土壤测试实验室数据自动采集处理与推荐施肥系统

为了提高测土配方施肥中土壤测试的工作效率和测试数据采集、处理的准确性,针对土壤养分测试技术的工作流程,经过多年的研究与实践,应用计算机技术、数据库技术和网络技术,研制设计了土壤样品测试数据的自动采集、分析、入库和计算机自动对作物进行推荐施肥的分析控制系统。该系统已广泛应用于我国的测土配方施肥。     

基于ASI法的滨海滩涂地水稻测土推荐磷、钾施用量的验证

运用土壤养分状况系统研究法(ASI)进行土壤测定和水稻肥料推荐,通过田间小区试验对滨海滩涂地水稻推荐磷、钾施用量进行验证。结果表明,在其它营养元素的施用量均在最佳推荐量条件下,ASI法测土推荐的磷(P2O5)、钾(K2O)最佳施用量(90 kg/hm2、105 kg/hm2)处理的水稻有效分蘖数、穗实粒数、千粒重及产量均是最佳的;且施磷能够显著增加水稻的有效分蘖数,施钾能够显著增加水稻穗粒数和千粒重,最终达到增产的目的。因此,运用ASI法对滨海滩涂地水稻进行测土推荐磷、钾肥的施用量是基本合理的。     

Carbon sequestration dynamic,trend and efficiency as affected by 22‐year fertilization under a rice–wheat cropping system

The maintenance and accumulation of soil organic carbon (SOC) in agricultural systems is critical to food security and climate change, but information about the dynamic trend and efficiency of SOC sequestration is still limited, particularly under long‐term fertilizations. In a typical Purpli‐Udic Cambosols soil under subtropical monsoon climate in southwestern China this study thus estimated the dynamic, trend and efficiency of SOC sequestration after 22‐year (1991–2013) long‐term inorganic and/or organic fertilizations. Nine fertilizations under a rice–wheat system were examined: control (no fertilization), N, NP, NK, PK, NPK, NPKM (NPK plus manure), NPKS (NPK plus straw), and 1.5NPKS (150% NPK plus straw). Averagely, after 22‐years SOC contents were significantly increased by 4.2–25.3% and 10.2–32.5% under these fertilizations than under control conditions with the greatest increase under NPKS. The simulation of SOC dynamic change with an exponential growth equation to maximum over the whole fertilization period predicted the SOC level in a steady state as 18.1 g kg^?1 for NPKS, 17.4 g kg^?1 for 1.5NPKS, and 14.5–14.9 g kg^?1 for NK, NP, NPK, and NPKM, respectively. Either inorganic, organic or their combined fertilization significantly increased crop productivity and C inputs that were incorporated into soil ranging from 0.91 to 4.63 t (ha · y)^?1. The C sequestration efficiency was lower under NPKM, NPKS, and 1.5NPKS (13.2%, 9.0%, and 10.1%) than under NP and NPK (17.0% and 14.4%). The increase of SOC was asymptotical to a maximum with increasing C inputs that were variedly enhanced by different fertilizations, indicating an existence of SOC saturation and a declined marginal efficiency of SOC sequestration. Taken all these results together, the combined NPK plus straw return is a suitable fertilizer management strategy to simultaneously achieve high crop productivity and soil C sequestration potential particularly in crop rotation systems.     

施氮和秸秆还田对小麦-玉米轮作农田硝态氮淋溶的影响

连续4 a采用渗漏计测定法研究了陕西关中小麦-玉米轮作区施氮和秸秆还田对土壤剖面90 em处NO3--N淋溶的影响.结果表明,NO3--N淋洗主要发生在7、8、9月份或灌溉后,年际间变异较大.监测期内各处理渗漏液NO3--N浓度和淋失量的变幅为0～103.5 mg L-1和0～21.8 kg hm-2,二者均随施氮量的增加呈增加趋势.小麦施氮150 kg hm-2、玉米施氮180 kg hm-2时,连续4a作物均能获得高产.施氮量继续增加,产量不再增加,0 ～100 cm土层NO3--N累积量和90 cm处NO3--N淋失量却相应增加.秸秆还田2 a后作物显著增产,2010年和2011年分别增产15.1％和14.2％,但对NO3--N累积和淋溶的影响不显著.回归分析显示,NO3--N年淋失量和0～ 100 cm土层累积量均随年施氮量的增加呈指数形式增加,说明施氮量越高,NO3--N年淋失量和累积量越高,二者占施氮量的比例也越高.     

