Yield and soil nutrient balance of a sugarcane plant–ratoon system with conventional and organic nutrient management in sub-tropical India

A 3-year field trial of sugarcane, comprising 11 treatment combinations of different organic manures with and without Gluconacetobacter diazotrophicus (Gd), NPK and an absolute control, on an inceptisol was conducted to assess the effect of these treatments on sugarcane total and economic yield, the benefit:cost ratio, nutrient balance and soil quality in a sugarcane plant–ratoon system. The highest cane yield (78.6 t ha⁻¹) was recorded in the plant crop given vermicompost + Gd, whereas ratoon yields (first and second) were highest (80.8 and 74.9 t/ha⁻¹, respectively) with sulphitation press mud cake (SPMC) + Gd. In both plant and ratoon crops, a number of different organic manures produced the highest cane yield that was also statistically similar to those obtained with using the recommended NPK levels (76.1, 78.2 and 71.7 t/ha for plant crop and subsequent two ratoons, respectively). The highest benefit:cost (B:C) ratio in the plant and two ratoon crops (1.28, 2.36, 2.03 respectively) were obtained with the addition of SPMC + Gd. The nutrient balance for NPK in the soil was highest in the SPMC + Gd treatment. The highest increase in organic C (94%) and total N (87%), in comparison to the initial level, and soil microbial biomass C (113%) and soil microbial biomass N (229%), in comparison to the control treatment, was recorded with the addition of SPMC + Gd. The maximum decrease in soil bulk density (BD) (12%) with an increase in soil aggregate (17%) and water infiltration rate (35%) was obtained with the addition of SPMC. Overall, the sugarcane crop responded well to different organic manures in a multiple ratooning system with a better economic output and improved soil quality. Strategic planning in terms of an integrated application of these manures with inorganic chemicals will not only sustain our soils but will also be beneficial for our farmers in terms of reducing their dependence and expenditure on chemical fertilizers.     

Effect of organic inputs from agroforestry species and urea on crop yield and soil properties at Wondo Genet, Ethiopia

The effect of combined inputs of green manure (GM) and urea on maize (Zea mays L.) productivity and soil characteristics was studied in an on-farm trial at Wondo Genet, southern Ethiopia. The GM species used were the legumes Albizia gummifera G.F. Gmel and Milletia ferruginea (Hochst.) Baker and the non-legumes Cordia africana Lam and Croton macrostachyus Del. The GM and urea were applied separately or combined in different proportions to give equal rates of 100 kg N ha⁻¹, while varying amounts of P and K were supplied by the GM. The experiment was carried out for two consecutive cropping seasons, but treatments were applied only during the first season. Yield increased by 10–84% in the combined treatments compared to the control, with the increase being significant in those treatments containing GM from Cordia and Croton, which had higher P and K but lower N and total polyphenol contents than those from Albizia and Milletia. Increasing the proportion of GM from the non-legumes tended to increase yield, but the opposite was true when the proportion of GM from the legumes was increased. This suggests that N interacted negatively with polyphenols, and/or the P and K supply from GM was more important than that of N. However, treatment effects on soil properties were not pronounced. It was concluded that a ȁ8modestȁ9 input of ≤3.0 Mg ha⁻¹ GM from Cordia/Croton might effect a reasonable yield but that the additional use of inorganic fertilisers is necessary for the GM to have a substantially increased effect. In addition, when organic materials having both high N and high total polyphenol contents (e.g. Albizia and Milletia) are used, they should constitute the smaller proportion of the GM/fertiliser mixture.     

Yield response of maize (Zea mays L.) to crop residue management on two major soil types Of Alemaya, Eastern Ethiopia: I. Effects of varying rates of applied and residual N and P fertilizers

Field trials were conducted on two soil types for seven years (1988–1994) to investigate grain yield response of maize to crop residue application as influenced by varying rates of applied and residual N and P fertilizers. Yearly application of N and P fertilizers at both one-half and full recommended rates resulted in grain yield increases of more than 500 and 1100 kg ha-1, respectively over application of only crop residue. Moreover, grain yield responses due to residual N and P fertilizers applied only during the first year were found to be comparable to the yearly applications of these fertilizers. Rainfall and soil type have exerted considerable influences on the grain yield response obtained in this study. Grain yield exhibited a corresponding decrease with decreasing rainfall. Grain yield increases on Typic Pellustert were relatively higher than on Typic Ustorthent.     

