Losses of 15N-nitrogen by plant–soil system after herbicide application on black oat

Recent studies have demonstrated that the use of glyphosate or glufosinate-ammonium herbicides for some cover crop desiccation in conservationist systems could favor nitrogen (N) losses from the soil–plant system. In this context, the objective of this study was to evaluate the losses of N by the plant–soil system after the desiccation of black oat (Avena strigosa Schreb.) with the application of herbicides glyphosate, glufosinate-ammonium, or paraquat. Two greenhouse experiments were implemented using black oat plants fertilized with labeled (¹⁵N) ammonium nitrogen, and the N loss of the plant–soil system was quantified. The desiccation of black oat with glyphosate caused a reduction in root dry mass by approximately 60% in both experiments. The glyphosate and glufosinate-ammonium reduced the amount of N present in the aboveground portion; however, the paraquat herbicide did not modify it. None of the herbicides applied affected N losses in the black oat plant–soil system. However, 5–15% of the N applied as fertilizer was lost up to harvest. The results suggest that black oat can be used as a cover crop in direct sowing in order to avoid nitrogen losses in the soil–plant system.     

Marandu Palisadegrass Mineral Nutrition and Production Related to Nitrogen and Potassium Supply

Nitrogen (N) and potassium (K) fertilization play a key role in forage crops and can significantly increase yields of ‘Marandu’ palisadegrass [Brachiaria brizantha (Hochst. exA. Rich.) Stapf.], one of the most important forage crops in Brazil. This study aimed to identify the concentrations of total N and K, nitrate (NO₃^?), and ammonium (NH₄⁺), chlorophyll meter readings (SPAD), and nitrate reductase activity (At-RNA) required to maximize yield. Plants were grown in quartz substrate and treated with nutrient solutions that ranged from 2 to 33 mmol L^?1 for N and 0.5 to 11 mmol L^?1 for K. Dry matter production and At-RNA increased with increasing N and K supplies. SPAD readings correlated strongly with N leaf concentration and dry matter production and can be used to assess the N status of this species. The supply of N and K in the fertilization promoted high yield and adequate N and K concentration for plant metabolism.     

Non-labile phosphorus acquisition by Brachiaria

Brachiaria are tolerant to low phosphorus (P) soils and may enhance P soil availability. The identification of mechanisms driving this effect is important. Our objective was to determine responses of palisade grass and ruzigrass to mineral oxide-bound P. Palisade grass (Brachiaria brizantha) and ruzigrass (Brachiaria ruziziensis) were grown in nutrient solution (NS), where P was supplied as goethite and amorphous aluminum-oxide (Al-oxide). Only half of each pot received P. Dry matter yields of Brachiaria species having oxide-P as the sole P source were similar to those grown with water-soluble P. Inorganic P was found in the NS after 7 days, and organic P at 14 days after plant emergence. The presence of dissolved organic carbon (DOC) indicates an intense and quick response of the root system to the treatments. Results indicate enzyme and/or organic acids (OAs) root exudation as a strategy of these plants to access soil sparingly soluble P forms.     

Photosynthesis and Leaf Area of Brachiaria brizantha in Response to Phosphorus and Zinc Nutrition

Phosphorus (P) and zinc (Zn) are important determinants of plant productivity, particularly in the tropical grasslands of Brazil. Nutrient deficiency is one of the most important factors limiting plant productivity, decreasing photosynthesis efficiency and plant development. The present study investigates in Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. ‘Marandu’: 1) the gas exchange measurements; 2) the total leaf area development; and 3) the dry matter production due to P and Zn nutrition. Plants of B. brizantha cv. ‘Marandu’ were grown in nutrient solution under five rates of P (0.1, 0.6, 1.1, 1.6, and 2.1 mmol L^?1) and five rates of Zn (0.00, 0.75, 1.5, 2.25, and 3.00 μmol L^?1), in a fractioned factorial. Plants were harvested two times. Phosphorus supply increased carbon dioxide (CO₂) assimilation and stomatal conductance, and decreased intercellular CO₂. The interaction P rates x Zn rates were significant for the total leaf area variables and shoot dry matter in the second growth period. The nutrition of P and Zn interfered in the B. brizantha productivity by changing the grass photosynthesis and leaf area.     

