Field‐Based screening methodology to improve tolerance of common bean to low‐P soils

Abstract

Phosphorus (P) limits common bean (Phaseolus vulgaris L.) production throughout sub‐Saharan Africa, where P fertilizer is not affordable to the vast majority of smallholder farmers. Genetic differences in bean performance in low‐P soils suggest that low P tolerance could be improved. Earlier breeding efforts have not been successful, in part due to the challenges of selecting genotypes with improved performance in a heterogeneous soil environment. A field based screening method for low P tolerance has been developed, based on evaluating soil status and ameliorating edaphic compounding factors. The soil is classified as an Oxic Haplustalf and is representative of the unimodal, mid‐to‐high altitude bean growing regions of Southern Africa. The soil has very low zinc (Zn) and nitrogen (N) contents, which reduced growth markedly. After amelioration of these edaphic complications, P response could be quantified. A promising genotype CAL 143 was selected which consistently expressed, over two growing seasons, low P tolerance and high yield responsiveness to moderate fertilizer P application.     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.     

Is it necessary to adjust nitrogen recommendations for tillage and wheat residue management in irrigated sweet corn?

ABSTRACT

Conservation tillage practices have gained interests. A 2-year field study (2014–2015) was conducted to evaluate four N rates (0, 69, 138, and 207 kg N ha^?1) effects on irrigated sweet corn (Zea mays L.) grown with or without wheat (Triticum aestivum L.) residue removal and conventional (CT), reduced (RT), or no-tillage (NT) practices near Shiraz, Iran. After 2 years, maximum marketable yield occurred at 156 and 159 kg N ha^?1 under CT and NT, respectively, while yield was tended to be increased with increasing N rates under RT. Increasing N rate increased total plant N uptake, shoot, and grain N accumulation. The lowest nitrogen use efficiency (NUE) was obtained under NT, while RT and CT either showed similar effects or RT was superior over CT. Soil total N was greater under CT and residue retention showed 18% and 14% higher N concentration than residue removal in 2014 and 2015, respectively. Soil organic matter was the highest (2.59%) under RT with residue retention and 138 kg N ha^?1. Conservation tillage needs more N rather than CT during transition from conventional to conservation agriculture practices, but it is based on the short-term results and evaluation of long-term experiment is highly recommended.     

Is it possible by use of heavy fertilization to boost the small yields normally obtained from arable land with unfavourable natural qualities to the yield levels of favourable land?

Five field experiments, belonging to the Swedish long‐term soil fertility experimental project initiated in 1957, are situated in the very south of the country, two of them on land of favourable natural conditions and three on less favourable areas. The experimental design consists of all 16 combinations between four N and four PK treatments in two 4‐year crop rotations, with and without livestock. In the livestock rotation a clover/grass leg is cropped and cattle manure added once per rotation. One weakly (B1), one ordinary (C2), and one heavily (D3) fertilised NPK‐treatment in both crop rotations were examined in order to compare yields of less favourable with yields of favourable sites. The last five rotation sequences were used.

In both rotations, D3 yields of the less favourable sites were superior to B1 yields of the favourable sites, except for winter wheat in the livestock rotation, for which the B1 yield at the favourable sites was superior. In contrast, D3 yields of the less favourable sites were generally lower than the C2 yields of the favourable sites except for clover/grass ley in the livestock rotation and oil seed rape in the rotation without livestock, for which the D3 and C2 yields were the same statistically.     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

Identification of the effects of long-term application of nitrogen fertilizer on the availability of 11 elements in soils and their supply to ‘Jonathan’ apple trees by using simultaneous multi-element analysis

Abstract

The objective of this study was to investigate the effects of long-term application of ammoniacal N fertilizer for 43?years on the availability of 10 essential elements (B, N, Mg, K, Ca, Mn, Fe, Ni, Cu, and Zn) and Al in root-zone soils and their supply to ‘Jonathan’ apple trees. To achieve this objective, we used simultaneous multi-element analysis. To estimate the soil depth from which the apple trees took up these elements, we calculated the ratios of their concentrations in the N fertilized plot (N plot) to those in the no N plot (0?N plot) (N/0N ratio). Long-term N fertilization significantly increased the fruit and leaf N/0N ratios of N and Mn and significantly decreased that of K. These ratios in the fruits and leaves were similar to those in the 20–90?cm soil layer. This result suggests that N, K, and Mn in the fruits and leaves were supplied from the 20–90?cm soil layer. The N/0N ratios of all 11 elements in the fruits and leaves were significantly positively correlated with those in the 20–90?cm soil layer, but not in the 0–20?cm soil layer. Our findings indicate that long-term N fertilization altered the tree nutrition of not only N, but also K and Mn. These changes in the tree nutrition were ascribed to the fertilizer-induced changes in the availability of elements in the subsoils.     

