Soil water effects on the use of heat units to predict crop residue carbon and nitrogen mineralization

Soil heat units (degree days) have previously been shown to predict net N mineralization from crop residues and papermil sludge. The present study was designed to identity the effects of soil water potential on predictions of mineralization with heat units and to compare field and laboratory results of white lupin (Lupinus albus L. cv. Ultra) N mineralization. Lupin-amended soil and unamended controls were incubated at factorial combinations of temperature (15, 20, and 25°C) and soil moisture (-0.30,-0.03, and-0.01 MPa) for 198 days. Incorporation of the lupin residue resulted in net N immobilization. No net N mineralization had been observed for any temperature at a soil moisture level of-0.30 MPa by the close of the incubation study. The number of heat units that accumulated until commencement of net N mineralization did not differ for five of the six remaining temperature x water treatment combinations.The number of heat units that accumulated until net N mineralization began (2058–2814 degree-days) in the present study were similar to those reported in a complementary field study (1990–2360 degree-days). Temperature and moisture interactively affected lupin-residue C mineralization. The cumulative substrate C that had evolved by the time of net N mineralization did not differ for a given temperature between soil moisture levels of-0.03 and-0.01 MPa. Heat units were not useful for describing crop-residue C mineralization in this study. Heat units appear to adequately predict net N mineralization from organic residues at soil water potentials within the-0.03 to-0.01 MPa range, but may not be valid for prolonged drier conditions.     

Decomposition of mulched versus incorporated crop residues: Modelling with PASTIS clarifies interactions between residue quality and location

Crop residue management has been shown to significantly affect the decomposition process of plant debris in soil. In previous studies examining this influence, the extrapolation of laboratory data of carbon and/or nitrogen mineralization to field conditions was often limited by a number of interactions that could not be taken into account by a mere experimental approach. Therefore, we demonstrated the interactive effect between crop residue location in soil (mulch vs. incorporation) and its biochemical and physical quality, in repacked soil columns under artificial rain. Decomposition of ¹³C and ¹⁵N labelled rape and rye residues, with associated C and N fluxes, was analysed using the mechanistic model PASTIS, which turned out to be necessary to understand the interacting factors on the C and N fluxes. The influence of soil and residue water content on decomposition and nitrification was evaluated by the moisture limitation factor of PASTIS. This factor strongly depended on residue location and to a smaller extent on physical residue properties, resulting in a lower decomposition rate of about 35% for surface placed compared to incorporated residues. Irrespective of its placement, the biochemical residue quality (e.g. N availability for decomposition, amount of soluble compounds and lignin) was responsible for a faster and more advanced decomposition of about 15% in favour of rye compared to rape, suggesting only a limited interaction between residue quality and its location. Net N mineralization after nine weeks was larger for rye than for rape, equivalent to 59 and 10 kg NO₃⁻-N ha⁻¹ with incorporation, and 71 and 34 kg NO₃⁻-N ha⁻¹ with mulch, respectively. This net N mineralization in soil resulted from the interaction between soil water content, depending on residue placement, and N availability, which was determined by the biochemical residue quality. Moisture limitation appeared more important than N limitation in the decomposition of mulched residues. Modelling of gross N mineralization and immobilization also revealed that leaving crop residues at the soil surface may increase the risk of nitrate leaching compared to residue incorporation, if (i) soil water content under mulch is larger than with residue incorporation (more gross N mineralization), and (ii) availability to the applied C-source is limited (less gross N immobilization). Scenario analyses with PASTIS confirmed the importance of moisture conditions on the decomposition of mulched residues and the small interaction between biochemical crop residue quality and its location in soil.     

Mineralisation of crop residues on the soil surface or incorporated in the soil under controlled conditions

In the present work, we compare the effect of mature crop residues mixed into a ferralitic soil or placed as a single layer on soil surface on the mineralisation of C and N over 55 days. As residues, we used dry stems of rice, soybean, sorghum, brachiaria and wheat. There were no significant effects of residue placement on C mineralisation kinetics. Decomposition of the residues on the soil surface slightly increased net N mineralisation for residues having the smallest C/N ratio.     

