Build-up Of Fertility Research Articles

Temporal soil fertility with organic nitrogen sources in acidic soil of Meghalaya

A field experiment was conducted at CAU, Umiam, Meghalaya during kharif 2017 to investigate the effect of nitrogen application through urea and Azolla on temporal soil fertility build-up under low land rice cultivation at 30, 60, 90 days after transplanting (DAT) and at maturity in acidic soil. The experiment consists of six treatments with and without Azolla incorporation laid out in RBD with four replications. The application of 60 kg N/ha through urea along with Azolla incorporation @16000 kg/ha (T6) recorded highest available N (289.98 kg/ha) after harvest which was significantly superior over control (227.45 kg/ ha) with 9.1% increase. Similarly, this treatment recorded highest available P, K and OC i.e. 20.6, 192.3, 2.1 kg/ha after harvest followed by T5 and T2. Further, it was also observed that available P, K and OC in T6 were statistically significant over T4 whereas T5 was significant over T3 with respect to advancement in crop age.

Litter production and litter dynamics in different agroforestry systems in the arid western region of India

ABSTRACT Litterfall production, decomposition and nutrient release was investigated for three prominent agroforestry tree species, Prosopis cineraria, Tecomella undulata and Hardwickia binata, grown in the arid western region of India. The highest litterfall was recorded for H. binata (9.44 Mg ha−l y−1) followed by P. cineraria (8.94 Mg ha−l y−1) and T. undulata (3.74 Mg ha−l y−1). It took 15, 12 and 9 months for decomposition of 90% of the litter of H. binata, P. cineraria and T. undulata, respectively. Regression analysis showed that rainfall and air temperature had significant impacts on the decomposition process. Soil moisture and soil microbial biomass carbon showed high correlations (R2 > 0.70, p < 0.01) with litter decay. The rate of release of N (k N = 0.0014, surface (0–15 cm); k N = 0.0015, sub-surface (15–30 cm)) and K (k K = 0.0041, surface; k K = 0.0047, sub-surface) was highest from P. cineraria, whereas release rates of P were statistically equivalent for all species. N release from the decomposing litter increased initially, but then decreased as decomposition progressed. Concentrations of P, K and Mg in the litter decreased throughout the decomposition, with some fluctuations in P and Mg for P. cineraria and H. binata at the later stage. Ca release did not follow any specific trend. P. cineraria, with considerable amounts of litterfall, the highest nutrient inputs to the soil and the most rapid release of nutrients during the decomposition, was concluded to facilitate greater fertility build-up of the soil compared with the other two species.

Microbial metabolic efficiency and community stability in high and low fertility soils following wheat residue addition

Soil microbial metabolic efficiency and microbial community stability following the amendment of plant residue to soils are of great importance to the improvement of soil carbon storage and soil fertility. However, heterogeneity of microbial metabolic efficiency and community stability in soils with different fertility defined based on the crop yield, as well as the underlying mechanisms still remains elusive. Here, soils with high and low fertility (HF and LF) were incubated with 13C-labeled wheat residue and analyzed periodically for microbial metabolic quotient and functional bacterial populations using DNA-stable isotope probing technique combined with high-throughput sequencing. Results revealed that soil organic matter (SOM) decomposers following wheat residue amendment were suppressed in HF but stimulated in LF, leading to a higher microbial metabolic efficiency and lower priming effect in HF. This difference in SOM decomposers' responses could be due to that microbes in nutrient- limited LF has to mine recalcitrant SOM for nutrient requirement to support the utilization of wheat residue, the ample nutrients in HF, however, render the microbes to directly utilize wheat residue. Both the resistance (disturbance stability) and resilience (temporal stability) of bacterial community were higher in HF than in LF following disturbance of wheat residue addition. Higher abundance and lower composition variation of wheat residue decomposers in HF than in LF might result in the higher stability of microbial community in HF. The results suggest that plant residue amendment to fertile soils is likely more effective for soil carbon accumulation and soil fertility buildup than to infertile soils, due to higher microbial metabolic efficiency and higher microbial community stability.