Response of nitrogen fixation,nodule activities,and growth to potassium supply in water‐stressed broad bean

Three‐week‐old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 20 and 10%) for five weeks. Half of the stressed plants was treated with potassium chloride (KC1) at 10 (K₁) and 150 mg (K₂)/kg soil at the beginning of water deficit. Nodulation was examined and some nodule activities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stress. Soluble carbohydrate contents of nodules, however, was significantly increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was accumulated. The results indicate that K supply, particularly at the 150 mg/kg soil level, increased faba bean resistance to water stress.     

Is nitrate reduction to nitrite possible in glucose-amended alkaline saline soil under aerobic conditions?

A phylogenetic analysis of the archaeal community in the soil of the former Lake Texcoco showed that some of the clones identified were affiliated to Archeae that reduce nitrate (NO₃^?) to nitrite (NO₂^?) and NO₂^? to unknown products under aerobic conditions. Previous research suggested that this indeed might occur when an easily decomposable C-substrate is available, but little is known about the factors that control the possible processes involved. The sandy clay loam soil with pH 10 and electrolytic conductivity 56 dS m^?1 was spiked with 1000 mg glucose-C kg^?1 soil (GLUCOSE pre-treatment), 200 mg NO₃^?-N kg^?1 soil (NITRATE pre-treatment), or left unamended (CONTROL pre-treatment) and conditioned for eight days. Pre-treated soil was then added with 1000 mg glucose-C kg^?1 soil and 200 mg NO₃^?-N kg^?1 soil and amended with ammonium (NH₄⁺) (AMM treatment) and l-glutamine (GLUT treatment), acetylene (C₂H₂) (ACE treatment), oxygen (O₂) (OXI treatment), left untreated (CON treatment) or sterilized. No abiotic factors affected concentrations of NH₄⁺, NO₂^? or NO₃^?. In the CONTROL pre-treatment, concentration of NO₃^? decreased 170 mg N kg^?1 soil within 72 h, in the GLUCOSE pre-treatment with 182 mg N kg^?1 soil within 2 h and in the NITRATE pre-treatment with 272 mg N kg^?1 soil within 168 h. Mean concentration of NO₂^? was 3.2 mg N kg^?1 soil in unamended soil, 5.7 mg N kg^?1 soil in the CONTROL pre-treatment, but >20 mg kg^?1 soil in the GLUCOSE pre-treatment and ≥40 mg kg^?1 in the NITRATE pre-treatment. The application of NO₃^? and glucose increased the mean concentration of NH₄⁺ compared to the unamended soil independently of pre-treatment. It was found that microorganisms in the alkaline saline soil of the former Lake Texcoco can reduce concentrations of NO₃^? while releasing NO₂^? under aerobic conditions when an easy decomposable substrate is available without it being directly related to microbial activity and this being more outspoken when glucose or nitrate were previously added.     

Is glomalin an appropriate indicator of forest soil reactive nitrogen status?

