Potassium supplying capacity in Argentine soils and plant uptake rate

Abstract

Exchangeable potassium (K) is the readily available form but when this pool is not sufficient, plants must be supplied from less labile forms of this nutrient. In this study, the contribution of nonexchangeable K to plant nutrition and the uptake rate of this nutrient in successive harvests were investigated. A greenhouse experiment was performed sowing annual ryegrass (Lolium multiflorum sp) on four agricultural soils with a wide range in exchangeable K concentration. The soils were a) Acuic Argiudol, b) Entic Hapludol, c) Typic Argiudol (Ordoñez and M. Juarez). Five harvests were conducted resowing after each one. Soil K extractable with 0.01 M CaCl₂, exchangeable and nonexchangeable K was determined. Plant analyses were conducted to asses total K. The highest nonexchangeable K contribution to the total K uptaken by plants (in percentage) was observed in the Acuic Argiudol soil due to its low exchangeable K concentration. For the Typic Argiudol soils, this contribution varied according to exchangeable K concentration (Ordoñez soil) or according to the clay content and the mineralogy (M. Juarez). For all soils, the highest plant uptake rate was for the first harvests corresponding to the uptake of soluble K and the K located in the most labile positions in the exchange complex. This fact is confirmed by the high correlation obtained between the uptake rate and the amount of K extracted with CaCl₂ (p<0.05). For subsequent harvests, a progressive decrease of K uptake rate was observed. In the fifth harvest plant uptake mostly depends on the nonexchangeable K concentration (p<0.05). The Acuic Argiudol soil, presents a special behavior ? given that it reaches the minimum rate in the third harvest due to the low concentration of all K forms of this soil.     

几种酸性土壤供氮力测定方法的综合评价

模拟旱地条件进行黑麦草盆栽试验,对不同供氮力指标与黑麦草吸氮量相关性进行研究,结果表明,短期好气培养法测定的可矿化氮与吸氮量相关系数为0.820;氯化钾与氯化钙浸提的硝态氮与黑麦草吸氮量的相关系数分别为0.892和0.916,表明硝态氮含量作为土壤供氮能力指标具有一定的稳定性;微生物量氮的测定结果不够稳定且与黑麦草吸氮量相关性不高(r=0.751).分析表明,氯仿熏蒸-浸提全氮与吸氮量的相关性最好,相关系数可达0.941,是一个较好的供氮力指标.     

Chloritization in lowland paddy soils

This paper is concerned with the alteration of clay minerals which takes place when well-aerated lowland soils (Brown lowland soils) are cultivated for growing rice. For this purpose the clay mineral compositions of paddy soils were compared with those of adjacent arable soils at four locations.

In the case of arable soils a larger part of the 14Å spacings collapsed to 10Å on treatment with NH₄NO₃ solution, or on drying at about 100°C, whereas in paddy soils the spacings were more stable to thelie treatments. Cation exchange capacities of clays were always smaller In paddy soils than in arable soils. Alternate treatments of reduction and oxidation somewhat increased the stability of the 14Å spacings to heat treatment.

These results indicate that chloritization is a very common process occurring in lowland paddy sons. Chloritization In paddy soils appears to be closely associated with the seasonal cycle of reduction and oxidation.     