Effects of Area Closure on Selected Soil Physico-Chemical Properties in Hidabu Abote District, North Shewa Zone, Oromia

This study was conducted at sire moresse area closure, Hidabu abote district, North shewa zone, Oromia Regional State to evaluate the effects of area closure on selected physic-chemical properties of soils. In this study area closure sites were compared with adjacent open grazing land in similar landscape positions for soil fertility buildup. Soil samples were collected from the experimental fields using Randomized Complete Block Design (RCBD) with factorial arrangement to evaluate selected soil physico- chemical properties. Data analyses were carried out using analysis of variance appropriate to general linear model (GLM). A total of 36 undisturbed and 36 disturbed soil samples were collected from both closed and open grazing land at 10 and 20 cm sampling depths along each slope position with three replication. The result of the study indicated that the mean value of most of soil physical and chemical properties were higher at area closure than adjacent open grazing land and also higher at bottom slope position than middle and upper slope position. The mean of Air filled porosity and Bulk density were lower at both area closure management practices and bottom slope position. Bulk density, Total Porosity, volumetric soil moisture content and saturated hydraulic conductivity at 20 cm sampling depth were shows significantly different with respect to management practices. Similarly, soil chemical properties such as EC, OC, AvP and CEC were shows significantly different with respect to management practices. Soil structure quality, Texture, BD, TP, SMC, EC and TN were shows significantly different under the three slope position. The overall output from the research showed that physical and chemical properties of soil in area closure areas are improving. Area closures act as important sinks of water and reduce soil erosion. From this study it was possible to conclude that area closure improves soil physical and chemical properties.

Soil organic carbon sequestration and fertility response to newly-built terraces with organic manure and mineral fertilizer in a semi-arid environment

Terraces are a popular and widely-distributed engineered agricultural landscape in mountainous regions. In this study, the effects of adding manure on soil organic C (SOC) sequestration, soil aggregate distribution, C/N ratio and activities of enzyme were evaluated in newly-built terraces over 7 growing seasons from 2004 to 2010 on the semi-arid Loess Plateau of China.Experimental treatments including CK (control treatment with no fertilizer), NP (nitrogen and phosphorus), M (manure) and MNP (manure, nitrogen and phosphorus) were employed with a field pea–spring wheat–potato cropping system. SOC built up quickly in M and MNP treatments, while applying fertilizer alone (NP) was not effective in increasing soil C. The C sequestration rates are high in the early stages in manure treatments, and then decrease with consequent increases of soil C pool and finally became zero as soil C reaches an equilibrium level. The simulation results showed that the maximum increase of SOC in newly-built terraces was 3.4gkg−1. Organic amendment significantly increased soil water stable macro-aggregates (>0.25mm). The largest aggregates (>2mm) in manure treatments have important implications for C sequestration, with 29.4% and 30.6% of total SOC in M and MNP, respectively. Application of fertilizer alone could not form the largest aggregates (>2mm) in the 7 years. SOC content was significantly higher in M and MNP than in CK and NP in all soil aggregate size classes. Manure treatments improved soil C/N ratio, while fertilizer treatment (NP) decreased soil C/N ratio. A significant sigmoid relationship was found between C/N ratio and cumulative inputs of SOC and TN in manure treatments, and a significant logistic relationship was found C/N ratio and cumulative TN inputs in NP treatment. After 7 years, fertilizer alone was as important as manure for improving activity of urease. Manure treatments improved activities of alkaline phosphatase and β-glucosidase compared with no manure treatments. The overall results show that applying fertilizer alone (NP) was not effective in accelerating the build-up of fertility and adding manure is essential in improving soil fertility and accelerating the build-up of fertility in newly-built terraces in a semi-arid environment.

Nitrate leaching and residual effect in dairy crop rotations with grass–clover leys as influenced by sward age, grazing, cutting and fertilizer regimes

Intensive dairy farming, with grass-arable crop rotations is challenged by low N use efficiency that may have adverse environmental consequences. We investigated nitrate leaching and N fertility effects of grass–clover leys for five years in two organic crop rotations with different grassland proportions (33 and 67%) and five grassland managements in terms of cutting, grazing, fertilization and combinations thereof. In grass–clover, the combination of fertilization and grazing caused excessive leaching (average 60kg Nha−1) but leaving out either fertilization or full-time grazing substantially reduced leaching losses to on average 23kg Nha−1. There was no linear relationship between sward age and nitrate leaching. The annual N surplus of the grasslands was only weakly related to nitrate leaching (R2=0.05, P<0.01). The residual effect of grassland cultivation was highest following grazing and fertilization and lowest without fertilization or cutting-only management and was not influenced by grassland age. The arable part of the mixed crop rotation was nitrate leaky where crop coverage in autumn was insufficient. Nitrate leaching following the crops may roughly be divided into four groups: (1) low leaching (<10kg Nha−1) consisting of the barley wholecrop undersown with Italian ryegrass, (2) medium–low leaching (10–20kg Nha−1) consisting of barley with grass–clover undersown and the 1-yr-old grasslands, (3) medium leaching (25–50kg Nha−1) consisting of barley–pea and 2-4-yr-old grasslands with the 2-yr-old leaching the most (36–46kg Nha−1), and (4) high leaching (>50kg Nha−1) with lupin and maize, where especially maize was consistently high in all five years (average 81kg Nha−1). Great care should be taken during all phases of the dairy crop rotation where grasslands cause considerable build-up of fertility. With due care and the best management practice, nitrate leaching losses may be reduced to low levels.

