Identification of nutrients limiting cassava yield maintenance on a sedimentary soil in southern Benin,West Africa

Market opportunities will drive intensification of cassava production and fertilizer will play a role in this. A trial was initiated on 15 farmers fields (replications) in one village territory in Benin on a relatively fertile sedimentary soil site to identify nutrients limiting cassava yield using nutrient omission plots over three cropping years. There was no response to fertilizer in the first year when fresh root yields in the unamended control averaged 19.1 t ha^–1. In the second year, the control yield was 16 t ha^–1 and there were significant reductions from withholding P (3.5 t ha^–1) and K (2 t ha^–1) from a complete fertilizer regime. Nutrient balance after 1 and 2 years (cumulative) showed substantial P and K deficits in unamended plots. In the third year, the control yield was 12.9 t ha^–1 and effects of withholding K (5.3 t ha^–1), P (5.0 t ha^–1) and N (3.0 t ha^–1) were statistically significant. Soil K was a significant source of variation in yield in the third year. In the third year of annual nutrient additions soil P and K in the top 0.3 m were increased by 37 and 40%, respectively. Based on the cumulative nutrient balance calculation, the annual application needed to compensate nutrient depletion was 13 kg N, 10 kg P, and 60 kg K ha^–1. Partial budget analysis based on these amounts of fertilizer suggested that investment was clearly justified in the third year of continuous cropping at current low cassava prices.     

Influence of continuous fertilization to a maize-wheat system on the changes in soil fertility

The effect of continuous application of rates of N (40, 80 and 120 kg N ha^–1), P (0, 17.5, and 35 kg P ha^–1) and K (0 and 33.2 kg K ha^–1) to a maize-wheat annual sequence on the changes in soil fertility after harvest of maize and wheat in their 11th cycle are reported. The organic carbon (O.C.), available nutrients and micronutrients tended to decline with cropping. Application of N or P significantly increased O.C. status of the soil both after harvest of maize and wheat. Potassium addition also increased the O.C. status but significant differences were observed only after wheat harvest (22nd crop). The available N status of the soil increased significantly with N application whereas a declining trend occurred with P dressings. Potassium application did not affect the soil available N content. The maximum decline in available P status was observed under N₁₂₀ P₀ K_33.2 treatment whereas a significant increase occurred in P treated plots. The available K status continued to decline in plots receiving increasing rates of N and NP fertilizers. The soil available K status was maintained to its initial content in plots receiving fertilizer K with increasing rates of N with or without P. Continuous application of increasing levels of N (averaged over PK) depleted the soil of DTPA-extractable Fe, Mn, Zn and Cu content. The addition of P also resulted in a decline in the status of Mn and Cu whereas the Fe and Mn content of the soil was increased. The available micronutrients content was least affected by K additions. The contents of organic carbon, available N and K in differentially fertilized plots were higher after harvest of 22 crops (wheat) than 21 crops (maize) while the reverse occurred in respect of available P and micronutrients.     

Distribution of acid extractable P and exchangeable K in a grassland soil as affected by long-term surface application of N, P and K fertilizers

Information on the fate and distribution of surface-applied fertilizer P and K in soil is needed in order to assess their availability to plants and potential for water contamination. Distribution of extractable P (in 0.03 M NH₄F + 0.03 M H₂SO₄ solution) and exchangeable K (in neutral 1.0 M ammonium acetate solution) in the soil as a result of selected combinations of 30 years (1968–1997) of N fertilization (84–336 kg N ha^–1), 10 years of P fertilization (0–132 kg P ha^–1), and 14 years of K fertilization (0 and 46 kg K ha^–1) was studied in a field experiment on a thin Black Chernozem loam under smooth bromegrass (Bromus inermis Leyss.) at Crossfield, Alberta, Canada. Soil samples were taken at regular intervals in October 1997 from 0–5, 5–10, 10–15, 15–30, 30–60, 60–90 and 90–120 cm layers. Soil pH decreased with N rate and this declined with soil depth. Increase in extractable P concentration in the soil reflected 10 years of P fertilization relative to no P fertilization, even though it had been terminated 20 years prior to soil sampling. The magnitude and depth of increase in extractable P paralleled N and P rates. The extractable P concentration in the 0–5 cm soil layer increased by 2.2, 20.7, 30.4 and 34.5 mg P kg^–1 soil at 84, 168, 280 and 336 kg N ha^–1, respectively. The increase in extractable P concentration in the 0–15 cm soil depth was 1.5 and 12.8 mg P kg^–1 soil with application of 16 and 33 kg P ha^–1 (N rate of 84 N ha^–1 for both treatments), respectively; and it was 81.6 and 155.2 mg P kg^–1 soil with application of 66 and 132 kg P ha^–1 (N rate of 336 N ha^–1 for both treatments), respectively. The increase in extractable P at high N rates was attributed to N-induced soil acidification. Most of the increase in extractable P occurred in the top 10-cm soil layer and almost none was noticed below 30 cm depth. Surface-applied K was able to prevent depletion of exchangeable K from the 0–90 cm soil, which occurred with increased bromegrass production from N fertilization in the absence of K application. As only a small increase of exchangeable K was observed in the 10–30 cm soil, 46 kg K ha^–1 year^–1 was considered necessary to achieve a balance between fertilization and bromegrass uptake for K. The potential for P contamination of surface water may be increased with the high N and P rates, as most of the increase in extractable P occurred near the soil surface.     

