Simple models and concepts as tools for the study of sustained soil productivity in long-term experiments. II. Crop nutrient equivalents, balanced supplies of available nutrients, and NPK triangles
Janssen, B.H. - \ 2011
Plant and Soil 339 (2011)1-2. - ISSN 0032-079X - p. 17 - 33.
organic-matter - rice - fertility - phosphorus - nitrogen - vietnam - quefts - delta
Two NPK factorial trials, one in Vietnam and one in The Netherlands were (re-)analyzed to find causes of success or failure with regard to sustained soil productivity, using the concept of crop nutrient equivalents (CNE). A (k)CNE is the quantity of a nutrient that, under conditions of balanced nutrition, has the same effect on yield as 1 (k)g of nitrogen. The percentages the nutrients take in the (k)CNE sum of N, P and K are plotted along the sides of a triangle. Soil, crop and input NPK are indicated in the triangle. Balanced crop NPK is found in the centre of the triangle, and required NPK inputs are on a straight line in the extension of the line trough the point of soil NPK and the centre. Experimental inputs were compared with inputs required for balanced NPK. In Vietnam, responses to P and soil available N:P:K pointed to severe shortage of P. Rice yields increased over time in dry but not in wet seasons. The lower yields in wet seasons were ascribed to insufficiently long periods between the dry and the next wet seasons for replenishment of labile soil P. In the Netherlands, four crops were grown in rotation on a former sea bottom. Only N had a strong effect on yield. Soil available N:P:K revealed low N, very high K and medium P. Recovery of fertilizer N was high because of capillary rise of groundwater and absence of leaching. In both trials, first-season chemical crop analysis would directly have detected disproportions of soil available N, P and K. This knowledge could have improved the experimental designs, optimized nutrient use efficiency and minimized losses of N and K to the environment
Mineral fertilizer response and nutrient use efficiencies of East African highland banana (Musa spp., AAA-EAHB, cv. Kisansa)
Nyombi, K. ; Asten, P.J.A. van; Corbeels, M. ; Taulya, G. ; Leffelaar, P.A. ; Giller, K.E. - \ 2010
Field Crops Research 117 (2010)1. - ISSN 0378-4290 - p. 38 - 50.
irrigated lowland rice - farming systems - soil fertility - uganda - yield - management - nitrogen - weevil - quefts - plant
Poor yields of East African highland bananas (Musa spp., AAA-EAHB) on smallholder farms have often been attributed to problems of poor soil fertility. We measured the effects of mineral fertilizers on crop performance at two sites over two to three crop cycles; Kawanda in central Uganda and Ntungamo in southwest Uganda. Fertilizers were applied at rates of 0N-50P-600K, 150N-50P-600K, 400N-0P-600K, 400N-50P-0K, 400N-50P-250K and 400N-50P-600K kg ha_1 yr_1. In addition 60Mg-6Zn-0.5Mo- 1B kg ha_1 yr_1 was applied to all treatments, with the exception of the control plots which received no fertilizer. Fresh bunchmass and yield increased with successive cycles. Yield increases above the control ranged from 3.1 to 6.2 kg bunch_1 (average bunch weight for all treatments 11.5 kg bunch_1) and 2.2- 11.2Mg ha_1 yr_1 (average yield for all treatments 15.8 Mg ha_1 yr_1) at Kawanda, compared with 12.4- 16.0 kg bunch_1 (average bunch weight for all treatments 14.7 kg bunch_1) and 7.0-29.5 Mg ha_1 yr_1 (average yield for all treatments 17.9 Mg ha_1 yr_1) at Ntungamo. The limiting nutrients at both sites were in the orderK > P > N. Potassium,Nand P foliar nutrient mass fractions were below previously established Diagnosis and Recommendation Integrated System (DRIS) norms, with the smallest K mass fractions observed in the best yielding plots at Ntungamo. Total nutrient uptakes (K > N > P) were higher at Ntungamo as compared with Kawanda, probably due to better soil moisture availability and root exploration of the soil. AverageN, P andKconversion efficiencies for twocrop cycles at both sitesamounted to 49.2 kg finger DM kg_1 N, 587 kg finger DM kg_1 P and 10.8 kg finger DM kg_1 K. Calibration results of the model QUEFTS using data fromNtungamo were reasonable (R2 = 0.57, RMSE = 648 kg ha_1). Using the measured soil chemical properties and yield data froman experiment atMbarara in southwest Uganda, the calibrated QUEFTSmodel predicted yields well (R2 = 0.68, RMSE = 562 kg ha_1). We conclude that banana yields can be increased by use of mineral fertilizers, but fertilizer recovery efficiencies need to improve substantially before promoting wide-scale adoption
Yield gaps, nutrient use efficiencies and response to fertilisers by maize across heterogeneous smallholder farms of western Kenya
Tittonell, P.A. ; Vanlauwe, B. ; Corbeels, M. ; Giller, K.E. - \ 2008
Plant and Soil 313 (2008)1-2. - ISSN 0032-079X - p. 19 - 37.