中国玉米土壤速效钾丰缺指标与适宜施钾量研究

对自20世纪80年代以来我国开展的玉米土壤速效钾丰缺指标与适宜施钾量研究进行了系统总结。结果表明,30年来我国玉米土壤速效钾丰缺指标出现了降低趋势;不同区域玉米土壤速效钾丰缺指标差异很大,缺钾处理相对产量90%的速效钾含量指标变动于75~215 mg/kg之间;我国玉米土壤速效钾丰缺指标研究存在许多空白区域;我国玉米土壤缺钾较为普遍,速效钾丰缺级别集中于级别较高的第2和3级,缺钾处理相对产量大多介于80%~100%之间;土壤养分丰缺指标研究的试验点数不宜过少,各试验点土壤养分含量分布不宜过于集中,丰缺指标高端和低端采用外推数据需谨慎,并应予以注明;适宜施钾量与土壤速效钾丰缺级别线性负相关,与目标产量线性正相关;当钾肥当季利用率为50%、目标产量为10.5 t/hm~2时,玉米土壤速效钾丰缺级别由高到低第1~7级的适宜施钾量分别为K2O 0、44、88、132、176、221和265 kg/hm~2。     

Soil carbon and nitrogen changes as affected by tillage system and crop biomass in a corn–soybean rotation

A wide range of tillage systems have been used by producers in the Corn-Belt in the United States during the past decade due to their economic and environmental benefits. However, changes in soil organic carbon (SOC) and nitrogen (SON) and crop responses to these tillage systems are not well documented in a corn–soybean rotation. Two experiments were conducted to evaluate the effects of different tillage systems on SOC and SON, residue C and N inputs, and corn and soybean yields across Iowa. The first experiment consisted of no-tillage (NT) and chisel plow (CP) treatments, established in 1994 in Clarion–Nicollet–Webster (CNW), Galva–Primghar–Sac (GPS), Kenyon–Floyd–Clyde (KFC), Marshall (M), and Otley–Mahaska–Taintor (OMT) soil associations. The second experiment consisted of NT, strip-tillage (ST), CP, deep rip (DR), and moldboard plow (MP) treatments, established in 1998 in the CNW soil association. Both corn and soybean yields of NT were statistically comparable to those of CP treatment for each soil association in a corn–soybean rotation during the 7 years of tillage practices. The NT, ST, CP, and DR treatments produced similar corn and soybean yields as MP treatment in a corn–soybean rotation during the 3 years of tillage implementation of the second experiment. Significant increases in SOC of 17.3, 19.5, 6.1, and 19.3% with NT over CP treatment were observed at the top 15-cm soil depth in CNW, KFC, M, and OMT soil associations, respectively, except for the GPS soil association in a corn–soybean rotation at the end of 7 years. The NT and ST resulted in significant increases in SOC of 14.7 and 11.4%, respectively, compared with MP treatment after 3 years. Changes in SON due to tillage were similar to those observed with SOC in both experiments. The increases in SOC and SON in NT treatment were not attributed to the vertical stratification of organic C and N in the soil profile or annual C and N inputs from crop residue, but most likely due to the decrease in soil organic matter mineralization in wet and cold soil conditions. It was concluded that NT and ST are superior to CP and MP in increasing SOC and SON in the top 15 cm in the short-term. The adoption of NT or CP can be an effective strategy in increasing SOC and SON in the Corn-Belt soils without significant adverse impact on corn and soybean yields in a corn–soybean rotation.     

