Nutrient-holding Capacity Research Articles

SEASONAL NITROGEN BUDGETS OF MATURE CITRUS TREES ON A SANDY ENTISOL

Approximately 30% of Florida citrus is grown on well-drained Entisols with low nutrient-holding capacity, which are prone to high nitrogen (N) leaching losses. However, increasing application frequency of N-fertilizer via multiple fertigations does not increase crop yield, whereas in agronomic crops, such an approach typically enhances N uptake efficiency. We assessed seasonal tree N tissue concentration dynamics as affected by N rate for mature fourteen-year-old ‘Hamlin’ orange (Citrus sinensis L. Osbeck) trees on either Carrizo citrange (C. sinsensis L. Osbeck X Poncirus trifoliata L. Raf.) or Swingle citrumelo (C. paradisi Macf. X P. trifoliata L. Raf.) rootstocks. Nitrogen was applied as ammonium nitrate in six split fertigation applications with N target values of 179 and 269 kg ha−1yr−1. Leaf, twig, and branch bark tissue N concentrations decreased through the spring to minima in May and June. This time period corresponds to a period of high N demand associated with both vegetative and reproductive growth. Tissue N concentrations increased from late spring minimums to fall and winter maximum concentrations. Reduction in branch bark and wood tissue N concentrations may have been due to a redistribution of N to leaf, twig, and fruit tissues in response to low N supply. The majority of the spring N should be supplied prior to May.

Soil Fertility Potential for Rice Production in West African Lowlands

In this paper, we review the soil fertility characteristics and the nature of material in the West African lowlands in comparison with paddy soils in tropical Asia to examine their potential for rice cultivation. Soil samples collected from major lowland ecosystems, i.e., inland valleys (185 locations) and flood plains (62 locations), in 13 countries (Benin, Burkina Faso, Cameroon, Cote d'Ivoire, Ghana, Guinea, Niger, Nigeria, Liberia, Mali, Senegal, Sierra Leone, and Togo) generally show low values of pH, total C and N, available (Bary-2) P, exchangeable Ca and Mg, effective cation exchange capacity (ECEC), and clay content. These properties of the 87 topsoil samples selected from 247 collected samples are well associated with mineralogical composition. The clay and primary minerals predominantly consist of kaolinite and quartz, respectively, which suggests that the lowland soils in the region have low nutrient-holding capacity and a limited potential for inherent nutrient supply. In general, soil pH, available P, exchangeable bases (Ca, Mg, K, and Na), and ECEC decrease while total C, total N and exchange acidity (Al and H) increase with increasing rainfall. This tendency is mostly explained by the enhanced biomass production and soil weathering sequence governed by the climate. In terms of rice production, the lowland soils in West Africa have lower values of general fertility parameters and poorer mineralogical characteristics compared to paddy soils in tropical Asia, which includes Bangladesh, Cambodia, India, Indonesia, Malaysia, Myanmar, Philippines, Sri Lanka, and Thailand. In addition, deficit levels of S and Zn for rice production are widely observed in the lowland soils in West Africa. These findings suggest that soil fertility characteristics show substantially less potential for rice production in West Africa than in tropical Asia.

Monitoring of Nitrate Leaching in Sandy Soils

Proper N fertilizer and irrigation management can reduce nitrate leaching while maintaining crop yield, which is critical to enhance the sustainability of vegetable production on soils with poor water and nutrient-holding capacities. This study evaluated different methods to measure nitrate leaching in mulched drip-irrigated zucchini, pepper, and tomato production systems. Fertigation rates were 145 and 217 kg N ha(-1) for zucchini; 192 and 288 kg N ha(-1) for pepper; and 208 and 312 kg N ha(-1) for tomato. Irrigation was either applied at a fixed daily rate or based on threshold values of soil moisture sensors placed in production beds. Ceramic suction cup lysimeters, subsurface drainage lysimeters and soil cores were used to access the interactive effects of N rate and irrigation management on N leaching. Irrigation treatments and N rate interaction effects on N leaching were significant for all crops. Applying N rates in excess of standard recommendations increased N leaching by 64, 59, and 32%, respectively, for pepper, tomato, and zucchini crops. Independent of the irrigation treatment or nitrogen rate, N leaching values measured from the ceramic cup lysimeter-based N leaching values were lower than the values from the drainage lysimeter and soil coring methods. However, overall nitrate concentration patterns were similar for all methods when the nitrate concentration and leached volume were relatively low.

