveys of plant growth and survival every 20 days from November 2010 to April 2011.Important findings Overall, nutrient addition increased seedling survival and the magnitude of this effect was similar among sites. We did not observe an additive effect of the N + P treatment on survival. Similarly, we observed a positive effect of nutrient addition on seedling growth, but this effect was contingent upon site; regarding survival, the effects of N and P on seedling growth were not additive. These results suggest that seedling recruitment and growth in the three dominant species of trees in Yucatan are limited by nutrient availability but that the magnitude of this effect, particularly on seedling growth, is specific for species and site.     

Bt抗虫杂交棉叶片营养元素含量变化及其与产量的关系

为了比较杂交棉不同品种、不同世代棉花叶片营养元素含量的差异,于2003、2004年以Bt抗虫杂交棉NZ62、H64、H16的杂交种一代、二代和三代为材料,在湖南长沙进行了研究。田间试验在湖南农业大学试验基地进行,采用随机区组试验,设4次重复,4行区,小区面积13．4m^2。分别于棉花盛花期、吐絮期两个时期,在每个试验小区连续取10株棉株的倒数第4叶和倒数第2叶,测定棉叶的全量N、P、K、B、Cu、Zn、Fe、和Mn的含量。研究结果表明：不同品种花铃期养分含量除P以外均存在显著差异,且变化趋势基本一致,均以NZ62含量最高,H16次之,H64最低,差异达显著水平（P〈5％）。吐絮期不同品种叶片的N、P、K和B含量均不存在显著差异,而Cu、Zn、Mn营养含量均存在显著差异,NZ62比H16和H64高;不同世代花铃期F1棉株叶片的N、K、Cu、Zn、Fe、Mn和B的含量显著高于F2、F3（P〈5％）,而F2、B的含量变化基本一致,F1代棉株对营养元素的吸收与F2、F3代棉株相比具有显著的杂种优势。F2、F3代优势衰退与其叶片营养元素含量减少相符合。但吐絮期不同世代之间没有显著差异。相关分析表明,花铃期棉花叶片含N量、含K量与子棉产量和皮棉产量有显著相关（P〈5％）,而吐絮期的这两个元素的含量与棉花产量无显著相关（P〉5％）。无论是花铃期还是吐絮期,B元素的含量与子棉、皮棉产量的相关均达到极显著水平（P〈1％）。     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

Nitrate reductase activity,biomass, yield,and quality in cotton in response to nitrogen fertilization

In the production of cotton (Gossypium hirsutum L.), nitrogen fertilization is one of the most costly crop practices, but important to reach high yields. However, high nitrogen (N) content in plants does not always translate into a high fibre production. One way of assessing the efficiency of the N fertilizer is through the enzymatic activity of the nitrate reductase (NR). This is a key enzyme in N assimilation, whose activity is regulated by a number of endogenous and exogenous factors that determine yield. The aim of this study was to assess the effect of N fertilization on yield, fibre quality, biomass, and NR enzymatic activity in vivo in the cotton variety Fiber Max 989. The evaluated application rates were 0, 50, 100, and 150 kg/ha of N, using urea as a source (46% N) in a randomizedblock design with three replicates. At harvest, the maximum yield of seed cotton and the greatest accumulation of total foliar biomass through time was reached after applying 150 kg N/ha. The different N-application rates did not affect the components of cotton-fibre quality. The activity of endogenous NR was greater on plants where 150 kg N/ha were applied. The highest cotton yield and N contents were obtained on these plants. Therefore, the NR activity in vivo could be used as a bioindicator of the N nutritional level in cotton.     

Effects of Nutrient Limitation on Aboveground Carbon Dynamics during Tropical Dry Forest Regeneration in Yucatán,Mexico

Tree growth (as diameter increment), litterfall production, and litter biomass were studied in two secondary tropical dry forests of the Yucatán Peninsula under four treatments of nutrient addition. The studys objective was to assess how variations in the nutrient supply affect aboveground net primary production and carbon (C) accumulation on the floor of two forests in different stages of regeneration. The study included an area of young forest (10 years old) with phosphorus (P)-poor soils and an area of old forest (around 60 years old) where soil P was comparatively less limiting. Four replicate plots (12 × 12 m) at each forest were either left intact (controls) or fertilized with nitrogen (N), P, or N plus P during 3 consecutive years. After 3 years of fertilization, relaxation of the constraints on nutrient limitation resulted in increased trunk growth rates at both the young and old forests. This effect was more pronounced with the addition of P or N plus P (trunk growth doubled with respect to controls), whereas N addition increased tree growth by 60% in comparison to trees in plots without nutrient supplements. In both forests, there were no significant differences in litterfall production among treatments during the first 2 years after fertilization. In the 3rd year of nutrient addition, litterfall production was significantly higher in plots fertilized with N plus P compared to control plots at both forest sites; however, changes in litterfall were not accompanied by litter accumulation in the floor of the two forests. The results of this study support the hypothesis that there is nutrient limitation during tropical dry forest regeneration. They further show that it may be maintained in the long term during secondary succession.     