氮肥和秸秆施用对稻麦轮作体系下土壤剖面N_2O时空分布的影响

通过气体原位采集系统对稻麦轮作体系下土壤剖面不同层次N2O浓度动态变化进行了两年田间原位监测。共设4个处理:对照(N0S0)、施氮无秸秆(N1S0)、配施低量秸秆(N1S1)以及配施高量秸秆(N1S2)。结果表明,土壤剖面N2O浓度具有明显的时空分布特征:各处理在小麦和水稻生长前期均出现明显的浓度峰值,施加氮肥加大峰值,添加高量秸秆降低峰值。水稻生长季N2O主要产生在近表层土壤(7 cm和15 cm),N2O浓度两年均为15 cm≥7 cm≥30 cm≥50 cm;小麦生长季N2O主要产生在下层土壤(30 cm和50 cm)。与N0S0相比,施加氮肥3个处理均显著增加土壤剖面各层次的N2O浓度(p0.05),其中N1S0处理各土层N2O浓度是N0S0处理对应土层的2倍~3倍。配施高量秸秆(N1S2)能显著减少近表层土壤N2O浓度。     

等养分条件下稻草还田替代双季早稻氮钾肥比例的研究

【目的】研究等量氮磷钾养分投入条件下,长期稻草原位全量还田配施化肥对双季早稻氮 (N)、磷 (P)、钾 (K) 养分吸收累积、转运及养分利用的影响,为南方稻区稻草资源有效利用,维持并提高土壤肥力及水稻合理施肥提供理论依据。【方法】以江西温圳国家级耕地质量监测点长期定位试验为研究对象,陆两优 996 为供试材料,在不施化肥和施用化肥基础上设稻草还田、稻草烧灰还田和稻草不还田共 6 个处理,除空白对照外,所有处理养分投入量相等。于 2015 年在早稻移栽期、分蘖期、幼穗分化期、抽穗期和成熟期取地上部植株样,分析水稻植株不同部位的 N、P、K 含量和累积量以及转运比例,并计算 N、P、K 养分利用效率。【结果】稻草还田提高了水稻产量,施肥条件下稻草还田处理比稻草烧灰还田和稻草不还田处理平均增产 2.9%～ 6.4%,比不施肥区产量增幅高达 23.8%～ 26.0%,且差异达显著水平。无论是施肥区处理,还是无肥区处理,与稻草烧灰还田和稻草不还田处理相比,稻草还田植株中 K 含量及 N、P、K 积累量在整个生育期均较高,而 N、P 含量在生育后期较高,N、P、K 积累量以施肥区处理大于相应的无肥区处理;稻草还田提高水稻 N、P、K 养分农学效率、回收率和养分偏生产力,且 N、K 差异达显著水平,同时显著增加 K 的收获指数;稻草还田还提高了抽穗至成熟期茎鞘中 N、P、K 的转运量、转运率及转移养分对籽粒的贡献率,而叶片各处理间差异不显著。【结论】稻草还田配施化肥能提高水稻产量,同时还可以调节 N、P、K 养分的积累和转运,提高养分的吸收利用效率。本试验条件下,稻草还田可替代化肥氮肥 (N) 29.5%、磷肥 (P₂O₅) 4.0% 和钾肥 (K₂O) 50.0%。综合考虑,稻草还田相比稻草烧灰还田而言是南方稻区土壤养分管理实现高效利用的有效途径之一。     