Soil sulfur fractions dynamics and distribution in a tropical grass pasture amended with nitrogen and sulfur fertilizers

Soil sulfur (S) partitioning among the various pools and changes in tropical pasture ecosystems remain poorly understood. Our study aimed to investigate the dynamics and distribution of soil S fractions in an 8‐year‐old signal grass (Brachiaria decumbens Stapf.) pasture fertilized with nitrogen (N) and S. A factorial combination of two N rates (0 and 600 kg N ha^–1 y^–1, as NH₄NO₃) and two S rates (0 and 60 kg S ha^–1 y^–1, as gypsum) were applied to signal grass pastures during 2 y. Cattle grazing was controlled during the experimental period. Organic S was the major S pool found in the tropical pasture soil, and represented 97% to 99% of total S content. Among the organic S fractions, residual S was the most abundant (42% to 67% of total S), followed by ester‐bonded S (19% to 42%), and C‐bonded S (11% to 19%). Plant‐available inorganic SO₄‐S concentrations were very low, even for the treatments receiving S fertilizers. Low inorganic SO₄‐S stocks suggest that S losses may play a major role in S dynamics of sandy tropical soils. Nitrogen and S additions affected forage yield, S plant uptake, and organic S fractions in the soil. Among the various soil fractions, residual S showed the greatest changes in response to N and S fertilization. Soil organic S increased in plots fertilized with S following the residual S fraction increment (16.6% to 34.8%). Soils cultivated without N and S fertilization showed a decrease in all soil organic S fractions.     

Effect of ammonium and phosphorus supply on h+ production in gel by two tropical forage grasses

The effect of the supply of ammonium (NH₄ ⁺) and phosphorus (P) in gel on the amounts of hydrogen ion (H⁺) excreted from plant roots was studied with Brachiaria humidicola (a highly acid‐soil tolerant tropical grass) and B. brizantha (less acid‐soil tolerant) grown in soil in a glasshouse. The H⁺ production was measured over 24 h in agar gel containing full nutrient solution with a range of NH/‐N levels (0, 0.25, 0.5, and 5.0 mM NH₄ ⁺‐N). Highly soluble P, K₂HPO₄, or relatively insoluble P, rock P, was supplied at four concentrations (0, 11.5, 34.5, or 115 μM p) in the gel. Increasing NH₄ ⁺ concentration in the gel increased H⁺ production for both grasses, but there was some inhibition of growth for B. brizantha at the highest N concentration. For B. humidicola, but not B. brizantha H⁺ production was greater with 34.5 μM K₂HPO₄ than 11.5 μM K₂HPO₄. At 34.5 μM P for both grasses there was no difference in H⁺ production when P was supplied as rock P or K₂HPO₄. With 11.5 μM P both grasses produced less acid in the gel with the rock P compared with K₂HPO₄. The reduced H⁺ production is probably due to a lower availability of P in the rock P compared with K₂HPO₄. This effect was greater with B. brizantha than B. humidicola, implying that 11.5 μM rock P was not able to supply sufficient P for the growth of B. brizantha. Brachiaria humidicola was able to dissolve more rock P than B. brizantha or alternatively, the growth of B. humidicola was less adversely affected by the low P supply from rock P than B. brizantha. Plant‐induced acidity does not seem to occur as a response to a lack of available P, but rather these grasses only produce acid if there are enough nutrients for growth, i.e., both NH₄ ⁺ and P. If either N or P is limiting, growth is limited as is NH₄ ⁺ uptake, so that H⁺ production is curtailed.     