Influence of different manuring systems with and without biogas digestion on soil organic matter and nitrogen inputs,flows and budgets in organic cropping systems

Nitrogen (N) and carbon (C) cycles are closely linked in organic farming systems. Use of residues for biogas digestion may reduce N-losses and lead to higher farmland productivity. However, digestion is connected to large losses of organic C. It is the purpose of this paper (1) to compare farming systems based on liquid slurry and solid farmyard manure regarding the N, C and organic dry matter (ODM) inputs and flows, (2) to analyse the effect of digestion on soil N, C and ODM inputs and flows within the cropping system, (3) to assess the effects of organic manure management on biological N₂ fixation (BNF), and (4) to assess the effect of biogas digestion on the sustainability of the cropping systems in terms of N and C budgets. The BNF by clover/grass-leys was the most important single N input, followed by the BNF supplied by legume cover cropping. Growth of crops in organic farming systems is very often N limited, and not limited by the soil C inputs. However, balances of N inputs showed that the implemented organic farming systems have the potential to supply high amounts of N to meet crop N demand. The level of plant available N to non-legume main crops was much lower, in comparison to the total N inputs. Reasons were the non-synchronized timing of N mineralization and crop N demand, the high unproductive gaseous N losses and an unfocussed allocation in space and time of the circulating N within the crop rotation (e.g. allocation of immobile manures to legumes or of mobile manures to cover crops). Simultaneously, organic cropping systems very often showed large C surpluses, which may be potentially increased the N shortage due to the immobilization of N. Soil organic matter supply and soil humus balance (a balance sheet calculated from factors describing the cultivation effects on humus increasing and humus depleting crops, and organic manure application) were higher in cropping systems based on liquid slurry than in those based on solid farmyard manure (+19%). Simultaneously, soil N surplus was higher due to lower gaseous N losses (+14%). Biogas digestion of slurry had only a very slight effect on both the soil N and the soil C budget. The effect on the N budget was also slight if the liquid slurry was stored in closed repositories. Digestion of residues like slurry, crop residues and cover crops reduced in a mixed farming system the soil C supply unilaterally (approximately −33%), and increased the amounts of readily available N (approximately +70–75%). The long-term challenge for organic farming systems is to find instruments that reduce N losses to a minimum, to keep the most limiting fraction of N (ammonia-N) within the system, and to enhance the direct manuring effect of the available manures to non-legume main crops.     

Quantifying the effect of soil organic matter on indigenous soil N supply and wheat productivity in semiarid sub-tropical India

A field experiment was conducted on a loamy sand soil for six years to quantify the effect of soil organic matter on indigenous soil N supply and productivity of irrigated wheat in semiarid sub-tropical India. The experiment was conducted by applying different combinations of fertilizer N (0–180 kg N ha⁻¹), P (0–39 kg P ha⁻¹) and K (0–60 kg K ha⁻¹) to wheat each year. For the data pooled over years, fertilizer N together with soil organic carbon (SOC) and their interaction accounted for 75% variation in wheat yield. The amount of fertilizer N required to attain a yield goal decreased as the SOC concentration increased indicating enhanced indigenous soil N supply with an increase in SOC concentration. Besides SOC concentration, the soil N supply also depended on yield goal. For a yield goal of 4 tons ha⁻¹, each ton of SOC in the 15 cm plough layer contributed 4.75 kg N ha⁻¹ towards indigenous soil N supply. An increase in the soil N supply with increase in SOC resulted in enhanced wheat productivity. The contribution of 1 ton SOC ha⁻¹ to wheat productivity ranged from 15 to 33 kg ha⁻¹ across SOC concentration ranging from 3 to 9 g kg^-1 soil. The wheat productivity per ton of organic carbon declined curvilinearly as the native SOC concentration increased. The change in wheat productivity with SOC concentration shows that the effect of additional C sequestration on wheat productivity will depend on the existing SOC concentration, being higher in low SOC soils. Therefore, it will be more beneficial to sequester C in soils with low SOC than with relatively greater SOC concentration. In situations where the availability of organic resources for recycling is limited, their application may be preferred in soils with low SOC concentration. The results show that an increase in C sequestration will result in enhanced wheat productivity but the increase will depend on the amount of fertilizer applied and the existing fertility level of the soil.     