5年定位试验条件下钾肥用量对双季稻产量和施钾效应的影响

通过5年定位试验（2008~2012年）, 研究不同钾肥施用量对水稻产量、植株钾素含量、钾素积累量、钾肥利用率、土壤钾素含量、钾素平衡和钾肥经济效益的影响。试验施钾量（K2O）从低到高设K0（不施钾）、K1（早稻84 kg/hm2、晚稻105 kg/hm2）、K2（早稻120kg/hm2、晚稻 150 kg/hm2）、K3（早稻156kg/hm2、晚稻195 kg/hm2）和K4（早稻192kg/hm2、晚稻 240kg/hm2）5个处理。5年的试验结果表明, 施钾能显著提高早、晚稻产量,在一定施钾量范围内,水稻产量随施钾量的增加而增加;施钾能促进水稻植株对钾素的吸收和积累,尤其是稻草对钾素的吸收和积累;早、晚稻的钾肥农学效应均以K2处理最高（早稻3.12 kg/kg、晚稻3.70 kg/kg）;钾肥利用率以K1处理最高（早稻41.2%、晚稻76.4%）,并随施钾量提高而降低;不同施钾量对土壤钾素含量有明显影响,土壤速效钾、缓效钾和土壤全钾均随施钾量的增加而增加,且不同处理间土壤速效钾含量差异达极显著水平（P＜0.01）;连续种植5年10季水稻后,K0、K1和K2处理的土壤钾素亏缺（K 127.1kg/hm2、 58.3kg/hm2和10.8kg/hm2）,亏缺量随施钾量的增加而降低; K3和K4处理的土壤钾素盈余（48.0 kg/hm2 和109.2kg/hm2）,盈余量随施钾量的增加而增加。在经济效益上,早、晚稻产投比均以K2处理最高（早稻1.04、晚稻1.27）。综合考虑施钾的增产效应、经济效益和土壤钾素养分平衡等因素,建议该双季稻区早稻施钾量在K2O 120~156 kg/hm2、晚稻施钾量在K2O 150~195kg/hm2范围内较为适宜。     

Soil physical fertility and crop performance as affected by long term application of FYM and inorganic fertilizers in rice–wheat system

Soil fertility, one of the important determinants of agricultural productivity, is generally thought to be supplemented through the application of nutrients mainly through inorganic fertilizers. The physical fertility of the soil, which creates suitable environment for the availability and uptake of these nutrients, is generally ignored. The present study aims to characterize the soil physical environment in relation to the long term application of farm yard manure (FYM) and inorganic fertilizers in rice–wheat. The treatments during both rice and wheat crops were (i) farm yard manure @ 20 t ha⁻¹ (FYM); (ii) nitrogen @ 120 kg ha⁻¹ (N₁₂₀); (iii) nitrogen and phosphorus @ 120 and 30 kg ha⁻¹ (N₁₂₀P₃₀) and (iv) nitrogen, phosphorus and potassium @ 120, 30 and 30 kg ha⁻¹ (N₁₂₀P₃₀K₃₀) in addition to (iv) control treatment, i.e. without any fertilizer and/or FYM addition. The treatments were replicated four times in randomized block design in a sandy loam (typic Ustipsament, non-saline, slightly alkaline). Bulk density, structural stability of soil aggregates and water holding capacity of 0–60 cm soil layer were measured.

The average mean weight diameter (MWD) was highest in FYM-plots both in rice (0.237 mm) and wheat (0.249 mm) closely followed by that in N₁₂₀P₃₀K₃₀ plots. The effect of FYM in increasing the MWD decreased with soil depth. The addition of both FYM and N₁₂₀P₃₀K₃₀ increased the organic carbon by 44 and 37%, respectively in rice. The total porosity of soil increased with the application of both FYM and N₁₂₀P₃₀K₃₀ from that in control plots. In 0–15 cm soil layer, the total porosity increased by 25% with FYM from that in control plots. This difference decreased to 13% in 15–30 cm soil layer. The average water holding capacity (WHC) was 16 and 11% higher with FYM and N₁₂₀P₃₀K₃₀ application from that in control plots. The MWD, total porosity and WHC improved with the application of balanced application of fertilizers. The grain yield and uptake of N, P and K by both rice and wheat were higher with the application of FYM and inorganic fertilizers than in control plots. The carbon sequestration rate after 32 years was maximum (0.31 t ha⁻¹ year⁻¹) in FYM-plots, followed by 0.26 t ha⁻¹ year⁻¹ in N₁₂₀P₃₀K₃₀-plots, 0.19 t ha⁻¹ year⁻¹ in N₁₂₀P₃₀ and minimum (0.13 t ha⁻¹ year⁻¹) in N₁₂₀-plots.     

