Changes in amount of organic and inorganic fractions of nitrogen in an Eutrochrept soil after long‐term cropping with different fertilizer and organic manure inputs

The influence of 30 years of cropping with different fertilizer and farmyard manure (FYM) inputs on the contents and depth distribution of organic C, total N (N_t), soil mineralizable N, and organic and inorganic N fractions was investigated in an Eutrochrept. Continuous application of 100 %NPK(+S), 150 %NPK(+S), and 100 %NPK(+S)+FYM led to a marked increase in organic C, total N, hydrolyzable N (viz., amino acid N, hydrolyzable NH₄‐N, hexose amine N, and unidentified hydrolyzable N), and nonhydrolyzable N as compared to an adjacent fallow. The contents of the various organic N fractions were largest in surface soil and thereafter decreased with the depth. However, at 30 – 45 cm depth the content of organic C was not affected by the different treatments except 100 %NPK(+S)+FYM. On the other hand, continuous cropping without fertilization resulted in a depletion of total hydrolyzable N in control over fallow by 27.2 % (0–15 cm), 19.6 % (15–30 cm), and 4.7 % (30–45 cm). The incorporation of FYM with 100 %NPK(+S) resulted in greater contents of soil mineralizable N as compared to 100 %NPK(+S) (0–15, 15–30 cm). The proportion of hydrolyzable N (57–76 % of N_t) decreased and that of nonhydrolyzable N (22–40 % of N_t) increased with depth. The proportion of amino acid N (19–26 % of N_t), hexose amine N (2.1–3.5 % of N_t) and unidentified hydrolyzable N (17–27 % of N_t) decreased with depth. All organic soil N fractions including even nonhydrolyzable N in surface and subsurface soils were highly significantly correlated with soil mineralizable N derived from incubations under waterlogged and aerobic conditions. The best correlation to mineralizable N was found for amino acid N and the least significant correlation for nonhydrolyzable N.     

Soil quality indices for evaluation of long‐term land use and soil management practices in semi‐arid sub‐tropical India

Land use changes and soil management can potentially alter soil quality. A study was conducted to assess the long‐term (>20 years) effects of perennial trees (PT), vegetable crops (VC), rice–wheat (RW) system, sewage‐irrigated fields (SF), maize–wheat (MW) system and uncultivated soils (US) on soil quality. Soil physical quality parameters were significantly affected only in the SF system when compared with the US soil, particularly for bulk density (BD 1·51 Mg m⁻³ in SF vs. 1·34 in US). Among chemical parameters, electrical conductivity was high in SF, and soil nutrients (N, P, K, S, Zn, Fe, Cu and Mn) were well above the critical limits of deficiency in all the systems. Soil parameters were integrated into soil quality indices (SQIs) by unscreened transformation and principal component analysis (PCA). SQI observed under each system were compared with the US to assess the degree of degradation. Mean SQI differences showed that PT (+16·02 per cent), VC (+4·80 per cent), RW (+10·04 per cent), and MW (+11·30 per cent) are aggrading, whereas SF (−2·06 per cent) is degrading with respect to the reference soil (US). Adoption of MW system proved to be better than traditional RW; and in general agricultural crops have a significant advantage than VC, in terms of maintaining soil quality. Sewage irrigation is not a sustainable practice and long‐term use may degrade the soil. Among the SQIs, PCA with nonlinear scoring function (NLSF) based SQI was effective in judging land degradation due to soil quality changes as affected by long‐term land use and soil management practices. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Effect of straw amendment modes on soil organic carbon,nitrogen sequestration and crop yield on the North‐Central Plain of China