Nitrogen mineralization and availability of mixed leguminous and non-leguminous cover crop residues in soil

Whereas non-leguminous cover crops such as cereal rye (Secale cereale) or annual ryegrass (Lolium multiflorium) are capable of reducing nitrogen (N) leaching during wet seasons, leguminous cover crops such as hairy vetch (Vicia villosa) improve soil N fertility for succeeding crops. With mixtures of grasses and legumes as cover crop, the goal of reducing N leaching while increasing soil N availability for crop production could be attainable. This study examined net N mineralization of soil treated with hairy vetch residues mixed with either cereal rye or annual ryegrass and the effect of these mixtures on growth and N uptake by cereal rye. Both cereal rye and annual ryegrass contained low total N, but high water-soluble carbon and carbohydrate, compared with hairy vetch. Decreasing the proportion of hairy vetch in the mixed residues decreased net N mineralization, rye plant growth and N uptake, but increased the crossover time (the time when the amount of net N mineralized in the residue-amended soil equalled that of the non-amended control) required for net N mineralization to occur. When the hairy vetch content was decreased to 40% or lower, net N immobilization in the first week of incubation increased markedly. Residue N was significantly correlated with rye biomass (r=0.81, P<0.01) and N uptake (r=0.83, P<0.001), although the correlation was much higher between residue N and the potential initial N mineralization rate for rye biomass (r=0.93, P<0.001) and N uptake (r=0.99, P<0.001). Judging from the effects of the mixed residues on rye N Concentration and N uptake, the proportion of rye or annual ryegrass when mixed with residues of hairy vetch should not exceed 60% if the residues are to increase N availability. Further study is needed to examine the influence of various mixtures of hairy vetch and rye or annual ryegrass on N leaching in soil. Received: 10 March 1997     

Phosphorus release during decomposition of crop residues under conventional and zero tillage

Field experiments were conducted at Fort Vermilion (58°23′N 116°02′W), Alberta, to determine phosphorus (P) release patterns from red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues in the 7th and 8th years of conventional and zero tillage. Phosphorus contained in crop residues ranged from 1.5 kg ha⁻¹ in pea to 9.2 kg ha⁻¹ in clover GM, both under zero tillage. The patterns of P release over a 52-week period sometimes varied with tillage, i.e., a greater percentage of GM residue P was released under conventional tillage than under zero tillage in the first 2–10 weeks of residue placement. Wheat residues resulted in net P immobilization under zero tillage, but the amounts immobilized were less than 1 kg ha⁻¹. When net P mineralization occurred, the percentage of P released ranged from 24% of wheat P under conventional tillage to 74% of GM P under conventional tillage. The amounts of P released were 0.4 kg ha⁻¹ from wheat, 0.8 kg ha⁻¹ from canola, 0.4 kg ha⁻¹ from pea and 5.1–5.6 kg ha⁻¹ from clover GM residues. Therefore, only GM residues recycled agronomically significant amounts of P for use by subsequent crops in rotation. Phosphorus release was positively correlated with residue P concentration and negatively correlated with C/P and lignin/P ratios.     

氮肥减施和秸秆还田对土壤固定态铵含量的影响

   固定态铵作为土壤氮素的暂存库,其含量的变化能够影响土壤的保氮供氮功能,而深入探究氮肥减施对土壤固定态铵的影响及其对秸秆还田的响应,可为优化农田氮肥管理提供理论依据。   依托位于中国东北黑土区玉米种植系统连续9年全量玉米秸秆覆盖归还的保护性耕作试验平台,通过设置玉米秸秆不还田（S0）、秸秆还田量33%（S33）和秸秆全量覆盖还田（S100）3个秸秆还田量处理,以及240 kg hm⁻²（N240）、190 kg hm⁻²（N190）、135 kg hm⁻²（N135）、0 kg hm⁻²（N0）4个氮素施用水平,研究氮素减施3年后土壤固定态铵总量的变化以及不同秸秆还田量对固定态铵的影响。   秸秆不还田时,土壤固定态铵总量随施氮量降低而逐渐下降,且在不施氮肥处理（N0）时显著低于施氮肥处理;在S33N190时土壤－作物系统出现氮素缺乏,并且随施氮量的下降土壤固定态铵降低量与氮素缺乏量之间具有显著的正相关关系。在所有氮肥水平,秸秆还田尤其是全量秸秆还田均有利于缓解固定态铵的释放,但在N135处理时秸秆效应较弱。整体上,与对照相比,S100N190处理土壤固定态铵的降低量最小。另外,秸秆还田降低了施肥处理土壤硝态氮含量。   在氮肥减施条件下,土壤固定态铵可以释放供氮,氮肥减施20%配合免耕全量秸秆覆盖还田可在保持土壤固定态铵库相对稳定的基础上,维持土壤-作物系统的氮素平衡。     

作物模型研究进展

作物模型的研究和应用有利于科研成果的综合集成、作物种植管理决策的现代化和辅助国家决策,是农业研究中的重要工具。一个完整的作物模型一般包括作物生长模块、水分运动模块与氮素迁移转化模块。这三者相互联系,相互影响。本文对上述3个模块的发展历程以及应用比较广泛、综合性比较强的几个模型进行综述,对比各自的优缺点,指出了作物模型今后的发展方向。     

Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues

 We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m^–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO₃ ^–-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m^–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m^–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m^–3, will affect some microbially driven processes. Received: 10 June 1999     

Seasonal nitrification measurements with different species of forest litter applied to granite-sand-filled lysimeters in the field

Summary The biodegradation of litter from Festuca silvatica, Abies pectinata, Fagus silvatica, Calluna vulgaris, Picea abies associated with forest brown acid soils or with podzolic soils was studied in field lysimeters filled with granite sand. Analysis of the leachates collected during 2 years made it possible to determine NO _inf3 ^sup- , NH _inf4 ^sup+ , and soluble organic N production in order to investigate the specific influence of the different species of litter on the mineralization of organic N and the variations in nitrification. With Festuca silvatica (grass), active nitrification was observed after the addition of fresh litter in autumn (fall of leaves). Nitrification remained significant in winter, reached a maximum in spring until early summer, and then decreased after mineralization of the easily mineralizable organic N. Nitrification was the major N transformation process in this litter. The addition of fresh litter of Abies pectinata (fir), Fagus silvatica (beech), Calluna vulgaris (heather), and Picea abies (spruce) in autumn induced an inhibition of nitrification during winter and spring. With these litter species, nitrification started again by the end of spring and was at a maximum in summer and autumn until leaf fall. By comparison with Festuca, inhibition observed in winter and spring with the other litter species was definitely due to the chemical composition of the leaves. Simultaneously, a lower C mineralization of these plant material occured. These litter species, in particular Calluna and Picea released leachates containing significant amounts of soluble organic N that were only slightly decomposed. We conclude that NO _inf3 ^sup- production outside of the plant growth period can definitely be involved in soil acidification and weathering processes.     

外源氮输入对土壤有机碳矿化和凋落物分解的影响

目前,由人类活动造成的陆地生态系统氮输入量已经远远超过了其自身的生物固氮,外源氮输入的增多已经并将继续对土壤有机碳矿化和凋落物分解产生影响。本文分析了国内外有关氮输入增多对土壤有机碳矿化和凋落物分解的影响及其机理:由于研究点环境状况不同,凋落物性质的差异和分解阶段的不同等原因,氮输入对土壤有机碳矿化的结果主要表现为抑制或促进作用;对凋落物分解的影响表现为促进、无影响和抑制三种效果,有关其作用机理还有待进一步深入研究。着重指出对于作为大气CO2\"汇\"的沼泽湿地,氮输入的增多能够对其碳\"汇\"功能产生影响,因此进行氮输入对湿地土壤有机碳矿化和凋落物分解方面的研究,对于探讨湿地碳循环对外源氮输入的响应及其机理非常重要。     

不同利用方式下土壤有机氮素矿化特征的研究

采用长期淹水密闭培养-间歇淋洗法(30℃),测定了长期(16年)定位的水田、旱地和林地土壤有机氮素的矿化氮数量,利用一级反应动力学模型对有机氮素的矿化过程进行了拟合,并探讨了不同利用方式下土壤有机氮素的矿化特征。结果表明,3种利用方式下土壤有机氮素的矿化过程均可用一级反应动力学模型很好地拟合;任意两种土壤利用方式之间的N0值差异均达1%显著水平,水田与旱地、林地之间的k值差异均达1%显著水平,而旱地与林地之间的k值差异则达5%显著水平,林地土壤氮素矿化势最大(72.96 mg kg-1),约为旱地和水田土壤的1.3倍和7.4倍,水田土壤氮素矿化速率最大(0.0908 d-1),约为旱地和林地土壤的4.1倍和2.3倍;旱地和林地土壤供氮能力大小相接近,分别为88.24 mg kg-1和89.11 mg kg-1,约为水田土壤的2倍左右。由此可见,长期(16年)不同利用方式对土壤有机氮素矿化特征影响显著,水田土壤可供矿化的有机氮数量最少且矿化时间最为短暂,旱地土壤可供矿化的有机氮数量较多且矿化时间最为缓慢持久,林地土壤可供矿化的有机氮数量最多且矿化时间较为缓慢持久。     

A rapid procedure for estimating nitrogen mineralization in manured soil

 A routine soil testing procedure for soil N mineralization is needed that is rapid and precise. Not accounting for N mineralization can result in the over-application of N, especially in soils with a history of manure application. Our objectives were to compare results from a recently proposed rapid laboratory procedure with: (1) long-term N mineralization under standard laboratory conditions, and (2) actual forage N uptake from soil receiving dairy cattle (Bos taurus) manure in a 2-year field study. The rapid procedure is based on the quantity of CO₂-C evolved during 24 h under optimum laboratory conditions following the rewetting of dried soil. Dairy cattle manure was surface applied beginning in 1992 at annual rates of 0, 112, 224, or 448 kg N ha^–1 to field plots on a Windthorst fine sandy loam soil (fine, mixed, thermic Udic Paleustalf) near Stephenville, Texas (32°N, 98°W). Results of the one-day CO₂ procedure were highly correlated with soil N mineralized from samples collected in March of 1995 (P=0.004) and 1996 (P<0.001) and with forage N uptake (P<0.001) both years of the study. Residual inorganic N in the same soil samples was poorly correlated with soil N mineralization and forage N uptake. Received: 23 February 2000     