Reclamation of saline‐sodic soil under a rice–wheat system by horizontal surface flushing

Saline sodic soil with a high content of soluble carbonates is one of the important agricultural soils on the Central Indo‐Gangetic plains and elsewhere. Conventional reclamation procedures using gypsum application followed by vertical leaching (GC) is uneconomic; high ECe and precipitation of applied gypsum, reacting with soluble carbonates, reduce the efficacy of gypsum in these soils. This paper reports results from a project designed to evaluate reclamation by irrigation of the ploughed soil and turning of soil with a power tiller followed by flushing of standing water after 24 h, a second flushing after 7 days and subsequent application of gypsum and vertical leaching (GF2). Average rice and wheat production after GF2 significantly increased (25 and 62%, respectively) over the conventional practice. Compared with conventional treatment, GF2 significantly reduced the ECe and SAR of the soil and improved physical properties such as ζ‐potential, dispersible clay content, water stable aggregates expressed as MWD, and saturated hydraulic conductivity. Split application of gypsum between flushing (GF1/2 and GF2/3) gave similar results to GF2 in terms of soil amelioration and crop production.     

Soil enzymatic activity as affected by long term application of farm yard manure and mineral fertilizer under a rainfed soybean–wheat system in N-W Himalaya

Long-term experimental sites are expected to provide important information regarding soil properties as affected by management practices. This study was designed to examine the effects of continuous fertilization, and manuring on the activities of enzymes involved in mineralization of C, N, and P on a long term (33 years) field trial under sub-temperate conditions in India. Treatments at the site included application of recommended doses of nitrogen and phosphorus (NP), nitrogen and potassium (NK), nitrogen, phosphorus and potassium (NPK), farmyard manure (FYM) with N (N + FYM), FYM with NPK (NPK + FYM) and un-amended control (C). The study was done under rainfed soybean–wheat rotation. Manure application increased soil carbohydrate, dehydrogenase, acid and alkaline phosphatases, cellulase, and protease activity significantly. Urease activity was not influenced by the manure treatment and the activity was highest in controls. Both acid and alkaline phosphatase activities were negatively influenced by chemical fertilizer treatment. Almost all the enzymes studied were significantly correlated with soil C content. The results suggest that application of FYM directly or indirectly influences the enzyme activity and it in turn regulates nutrient transformation.     

Soil quality effects of tillage and residue under rice–wheat cropping on a Vertisol in India

Soil quality in rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping systems is governed primarily by the tillage practices used to fulfill the contrasting soil physical and hydrological requirements of the two crops. The objective of this study was to develop a soil quality index (SQI) based on bulk density (BD), penetration resistance (PR), water stable aggregates (WSA) and soil organic matter (OM) to evaluate this important cropping system on a Vertisol in India. Regression analysis between crop yield and SQI values for various tillage and crop residue management treatments indicated SQI values of 0.84–0.92, 0.88–0.93 and 0.86–0.92 were optimum for rice, wheat and the combined system (rice + wheat), respectively. The maximum yields for rice and wheat were 5806 and 1825 kg ha⁻¹ occurred at SQI values of 0.85 and 0.99, respectively. Using zero tillage (ZT) for wheat had a positive effect on soil quality regardless of the treatments used for rice. Regression analyses to predict sustainability of the various tillage and crop residue treatments showed that as puddling intensity for rice increased, sustainability without returning crop residues decreased from 6 to 1 years. When residue was returned, the time for sustainable productivity increased from 6 to 15 years for direct seeded rice, 5 to 11 years with low-intensity puddling (P₁) and 1 to 8 years for high-intensity (P₂) puddling. For sustainability and productivity, the best practice for this or similar Vertisols in India would be direct seeding of rice with conventional tillage and residues returned.     