Modeling Effect of Residual Nitrogen on Response of Corn to Applied Nitrogen

Abstract

The logistic model has been used extensively to describe crop response to applied nutrients and water availability. It contains three parameters that can be estimated from data by regression analysis. One of the parameters refers to the reference state of the system, either at zero applied nitrogen (N) or applied N to reach 50% of maximum yield (N _1/2). A negative value of N _1/2 indicates that the soil already contains more than enough N to reach 50% of maximum yield. In the present analysis, data from a field study at Watkinsville, Georgia, which measured response of corn [Zea mays (L.) Pers.] to applied N following plowunder of grass sod is used to verify this point. It was found that N _1/2 shifted from –50 kg ha^?1 in the first year to +25 kg ha^?1 after several years. Availability of N from decaying vegetation declined exponentially with time. The time constant for decomposition and nitrification was 2 years. Total amount of N released from the vegetation was estimated as 190 kg ha^?1.     

Mycorrhiza and phosphate protection of tropical grass species against heavy metal toxicity in multi-contaminated soil

In this paper, the effects of arbuscular mycorrhizal (AM) fungi and phosphate amendments on protection of the tropical grass Brachiaria decumbens Stapf. against metal toxicity caused by Zn, Cd, Cu, and Pb were studied in a sterilized soil. Plants inoculated with a mixture of AM fungi (Acaulospora morrowiae, Gigaspora albida, and Glomus clarum) isolated from a heavy-metal-contaminated site or amended with P (added as triple superphosphate) exhibited marked positive growth responses, indicating the ameliorating effects of these two factors. Soil metal concentrations needed to inhibit plant growth by 50% were around twofold higher for AM plants as compared to those for non-inoculated ones. Similarly, phosphate showed ameliorating effects for B. decumbens, but its effects were not related to mycorrhizal conditions. Although mycorrhiza and phosphate act independently, their protecting effects were additive. Metal bioaccumulation factor of B. decumbens is high, especially for Cd; but AM inoculation prevents metal transference from roots to shoots, retaining these metals in the roots. AM fungus and phosphate represent a promising tool for enhancing ground vegetation in heavy-metal-contaminated sites.     

Variations in nitrogen uptake and nitrate-nitrogen concentration among sorghum groups

Nitrogen uptake and nitrate-N concentration in forage sorghums, which are related to ground water pollution or feed quality under conditions of crop fertilization by only animal wastes, were examined. Seventy-four genotypes of sorghum and Sudan grass were tested. They were classified into 4 groups; grain type and dual purpose type sorghums (6 and 13 genotypes, respectively, Sorghum bicolor Moench), sorgo type sorghum (21, S. bicolor), Sudan type sorghum (22, S. bicolor × S. sudanense (Piper) Stapf), Sudan grass (12, S. sudanense). There was a strong correlation between dry matter (DM) yield and N uptake, with the sorgo type producing the highest DM matter yield and showing the highest N uptake. Nitrate-N, which causes nitrate poisoning of ruminants, was detected mostly in the stem of all the genotypes. The nitrate-N concentration based on DM could be calculated accurately by multiplying the nitrate-N concentration of stem on a fresh matter basis by the DM partitioning ratio of stem divided by the DM concentration of stem. The grain type and the dual purpose type of sorghums with dry stem showed the lowest nitrate-N concentration because these plants had a lower DM partitioning ratio of stem and higher DM concentration of stem. Sudan grass and Sudan type sorghum with the genetic background of Sudan grass showed higher nitrate-N concentrations owing to their ability to accumulate nitrate-N.     

Aluminum stress stimulates the accumulation of organic acids in root apices of Brachiaria species