石灰性土壤起始NO3——N对土壤供氮能力测定方法的影响

在陕西省的澄城、永寿、杨陵 3地区选取有机质、全N、硝态N含量差异较大的 17个石灰性土壤 ,分别在淋洗与未淋洗土壤起始NO3--N后 ,利用盆栽试验探讨土壤NO3--N淋洗前、后 ,不同方法测定的已矿化N和可矿化N与小麦吸N量之间的相关性。结果表明 ,未淋洗土壤起始NO3--N ,用KCl直接浸取、KCl煮沸法所浸取以及通气培养前CaCl2 所淋洗的起始NO3--N均与小麦吸N量密切相关 ,相关系数 (r)分别为 0.934 ,0.856和 0.862 ,均达1%显著水准。与此相反 ,通气培养、淹水培养、沸水煮沸、碱性高锰酸钾、酸性高锰酸钾及碱解扩散等方法所提取的可矿化N与小麦吸N量间无显著相关。淋洗土壤起始NO3--N后 ,用KCl直接浸取、KCl煮沸法浸取以及通气培养前CaCl2 所淋洗的起始NO3--N与小麦吸N量之间的相关系数明显降低 ,达不到 5%的显著水准。而通气培养、淹水培养、沸水煮沸、碱性高锰酸钾、酸性高锰酸钾及碱解扩散等方法所提取的可矿化N与小麦吸N量之间相关系数却明显提高 ,都达到 5%或 1%的显著水平。其中变化最明显的是淹水培养 1周矿化出的NH4+-N、通气正式培养 2周矿化出的NO3--N及碱解扩散出的NH4+-N ,其与小麦地上部吸N量之间的相关系数 (r)分别由淋洗前的0.443,0.119,0.259增加到淋洗后的 0.866 ,0.767,0.763。说明可矿化N反映土壤供N能力不佳是因为受起始NO3--N的干扰和影响，在土壤NO3--N含量较高的情况下，要正确评价可矿化N测定方法必须考虑NO3--N的作用。     

Evaluation of a perfusion system for investigation of the sulphur supplying capacity of soils

Abstract

A simple and open perfusion system is described for studying the sulphur (S)‐supplying capacity of soils. A range of soils were perfused at frequent intervals and the leachates analysed for inorganic and total S. Results were compared with plant S‐offtake from the same soils. Although greater amounts of S were removed in the perfusion system, data from the two techniques correlated strongly, suggesting the perfusion system can be used to estimate the S‐supplying capacity of soils.     

Nitrogen and phosphorus constrain labile and stable carbon turnover in lowland tropical forest soils

Tropical forests contain a large stock of soil carbon, but the factors that constrain its mineralization remain poorly understood. Microorganisms, when stimulated by the presence of new inputs of labile organic carbon, can mineralize (‘prime’) soil organic matter to acquire nutrients. We used stable carbon isotopes to assess how nutrient demand and soil properties constrain mineralization of added labile (sucrose) carbon and pre-existing (primed) soil carbon in tropical forest soils. In a series of lowland tropical forest soils from Panama, we found that the mineralization of fresh labile carbon was accelerated foremost by phosphorus addition, whereas the mineralization of pre-existing soil carbon was constrained foremost by nitrogen addition. However, there was variation in the relative importance of these nutrients in different soils and the largest effects on the acceleration of sucrose metabolism and constraint of priming occurred following the addition of nitrogen and phosphorus together. The respiration responses due to sucrose or primed soil carbon mineralization were reduced at pH below 4.8 and above 6.0. We conclude that in these tropical forest soils, phosphorus availability is more important in promoting microbial mineralization of sucrose carbon, whereas nitrogen availability is more important in constraining the priming of pre-existing soil organic carbon. This response likely arises because nitrogen is more closely coupled to organic matter cycling, whereas phosphorus is abundant in both organic and inorganic forms. These results suggest that the greatest impact of priming on soil carbon stocks will occur in moderately acidic tropical forest soils of low nitrogen availability. Given long-term changes in both atmospheric carbon dioxide and nitrogen deposition, the impact of priming effects on soil carbon in tropical forest soils may be partially constrained by the abundance of nitrogen.     

Use of intensity and capacity measurements to assess the potassium supplying power of soils

Abstract

For depletions of soil exchangeable potassium of between 15 and 50%, potassium concentrations in ryegrass and strawberry leaf were linearly related to pAR^O _K√BC^O where AR^O _K is the equilibrium potassium activity ratio and BC^O is the slope, measured at AR^O _K of the curve relating the quantity of labile potassium and the activity ratio. Potassium supplying power as measured by pAR^O _K√BC^O could also be expressed as a function of the equilibrium activity ratio and the mineral component of the cation exchange capacity of the soil.     