A REVIEW ON PLANT WITHOUT SOIL - HYDROPONICS

With the advent of civilization, open field/soil-based agriculture is facing some major challenges; most importantly decrease in per capita land availability. In 1960 with 3 billion population over the World, per capita land was 0.5 ha but presently, with 6 billion people it is only 0.25 ha and by 2050, it will reach at 0.16 ha. Due to rapid urbanization and industrialization as well as melting of icebergs (as an obvious impact of global warming), arable land under cultivation is further going to decrease. Again, soil fertility status has attained a saturation level, and productivity is not increasing further with increased level of fertilizer application. Besides, poor soil fertility in some of the cultivable areas, less chance of natural soil fertility build-up by microbes due to continuous cultivation, frequent drought conditions and unpredictability of climate and weather patterns, rise in temperature, river pollution, poor water management and wastage of huge amount of water, decline in ground water level, etc. are threatening food production under conventional soil-based agriculture. Under such circumstances, in near future it will become impossible to feed the entire population using open field system of agricultural production only. Naturally, soil-less culture is becoming more relevant in the present scenario, to cope-up with these challenges. In soil-less culture, plants are raised without soil. Improved space and water conserving methods of food production under soil-less culture have shown some promising results all over the World.

Runoff capture through vegetative barriers and planting methodologies to reduce erosion, and improve soil moisture, fertility and crop productivity in southern Orissa, India

Use of perennial grasses as vegetative barriers to reduce soil erosion from farm and non-farm lands is increasing world-over. A number of perennial grasses have been identified for their soil conserving properties, but their effectiveness varies with location and method of planting. Installing vegetative barriers in combination with suitable mechanical measures, like bunds or trenches or both, on the appropriately spaced contours may enhance their conservation potential. Hence, the effect of vegetative barriers, viz., sambuta (Saccharum spp.)—a local grass, vetiver (Vetiveria zizanioides) and lemongrass (Cymbopogon citratus) planted in combination with trench-cum-bund, on runoff, soil loss, nutrient loss, soil fertility, moisture retention and crop yield in the rainfed uplands, was studied in Kokriguda watershed in southern Orissa, India through 2001–2005. However, runoff, soil and nutrient losses were studied for 2002, 2003 and 2004 only. Analysis of the experimental data revealed that on a 5% slope, the lowest average runoff (8.1%) and soil loss (4.0 Mg ha−1) were observed in the sambuta + trench-cum-bund treatment followed by vetiver + trench-cum-bund (runoff 9.8%, soil loss 5.5 Mg ha−1). Lemongrass permitted the highest runoff and soil loss. Further, the conservation effect of grass barriers was greater under bund planting than berm planting. Minimum organic C (50.02 kg ha−1), available N (2.49 kg ha−1) and available K (1.56 kg ha−1) loss was observed under sambuta with bund planting. The next best arrester of the soil nutrients was vetiver planted on bund. Significantly better conservation of nutrients under sambuta and vetiver resulted in the soil fertility build-up. Soil moisture content was also higher in the sambuta and vetiver than lemongrass treated plots. Increase in the yield of associated finger millet (Eleusine coracana (L.) Gaertn.) due to vegetative barriers ranged from 18.04% for lemongrass to 33.67% for sambuta. Further, the sambuta and vetiver treated plots produced 13.23 and 11.86% higher yield, respectively, compared to the plots having lemongrass barrier (1.17 Mg ha−1). Considering the conservation potential, and crop yield and soil fertility improvements, the sambuta barrier with trench-cum-bund is the best conservation technology for treating the cultivated land vulnerable to water erosion. Farmers also showed greater acceptance for the sambuta barrier as it is erect growing and available locally. Vetiver with-trench-cum bund can be the second best option.

Effects of farmyard manure on soil organic carbon stock, the pattern of fertility build-up, and plant growth in ‘Mallika’ mango (Mangifera indica L.)