Aluminum‐resistant Brachiaria decumbens Stapf cv. Basilisk (signalgrass) and closely related, but less resistant Brachiaria ruziziensis Germain & Evrard cv. Common (ruzigrass) both accumulated high concentrations of aluminum (Al) in roots. Approximately two thirds of the total Al was complexed by soluble low‐molecular‐weight ligands, suggesting that it had been taken up into the symplasm. We therefore investigated whether these species might employ Al‐chelating organic acids for internal detoxification of Al taken up by root apices, the primary site of Al injury. Unlike root apices of other Al‐resistant plant genotypes, which secrete organic‐acid anions to detoxify Al externally, apices of Brachiaria species accumulated organic acids within the tissue. A comparison with whole roots showed that this preference for accumulation (as opposed to secretion) was restricted to apices. Citric acid, and to a lesser extent trans‐aconitic acid, accumulated in a uniform dose‐dependent manner in root apices of both species as their Al content increased under Al‐toxic growth conditions. Their accumulation was accompanied by a stimulation of malate synthesis in Al‐resistant B. decumbens, while it occurred at the expense of malate in Al‐sensitive B. ruziziensis. These data suggest a role of organic acids in the internal detoxification of Al in root apices of both Brachiaria species, presumably contributing to their comparatively high basal level of Al resistance. Yet internal detoxification of Al by organic acids does not appear to be the principal mechanism responsible for the superior resistance of B. decumbens.     

Seasonal Changes of Shoot Nitrogen Concentrations and 15N/14N Ratios in Common Reed in a Constructed Wetland

Abstract

Nitrogen (N) concentrations and stable N isotope abundances (δ¹⁵N) of common reed (Phragmites australis) planted in a constructed wetland were measured periodically between July 2001 and May 2002 to examine their seasonal variations in relation to N uptake and N translocation within common reed. Nitrogen concentrations in P. australis shoots were higher in the growing stage (7.5 to 24.8 g N kg^?1) than in the senescence stage (4.2 to 6.8 g N kg^?1), indicating N translocation from shoots to rhizomes. Meanwhile, the corresponding δ¹⁵N values were higher in the senescence stage (+12.2 to +22.4‰) than in the growing stage (+5.1 to +11.3‰). Coupled with the negative correlation (R²=0.24, P<0.05, n=18) between N concentrations and δ¹⁵N values of shoots in the senescence stage, our results suggested that shoot N became enriched in ¹⁵N due to N isotopic fractionation (with an isotopic fractionation factor, α_s/p, of 1.012) during N translocation to rhizomes. However, the positive correlation between N concentrations and δ¹⁵N values in the growing stage (R²=0.19, P<0.001, n=54) suggested that P. australis relies on N re‐translocated from rhizome in the early growing stage and on mineral N in the sediment during the active growing stage. Therefore, seasonal δ¹⁵N variations provide N‐isotopic evidence of N translocation within and N uptake from external N sources by common reed.     

Nitrogen losses from outdoor pig farming systems

Abstract. Nitrogen losses via nitrate leaching, ammonia volatilization and nitrous oxide emissions were measured from contrasting outdoor pig farming systems in a two year field study. Four 1‐ha paddocks representing three outdoor pig management systems and an arable control were established on a sandy loam soil in Berkshire, UK. The pig management systems represented: (i) current commercial practice (CCP) ‐ 25 dry sows ha^?1 on arable stubble; (ii) ‘improved’ management practice (IMP) ‐ 18 dry sows ha^?1 on stubble undersown with grass, and (iii) ‘best’ management practice (BMP) 12 dry sows ha^?1 on established grass. Nitrogen (N) inputs in the feed were measured and N offtakes in the pig meat estimated to calculate a nitrogen balance for each system. In the first winter, mean nitrate‐N concentrations in drainage water from the CCP, IMP, BMP and arable paddocks were 28, 25, 8 and 10 mg NO₃ l^?1, respectively. On the BMP system, leaching losses were limited by the grass cover, but this was destroyed by the pigs before the start of the second drainage season. In the second winter, mean concentrations increased to 111, 106 and 105 mg NO₃‐N l^?1 from the CCP, IMP and BMP systems, respectively, compared to only 32 mg NO₃‐N l^?1 on the arable paddock. Ammonia (NH₃) volatilization measurements indicated that losses from outdoor dry sows were in the region of 11 g NH₃‐N sow^?1 day^?1. Urine patches were identified as the major source of nitrous oxide (N₂O) emissions, with N₂O‐N losses estimated at less than 1% of the total N excreted. The nitrogen balance calculations indicated that N inputs to all the outdoor pig systems greatly exceeded N offtakes plus N losses, with estimated N surpluses on the CCP, IMP and BMP systems after 2 years of stocking at 576, 398 and 264 kg N ha^?1, respectively, compared with 27 kg N ha^?1 on the arable control. These large N surpluses are likely to exacerbate nitrate leaching losses in following seasons and make a contribution to the N requirement of future crops.     