农田土壤中氮同位素分级与硝化能力的关系研究

A laboratory-based aerobic incubation was conducted to investigate nitrogen(N) isotopic fractionation related to nitrification in five agricultural soils after application of ammonium sulfate((NH4)2SO4). The soil samples were collected from a subtropical barren land soil derived from granite(RGB),three subtropical upland soils derived from granite(RQU),Quaternary red earth(RGU),Quaternary Xiashu loess(YQU) and a temperate upland soil generated from alluvial deposit(FAU). The five soils varied in nitrification potential,being in the order of FAU YQU RGU RQU RGB. Significant N isotopic fractionation accompanied nitrification of NH+4. δ15N values of NH+4 increased with enhanced nitrification over time in the four upland soils with NH+4 addition,while those of NO-3 decreased consistently to the minimum and thereafter increased. δ15N values of NH+4 showed a significantly negative linear relationship with NH+4-N concentration,but a positive linear relationship with NO-3-N concentration. The apparent isotopic fractionation factor calculated based on the loss of NH+4 was 1.036 for RQU,1.022 for RGU,1.016 for YQU,and 1.020 for FAU,respectively. Zero- and first-order reaction kinetics seemed to have their limitations in describing the nitrification process affected by NH+4 input in the studied soils. In contrast,N kinetic isotope fractionation was closely related to the nitrifying activity,and might serve as an alternative tool for estimating the nitrification capacity of agricultural soils.     

Efficiency and energy use in puddling of lowland rice grown on Vertisols in Central India

Transplanting of rice seedling in puddled soil is one of the most widely used cultivation practices. The present research is aimed at determining what specific implements are needed to obtain optimal puddle bed for transplantating. Puddling experiments were carried out by the use of pair of bullocks with traditional country plough (T₁), pair of bullocks with lug wheel puddler (T₂), power tiller with rotary puddler (T₃), tractor with cage wheel and 9-tine cultivator (T₄) and tractor with cage wheel and rotavator (T₅). One summer ploughing was done at friable moisture condition (18.6% db) and then tilled soil was flooded to saturation (24 h) for preparation of puddled bed. Weeding efficiency, puddling depth, percentage increase in bulk density, puddling index, percolation rate and grain yield of paddy were studied for the above treatments. Puddling performance by different implements in comparison to the traditional animal drawn country plough (T₁) shows that there is a definite reduction in time requirement for field preparation. Increase in weeding efficiency, bulk density, grain yield and puddling index were also observed. The highest values of weeding efficiency and puddling index were found 98.6% and 79.3, respectively, for rotavator (T₅). The total time requirement for preparation of puddle field for treatment T₄ (tractor with cultivator) was found to be the lowest (9.4 h ha⁻¹) with 67% weeding efficiency and 62.7 puddling index as compared to all other alternatives tested. Energy requirement for preparation of puddle field was found highest (2390 MJ ha⁻¹) for rotavator (T₅) followed by T₃, T₄, T₁, and T₂ treatments.     

Biomorph silica in meadow soils of the Mid-Amur lowland

On the basis of an analysis of the gross composition and morphology of the particles of soil samples from the Mid-Amur lowlands, it is shown that the biomorph silica of the meadow soils with bleached horizons is represented by meadow forms of phytoliths (mainly true grasses). In the upper profile part of the AUg horizon, frustules of diatom algae are found, while no spicules of sponges are registered. The upper part of the profile is characterized by the highest degree of weathering of the phytolith silica. In the lower part, they are better preserved. In this part of the profile, diatoms are represented by small-celled species around 2 μm in size (supposedly, spores of Cyclotella sp.). The presence of such algae in the water-peptized silt is associated with the process of migration down the profile.     