鲁北地区地膜覆盖对棉花需水量、作物系数及水分利用效率的影响

作物系数和需水量是制定作物灌溉制度和计算区域水资源平衡的重要参数,不同气候和不同栽培条件下作物系数和需水量会发生变化。本文通过大田试验,以水量平衡法计算作物需水量、以Penman-Monteith公式计算参照作物蒸散量和作物系数。结果表明,鲁北地区棉花地膜覆盖栽培比露地栽培生育期内作物需水量减少101.5mm,作物系数降低17.6%,水分利用效率增加29.3%。     

Crop residue position and interference with wheat seedling development

Unweathered crop residues can produce growth-inhibiting substances, stimulate pathogen growth, and immobilize nutrients. The location of seed relative to residue may be an important factor in the early health of a crop. This greenhouse study simulated sowing conditions possible under annual dryland winter wheat (Triticum aestivum L.) production to evaluate the likelihood of inhibitory effects. We placed newly harvested, unweathered winter wheat residue on the soil surface, mixed with the seed, immediately above the seed, or 3 cm below the seed. Treatments using a plastic residue substitute and treatments using pasteurized soil and residue provided comparisons to the natural soil and wheat residue. Residue mixed with or placed above the seed caused a temporary delay in emergence. Since this occurred with both wheat and plastic residue, the delay is explained by the physical impedance of coleoptile growth. Wheat residue 3 cm below the seed reduced the height and rate of wheat plant development, indicating a biological inhibitory effect of the wheat residue. This reduction in height and development rate at 20 days after planting did not occur when the soil and residue were pasteurized. We conclude that winter wheat seedling growth can be inhibited if roots encounter unweathered residues.     

Soil C balance in a long-term field experiment in relation to the size of the microbial biomass

Soil C balances were calculated in a field experiment started in 1956. Treatments include a fallow and soils receiving different N fertilizers or organic amendments. By assuming the absence of a priming effect, the degree of mineralization of crop residues and organic amendments was calculated. Crop residue mineralization was not affected by a more than 50% decrease in the size of the microbial biomass in soil fertilized with (NH₄)₂SO₄, which had caused the pH of this soil to drop from 6.6 to 4.4. More C had accumulated per unit C input in peat-and sewage sludge-amended soils than in any of the other soils, suggesting that peat and sewage sludge were more resistant to microbial attack. Recalcitrance of substrate C was an adequate explanation for the low ratio of biomass C to soil C in the peat-amended soils, but not in the sewage sludge-amended soil. There was a close linear relationship (r=0.94) between the content of microbial biomass C in the soil measured in 1990 and cumulative C losses from the soil since 1956. Compared to the relationship between soil biomass C and soil organic C concentrations, the linear relationship between microbial C and cumulative C losses suggested that the significantly reduced biomass in the sewage sludge-amended soil was at least partially due to the presence of toxic substances (presumably elevated heavy metal concentrations) in this soil and was probably not affected by the somewhat low pH (5.3) in this soil.     

秸秆还田与施氮对冬小麦生长发育及水肥利用率的影响

田间试验研究了小麦-玉米一年两熟耕作区玉米秸秆还田与氮肥配施和化肥单施对冬小麦生长发育、籽粒产量及氮肥表观利用率和水分利用效率的影响。结果表明, 施氮量相同时, 秸秆与氮肥配施越冬前和拔节期冬小麦总茎数和单株分蘖数低于化肥单施, 施氮量在75~225 kg·hm^-2 时, 植株干重高于化肥单施; 孕穗期到成熟期植株干重、成穗率和产量构成因素秸秆与氮肥配施处理高于化肥单施处理, 籽粒产量增加58.9~339.6kg·hm^-2, 水分生产率提高0.026~0.083 kg·m^-3。施氮量在75 kg·hm^-2 时, 秸秆与氮肥配施的氮肥表观利用率低于化肥单施; 在150~300 kg·hm^-2 时高于化肥单施。因此, 针对目前黄淮海麦区小麦-玉米一年两熟种植制度下, 秸秆还田前期生物争氮、后期供肥能力增强的特点, 秸秆连续还田后配施纯氮225 kg·hm^-2, 可有效提高灌水和氮肥利用率, 实现冬小麦高产高效栽培。