Soil aggregation and distribution of carbon and nitrogen in different fractions under long-term application of compost in rice–wheat system

Soil organic matter improves the physical, chemical and biological properties of soil, and crop residue recycling is an important factor influencing soil organic matter levels. We studied the impact of continuous application of rice straw compost either alone or in conjunction with inorganic fertilizers on aggregate stability and distribution of carbon (C) and nitrogen (N) in different aggregate fractions after 10 cycles of rice–wheat cropping on a sandy loam soil at Punjab Agricultural University research farm, Ludhiana, India. Changes in water stable aggregates (WSA), mean weight diameter (MWD), aggregate-associated C and N, total soil C and N, relative to control and inorganically fertilized soil were measured. Total WSA were significantly (p = 0.05) higher for soils when rice straw compost either alone or in combination with inorganic fertilizers was applied as compared to control. The application of rice straw compost either alone or in combination with inorganic fertilizers increased the macroaggregate size fractions except for 0.25–0.50 mm fraction. The MWD was significantly (p = 0.05) higher in plots receiving rice straw compost either alone at 8 tonnes ha⁻¹ (0.51 mm at wheat harvest and 0.41 mm at rice harvest) or at 2 tonnes ha⁻¹ in combination with inorganic fertilizers (0.43 and 0.38 mm) as compared to control (0.34 and 0.33 mm) or inorganically fertilized plots (0.33 and 0.31 mm). The macroaggregates had higher C and N density compared to microaggregates. Application of rice straw compost at 2 tonnes ha⁻¹ along with inorganic fertilizers (IN + 2RSC) increased C and N concentration significantly over control. The C and N concentration increased further when rice straw compost at 8 tonnes ha⁻¹ (8RSC) was added. It is concluded that soils can be rehabilitated and can sustain the soil C and N levels with the continuous application of rice straw compost either alone or in combination with inorganic fertilizers. This will also help in controlling the rising levels of atmospheric carbon dioxide.     

Long‐term effects of fertilizer and manure applications on soil quality and yields in a sub‐humid tropical rice‐rice system

Widespread yield stagnation and productivity declines in the rice–rice cropping system have been reported and many of the associated issues are related to soil quality. A long‐term experimental study was initiated in 1969 to assess the impact of continuous cultivation of rice as a single crop grown in wet as well as dry seasons using varying levels of chemical fertilizer and manure applications on soil quality indicators (physical, chemical and biological), a sustainable yield index (SYI) and a soil quality index (SQI). The treatments comprised chemical fertilizers and farmyard manure (FYM) either alone or in combination viz. control, N, NP, NK, NPK, FYM, N+FYM, NP+FYM, NK+FYM and NPK+FYM, laid out in a randomized complete block design with three replications. Soil samples were collected after the wet season rice harvest in 2010 and were analysed for physical, chemical and biological indicators of soil quality. A SYI based on long‐term yield data and SQI using principal component analysis (PCA) and nonlinear scoring functions were calculated. Application of NPK fertilizers in combination with FYM significantly increased the average grain yield of rice in both wet and dry seasons and enhanced the sustainability of the system compared to the control and plots in receipt of fertilizers. The SYI for the control was higher in the wet season than in the dry one, whereas the reverse was true for NPK+FYM treatment. The value of the dimensionless SQI varied from 1.46 in the control plot to 3.78 in the NPK+FYM one. A greater SYI and SQI in the NPK+FYM treatment demonstrated the importance of using a chemical fertilizer in combination with FYM. For the six soil quality indicators selected as a minimum data set (MDS), the contribution of DTPA‐Zn, available‐N and soil organic carbon to the SQI was substantial ranging from 59.4 to 85.7 per cent in NPK+FYM and control plots, respectively. Thus, these soil parameters could be used to monitor soil quality in a subhumid tropical rice–rice system.     