We quantified the effects of different straw return modes on soil organic carbon (SOC), total nitrogen content (TN) and C:N ratios in a wheat/maize double‐cropping agricultural system by analysing their content in different soil aggregate sizes and density fractions under four modes of straw return: (a) no return/retention of wheat and maize straw (Control); (b) retention of long wheat stubble only (Wheat Stubble); (c) retention of long wheat stubble and return of chopped maize straw (Mixed); and (d) return of chopped wheat and maize straw (Both Chopped). The Mixed and Both Chopped straw return modes produced the highest crop yields. Relative to the Control, SOC stock was 9.6% greater with the Mixed treatment and 14.5% greater with the Both Chopped treatment, whereas the Wheat Stubble treatment had no effect on SOC. Mixed and Both Chopped significantly enhanced TN stock relative to the Wheat Stubble and Control treatments. Compared with the Control, the Mixed and Both Chopped treatments increased the mass proportions of large macroaggregates and reduced the silt plus clay fraction; Mixed and Both Chopped caused a significant increase in SOC and TN in large and small macroaggregates; the Mixed treatment significantly increased SOC content in the coarse and fine intra‐aggregate particulate organic matter (iPOM) density fractions of large macroaggregates, whereas Both Chopped increased SOC in the coarse iPOM, fine iPOM and mineral‐associated organic matter (mSOM) density fractions of both large and small macroaggregates; and Mixed and Both Chopped enhanced TN content in coarse iPOM and fine iPOM within small macroaggregates. Although the Mixed treatment was slightly less effective at improving C sequestration in agricultural fields than the Both Chopped treatment, the Mixed treatment may nonetheless be the optimal plant residue management mode in terms of minimizing time and labour due to its ability to improve soil structure, maintain organic carbon levels and provide a means of sustainable crop production in intensive wheat/maize double‐cropping systems.     

Long‐term fertilization and manuring effects on physically separated soil organic‐matter pools under continuous wheat cropping at a rainfed semiarid site in China

An essential prerequisite for a sustainable soil use is to maintain a satisfactory soil organic‐matter (OM) level. This might be achieved by sound fertilization management, though impacts of fertilization on OM have been rarely investigated with the aid of physical fractionation techniques in semiarid regions. This study aimed at examining changes in organic C (OC) and N concentrations of physically separated soil OM pools after 26 y of fertilization at a site of the semiarid Loess Plateau in China. To separate sensitive OM pools, total macro‐OM (> 0.05 mm) was obtained from bulk soil by wet‐sieving and then separated into light macro‐OM (< 1.8 g cm^–3) and heavy macro‐OM (> 1.8 g cm^–3) subfractions; bulk soil was also differentiated into light OM (< 1.8 g cm^–3) and mineral‐associated OM (> 1.8 g cm^–3). Farmyard manure increased concentrations of total macro‐OC and N by 19% and 25%, and those of light fraction OC and N by 36% and 46%, compared to no manuring; both light OC and N concentrations but only total macro‐OC concentration responded positively to mineral fertilizations compared to no mineral fertilization. This demonstrated that the light‐fraction OM was more sensitive to organic or inorganic fertilization than the total macro‐OM. Mineral‐associated OC and N concentrations also increased by manuring or mineral fertilizations, indicating an increase of stable OM relative to no fertilization treatment, however, their shares on bulk soil OC and N decreased. Mineral fertilizations improved soil OM quality by decreasing C : N ratio in the light OM fraction whereas manuring led to a decline of the C : N ratio in the total macro‐OM fraction, with respect to nil treatment. Further fractionation of the total macro‐OM according to density clarified that across treatments about 3/4 of total macro‐OM was associated with minerals. Thus, by simultaneously applying particle‐size and density separation procedures, we clearly demonstrated that the macro‐OM differed from the light OM fraction not only in its chemical composition but also in associations with minerals. The proportion of the 0.5–0.25 mm water‐stable aggregates of soil was higher under organic or inorganic fertilizations than under no manure or no mineral fertilization, and increases in OC and N concentrations of water‐stable aggregates as affected by fertilization were greater for 1–0.5 and 0.5–0.25 mm classes than for the other classes. Results indicate that OM stocks in different soil pools can be increased and the loose aggregation of these strongly eroded loess soils can be improved by organic or inorganic fertilization.     

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.     

Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice‐wheat cropping system

A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis‐à‐vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5 mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1 mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro‐ and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers.     