In this paper we address total glomalin‐related soil protein (T‐GRSP) as a possible indicator of differences in forest soils related to reactive nitrogen and forest composition. We focused especially on the relationship between T‐GRSP (g kg⁻¹), soil organic carbon (SOC), and reactive nitrogen (N_r) availability among different categories of temperate forests and different horizons. Our study included 105 sampling sites divided into 5 categories, which vary in elevation and tree species composition (coniferous, deciduous, mixed). We detected significantly higher T‐GRSP and SOC in the F+H horizon under conifers. We assume that this observation might be attributed to suppression of decomposition of T‐GRSP and SOC by nature of coniferous litter. The lack of significant differences in T‐GRSP/SOC among the categories and the positive correlations between T‐GRSP and SOC in most of the categories confirmed the strong relationship of T‐GRSP with SOC. We found a significantly higher content of T‐GRSP in the F+H horizon for all studied forest categories. However, the contribution of T‐GRSP to SOC is significantly higher in the A horizon, which might be caused by stabilization of glomalin by mineral fraction, including clay minerals or by the belowground origin of glomalin. We found the increase of SOC with increasing N_r in the A horizon for most categories of forest. T‐GRSP follows this trend in the case of deciduous forests (decid), mixed forest (mixed), and mountain forests (mount). On the other hand, we detected a decrease of T‐GRSP with increasing N_r in the F+H horizon of coniferous forests (conif). Moreover the T‐GRSP/SOC decreases with the increase of N_r in the A horizon of conif, mixed and mount, which points to the higher sensitivity of forest with prevalence of coniferous trees. Our observations have confirmed an ecosystem‐specific relationship between T‐GRSP, SOC and N_r. We concluded that T‐GRSP in combination with T‐GRSP/SOC has the potential to reveal qualitative changes in soil organic matter (SOM) connected with increasing N_r.     

What soil information do crop advisors use to develop nitrogen fertilizer recommendations for grain growers in New South Wales,Australia?

The Australian grains industry relies on mineralized nitrogen (N) from soil organic matter and plant residues, but fertilizer N is increasingly needed to optimize yields. Most farmers are guided on N fertilizer requirements by commercial crop advisors. We surveyed (n = 132) and interviewed (n = 11) New South Wales grains advisors to gauge the usage of soil process understanding, soil data and decision support systems (DSSs) when developing N recommendations. Soil moisture at sowing, seasonal forecasts, crop rotation, soil mineral N, financial risk profiles and paddock history were all used to prepare N fertilizer advice, but stored soil moisture was most important. Farmer confidence in soil N testing was low due to high spatial variability. Most advisors calculated N fertilizer required for yields within 10%–15% of crop potential, but clients’ attitude to financial risk guided final N recommendations. Conservative growers preferred a low input system, while more reliable rainfall or greater reliance on stored soil water led growers to apply higher N rates to maximize long‐term profits. Advisors preferred “rules‐of‐thumb,” simple DSSs and knowledge of crop growth, to elaborate DSSs requiring detailed inputs and soil characterization. Few used in‐crop N sensing. N decision methodologies need to be updated to account for changes in soil fertility, cropping systems and farming practices. New research is needed to answer practical questions regarding soil N mineralization and N losses associated with alternative N application practices and extreme weather events. Training of new advisors in N processes and DSS use needs to be ongoing.     

Does the source of nitrogen affect the response of subterranean clover to prolonged root hypoxia?

Nitrogen (N) is taken up by most plant species in the form of nitrate (NO ) or ammonium (NH ). The plant response to continuous ammonium nutrition is species‐dependent. In this study, the effects of the source of N nutrition (NO , NH , or the mixture of NO and NH ) on the response of clover (Trifolium subterraneum L. cv. 45C) plants to prolonged root hypoxia was studied. Under aerobic conditions, plant growth was strongly depressed by NH , compared to NO or mixed N nutrition, as indicated by the significant decrease in root and shoot‐dry‐matter production (DW), root and shoot water contents (WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters (F₀, F_v/F_m). However, the N source had no effect on chlorophyll a–to–chlorophyll b ratio. Under hypoxic conditions, the negative effects of root hypoxia on plant‐growth parameters (DW and WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters were alleviated by NH rather than NO supply. Concomitantly, shoot DW–to–root DW ratio, and root and leaf NH concentrations were significantly decreased, whereas root and leaf carbohydrate concentrations, glutamine synthetase activities, and protein concentrations were remarkably increased. The present data reveal that the N source (NO or NH ) is a major factor affecting clover responses to hypoxic stress, with plants being more tolerant when NH is the N form used. The different sensitivity is discussed in terms of a competition for energy between nitrogen assimilation and plant growth.     

Is the potential for the formation of common mycorrhizal networks influenced by fire frequency?