soil fertility - quantitative-evaluation - resource-allocation - crop productivity - management - variability - gradients - quefts - rice
The need to promote fertiliser use by African smallholder farmers to counteract the current decline in per capita food production is widely recognised. But soil heterogeneity results in variable responses of crops to fertilisers within single farms. We used existing databases on maize production under farmer (F-M) and researcher management (R-M) to analyse the effect of soil heterogeneity on the different components of nutrient use efficiency by maize growing on smallholder farms in western Kenya: nutrient availability, capture and conversion efficiencies and crop biomass partitioning. Subsequently, we used the simple model QUEFTS to calculate nutrient recovery efficiencies from the R-M plots and to calculate attainable yields with and without fertilisers based on measured soil properties across heterogeneous farms. The yield gap of maize between F-M and R-M varied from 0.5 to 3 t grain ha-1 season-1 across field types and localities. Poor fields under R-M yielded better than F-M, even without fertilisers. Such differences, of up to 1.1 t ha-1 greater yields under R-M conditions are attributable to improved agronomic management and germplasm. The relative response of maize to N-P-K fertilisers tended to decrease with increasing soil quality (soil C and extractable P), from a maximum of 4.4-fold to -0.5- fold relative to the control. Soil heterogeneity affected resource use efficiencies mainly through effects on the efficiency of resource capture. Apparent recovery efficiencies varied between 0 and 70% for N, 0 and 15% for P, and 0 to 52% for K. Resource conversion efficiencies were less variable across fields and localities, with average values of 97 kg DM kg-1 N, 558 kg DM kg-1 P and 111 kg DM kg-1 K taken up. Using measured soil chemical properties QUEFTS over-estimated observed yields under F-M, indicating that variable crop performance within and across farms cannot be ascribed solely to soil nutrient availability. For the R-M plots QUEFTS predicted positive crop responses to application of 30 kg P ha-1 and 30 kg P ha-1 + 90 kg N ha-1 for a wide range of soil qualities, indicating that there is room to improve current crop productivity through fertiliser use. To ensure their efficient use in sub-Saharan Africa mineral fertilisers should be: (1) targeted to specific niches of soil fertility within heterogeneous farms; and (2) go hand-in-hand with the implementation of agronomic measures to improve their capture and utilisation.
Soil fertility evaluation and management by smallholder farmer communities in northern Tanzania
Mowo, J.G. ; Janssen, B.H. ; Oenema, O. ; German, L.A. ; Mrema, J.P. ; Shemdoe, R.S. - \ 2006
Agriculture, Ecosystems and Environment 116 (2006)1-2. - ISSN 0167-8809 - p. 47 - 59.
systems - africa - quefts
The objective of this paper is to compare soil fertility evaluation based on experience and knowledge of smallholder farmer communities with the evaluation by scientists based on soil analysis and model calculations. The role of the smallholder farmer community in soil fertility evaluation and management was examined from two `research for development¿ projects in northern Tanzania. These are the African Highlands Initiative (AHI) and the Soil Water Management Research Group (SWMRG). Participatory approaches were applied by both projects. Farmers¿ experience and knowledge of local indicators of soil quality were used in identifying soil fertility constraints and in generating resource flow maps. The farmers¿ evaluation of soil fertility was compared with soil analytical data and with calculations of maize yields by the model QUEFTS. Farmers¿ indigenous knowledge in soil fertility evaluation mostly agreed with laboratory analysis and model calculations by QUEFTS. Model calculations identified potassium as the most limiting nutrient in the highlands in northeastern Tanzania for yields less than 3 t ha¿1 and phosphorus for yields higher than 4 t ha¿1. In Maswa (Lake Victoria Basin) nitrogen was most limiting. Given that farmers¿ evaluation of soil fertility is relative to what they see around them, there is a need to verify their observations, but also the interpretation of laboratory data by models like QUEFTS requires continuous and critical validation. Both projects have shown that there is scope to reverse the trends of declining soil fertility in smallholder farms in northern Tanzania. Essential was that the interaction with scientists has built confidence in the farmers because their knowledge in addressing soil fertility constraints was recognized.
Analysis of the effects of rotational woodlots on the nutrition and yield of maize following trees in western Tanzania
Nyadzi, G.I. ; Janssen, B.H. ; Oenema, O. - \ 2006
Agriculture, Ecosystems and Environment 116 (2006)1-2. - ISSN 0167-8809 - p. 93 - 103.