Carbon sequestration and relationship between carbon addition and storage under rainfed soybean–wheat rotation in a sandy loam soil of the Indian Himalayas

Soil organic matter (SOM) contributes to the productivity and physical properties of soils. Although crop productivity is sustained mainly through the application of organic manure in the Indian Himalayas, no information is available on the effects of long-term manure addition along with mineral fertilizers on C sequestration and the contribution of total C input towards soil organic C (SOC) storage. We analyzed results of a long-term experiment, initiated in 1973 on a sandy loam soil under rainfed conditions to determine the influence of different combinations of NPK fertilizer and fertilizer + farmyard manure (FYM) at 10 Mg ha⁻¹ on SOC content and its changes in the 0–45 cm soil depth. Concentration of SOC increased 40 and 70% in the NPK + FYM-treated plots as compared to NPK (43.1 Mg C ha⁻¹) and unfertilized control plots (35.5 Mg C ha⁻¹), respectively. Average annual contribution of C input from soybean (Glycine max (L.) Merr.) was 29% and that from wheat (Triticum aestivum L. Emend. Flori and Paol) was 24% of the harvestable above-ground biomass yield. Annual gross C input and annual rate of total SOC enrichment were 4852 and 900 kg C ha⁻¹, respectively, for the plots under NPK + FYM. It was estimated that 19% of the gross C input contributed towards the increase in SOC content. C loss from native SOM during 30 years averaged 61 kg C ha⁻¹ yr⁻¹. The estimated quantity of biomass C required to maintain equilibrium SOM content was 321 kg ha⁻¹ yr⁻¹. The total annual C input by the soybean–wheat rotation in the plots under unfertilized control was 890 kg ha⁻¹ yr⁻¹. Thus, increase in SOC concentration under long-term (30 years) rainfed soybean–wheat cropping was due to the fact that annual C input by the system was higher than the required amount to maintaining equilibrium SOM content.     

Short‐term Impacts on Soil‐quality Assessment in Alternative Land Uses of Traditional Paddy Fields in Southern Brazil

No‐till, crop diversity and integrated crop–livestock systems are proposed managements to increase agriculture sustainability in the rice paddies of the Southern Brazilian lowlands and avoid degradation in the region. Because soil is considered a key medium in which management modifications can be measured, our study aimed to evaluate soil‐quality impacts by measuring carbon and nitrogen stocks and microbial activity 18 months after the adoption of different paddy‐farming systems in an Albaqualf soil of Southern Brazil. The treatments consisted of five paddy‐farming systems with a range of vegetation diversity (both in time and in space) and grazing seasons. In addition, a reference area (i.e. native forest) was sampled for comparison. We verified that soil quality was affected over the short term through the adoption of no‐till, crop diversity and integrated grazing practices. However, during the study period, only the system with low anthropic and/or mechanical intervention and high plant diversity differed from the traditional paddy land‐use approach in Brazil in terms of soil‐quality effects. This system achieved a carbon management index of 49 (approximately half that of the native forest) and had the highest enzymatic activity (similar to native forest). These outcomes were primarily due to an increase in the particulate organic matter fraction of the soil carbon stock (4·6 Mg ha⁻¹ more than in rice monocropping). To evaluate changes in soil quality over the long term, additional studies are required. Copyright © 2016 John Wiley & Sons, Ltd.     

The effects of compost in a rice–wheat cropping system on aggregate size,carbon and nitrogen content of the size–density fraction and chemical composition of soil organic matter,as shown by 13C CP NMR spectroscopy