SummaryA field experiment was conducted on mango (Mangifera indica L.) to study the effects of farmyard manure (FYM) on soil organic carbon (SOC) content and on the build-up of fertility over three growing seasons (2006–2007, 2007–2008, and 2008–2009) at Bhubaneswar, Orissa, India. Five treatments, including the application of FYM at 5.0 kg plant–1, 7.5 kg plant–1, or 10.0 kg plant–1, the recommended dose of a chemical fertiliser (RDF; N:P:K=75:20:60), and a non-fertilised control, were evaluated in a randomised block design. The results indicated that SOC contents increased significantly in the FYM-treated plots. The highest SOC density (554 g m–2) and stock (5.55 Mg ha–1) were recorded in the treatment with FYM at 10 kg plant–1. The rate of increase in SOC density was highest (193 g m–2 year–1) with FYM at 10 kg plant–1, and lowest in the untreated control (15 g m–2 year–1). Regular addition of FYM had a positive effect on the build-up of soil fertility. However, the greatest increases in soil N, P, K contents were in the 7.5 kg plant–1 FYM treatment (means = 319.9, 19.1, and 270.8 kg ha–1 for N, P, K, respectively). Farmyard manure significantly influenced the growth parameters of mango trees over the three seasons. There was a positive and linear relationship between increasing rates of application of FYM and trunk cross-sectional area.

Plant-livestock-soil-hydrology interactions in the northeastern region of India

In a multidisciplinary study, highly significant interactional effects were found among land use, livestock component, soil properties and rainfall. On an average, 16.2 to 82.2 tonnes of sediment yield km−2 and more than 90% of rainwater was retained in-situ in new land use systems as against 3621.3 tonnes of sediment and 66.3% rainwater retention in shifting cultivation, because of poor land cover. Good vegetation cover reduced the runoff load, resulting in significant reduction in the soil and nutrient erosion. The average sediment yield was only 0.44%, 2.68%, 1.47%, 0.31%, 0.73% and 2.27% in livestock based, forestry, agro-forestry, agriculture, agri-horti-silvi-pastoral and horticulture land use systems of that of shifting cultivation. Highest average sediment yield was 704.3 t km−2 when the annual rainfall was 2770 mm and minimum 405.4 t km−2 when the annual rainfall was 1992 mm. More in-situ retention of rainwater helped in the availability of adequate moisture from the soil to the succeeding crops when the rainy season receded. The sediment yield varied according to the rainfall received during a particular year and the nature of vegetation in a particular land use. There was sufficient fertility build-up in the watersheds where animals were kept and after ten years of start of the study, no need of inorganic sources of nutrients was required. The organic carbon, humus, exchangeable calcium, magnesium, potassium and available phosphorus increased significantly in the new land use systems compared to shifting cultivation, however, the DTPA (Diethylene triamine penta acetic acid) extractable zinc, copper, iron and exchangeable aluminium decreased over the initial soil status. It showed that the vegetation in the new land uses had a smothering effect on the soil and increase in the elements had a favourable impact on the crop productivity.

Carbon loss from Brachystegia spiciformis leaf litter in the sandy soils of southern Mozambique

Leaves of Brachystegia spiciformis represent a substantial fraction of the total aboveground litter in bush fallow fields with sandy soils in southern Mozambique, where annual rainfall exceeds 600 mm. This species is one of the most important in the miombo woodland that is the natural vegetation of the region. Proper knowledge of the decomposition of its litter is therefore crucial for understanding processes responsible for natural build-up of fertility in agricultural soils abandoned to bush fallow during shifting cultivation. This study investigated the effects of soil water content and soil temperature on loss of organic carbon (C) from decomposing leaves in litterbags with 1 mm mesh size. The litterbags were buried 50 mm deep in recently abandoned agricultural fields cleared of any vegetation (Bare) and in more than 15-year-old bush fallow fields (Fallow) of sites covering a climatic transect with annual rainfall from 1,000 mm. Two patterns of C loss were observed, one in coastal and wetter agroecosystems (rainfall >600 mm) and the other in inland and drier agroecosystems (rainfall <600 mm). In the wetter agroecosystems C loss was faster, whereas in drier agroecosystems it was more sensitive to rainfall pulses. Similarly, C loss was faster in fallow fields than in bare fields. During summer, bare fields reached soil temperatures higher than the estimated upper boundary favourable for C loss from decomposing leaf litter at all sites. A simple dynamic decomposition model describing the C fraction remaining in the litterbags was developed. Coefficients of determination (R2) for the individual experimental units varied between 0.79 and 0.97. The general model for all sites and fields improved explanation of total variation from 81% to 86% when measured soil temperature and soil water content were used as modifiers of decomposition rate, compared with the standard negative exponential model. Root-mean-square error and systematic bias were 9.7% and 0.5% of initial C, respectively. Decomposition was more strongly affected by soil water content than by soil temperature and explained 75% of total variation. Thus, rainfall is the main driver of C loss from leaf litter in these agroecosystems.