Modeling rice seedling emergence and growth under tillage and residue management in a rice–wheat system on a Vertisol in Central India

Tillage and residue management practices are known to affect seedling emergence and growth. However, information on direct seeded rice (Oryza sativa L.) in rice–wheat (Triticum spp.) cropping system is lacking. Thus a study was undertaken under different tillage (conventional and zero tillage) and residue (residue-retained and removed) management options on rice seedling emergence and growth in rice–wheat system on a Vertisol of Central India. Seedling emergence was greater in residue removed plots compared to residue-retained one. Prediction of rice seedling emergence with the France and Thornley [Mathematical Models in Agriculture and Related Sciences, Butterworths, London, 1984] model and growth by the Logistic and Gompertz model, and Monomolecular model were also attempted. Emergence indicators showed that seedling emergence of rice was favored more by conventional tillage than zero tillage in wheat. Of the three models tested, the Gompertz model gave the best fit. The effect of tillage and residue of wheat on the estimated parameters of the models were also studied.     

土区长期施肥对小麦-玉米轮作体系钾素平衡与钾库容量的影响

本文研究了土区小麦-玉米轮作体系长期氮磷钾化肥不同配合施用方式及氮磷钾化肥与秸秆或有机肥配合施用对钾素平衡以及土壤钾库的影响。试验包括9个处理,分别为不施肥（CK）、单施氮（N）、氮钾（NK）、磷钾（PK）、氮磷（NP）、氮磷钾（NPK）、氮磷钾配合一季秸秆还田（SNPK）、氮磷钾配合低量有机肥（M1NPK）和高量有机肥（M2NPK）。结果表明,除NK、PK和M2NPK处理外,其它处理小麦和玉米钾的携出量均大于钾的投入量,导致土壤钾素处于亏缺状态,20年累计亏缺量为6174333 kg/hm2。与试验前相比,长期施肥种植没有显著影响土壤全钾含量; 长期施用钾肥显著提高土壤速效钾含量,但长期不施钾肥处理的土壤速效钾含量也未显著降低; 无论施钾与否土壤非交换性钾（Mactotal K）以及非交换性钾中更容易被HNO3溶解提取的钾（Step K）均明显低于试验前水平。表明土壤非交换性钾可以作为该土壤钾素消耗的指标。考虑到施钾肥的经济投入和现有资源高效利用（如秸秆、有机肥）,从长远的角度出发,维持土壤钾素肥力以及土地可持续生产力,土区小麦-玉米轮作体系采用秸秆全部还田或施有机肥是必要的。     

Soil acidity and aluminium toxicity as affected by surface liming and cover oat residues under a no-till system

A 3-year field trial examined in a long-term no-till system the effects of surface-applied lime and cover black oat ( Avena strigosa Schreb) residues on soil chemical attributes, root growth and grain yield of corn ( Zea mays L.) and soybean ( Glycine max L. Merrill) on a loamy, kaolinitic, thermic Typic Hapludox in Paraná State, Brazil. The treatments consisted of dolomitic lime broadcast on the soil surface at 0 or 12 t/ha, with and without cover of black oat residues. Corn and soybeans were grown without rainfall limitation. Applying lime on the surface improved soil acidity and decreased aluminium (Al) toxicity to a 10-cm depth 1 year after application. Surface liming increased pH and the content of exchangeable Ca²⁺ to a 20-cm depth, and decreased Al toxicity to a 40- to 60-cm depth, 3 years after application, indicating that the surface-applied lime moved deeper. Cover black oat residues did not favour the mobility of surface-applied lime to alleviate subsoil acidity and an increase in the Al³⁺ saturation level at the soil surface was found in unlimed plots with black oat residues. Root growth and grain yields of corn and soybean were not influenced by surface liming with or without cover black oat residue. Despite the soil acidity level, root length of corn and soybean ranged from 55 to 60% at 0- to 10-cm depth. The results suggest that Al toxicity is low in no-till systems during cropping seasons with adequate and well-distributed rainfall, but this effect is not related to the presence of cover oat residues.     