The amount,but not the proportion,of N2 fixation and transfers to neighboring plants varies across grassland soils

ABSTRACT

Biological nitrogen fixation (BNF) is an important nitrogen source for both N₂-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N₂-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with ¹⁵N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N₂ fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant^?1, which was significantly lower than that of the CN (6.18 mg N plant^?1) and HW (8.01 mg N plant^?1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant^?1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.     

Carbon Fluxes from Different Pools in a Mined Area under Reclamation in Minas Gerais State,Brazil

Despite the benefits of grass cultivation and organic fertilization in mining areas undergoing reclamation, these practices may be associated to CO₂ emissions and soil organic matter (SOM) losses by priming effect. In the present study, we evaluated the changes on SOM pools and C–CO₂ emissions in a bauxite‐mined area under reclamation fertilized with poultry litter (PL) (0, 10, 20, and 40 Mg ha⁻¹) and cultivated with Brachiaria brizantha . Increases of about 3·5 times in the soil labile C were observed 1 year after experiment establishment. High C–CO₂ fluxes and a significant positive priming effect were observed in the presence of B. brizantha , increasing native C mineralization by nearly 4·9 times. Nevertheless, no net soil C loss was detected, probably because of the C inputs derived from B. brizantha , which offset these losses. In fact, the grass increased total organic C by 45% when fertilized with 40 Mg PL ha⁻¹. The data obtained suggest that the cultivation of B. brizantha fertilized with PL can be a promising option for rapid recovery in SOM in areas under reclamation. Copyright © 2016 John Wiley & Sons, Ltd.     

Nitrogen nutrition and changes in the chemical attributes of the soil for cultivars of Brachiaria brizantha intercropped with Stylosanthes in different forage systems

ABSTRACT

Nitrogen in the soil-plant system is extremely complex, and any change in soil management or cultivated species can modify its dynamics. To minimize environmental problems and sustainably optimize agricultural production, it is necessary to understand the dynamics of nitrogen in the soil-plant system. Thus, the objective of this study was to evaluate plant nitrogen nutrition and changes in the chemical attributes of the soil for cultivars of Brachiaria brizantha intercropped with Stylosanthes in different forage systems. The experimental design consisted of randomized block experimental design was used, with three replicates. The treatments consisted of forage systems: Piata palisadegrass, Paiaguas palisadegrass, Stylosanthes cv. Campo Grande, row intercropping of Piata palisadegrass with Stylosanthes, mixed intercropping of Piata palisadegrass and Stylosanthes, row intercropping of Paiaguas palisadegrass and Stylosanthes, and mixed intercropping of Paiaguas palisadegrass and Stylosanthes. Evaluations were performed in winter, spring, summer, and autumn in the same plots and over a 2-year period. The intercropping of grasses and legumes positively influences the chemical characteristics of the soil and the nutritional status of the forage by improving the concentration of nutrients. Overall the row seeding method provided better nutrient concentrations. The second year provided higher nitrogen absorption but resulted in greater soil acidification.     