Influence of Long‐Term Application of Organic and Inorganic Fertilizer to Build Up Soil Fertility and Nutrient Uptake in Mint‐Mustard Cropping Sequence

Field experiment was conducted for 7 years continuously to evaluate the influence of combined application of organic and inorganic fertilizer on soil fertility buildup and nutrient uptake in mint (Mentha arvensis) and mustard (Brassica juncea) cropping sequence. Maximum organic carbon was observed under full supply of organic manure (T2; FYM at 20 t ha−1) averaged across all the Stages of cropping sequence. It was increased by 38, 50, and 51% in T2 in Stages I (after mint harvest/presowing of dhaincha), II (after incorporation of dhaincha (Sesbania aculeata)/presowing of mustard), and III (after harvest of mustard/preplanting of mint), respectively, over their respective controls. In general, magnitude of organic carbon was recorded higher in Stage II after green manuring of Sesbania compared with Stages I and III. Nitrogen availability in treated plots was increased by 26.0–89.9, 15.2–64.5, and 4.9–52.0% in Stages I (after mint harvest/presowing of Sesbania), II (after incorporation of dhaincha/presowing of mustard), and III (after harvest of mustard/preplanting of mint), respectively, over their respective control. Average across all the three Stages showed a positive balance of nitrogen (N), phosphorus (P), and potassium (K) in soil under different treatments. Mean of the three Stages indicated that maximum available N, P, and K were increased by 36.1, 129.0, and 65.20% in T4 (N:P:K: 133:40:40 and FYM at 6.7 t ha−1), T4 (N:P:K::133:40:40 and FYM at 6.7 t ha−1), and T3 (N:P:K::100:30:30 and FYM at 10 t ha−1), respectively, over their initial status. Supply of organic and inorganic fertilizer (T4; N:P:K::133:40:40 and FYM at 6.7 t ha−1) was found most suitable combination with respect to N, P availability in soil, and productivity of mint and mustard crop.

Soil fertility decline and economic policy reform in Sub-Saharan Africa

Two decades of economic reforms in Africa have not resulted in the anticipated growth in per capita agricultural production. Declining output–fertiliser price ratios, particularly for food crops, contributed to soil fertility depletion and agricultural stagnation. Current prices of agricultural products in Africa are depressed by asymmetric government food trade policies and by protective agricultural policies of OECD countries. Nor do they reflect the local and global environmental benefits of soil fertility build-up. There is an urgent need to consider the social costs and benefits of short-term price policies that supplement medium to long-term structural policies.

Effect of different rates of application of organic and nitrogen fertilizers in a rice-based cropping system

SUMMARYThe effect on soil fertility and crop performance of different organic fertilizers; paddy straw (PS), farmyard manure (FYM), water hyacinth compost (WHC) and tank silt (TS), at different rates of application and in combination with N fertilizer, was studied in a rice-based cropping system on an acid lateritic soil at Kharagpur, India, during 1985/86. Organic manuring of wet-season rice (first crop) with 5 t PS/ha 10 days before transplanting and 10 t FYM or 10 t WHC/ha at transplanting increased grain yield as much as the application of 30 kg N/ha. Increasing the rates of FYM and WHC application up to 15 t/ha increased yield but increasing the rate of PS beyond 5 t/ha did not. Response to increasing amounts of N was not linear; there was a significant increase up to 90 kg N/ha and a decrease when N was applied in conjunction with organic fertilizers. There was a significant increase in the N uptake of the rice but a decrease in the recovery of applied fertilizer N with the application of increasing rates of organic and N fertilizer.The organic C content of the soil after the rice harvest increased significantly after PS application, whereas there was more available N after WHC and FYM. Increasing the rate of application of PS up to 15 t/ha increased organic C but not available N. Mineral N fertilizer had little effect on fertility build-up. Grain yields of wheat and gram (Cicer arietinum), grown after rice without any additional fertilizer, increased significantly. The residual N effect of the previous crop on wheat or gram yield was small and adding fertilizer directly is considered essential for higher productivity in these crops in a rice-based cropping system.