We investigated the influence of fire return interval length on the ectomycorrhizal (ECM) community of a Pinus pinaster dominated forest and on the potential for common ECM networks (CMNs) between understorey shrubs and P. pinaster. ECM root tips were sampled from five shrub species belonging to the genera Arbutus, Cistus and Halimium and from maritime pine in four areas of central Portugal characterized by differing fire return interval length. Fungal symbionts were identified using molecular techniques with direct sequencing of the nrDNA ITS region.Twenty nine ECM species and sixteen non-ECM root inhabitants were identified. Six years after wildfire disturbance ECM species richness did not differ significantly between unburnt and burnt areas. Nine ECM fungal species were common to pine and shrubs and both their frequency of occurrence and proportion were significantly higher in the unburnt area when compared with both areas subjected to fire.Our study revealed that while the potential for CMNs between understorey shrub species and pine seemed to be maintained in the long fire return interval area, recurrent fires significantly reduced the frequency of occurrence and the proportion of common symbiont species. High fire frequencies could therefore delay the process of re-colonization by pine seedlings limiting their dispersal in new settings.     

Is the photometric method using acetone extracts to determine chlorophyll concentrations applicable to Mg‐deficient plants?

A conventional photometric method to determine chlorophyll concentrations in maize leaves was evaluated. It was tested whether in Mg‐deficient plant tissue the addition of MgCO₃ during pigment extraction converts protoporphyrin IX into chlorophyll, falsifying concentration measurements. The non‐destructive N‐tester was used as a reference for the destructive chlorophyll determination. It is shown that both methods are valid for the determination of chlorophyll concentration in Mg‐deficient leaves.     

More evidence that anaerobic oxidation of methane is prevalent in soils: Is it time to upgrade our biogeochemical models?

Estimating future fluxes of CH₄ between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, commonly occurs in 20 hydromorphic soils spanning a wide range of chemical properties. Bulk soil samples were collected under shallow water near the shoreline of 15 recently drained fish ponds in southern Bohemia (Czech Republic), as well as from below the water table at 3 peatland locations in northeast Scotland and 2 acid sulfate soils on the southern coast of Finland. Each soil slurry was incubated under both oxic and anoxic conditions, with or without the addition of alternative electron acceptors (SO₄²⁻ and NO₃⁻) or H₂PO₄⁻. Here, “oxic” and “anoxic” conditions refer to anoxic soil respectively incubated in a headspace containing air or argon. Using the isotope dilution method, we determined the gross production and oxidation rates of CH₄ after 2 days incubation under oxic headspace conditions, and after 2, 21 and 60 days incubation under anoxic conditions. Large differences in net CH₄ fluxes were observed between soil types and between incubation conditions. AOM was detected in each of the 20 bulk soil samples, which spanned >6 pH units and 2 orders of magnitude in organic C content. Significant positive relationships were found between AOM and gross CH₄ production rates under anoxic conditions, resulting in AOM rates that were sometimes higher than CH₄ oxidation rates under oxic headspace conditions. There was no relationship between net and gross CH₄ production rates, such that 2 soil types could display similar low net rates, yet conceal very large differences in gross rates. The effects of alternative electron acceptors on AOM were idiosyncratic and resulted in no net trend. We did find, however, a negative effect of SO₄²⁻ and H₂PO₄⁻ on gross CH₄ production rates under anoxic and oxic conditions respectively. Under oxic headspace conditions, CH₄ oxidation was related to soil organic C content. Taken collectively, our results suggest that AOM, or potential AOM, is prevalent over a wide range of soil types, that AOM may contribute substantially to CH₄ oxidation in soils, and that AOM in soils should be integrated to current process-based CH₄ cycling models.     

Is salt stress of faba bean (Vicia faba) caused by Na+ or Cl– toxicity?

The effect of sodium chloride (NaCl), sodium sulfate (Na₂SO₄), and potassium chloride (KCl) on growth and ion concentrations of faba bean (Vicia faba L. cv. Troy) was studied. After 14 or 15 d of isoosmotic treatment with 100 mM NaCl or 75 mM Na₂SO₄, respectively, plants developed toxicity symptoms. These symptoms were characterized by local and nonchlorotic wilting spots, which later turned to black, necrotic spots. In contrast to NaCl or Na₂SO₄ treatment, plants treated with 100 mM KCl did not show these symptoms. The symptoms occurred on those leaves that accumulated highest concentrations of Na⁺ and showed highest Na⁺ : K⁺ ratios. Our results indicate that Na⁺ toxicity inducing K⁺ deficiency is responsible for the spot necrosis of faba bean. Additionally, chlorotic symptoms occurred. The concentrations of Na⁺ and Cl^– were determined in chlorotic leaves and in isolated chloroplasts. The reduction of chlorophyll in leaves after NaCl exposure may be explained in terms of high Cl^– concentrations in the chloroplasts and appears to depend on high Na⁺ concentrations. Chlorotic toxicity symptoms can be avoided by additional Mg²⁺ application.     