Distribution and Sorption of Phosphate in a Savanna Soil Under Improved Pastures in Northern Nigeria

Abstract

Land use patterns affect soil nutrient transformation and availability. The study determined the distribution of phosphorus (P) fractions and sorption in five pasture fields composed of Andropogon gayanus, Brachiaria decumbens, Chloris gayana, Digitaria smutsii, and Stylosanthes guianensis. The objectives were to characterize P fractions in improved pastures and to determine the effect of forage species on soil P lability. Total P (P_t) across the pastures was not significantly different. Organic P (P_o) accounted, on the average, for 64% of P_t. Resin‐P, considered the plant‐available P, ranged from 4 to 10 mg kg^?1, suggesting acute P deficiency in the pastures. The sum of P fractions extracted by 0.5 M NaHCO₃, 0.1 M NaOH, and 1.0 M HCl, together with the resin‐P, accounted for less than 35% of P_t. Factor analysis indicated that plant‐available P approximated by resin‐P was furnished by ?HCO₃‐P_o mineralization and HCl‐P. The highest concentrations of ?HCO₃‐P_o and ?OH‐P_o were maintained by Brachiaria decumbens. Grouping P_i and P_o fractions into labile and nonlabile fraction showed that Brachiaria decumbens maintained the greatest concentration of labile P as a proportion of its P_t. The pasture soils sorbed between 31 and 65% of added P from a standard concentration of 50 mmol kg^?1. Phosphorus sorbed by soils from the pasture fields was in the order: Digitaria smutsii=Stylosanthes guianensis>Brachiaria decumbens=Chloris gayana>Andropogon gayanus, whereas resin recovery of sorbed P was greater in Brachiaria decumbens than other pastures. Between 82 and 92% of sorbed P was bound irreversibly. It was concluded that the relatively high concentration of labile P maintained by soil under Brachiaria decumbens was probably related to its capacity to sequester more carbon than the other pastures.     

施氮对茶园土壤氟和茶树新梢氟含量的影响

通过田间试验研究了不施肥(CK)、施氮360 kg?hm?2(T1)、施氮720 kg?hm?2(T2)处理下茶园土壤无机氮、p H、各形态氟含量的动态变化和春、夏、秋茶树新梢一芽四叶、一芽五叶氟含量,探讨茶园施氮对土壤和茶树新梢氟含量的影响。结果表明:1)茶园施氮后短期内(20~30 d)土壤水溶态氟含量显著降低,土壤交换态氟和铁锰结合态氟含量降低;长期(45~50 d)土壤水溶态氟含量的降低作用减弱,土壤交换态氟和铁锰结合态的含量增加;在试验结束时(164 d),与CK处理相比,T1处理0~20 cm土壤各形态氟含量降低,T2处理0~20 cm土壤各形态氟含量增加。2)0~20 cm茶园土壤水溶态氟、铁锰结合态氟与NH4+-N分别呈极显著负、正相关(P0.01),20~40 cm土壤水溶态氟、交换态氟与NO3?-N分别呈极显著正、负相关(P0.01)。土壤p H与土壤水溶态氟含量极显著负相关(P0.01),与其他3种形态氟含量相关性不显著。土壤铁锰结合态氟与交换态氟、有机结合态氟呈显著、极显著正相关,但与土壤水溶态氟均无显著相关性。3)春茶前后施氮可以降低春、夏、秋茶树新梢一芽四叶、一芽五叶氟含量,但未达显著水平。T1处理新梢氟含量的降低值为夏茶(25.15~27.95 mg?kg?1)秋茶(21.06~24.31 mg?kg?1)春茶(18.58~21.03 mg?kg?1),T2处理的降低值为秋茶(18.64~22.34 mg?kg?1)夏茶(7.79~14.14 mg?kg?1)春茶(3.52~7.30 mg?kg?1)。春、夏、秋茶树新梢氟含量主要受0~20 cm土壤无机氮和20~40 cm土壤p H的影响。因此推测施氮通过影响茶树根系氟的吸收和氟在叶片中的累积过程调控茶树新梢氟含量,该研究成果为合理利用施氮技术降低茶园土壤和茶树新梢氟含量提供了理论依据。     

Annual warm-season grasses vary for forage yield,quality, and competitiveness with weeds