Can Cover Crop-based Systems Reduce Vegetable Crop Fertilizer Nitrogen Requirements in the Southeastern United States?

Poor water- and nutrient-holding capacity of sandy soils, combined with intense leaching rainfall events, may result in excessive N-fertilizers losses from vegetable production systems. Three cover cropping (CC) systems were used to assess supplemental N-fertilizer requirements for optimal yields of selected vegetable crops. Fertilizer N-rates were 0, 67, 133, 200, and 267; 0, 131, and 196; and 0, 84, 126,168, and 210 kg N/h for sweet corn (Zea mays var. rugosa), broccoli (Brassica oleracea), and watermelon (Citrullus lanatus), respectively. Crop rotations consisted of sunn hemp (Crotalaria juncea) in Fall 2003 followed by hairy vetch (Vicia villosa), and rye (Secale cereale) intercrop or a fallow. During Spring 2004, all plots were planted with sweet corn, followed by either cowpea (Vigna unguiculata) or pearl millet (Pennisetum glaucum), which preceded a winter broccoli crop. Hairy vetch and rye mix benefited from residual N from a previous SH crop. This cropping system provided a 5.4 Mg/ha yield increment for sweet corn receiving 67 kg N/ha compared to the conventional system. For the 133 N-rate, CC-based systems produced similar yields compared to conventional systems amended with 200 kg N/ha. Pearl millet accumulated 8.8 Mg/ha—but only 69 kg N/ha—and potential yields with this system were 16% lower compared to cowpea system. For a subsequent watermelon crop, trends were reversed, possibly due to a delay in mineralization for pearl millet. Because of its persistent growth after mowing, hairy vetch hampered initial growth and shading also delayed fruit development. Although CC may accumulate up to 131 kg N/ha actual N benefits, N-fertilizer benefits were only 67 kg N/ha, which may be related to a lack of synchronization between N release and actual crop demand.

Nitrogen, Phosphorus, and Potassium Responses and Requirements in Calcareous Sand Greens

Calcareous sands are widely used in the construction of putting greens in the western USA. Plants growing on these sands frequently exhibit nutrient deficiencies and rapidly changing nutrient levels due to the low nutrient-holding capacity of this medium. Our objectives were to determine the effects of N, P, K, and N × K and P × K interactions on the growth of creeping bentgrass (Agrostis stolonifera Huds.) in calcareous sand greens. Measurements included visual ratings of turfgrass quality, soil and tissue nutrient levels, and golf ball roll distance. Creeping bentgrass plots receiving 5.5 kg P ha−1 yr−1 had lower quality than the remainder of the treatments (27.5–110 kg P ha−1 yr−1). Interactions between P and K were not observed. Ball roll was negatively correlated with soil test P. According to linear plateau regression analysis, soil test P level was 3.0 mg kg−1 soil, and tissue test P was 0.4% for maximum quality. Nitrogen fertilizer treatments increased turfgrass quality with each successively higher treatment. No N × K interactions were observed. No significant effect of K on turfgrass quality was observed; however, K rates increased soil test K, and tissue K showed a weak correlation (R2 = 0.13) with turfgrass quality. Potassium levels within the soil profile indicated leaching of K through the root zone. Alternative K fertilization methods (foliar, increased frequency, and slow-release forms) may be needed to improve K nutrition of bentgrass growing on calcareous sands.