Cropping leads to loss of soil organic matter: How can we prevent it?

<正>Soil organic matter (SOM), which associates carbon (C) to key plant nutrients, has been stored in soil for thousands of years. Scientists have long recognised its positive impact on key environmental functions such as food production and climate regulation. As soon as a virgin land (forest or grassland) is cultivated, there is a tendency for the soil to lose its SOM, and we still largely misunderstand the underlying mechanisms, leading to inappropriate decisions being taken to fight soi...     

Responses of bacterial and archaeal ammonia oxidisers of an acidic luvisols soil to different nitrogen fertilization rates after 9?years

It is still not clear which group of ammonia-oxidizing microorganisms plays the most important roles in nitrification in soils. Change in abundances and community compositions of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) under long-term different nitrogen (N) fertilization rates were investigated in an acidic luvisols soil using real-time polymerase chain reaction and denaturing gradient gel electrophoresis, respectively, based on the ammonia monooxygenase a-subunit gene. The experimental plan included the following treatments: control without N fertilization (N_CK), low N fertilization rate, middle N fertilization rate, and high N fertilization rate as 0, 100, 150, and 250?kg urea-N?ha^?1, respectively. Long-term different N fertilization rates did not significantly alter the total C and N contents of soil while it significantly decreased soil pH, which ranged from 5.60 to 5.20. The AOB abundance was more abundant in the N fertilization treatments than the N_CK treatment; the AOA abundance decreased by the increasing N fertilization rates, as did the ratios of AOA/AOB. The large differences in the potential nitrification rates among four treatments depended on the changes in AOA abundance but not to changes in AOB abundance. Phylogenetic analysis showed that the AOB communities were dominated by Nitrosospira clusters 1, 3, and 9 while all AOA sequences were grouped into soil/sediment cluster except for one sequence. Taken together, these results indicated that AOB and AOA preferred different soil N conditions and AOA were functionally more important in the nitrification than AOB in the acidic luvisols soil.     

Can differences in 15N natural abundance be used to quantify the transfer of nitrogen from legumes to neighbouring non-legume plant species?

Natural variations in the stable isotope ¹⁵N are often exploited in studies of N cycling in ecosystems. Lower ¹⁵N natural abundance in non-legume plants growing in association with legumes, compared with the non-legume grown alone in pure stands have been observed in cropping, forage, and agroforestry systems. Such observations have frequently been attributed to the transfer of biologically-fixed nitrogen (N) from the legume to the companion non-legume, and various methodologies have been employed to calculate the extent of the N transfer. While some of these ¹⁵N natural abundance-based estimates of N transfer were within the range previously reported using equivalent ¹⁵N-enriched techniques (<20% of non-legume plant N and <10 kg N ha⁻¹ derived from fixed N contributed by neighbouring legumes), many of the values obtained using natural abundance were much higher (30%–83% of the non-legume N derived from fixed N representing up to 30–40 kg N ha⁻¹) than generally measured by ¹⁵N-enriched methods; with even greater estimates being determined where data were available to allow N transfer to be re-calculated on the basis of total legume N rather than fixed N (42% to >100%, and up to 110 kg N ha⁻¹ per year). This review raises concerns about the assumptions behind the natural abundance approach, and provides some alternative interpretations for the observed differences in natural ¹⁵N abundance between plants grown in the presence and absence of legumes. It was concluded that simple comparative measures of non-legume δ¹⁵N alone cannot provide a quantitative estimate of N transfer between plant species if the dominant source and the isotopic identity of the transferred N cannot be validated, and if the extent of any isotopic fractionation associated with relevant N transformations occurring during transfer cannot be defined. To date this information is not forthcoming. There is a need to greatly improve our understanding of the transfer processes before the real value of the δ¹⁵N technology can be realized. In the first instance this will primarily be achieved by carefully executed experiments under controlled conditions, and in the field, employing both ¹⁵N natural abundance and enrichment approaches so estimates of transfer can be compared, and the data interrogated using modelling approaches to explore isotopic fractionation.