Phenols in rice soils

In a laboratory study on the distribution of phenols in rice soils, a humus-rich acid sulphate soil liberated more alkali-extractable phenols than an alluvial soil under both flooded and nonflooded conditions. Nonflooded conditions appeared to favour the release of phenols from the acid sulphate soil whereas in the alluvial soil no difference was apparent under the two water regimes. The addition of calcium carbonate to the acid sulphate soil further increased the production of phenols. Analysis of the solvent extract of the soils by thin-layer chromatography showed that both the soils contained vanillic acid and two unidentified phenols.     

Quantitative solid-state 13C NMR spectroscopy of organic matter fractions in lowland rice soils

Spin counting on solid‐state ¹³C cross‐polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32–81% of potential ¹³C NMR signal was detected. The observability of ¹³C NMR signal (C_obs) was higher in the mobile humic acid (MHA) than in the calcium humate (CaHA) fraction, and increased with increasing intensity of irrigated rice cropping. NMR observability appeared to be related to the nature of the organic carbon, with phenol‐ and methoxyl‐rich samples having the higher values of C_obs. The Bloch decay (BD) technique provided more quantitatively reliable ¹³C NMR spectra, as evidenced by values of C_obs in the range 91–100% for seven of the eight humic fractions studied. The BD spectra contained considerably more aryl and carbonyl signal, and less O–alkyl and alkyl signal, with the greatest differences between CP and BD spectra observed for the samples with low C_obs(CP). The causes of low CP observability were investigated using the spectral editing technique RESTORE ( RE storation of S pectra via T _CH and T O ne R ho (T_1ρH) E diting). Rapid T_1ρH relaxation was found to be primarily responsible for the under‐representation of carbonyl carbon, whereas inefficient cross‐polarization was primarily responsible for the under‐representation of aryl carbon in CP spectra. Proton NMR relaxation rates T_1H and T_1ρH were found to correlate with other NMR properties and also with cropping management. Non‐uniform rates of T_1H relaxation in two of the CaHA fractions enabled the generation of proton spin relaxation editing subspectra.     

Genotypic variation in grain mercury accumulation of lowland rice

A pot experiment with 38 commonly cultivated rice cultivars from the Yangtze River Delta was conducted in a greenhouse to study the effect of mercury (Hg) contamination of a paddy soil (4.7 mg Hg [kg soil]^–1) on crop growth and Hg accumulation in the grains. Mercury contamination differentially affected growth, grain yield, and Hg accumulation in brown rice of the tested cultivars. The average Hg concentration in the grains was significantly higher (p < 0.01) when plants were grown in the Hg‐contaminated compared to the control soil. Averaged over cultivars, the Hg concentration in brown rice exceeded the maximum permissible limit of 20 μg Hg kg^–1. Increasing Hg concentrations were associated with grain‐yield declines up to 70%. This yield decline was mainly due to a reduction in the number of panicles. Japonica cultivars tended to be generally less affected by Hg than indica cultivars. The two japonica cultivars Jiahua and Chunjiang 026 showed both low Hg concentrations and no Hg‐induced grain‐yield reduction. These cultivars may be preferred candidates for cultivation in Hg‐contaminated soils or for studies on possible Hg‐exclusion mechanisms.     

Micronutrient cation survey of lowland rice in sierra leone

Abstract

Lowland rice plants were sampled at two growth stages and analyzed for Zn, Cu, Mn, and Fe. Most of the sites were deficient in Cu and one‐third of the sites were rated deficient in Zn. All sites were in the adequate range with respect to Mn. Many Fe values were in the excess to toxic range. Average content of micronutrient cations in rice plants was uniformly greater 30 days after the rice was transplanted than 60 days after transplanting.

Correlations between extractable Mn in lowland soils and Mn in associated rice plants were highly significant with the DTPA extractant and significant with the HCl method, both 30 and 60 days after the rice was transplanted. With HCl, extractable Fe in lowland soils was highly correlated with Fe in associated rice plants, but this relationship was not as close with the DTPA extractant.