Indigenous views of soil erosion at Fandou Béri, southwestern Niger

Soil is being eroded from the village lands of Fandou Béri, in southwestern Niger, at rates of over 30 t ha −1 year −1, as measured by the 137Cs method. These figures exceed those that were used to label the Sahel a “hot spot” for soil erosion. The response to these data in international agronomic research organisations has been to make large investments in soil erosion research, but this contrasts with the meagre relative commitment to the problem by local Djerma (Zarma) and Fulani farmers. Farmers are more concerned about the loss of fertility than the loss of soil, per se, a viewpoint that embeds decisions about land use and conservation in a much broader decision-making process. Practices like paillage (laying of millet stalks) could be interpreted as tacit acknowledgement of erosion, but they have many other purposes. We ask, who is correct in their assessment of erosion—the villagers or the agronomists? By comparing scientific evidence, local views and measurements of erosion, we conclude that the farmers' opinions are a valid contribution to a complex argument that consists of short-, medium- and long-term issues. Short-term effects are acknowledged by both farmers and scientists. They include sand blasting of young crops, the burial or exposure of crops by floods or windstorms, and the removal of organic matter and nutrients. However, the amounts and values of the losses incurred in these ways are difficult to establish. In the medium term, significant losses of water- and nutrient-holding capacity only occur where erosion has drastically reduced soil thickness, but this affects very few fields. We believe that most of the soils in Fandou Béri are deep sands that can withstand many years of erosion before they lose significant production capacity. The longer-term issue is whether farmers should be asked to conserve soil for some abstract and distant purpose? The negative effects of erosion, at whatever scale, must be balanced against the maintenance of a community that depends on a holistically conceived system of risk-avoidance agriculture in which erosion may be unavoidable, given the current constraints of labour and the imperative to get a crop each year in the face of variable and unpredictable rainfall. The imposition of a rigorous system of soil conservation might threaten the cohesion of the community. Only a more open and productive debate between the scientific community, the state, and farmers can reach a more satisfactory framing of the ‘erosion problem’.

The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropics.

Many soils of the lowland humid tropics are thought to be too infertile to support sustainable agriculture. However, there is strong evidence that permanent or semi-permanent agriculture can itself create sustainably fertile soils known as 'Terra Preta' soils. These soils not only contain higher concentrations of nutrients such as nitrogen, phosphorus, potassium and calcium, but also greater amounts of stable soil organic matter. Frequent findings of charcoal and highly aromatic humic substances suggest that residues of incomplete combustion of organic material (black carbon) are a key factor in the persistence of soil organic matter in these soils. Our investigations showed that 'Terra Preta' soils contained up to 70 times more black carbon than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is chemically and microbially stable and persists in the environment over centuries. Oxidation during this time produces carboxylic groups on the edges of the aromatic backbone, which increases its nutrient-holding capacity. We conclude that black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.

SIGNIFICANCE OF MACROPOROSITY AND HYDROLOGY FOR SOIL MANAGEMENT AND SUSTAINABILITY OF AGRICULTURAL PRODUCTION IN A HUMID-TROPICAL ENVIRONMENT

This paper analyzes soil-related agronomic constraints in the Sitiung region of Indonesia that are directly related to low nutrient-holding capacity, macroporosity, and rainfall regime. This region receives 2500 to 3000 mm of rainfall per year, but nearly 50% of the rainfall is disposed of rapidly via internal drainage. Although rapid internal drainage reduces the risks of erosion, it leads to infertility, acidity, and Al toxicity. The physical structure of the soils is characterized by stable aggregates, with numerous macropores in the surface and a predominantly microporous subsoil matrix interspersed with a few larger macropores. Macropores account for about 29% of porosity in the surface and between 3 and 6% in the subsoil. The saturated hydraulic conductivity of the matrix containing macropores averages about 300 to 400 cm/day, whereas that of the microporous matrix is generally <1 cm/day. The structure facilitates rapid infiltration and leaching of rainfall. However, little opportunity exists for nutrients moving downward with drainage water to accumulate in the subsoil. The main reason for this seems to be the low hydraulic conductivity and the preponderance of excessive wetness in the subsoil. Drying seems to be essential for movement of nutrients into the subsoil matrix. However, most of the agronomic crops are sensitive to Al toxicity and fail to grow roots deeper than 10 to 15 cm. Thus, they suffer from water stress, despite heavy and frequent rainfall, and fail to cause drying of the subsoil. Problems of acidity, Al toxicity, and infertility worsen progressively where agricultural production consists mainly of Al-sensitive crops. Although liming with calcium carbonate improves the soil chemical environment, downward movement of lime is very slow. Deep liming is effective in improving rooting depth, crop water availability, and drying of the subsoil, but the technology is cost- and labor-intensive. Native vegetation, on the other hand, is able to grow roots to considerable depths and causes significant drying of the subsoil, even without soil amendments. Thus, production systems in which locally adapted vegetation of economic value is the main focus seem to be more sustainable and conducive to improving soil conditions.