Effects of plant residues on crop performance, N mineralisation and microbial activity including field CO2 and N2O fluxes in unfertilised crop rotations

The impacts of crop rotation and input of organic matter in the form of green manure crops, straw residues and incorporation of catch crops on crop yield, nitrogen uptake, microbial biomass and activity were studied in unfertilised crop rotations differing in input of plant residues, i.e., high-input rotations with a grass-clover crop and catch crops included and low-input cereal rotations without catch crops. The parameters studied included substrate induced respiration (SIR), hydrolysis of fluorescein diacetate (FDA), arylsulfatase activity (ASA), N mineralisation, N₂O emission, and soil respiration. These parameters were measured in bare soil plots, to estimate the effects of previous years' crops and input of plant residues. In neighbouring plots crop performances were registered by measuring yields, above-ground biomass and nitrogen uptake during the growing season. Generally, all measured parameters were significantly higher in the high-input than in low-input rotations. Estimates of metabolic quotients indicated that the microbial communities in the low-input rotations were less efficient in utilising the C sources than those in the high-input rotations. Calculations of N₂O emission factors indicate that the current IPCC methodology for estimating N₂O emission from plant residues needs to be improved.     

Effect of Substrate Composition (C/N/P ratio) on Microbial Community and Membrane Fouling Tendency of Biomass in Membrane Bioreactors

In this study, biomass characteristics including bacterial community, extracellular polymeric substances (EPS) production, and membrane fouling propensity were examined when the membrane bioreactors (MBRs) were fed with different substrates (i.e., different C/N/P ratios). Denaturing gradient gel electrophoresis (DGGE) analysis revealed that significant shifts of bacterial communities happened when increasing nitrogen or phosphorus loading in the MBRs, which followed in an almost similar way. At steady state, the biomass from the low C/N- and C/P-MBRs had comparable concentrations and produced similar EPS levels as those in the control MBR. However, the median particle size increased when the MBRs fed with low C/N- or C/P- substrate, possibly associated with the filamentous bacteria propagating in the MBRs. Increasing nitrogen or phosphorus loading 1-fold could not induce more serious membrane fouling compared to the control MBR.     

Effects of long-term fertilization and mulch on soil fertility in contour hedgerow systems: A case study on steeplands from the Three Gorges Area,China

The use of contour hedgerows is widely advocated to sustain crop production and reduce soil loss on steeplands in the Three Gorges Area of China. However, little is known about the effects of soil management on soil fertility within these systems, or about the spatial gradients in soil nutrients that may develop in terraces formed behind the vegetative barriers. Therefore, we carried out a study on the effects of various long-term soil management practices on soil fertility and spatial variation of fertility between hedgerows. At a site in the Three Gorges Area, China, we applied five treatments to a contour hedgerow system: control (no fertilizer and manure); chemical fertilizer (CF); chemical fertilizer and mulch (CF + MU); pig manure (PM); and mulch, pig manure, and chemical fertilizer (CF + PM + MU). Soil samples were collected from the topsoil horizon (0–20 cm) of the selected five treatments in 2006 after 11 crop cycles, and physical and chemical properties were analyzed. The results showed that chemical fertilizer clearly improves nutrient status of the topsoil, while pig manure also increased the amount of soil organic matter. This increase in organic matter was associated with an increase in soil aggregate stability, a reduction in bulk density, and reduced penetration resistance of the soil. Mulch with pig manure and chemical fertilizer was the best management practice for improving soil quality and crop yields in the Three Gorges Area. Further, mulch and pig manure addition also decreased the magnitude of the spatial variation, but did not offset the soil fertility gradients because tillage resulted in significant movement of soil. More favorable soil properties were found at the lower positions within each alley, regardless of the management practice applied.