In lowland soils, extractable Zn increased significantly and consistently with increases in Cu and Mn extracted with DTPA and HCl. Extractable Zn also increased significantly with increases in Fe when the HCl extractant was used, but not with DTPA.     

Analysis of phosphorus in two humic acid fractions of intensively cropped lowland rice soils by 31P‐NMR

The organic forms of phosphorus in the soil appear to be changing as rice growing intensifies and the soil is flooded for longer in tropical Asia. To examine these changes, we extracted the labile mobile humic acid (MHA) and more recalcitrant calcium humate (CaHA) fractions from soils supporting long‐term field trials in the Philippines and analysed them by solution ³¹P‐nuclear magnetic resonance (NMR) spectroscopy. Diester P and sugar‐diester P accumulated moderately with increasing intensity of irrigated rice cropping, reaching a combined 42% of all MHA‐P for a triple‐cropped irrigated field compared with 28% for fully aerated fields growing dryland crops. The mono‐ to diester P ratio decreased by 43% for the MHA and CaHA from the aerated fields to the triple‐cropped field. Smaller effects on forms of P were noted for the rates and type of N, P and K fertilizer and site effects. The effects of treatment and site were more noticeable in the MHA than in the CaHA. The proportions in the NMR spectra were tightly correlated with visible light absorption, concentrations of organic free radicals and H, and ¹⁵N‐NMR spectral proportions, which indicate the degree of humification. The MHA and CaHA accounted for only 0.6–8.3% and 0.9–5.7%, respectively, of total P; most of the P is inorganic.     

Accumulation of heterocyclic nitrogen in humified organic matter: a 15N‐NMR study of lowland rice soils

Recent intensification of cropping and the attendant longer submergence of the soil for lowland rice in tropical Asia appear to have altered the nature of the soil organic matter, and perhaps also nutrient cycling. To identify the dominant forms of organic nitrogen in the soils we extracted the labile mobile humic acid (MHA) and the more recalcitrant calcium humate (CaHA) fractions from soils under several long‐term field experiments in the Philippines and analysed them by ¹⁵N‐nuclear magnetic resonance spectroscopy. Amide N dominated the spectra of all humic acid (HA) samples (60–80% of total peak area). Its proportion of total spectral area increased with increasing intensity of cropping and length of time during which the soil was flooded and was greater in the MHA fraction than in the CaHA fraction. Simultaneously the spectral proportion of free amino N and other chemical shift regions decreased slightly with increasing length of submergence. Heterocyclic N was detected at modest proportions (7–22%) and was more prevalent in more humified samples, especially in the CaHA of aerated soils. Correlations of spectral proportions of heterocyclic N with other properties of the HA, reported elsewhere, were highly significant. Correlations were positive with visible light absorption (r= 0.86) and concentration of free radicals (r= 0.85), both of which are indices of humification, and negative with concentration of H (r= ?0.86), a negative index of humification. Correlations of spectral proportions of amide N with these properties were also highly significant but in each case of opposite sign to that of heterocyclic N. Proportions of heterocyclic N declined with increasing duration of submergence. The results suggest that (i) ¹⁵N‐NMR can reproducibly measure some portion of heterocyclic N, (ii) formation of heterocyclic N is associated solely with gradual humification occurring over many years, and (iii) the abundant phenols in the submerged rice soils did not promote formation of heterocyclic N, and hence some other process is responsible for a substantial decrease in the availability of native N associated with intensive rice cropping.     