Warm-season annual grasses may be suitable as forage crops in integrated weed management systems with reduced herbicide use. A 2-year field study was conducted to determine whether tillage system and nitrogen (N) fertilizer application method influenced crop and weed biomass, water use, water use efficiency (WUE), and forage quality of three warm-season grasses, and seed production by associated weeds. Tillage systems were zero tillage and conventional tillage with a field cultivator. The N fertilization methods were urea broadcast or banded near seed rows at planting. Warm-season grasses seeded were foxtail (Setaria italica L.) and proso (Panicum mileaceum L.) millets, and sorghum–sudangrass (Sorghum bicolor (L.) Moench × Sorghum sudenense Stapf.). Density of early emerging weeds was similar among treatments, averaging 51 m^?2. Millets exhibited higher weed density and weed biomass than sorghum–sudangrass. At harvest, sorghum–sudangrass produced significantly greater biomass and N accumulation than either millet. Water use (157 mm) and WUE (25.1 kg mm^-1 ha^?1) of total biomass did not vary among treatments or grass entries. Weed seed production by redroot pigweed and green foxtail was respectively 93 and 73% less in sorghum–sudangrass than proso millet. Warm-season grasses offer an excellent fit in semiarid cropping systems.     

Impacts of the nitrogen application on productivity and nutrients concentrations of the corn-Congo grass intercropping system in the dry season

ABSTRACT

The corn-grass intercropping system began to be used in the dry season, as it provides increased straw production for the no-tillage system. However, corn and grass are plants demanding in nitrogen. The corn cultivated in the dry season is called out-of-season corn in Brazil. The objective of this study was to evaluate the productivity and nutrients concentrations of out-of-season corn and Congo-grass intercropped in the no-tillage system, as a function of the nitrogen rates applied in sidedressing. The treatments were four nitrogen rates, 0, 30, 60 and 90?kg?ha^?1. The experimental design was randomised complete blocks with four replicates. The experimental period corresponded to the harvests of 2015 and 2016. There were evaluated: corn grain yield, dry mass production and nutrient concentration in the shoots of the plants intercropped. The evaluations were carried out at the physiological maturity stage of the corn and at the time of desiccation of the grass. Nitrogen increased grain yield and dry mass production of the plants intercropped. Nitrogen maximised the magnesium concentration in out-of-season corn and the nitrogen, calcium, magnesium and sulphur concentrations in Congo grass. Excess nitrogen promoted reduction of the phosphorus in the Corn-Congo grass intercropping system in the dry season.     

Organic‐Matter Lability and Carbon‐Management Indexes in Agrosylvopasture System on Brazilian Savannah

Abstract

The effect of the introduction of an agrosylvopasture (SASP) system on the changes in the carbon (C) of the soil and its lability were studied. Since 1993, this system has been annually implanted in Paracatu, MG. It was planted under eucalyptus forest abandoned after three cuts, when the brachiaria grass was established. The eucalyptususes were planted at 10×4 m spacing, and the following crops have been grown between the lines: rice in the first year, soybean in the second, and brachiaria in the third. After the third year, pasture of the meat cattle begins on brachiaria and remains until the end of the system cycle that was foreseen for the 11th year. A savannah area and another one with eucalyptusus under a conventional system were used as references to natural condition and the way the area is used before plantation of the SASP, respectively. Some samples aged 1, 2, 3, 6, and 10 years were collected in SASP. According to the obtained results, the following conclusions were drawn: (i) the C contents and stocks were affected before and during the plantation of the SASP by the use and management of SASP, as they were reduced in the first years of the system establishment but improved at the 10th year; (ii) the C from the particulate free light fraction (C_FLLP) that was extracted by potassium permangate (KMnO₄) was sensitive to the use and management, and so reflected the changes in total organic C (TOC); (iii) the more labile fractions of C that were extracted at different concentrations of sulfuric acid (H₂SO₄) satisfactorily reflected the changes in both use and management, whereas the less labile fractions were just slightly affected; and (iv) the C management index (IMC) calculated from C_FLLP was the most sensitive to the changes in use and management. However, when calculated from the C fraction 1 extracted by 3M H₂SO₄ (C_F1), it showed better reliability.