Twenty-five years of phosphate and potassium fertilization of a crop rotation

Effects of rate and placement of phosphate and potassium fertilizers was studied using a 4-year rotation of corn (Zea mays L.), soybeans (Glycine max L.), wheat (Triticum vulgare L.) and hay (later changed to corn). Yields increased with increased P until 22 kg P ha^–1 yr^–1 was applied. Yields increased with increased K applications to 140 kg K ha^–1 yr^–1. Broadcast P applications gave high yields than row applications. Crop response to P was affected more by soil P level than by application to the specific crop. Residual effect from K fertilizer applications did not last as long as the residual effect from P application. Soil tests for available P were closely correlated with rate of P application over the 25-year period. Soil tests for P were higher where P was banded where P was broadcast indicating less tie-up of P by the soil where less mixing occurred.Journal Paper No. 7910, Purdue University Agricultural Experiment Station.     

Fertigation versus broadcasting in an orange grove

A long-term experiment was carried out in a mature orange grove comparing broadcasting versus continuous application of nitrogen at three rates (80, 160, 280 kg ha^–1), 22 kg P ha^–1 and 126 kg K ha^–1 annually. The trees were irrigated with minispriklers wetting 70% of the soil area.The level of NO₃-N in the leaves varied according to the rate of N application. Leaf K and P content were not affected by fertilization. High N applications caused excess N in the soil solution. The rate of N application did not affect orange yield, fruit size or quality. Fertigation at 160 kg N ha^–1 caused higher yields than when the same amount of fertilizer was broadcast. At the high application rate, no differences between modes of application were found.This study was initiated by A. Bar-Akiva, who died suddenly early in 1986. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No 2104-E, 1987 series.(deceased)     

Balanced pasture fertilization in the Basque Country: I. Phosphorus and potassium budgets on dairy farms

Dairy farming is the main agricultural activity of the Basque Country. A dairy farm is characterized as a system with soils and crops, forage, cattle and manure as main components, and in such a system, nutrient cycling is very important to maintain soil fertility and optimize forage production. To quantify nutrient transfers in the cycle, a simple system was developed and has been applied to seventeen farms to examine its ability to achieve a balanced P and K fertilization. These farms have provided data on inputs (fertilizer, feeds, concentrates), pasture and manure management, and outputs (milk production), and soil samples have been taken from farm pastures. Phosphorus and K in excreta and uneaten pasture is used with a relatively high efficiency as suggested by the relatively high efficiency of P and K utilization by the pasture that usually ranges from 70 to 90%. Concentrate feeding (3000 kg cow^–1 yr^–1) represents one of the main P and K inputs in Basque Country dairy farms, averaging 26 and 66 kg ha^–1, respectively. Besides, release of K in the soil through slow liberation from non-exchangeable sites was estimated as 30 kg ha^–1. Thus, a high efficiency in excreta recycling would diminish substantially P and K mineral fertilizer needs. Farm nutrient budgets appear to be a convenient tool for determining nutrient shortages and surpluses at farm level, and thus they are considered as a first step to support a better management of maintenance fertilization of permanent pastures.     

Studies on the substitution of inorganic fertilizers with organic manure and their effect on soil fertility in rice—wheat rotation

Field studies on the substitution of N and P fertilizers with farm yard manure (FYM) and their effect on the fertility status of a loamy sand soil in rice—wheat rotation are reported. The treatments consisted of application of 12 t FYM ha^–1 in combination with graded levels of N and P. Application of fertilizer N, FYM and their different combinations increased the rice yield significantly. There was no significant response to P application. The magnitude of response to the application of 12 t FYM and its combined use with each of 40 kg and 80 kg N ha^–1 was 0.7, 2.2 and 3.9 t ha^–1 respectively. Application of 120 kg N ha^–1 alone increased the yield by 3.9 t ha^–1, and was comparable to rice yield obtained with 80 kg N and 12 t FYM ha^–1. This indicated that 12 t FYM ha^–1 could be substituted for 40 kg N as inorganic fertilizer in rice. In addition FYM gave residual effects equivalent to 30 kg N and 13.1 kg P ha^–1 in the succeeding wheat. The effect of single or combined use of inorganic fertilizers and FYM was significantly reflected in the build up of available N, P, K and organic carbon contents of the soil. The relationship for predicting rice yield and nutrients uptake were also computed and are discussed.     