Genotypic variation in grain cadmium concentration of lowland rice

Cadmium (Cd) contamination of paddy rice soils is commonly observed in the Yangtse River Delta, China. Large Cd uptake by rice plants and its translocation into the grains can entail human‐health risks. Genotypic variations in Cd uptake and a differential Cd partitioning into grains will be the basis for developing a rice screening or breeding tool for low grain Cd. A field experiment, conducted at the experimental farm of Jiaxing, Zhejiang province from 2002 to 2004, compared 38 rice genotypes of different types (indica vs. japonica) collected from the Yangtse River Delta. The results showed large differences in Cd concentrations in straw, brown rice, and grain chaff among the rice genotypes grown on Cd‐contaminated soil. Concentrations in brown rice ranged from 0.06 to 0.99 mg Cd kg^–1. The total Cd uptake in brown rice varied between 0.96 and 28.58 μg plant ^{– 1}. In general, indica‐type cultivars accumulated significantly more Cd than the japonica‐type cultivars. The Cd concentration in straw was highly correlated with that in brown rice. While significant differences in the Cd‐partitioning ratio (% share of total Cd uptake found in brown rice) among rice genotypes were observed, these were not correlated with Cd concentration of brown rice. This indicates that the Cd accumulation in rice grains appears to be governed mainly by the Cd uptake by the plant and probably not by differential Cd partitioning. The large genotypic variation suggests the possibility to lower the Cd content of rice by genotype selection. The development of such breeding tools should focus on low Cd uptake rather than Cd partitioning between straw and grain.     

山西省几种典型土壤供钾能力评价

从山西省主要农田土壤中选取有代表性的耕层土壤样品 19个 ,应用生物耗竭法并结合化学方法对该省主要土壤的供钾能力进行综合评价。研究表明 ,供试的 19个土壤中无论不同形态钾含量还是耗竭后土壤钾素 (速效钾、缓效钾 )最低水平值的大小和出现前耗竭的茬数、作物吸钾量均存在较大差异 ,并因土壤类型、取土地区不同而异。最低水平值和作物吸钾量是土壤供钾的重要特征参数。供试山西土壤的长期供钾能力按取土地区有从南至北逐渐下降的趋势 ,在不同土壤类型上有红粘土、潮土 黄绵土、褐土 栗褐土、栗钙土的趋势。     

Studies on the metabolism in roots of lowland rice

In the previous studies we investigated some characteristics of paddy root in comparison with shoot by analysis of inorganic elements¹⁾ and metabolizable forms of organic compounds²⁾ of shoot and root at successive growth stages, and found that the contents of the above-mentioned components in root were generally lower than those in shoot with few exceptions. From this it is concluded that in root the contents of the residual components, mainly cell wall substances, must be high. To ascertain this surmise, we carried out analysis of shoot, root and inflorescences of rice plant with respect to hemicellulose, cellulose and lignin which construct cell walls.     

Human energy expenditure in lowland rice cultivation in Malaysia

A study was undertaken to evaluate the human energy consumption of various field operations involved in lowland rice cultivation in Malaysia. Based on recorded average heart rates, fertilizing was found to be the most strenuous operation, with an average heart rate of 138 beats min(-1). There were no significant differences in the average heart rates of the subjects among the individual tasks within the first plowing, second plowing, and harvesting operations, with the average heart rates for these three tasks being 116, 106, and 106 beats min(-1), respectively. The corresponding energy expenditures were 3.90, 3.43, and 3.35 kcal min(-1). Loading the seed into the blower tank and broadcasting the seed were the most critical tasks for the seed broadcasting operation, with average heart rates of 124 and 136 beats min(-1), respectively. The highest energy expenditure of 418.38 kcal ha(-1) was observed for seed broadcasting, and the lowest energy expenditure of 127.96 kcal ha(-1) was for second plowing. The total seasonal human energy expenditure for rice cultivation was estimated to be 5810.71 kcal ha(-1), 55.7% of which was spent on pesticide spraying. Although the sample size in this study was relatively small, the results indicated that human energy expenditure per unit area (kcal ha(-1)) was positively linked to the average heart rate of the subjects and negatively linked to the field capacity. Thus, mechanization of certain tasks could decrease worker physical effort and fatigue and increase production.