Effects of VA mycorrhiza on yield and harvest index of field-grown pea

Summary A field experiment was carried out to study the influence of vesicular-arbuscular mycorrhiza (VAM) on nutrient uptake and growth of pea at two levels of P fertilizer. Pea was grown in dazomet-fumigated and non-fumigated soil, either with or without addition of inoculum of VAM fungi. Dazomet efficiently eliminated infection by indigenous VAM fungi, whereas roots from untreated soil were extensively infected. Inoculation with VAM fungi increased P uptake by peas in fumigated plots, but had no significant effect on dry matter production in either soil treatment. However, VAM developed less in inoculated fumigated than in untreated plots. Seeds of uninfected plants in fumigated plots contained only 56 and 81%, respectively, of the P and dry matter content of seeds of infected plants in untreated plots. The addition of 60 kg P ha⁻¹ also increased seed yields but to a smaller degree than VAM. The seed yield as a proportion of total shoot yield (harvest index) was higher in VAM infected than in uninfected peas but was unaffected by P fertilizer. The possible reasons for this are discussed.     

Effects of long-continued treatment on the mineral nitrogen content and mineralisable nitrogen of soil from selected plots of the Broadbalk experiment on continuous wheat,Rothamsted

Summary The changes in the ammonium-N and nitrate-N contents of bare fallow and soil under the first and third crops of winter wheat after fallow were followed on plots of Broadbalk Field, Rothamsted, which have received for each crop 14 tons farmyard manure (FYM) per acre, complete minerals (P, K, Na, Mg), or complete minerals + nitrogen fertilizers.More mineral N was produced during fallow on the plot receiving FYM than on the other plots. Soil under wheat also contained more mineral N on the FYM plots than elsewhere. Nitrogen fertilizers applied in the spring temporarily increased the mineral-N content of the soil, but were rapidly removed by the crop. Ammonium sulphate applied in the autumn was lost from the surface soil by the following March through nitrification and leaching.Twice as much mineral-N was produced when soil from the FYM plot was incubated as when soils from other plots were similarly treated. Nitrate formed during fallow was leached into the subsoil during the autumn and winter, and recovered by the wheat during the following spring and summer. Its existence is not detected by sampling the surface soil, nor by an incubation test. This source of nitrogen complicates the use of laboratory measurements to assess the fertilizer nitrogen required by winter wheat. Since the crop removed mineral N from the surface soil by March, estimation of the amount then present was also of no value for making fertilizer recommendations.     

Nutrient limitation of epilithic and epixylic biofilms in ten North American streams

1. Nutrient diffusing substrata were used to determine the effect of added inorganic nitrogen (N) and phosphorus (P) on the development of epilithic and epixylic biofilms in 10 North American streams. Four treatments of diffusing substrata were used: Control (agar only), N addition (0.5 m NaNO₃), P addition (0.5 m KH₂PO₄), and N + P combined (0.5 m NaNO₃ + 0.5 m KH₂PO₄). Agar surfaces were covered with glass fibre filters (for epilithon) or discs of untreated white oak wood veneer (for epixylon). 2. We found that if algae showed significant response to nutrient addition, N limitation (either N alone or N with P) was the most frequent response both on GF/F filters and on wood. Despite the low dissolved nutrient concentrations in our study streams, more than a third of the streams did not show any response to N or P addition. In fact, P was never the sole limiting nutrient for algal biofilms in this study. 3. Nutrient addition influenced algal colonisation of inorganic versus organic substrata in different ways. The presence of other biofilm constituents (e.g. fungi or bacteria) may influence whether algal biomass on wood increased in response to nutrient addition. Algae on organic and inorganic substrata responded similarly to nutrient addition in only one stream. 4. Fungal biomass on wood was nutrient limited in six of 10 study streams. N limitation of fungal biomass (with or without secondary P limitation) was most frequent, but P limitation did occur in two streams. 5. Our results show that biomass responses to nutrient addition by the heterotrophic and autotrophic components of the epixylic biofilm were different, though both experienced the same stream nutrient conditions. For algae and fungi growing on wood, limiting nutrients were rarely similar. Only three of nine streams showed the same biomass response to nutrient addition, including two that showed no significant change in biomass despite added nutrients.     

Field-specific potassium and phosphorus balances and fertilizer requirements for irrigated rice-based cropping systems

Fertilizer K and P requirements for rice (Oryza sativa L.) can be determined with site-specific nutrient management (SSNM) using estimated target yield, nutrient balances, and yield gains from added nutrient. We used the QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) model with >8000 plot-level observations to estimate the relationship between grain yield and nutrient accumulation in above-ground dry matter of irrigated rice with harvest index?≥?0.4. Predicted reciprocal internal efficiencies (RIEs) at 60–70% of yield potential corresponded to plant accumulation of 14.6 kg N, 2.7 kg P, and 15.9 kg K per tonne of grain yield. These RIEs enable determination of plant requirements for K and P and net output of K and P in harvested grain and removed crop residues at a target yield. Yield gains for nutrient applied to irrigated rice averaged 12% for K and 9% for P for 525 to 531 observations. For fields without certain yield gain, fertilizer K and P requirements can be determined by a partial maintenance approach (i.e., fertilizer input?<?output in nutrient balance), which considers nutrient supply mediated through soil processes and balances trade-offs between financial loss with full maintenance rates and risk of excessive nutrient depletion without nutrient application. When yield gains to an added nutrient are certain, partial maintenance plus yield gain can be used to determine fertilizer requirements. The SSNM-based approach and algorithms enable rapid development of field-specific K and P management.