Africa — how much fertilizer needed: Case study of Sierra Leone

The quantities of nitrogen, phosphorus and potassium supplied by an average African soil cleared from bush fallow, assuming no losses, were approximated. Values ranged from 23 to 120 Kg N ha^–1, 1.8 to 12 Kg P ha^–1, 47 to 187 Kg K ha^–1, depending on type of fallow, length of fallow, drainage and extent of depletion of native supplies. Additional amounts of 4 to 5 Kg N ha^–1, 4 to 6 Kg P ha^–1 and 14 to 20 Kg K ha^–1 are obtained from the ash.Using crop nutrient removal data and approximate efficiencies of native and fertilizer N, P and K, fertilizer requirements at the reconnaissance level were estimated for selected target yields. For newly cleared uplands at cropping/fallow ratio of 2:7, N fertilizer requirements for cassava (30 t ha^–1), maize (4 t ha^–1), and sweet potato (16 t ha^–1), were 138, 98, 42 kg ha^–1 respectively. Wetland rice (4 t ha^–1) required 55 kg N ha^–1. Corresponding P fertilizer requirements for cassava, maize, sweet potato, upland rice (1.5 t ha^–1) and ground-nut (1 t ha^–1) were 190, 80, 30, 30 and 16 kg P ha^–1 respectively. Wetland rice required 83 kg P ha^–1. Substantial residual values of applied P are to be expected. Cassava required 60 kg ha^–1 of K on newly cleared land. In soils of lowered nutrient status higher N, P, and K fertilizer requirements were indicated for all crops.Land use data from Sierra Leone were used to illustrate how the total quantities of N, P and K fertilizers in a country in the forest zone of Africa can be approximated. Fertilizer needs in Sierra Leone were in decreasing order P > N K. N, P and K requirements were estimated to be 10,000 t, 20,000 t and 4,000 t respectively. The nutrient balance sheet method described in this paper is a useful tool to estimate the order of magnitude of fertilizer requirement at selected target yields for countries in Africa.     

Response of lowland rice and common bean grown in rotation to soil fertility levels on a Varzea soil

Brazil has approximately 30 million hectares of lowland areas, known locally as Varzea, but very little is known about their fertility and crop production potential. A field experiment was conducted for three consecutive years to evaluate response of lowland rice (Oryza sativa L.) grown in rotation with common bean (Phaseolus vulgaris L.) on a Varzea (low, Humic Gley) soil. Rice was grown at low (no fertilizer), medium (100 kg N ha^–1, 44 kg P ha^–1, 50 kg K ha^–1, 40 kg FTE-BR 12 ha^–1), and high (200 kg N ha^–1, 88 kg P ha^–1, 100 kg K ha^–1, 80 kg FTE-BR 12 ha^–1 fritted trace element-Brazil 12 as a source of micronutrients) soil fertility levels. Green manure with medium fertility was also included as an additional treatment. Average dry matter and grain yields of rice and common bean were significantly (P < 0.01) increased with increasing fertilization. Across the three years, rice yield was 4327 kg ha^–1 at low fertility, 5523 kg ha^–1 at medium fertility, 5465 kg ha^–1 at high fertility, and 6332 kg ha^–1 at medium fertility with green manure treatment. Similarly, average common bean yield was 294 kg ha^–1 at low soil fertility, 663 kg ha^–1 at medium soil fertility, 851 kg ha^–1 at high fertility, and 823 kg ha^–1 at medium fertility with green manure treatment. Significant differences in nutrient uptake in bean were observed for fertility, year, and their interactions; however, these factors were invariably nonsignificant in rice.     

Fertilization of tropical rice: A case study on Bangkok plain

This study consisted of a survey on the nutritional status of rice plants in relation to nutrient application and yield in 70 farmers' fields in four provinces of Bangkok plain during the 1977 wet season. In addition a series of fertilizer experiments were carried out on rice experimental stations in the same provinces to study yield response to N and P fertilization and to develop a fertilizer recommendation system based on plant analysis.The average grain yield in the survey was 3.2 t ha^–1 and the early (high yielding varieties), medium (local) and late maturity (local) types yielded 3.3, 2.8 and 3.0 t ha^–1, respectively. The average amount of fertilizers applied to these maturity types were 33, 15 and 7 kg N ha^–1 and 15, 8 and 6 kg P ha^–1, respectively. Regression analysis indicated only a slight correlation between yield and any level of fertilizer application. On experimental stations yields over 6 t ha^–1 were obtained with applications of N over 100 kg ha^–1 and P over 22 kg ha^–1. Evaluation of nutritional status of plants based on plant analysis showed that in all provinces there were strong and widespread nutrient deficiences primarily of N and secondarily of P, and possibly of some other nutrients. Fertilizer application based on plant analysis gave high yield responses. It was concluded that the major constraints of yield on Bangkok plain are too low fertilizer application especially of N, and unbalanced fertilization of N and P.