A review of soil erosion potential associated with biomass crops

It has been estimated that up to 60 million hectares could be devoted to energy crop production in the U.S. Due to economic considerations, biomass crops will probably be produced on marginal cropland which is frequently highly erodible. Thus, the impact of herbaceous and woody biomass crop production on soil erosion must be addressed. Perennial grasses provide year-round soil cover, limiting erosion even with continued biomass harvest. Vigorous perennial herbaceous stands reduce water runoff and sediment loss and favor soil development processes by improving soil organic matter, soil structure and soil water and nutrient-holding capacity. Minimum tillage management of row crops reduces erosion compared with systems involving more frequent or more extensive tillage. Woody biomass plantations reduce water erosion by improving water infiltration, reducing impacts by water droplets, intercepting rain and snow and physically stabilizing soil by their roots and leaf litter. Shelterbelts reduce wind erosion when planted as shelterbelts and improve soil organic matter, soil structure and soil moisture in their leeward zone, reducing soil erodibility. Harvesting of woody biomass plantations may be accompanied by increased erosion. Forestry clear-cutting, especially on steep slopes, often results in a large increase in water erosion. For this reason, it is essential that woody biomass plantations be designed for rotational harvesting, even though this may result in higher harvesting costs.

Implications of Dairy Herd Size for Farm Material Transport, Plant Nutrient Management, and Water Quality

Farm material transport to, from, and within dairy farms can create zones of plant nutrient depletion and accumulation that range in scale from local to international. The introduction, adoption, and use of fertilizers have resulted in substantial movement of plant nutrients to dairy farms. Fertilizers contributed to enhanced crop growth and frequently the correction of soil nutrient deficiencies. They also represented an opportunity to replace plant nutrients exported from a farm in crops so that it was possible for some farms to specialize in the production of crops. These exported crops often became imports for other farms that specialized in livestock. However, the nutrient-holding capacity of soil on any farm is limited, so the potential for additions to the stock of nutrients, especially of P and K, on a farm can be expected to decrease with time. After a period of net nutrient additions on a dairy farm, the quantity of nutrients that can be accommodated is controlled by the productivity of the animals, the management of the animal handling facilities, and the off-farm purchases of feeds and other materials for the animals. Field and biophysical-economic simulation studies have demonstrated that interactions between alternative management strategies and societal perspectives about water quality and the biological and economic performance of dairy farms may sometimes lead to unexpected outcomes.

Water and nutrient management in sandy soils by compaction

Specific problems in the management of sandy soils of north-west India include their excessive permeability and their low water- and nutrient-holding capacities. Common soil features, constraints and productivity index of these sandy soils are discussed. Several studies indicated that subsoil compaction reduced water and nutrient losses and increased root-zone soil moisture retention in deep sandy soils. Such compaction saved irrigation water by 15–36% and increased soil productivity by 30–50%. The extent of nitrate losses and the favourable role of compaction in modifying soil hydraulic parameters, viz. moisture retention, infiltration and saturated hydraulic conductivity, which are important for improving their water and nutrient management, are discussed.

Management of Northern Gravel Sites for Successful Reclamation: A Review

In the Arctic and Subarctic, roads and other construction projects require large amounts of gravel to provide well-insulated, stable surfaces. Gravel pits create large disturbed, terrestrial areas and produce significant on-site and off-site impacts, at least some of which are long lasting or even permanent. Gravel substrates are difficult to revegetate since they typically have low moisture- and nutrient-holding capacities. There are several possible approaches to maximize the likelihood of successfully reclaiming northern gravel sites: (1) Minimize their areal extent and visual impact; (2) improve the substrate characteristics for plant growth by such measures as erosion control and reuse of topsoil; (3) select adapted biological materials; and (4) proper siting of gravel pits to enhance reinvasion of native plant species. The extreme conditions of most arctic and subarctic sites require site specific approaches. These conditions also increase the need to use native plant species and to utilize their successional strategies to develop appropriate reclamation plans for gravel sites.