Effect of combinations of organic materials and nitrogen fertilizer on growth, yield and nitrogen uptake of rice

SummaryIn a 2-year study, the growth and yield of lowland rice increased significantly with the combined use of organic materials and N fertilizer in an acid-lateritic soil. Application of farmyard manure (FYM) or water hyacinth compost (WHC) at 10 t/ha along with paddy straw (PS) at 2·5 t/ha increased grain yield by 28%, similar to the increase given by 30 kg N/ha as fertilizer. The combination of FYM and WHC with or without PS produced yields equivalent to those using 50–60 kg/ha N as fertilizer urea. Uptake of N increased but the recovery of applied N decreased both with the application of organic materials and with increasing N. Organic materials considerably improved the fertility status of the soil, as measured by % C and available N, after crop harvest, whereas N fertilizer made no impact on fertility build-up.

The dehesa: an agrosilvopastoral system of the Mediterranean region with special reference to the Sierra Morena area of Spain

A multidisciplinary team undertook a six-year investigation on the agro-ecological and socio-economic aspects of the dehesa system in the Sierra Norte area, a part of the Sierra Morena of the Sevilla Province, Western Andalusia, Spain. This paper summarizes its findings on the various agro-ecological features of the system and evaluates the system's functional aspects vis-a-vis the trends and developments in land use in the region over the past few centuries. The synergistic effects of tree cover on understorey grassland vegetation is discussed in terms of soil fertility build-up and favourable micro-climatic and hydrological features, and the potential use of this information in future research and development programmes to improve the dehesa system in the Mediterranean region is outlined.

The relevance of seral eutrophication and plant competition to the management of successional communities

Seral and plagioclimax communities such as chalk grassland, dune grassland, and heathland, are of great conservational importance in the United Kingdom, and considerable resources are directed towards their management in nature reserves and amenity areas. It is suggested that an important feature of these communities is their low fertility, especially with respect to nitrogen, and that this is directly related to their floristic diversity. Successional changes, usually involving scrub colonization, lead to a build-up in fertility, to loss of floristic diversity, and often to a reduction in the wildlife and amenity value. The traditional forms of management practised on such communities—including grazing, burning, and mowing—probably arrest seral development partially by preventing the build-up of fertility in the ecosystem. Some examples of mineral nutrient studies are considered, and it is suggested that a greater knowledge of nutrient budgets is fundamental to the scientific management of these communities.

Fertility build-up of rice field soils by blue-green algae

Fertility build-up of rice field soils by blue-green algae

Rôle of blue-green algae and different methods of partial soil sterilization on rice yield

Results of experiments during three consecutive seasons on the role of blue-green algae in combination with partial soil sterilization and chemical nutrients indicate high responses to algae inoculation and a fertility build-up of the soil. It is also seen that blue-green algae tend to produce better response in soils which are poor.

Changes in organic matter and pH in a podzolic soil as influenced by subterranean clover and superphosphate

A further investigation has been made on soils examined by Donald and Williams (1955) in a survey of the influence of superphosphate and subterranean clover (Trifolium subterraneum L.) on podzolic soils formed on granodiorite in the Crookwell district of New South Wales. The soil organic matter was found to have approximately constant proportions of carbon, nitrogen, sulphur, and phosphorus in the ratio 155 : 10 : 1.4 : 0.68, and it is suggested that the rate of build-up of soil organic matter under the clover pastures may have been limited by the amounts of sulphur supplied in the superphosphate top-dressings. The soil organic matter was found to have a cation-exchange capacity a t pH 7.0 of about 220 m-equiv./100 g, and increases in soil organic matter have led to substantial increases in the cation-exchange capacity of the soil. About 75 per cent. of the total cation-exchange capacity of the unimproved soils was due to organic matter while, in the most improved soils, this figure approached 90 per cent. The increases in cation-exchange capacity included increases in exchangeable hydrogen and were accompanied by decreases in soil pH. There were increases equivalent to 6.5 lb of exchangeable potassium, 25.5 Ib of exchangeable calcium, and 5.2 lb of exchangeable magnesium per acre in the surface 4 in. of soil for each hundredweight of superphosphate applied per acre. Increases in soil organic matter also resulted in increases in the field capacity which may reflect improvements in soil structure. Results indicate that heavier rates of superphosphate application would increase the rate of fertility build-up.