shifting cultivation - soil fertility - nitrogen - fallow - agroforestry - management - vegetation - nutrients - africa - quefts
Farmers in western Tanzania are establishing rotations of trees and crops in an attempt to overcome the shortage of wood, reverse deforestation of natural forests and improve soil fertility for food security enhancement. We compared fallows of Acacia crassicarpa, A. julifera, A. leptocarpa, Leucaena pallida and Senna siamea, with traditional bush fallow and continuous sole maize (Zea mays L.). The aim of the study was to analyze the effectiveness of fallow types in terms of N, P and K use by maize. Trees were intercropped with maize for the first 3 years. After 5 years, trees were harvested, wood components were removed, and leaves, twigs and grasses were incorporated into the soil. Factorial N, P, K trials were carried out with maize grown after the fallow types. Parameters studied were grain yield, uptake of N, P and K, and nutrient use efficiency. The effects of fertiliser were much stronger than the effects of fallow types. There was no clear effect of tree fallows on nutrient use efficiency of the following maize. Non-fertilized maize yielded more after acacia than after the other trees and natural fallow. Upon fertiliser application the influences of fallow types became weaker. Fertiliser N improved maize yields more than fertiliser P, and there was a positive NP interaction. Fertilizer K did not bring about clear effects. N recovery efficiency was improved by the application of P and vice versa. When fertilisers were applied, differences in average maize grain yields between tree fallows and natural fallow varied from 300 kg ha¿1 (for A. julifera) to minus 250 kg ha¿1 (for S. siamea). A yield increase of 300 kg maize grain could also be obtained by application of 10 kg fertiliser N or 8 kg fertiliser P. The best fallow type for soil fertility improvement was Acacia julifera suggesting that this acacia is mining the soil for P and K. In conclusion, benefits of rotational woodlots seem larger in terms of wood production than in terms of soil fertility restoration
Ideal and saturated soil fertility as bench marks in nutrient management; 2 interpretation of chemical soil tests in relation to ideal and saturated soil fertility
Janssen, B.H. ; Willigen, P. de - \ 2006
Agriculture, Ecosystems and Environment 116 (2006)1-2. - ISSN 0167-8809 - p. 147 - 155.
In a previous paper (Part 1), the ideal soil fertility and the saturated soil fertility were expressed on a relative scale, called soil fertility grade (SFG). In the current paper (Part 11), the relation between SFG and soil test values is discussed. The required uptake of nutrients from the soil is translated into soil organic carbon, P-Olsen, exchangeable K, and pH (H2O) using relationships developed for a model on Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). Target soil test values were calculated for target yields between 2 and 10 Mg ha(-1) season(-1). The required uptake of soil nitrogen is a function of target yield, and it is linearly related to soil organic carbon. Results of the calculations indicate that when target yields are less than 7-8 Mg ha(-1), stover must be incorporated to maintain soil organic carbon above the critical level of 6 g kg(-1). When yields are below 2 Mg ha(-1), also organic sources from outside the field have to be brought in. The interpretation of chemical soil test values according to the ISF-SSF framework may be rather difficult in practice, as is demonstrated with eight African soils. The major reason is that the soil supplies of N, P and K seldom are in the same proportions as in ISF-SSF. For none of the used African soils replacement input or a neutral nutrient budget would be the best management option. Replacement input will often lead to inefficient use and even waste of nutrients. Optimum soil test values depend on target yield, but the ratios of soil test values do not depend on target yield. Therefore key values were established for the ratio of soil organic carbon to P-Olsen and for the ratio of soil organic carbon to the square root of exchangeable K. Based on these key values, a new classification scheme with recommended input ratios is presented. The scheme has six classes for N and P ratios, and seven classes for N and K ratios. (c) 2006 Elsevier B.V. All rights reserved.
Nutrient management in tropical agroecosystems
Oenema, O. ; Janssen, B.H. ; Smaling, E.M.A. ; Hoffland, E. - \ 2006
Agriculture, Ecosystems and Environment 116 (2006)1. - ISSN 0167-8809 - p. 1 - 3.
soil fertility - agriculture - quefts
Some theoretical considerations on evaluating wastewater as a source of N, P and K for crops
Janssen, B.H. ; Boesveld, H. ; Rodriquez, M.J. - \ 2005
Irrigation and Drainage 54 (2005)S1. - ISSN 1531-0353 - p. S35 - S47.
fertility - quefts
The value of wastewater as a source of nutrients for crops depends on concentrations of nutrients, type of crop grown, and soil fertility level. Nutrients are immediately available to the crop, as long as they remain dissolved in wastewater and soil solution, but may be rendered less available by several soil processes. Some processes result in permanent loss (leaching, volatilization and erosion) and others in nutrient accumulation in the soil (microbiological immobilization, adsorption, precipitation). Hence, the proportions of nutrients taken up by plants are different than the proportions of nutrients applied via wastewater or fertilizers. Because soils and wastewater seldom contain nutrients in optimum ratios, a set of guidelines is presented to optimize wastewater irrigation. Some information on nutrients in plants, nutrient sources and soils is required to be able to apply the guidelines. Part of that information may not be available and has to be found in trials. Evaluation of wastewater as a nutrient source is not possible by simple comparisons of sources of wastewater and fertilizers, because effects of N, P and K in wastewater are confounded. A plea is made for factorial designs with combinations of wastewater and straight fertilizers