Soil organic carbon and physical properties as affected by long-term application of FYM and inorganic fertilizers in maize–wheat system

The physical quality of the soil, which creates suitable environment for the availability and uptake of the plant nutrients, is generally ignored. Though the effect of organic manures on soil physical quality has been widely appreciated but that of inorganic fertilizers is studied to a lesser extent. The present study carried out during 2004–2005 aims to characterize the soil physical quality in relation to the long-term (32 years) application of farmyard manure (FYM) and inorganic fertilizers in maize (Zea mays L.) wheat (Triticum aestivum L.) cropping system. The treatments during both maize and wheat crops were (i) farm yard manure at 20 Mg ha⁻¹ (FYM), (ii) nitrogen at 100 kg ha⁻¹ (N₁₀₀), (iii) nitrogen and phosphorus at 100 and 50 kg ha⁻¹ (N₁₀₀P₅₀) and (iv) nitrogen, phosphorus and potassium at 100, 50 and 50 kg ha⁻¹ (N₁₀₀P₅₀K₅₀) in addition to (v) control treatment, i.e. without any fertilizer and/or FYM addition. The treatments were replicated four times in randomized block design in a sandy loam (Typic Ustipsament, non-saline, slightly alkaline). Bulk density, organic carbon content, structural stability of soil aggregates and water holding capacity of 0–60 cm soil layer were measured.The application of FYM to maize increased the organic carbon by 16% whereas N₁₀₀P₅₀K₅₀ increased it by 21%. The increased organic matter with both FYM and N₁₀₀P₅₀K₅₀ increased the total soil porosity and decreased soil bulk density from that in control plots. The mean weight diameter (MWD) was highest in FYM plots of both maize (0.160 mm) and wheat (0.172 mm) closely followed by that in N₁₀₀P₅₀K₅₀ plots. The effect of FYM in increasing the MWD decreased with soil depth. The average water holding capacity (WHC) was higher with FYM and N₁₀₀P₅₀K₅₀ application than that in control plots. The MWD, total porosity, OC content and WHC improved with the application of balanced application of fertilizers. The grain yield and uptake of N, P and K by both maize and wheat were higher with the application of FYM and inorganic fertilizers than in control plots. The uptake of N, P and K increased with the application of FYM and N₁₀₀P₅₀K₅₀.     

Long-term effect of manure and mineral fertilizer application on the distribution of organic nitrogen fractions in soil under a rice–wheat cropping system

A long-term experiment was used to evaluate the effect of integrated nutrient management on the distribution of soil organic N fractions and their contribution to N nutrition of a rice–wheat system. Continuous application of mineral fertilizers, alone or in combination with organic manures for 7 years, led to a marked increase in total N, hydrolysable N (amino acid-N, amino sugar-N, ammonia-N, hydrolysable unknown-N) and non-hydrolysable N compared with their original status in soil. However, continuous rice–wheat cropping without any fertilization resulted in depletion of total N, hydrolysable N and non-hydrolysable N by 21.3, 23.5 and 15.1% over their initial status in surface soil. The effect of press mud (PM) treatment was more pronounced in increasing total and hydrolysable N compared with farmyard manure (FYM) or green manure (GM) treatment. Incorporation of PM, FYM and GM along with mineral fertilizers increased the total N content by 32.8, 18.3 and 5.1% and that of hydrolysable N by 25.7, 19.6 and 9.5%, respectively, over mineral fertilizer treatment. Among the most important fractions, amino sugar-N, amino acid-N and ammonia-N were found to be most the important fractions contributing to grain yield and nitrogen uptake of rice and wheat crops.