We investigated whether the long‐term application of compost from agricultural waste improved soil physical structure, fertility and soil organic matter (SOM) storage. In 2006, we began a long‐term field experiment based on a rice–wheat rotation cropping system, having a control without fertilizer (NF) and three treatments: chemical fertilizers (CF), pig manure compost (PMC) and a prilled mixture of PMC and inorganic fertilizers (OICF). Following the harvest of wheat in 2010, the mean‐weight diameter (MWD) of water‐stable aggregates and the concentration of C and N in bulk soil (0–20 cm; <2 mm fraction) were significantly greater (P < 0.05) in PMC and NF plots than in CF or OICF plots. Pig manure compost significantly increased the proportion of >5‐mm aggregates, whereas CF significantly increased the proportion of 0.45‐ to 1‐mm aggregates. The C and N contents of all density fractions were greater in PMC than in other treatments with levels decreasing in the following order: free particulate organic matter (fPOM) >occluded particulate organic matter (oPOM) > mineral‐combined SOM (mineral–SOM). Solid‐state ¹³C CPMAS NMR spectra showed that alkyl C/O‐alkyl C ratios and aromatic component levels of SOM were smaller in PMC and OICF plots than in CF plots, suggesting that SOM in PMC and OICF plots was less degraded than that in CF plots. Nevertheless, yields of wheat in PMC and NF plots were smaller than those in CF and OICF plots, indicating that conditions for producing large grain yields did not maintain soil fertility.     

Soil chemical quality changes and implications for fertilizer management after 11 years of no‐tillage wheat production systems in semiarid Morocco

A long‐term experiment comparing no‐till with conventional tillage systems across five rotations was evaluated 11 years after initiation. The objectives of the present paper are (1) to report differences in soil chemical properties (namely soil organic matter, total nitrogen, phosphorus, potassium and pH) that have resulted by converting from conventional to no‐till under contrasting cropping systems and (2) to draw tentative conclusions and recommendations on fertility status and fertilizer use and management. Soil in the no‐till system had increased surface soil organic C levels relative to conventional tillage regardless of rotation. In addition, depending on the rotation, the N and P content of the soil improved with no‐till compared with conventional tillage. In other words, no‐till has helped to retain soil organic matter (SOM), conserved more N, and resulted in increased extractable P and exchangeable K concentrations in the upper root‐zone. Hence, wheat produced in a no‐till system may receive more nutrients from decomposition of SOM and acidification of the seed zone. It is possible that lesser amounts of fertilizer nutrients will be needed because of the greater efficiency of nutrient cycling in no‐till systems relative to conventional systems. Copyright © 2001 John Wiley & Sons, Ltd.     

Impact of tillage and crop establishment methods on crop yields,profitability and soil physical properties in rice–wheat system of Indo‐Gangetic Plains of India

Conservation agriculture (CA) based on best‐bet crop management practices may increase crop and water productivity, as well as conserve and sustain soil health and natural resources. In a 2‐year study, we assessed the effects of tillage and crop establishment (TCE) methods on productivity, profitability and soil physical properties in a rice–wheat (RW) system. The six TCE treatments were used to study the impact, which are puddled transplanted rice followed by conventionally tilled wheat (CTPR–CTW), direct‐seeded rice on the flat followed by zero‐till wheat (CTDSR–ZTW), zero‐till direct‐seeded rice with residue followed by zero‐till wheat with residue (ZTDSR+R–ZTW+R), transplanted rice after rotavator puddling followed by zero‐till wheat (RTTPR–ZTW), transplanted rice after rotavator puddling followed by rotary till wheat (RTTPR–RTW) and farmer practice rice–wheat (FP–RW). Result of the study revealed that mean rice yield was not significantly affected by different TCE methods. Wheat planted with ZTDSR+R–ZTW+R gave 30% larger grain yield than FP‐RW. Overall, among all the TCE treatments, the RW system yields and net returns were maximum under ZTDSR+R–ZTW+R. The fastest mean infiltration rate (0.10 cm hr^–1) was registered in ZTDSR+R–ZTW+R plots, whereas the slowest was in FP‐RW plots (0.05 cm hr^–1). Bulk density at 15–20 cm soil depth was least in ZTDSR+R–ZTW+R (1.70 Mg m^–3) and greatest in FP‐RW (1.73 Mg m^–3). Results from this study revealed that conventionally tilled (CT) and transplanting of rice could be successfully replaced by adoption of the profitable double ZT–RW system.