István Sisák

Phosphorus flows and use efficiencies in production and consumption of wheat, rice, and maize in China

Increasing fertilizer phosphorus (P) application in agriculture has greatly contributed to the increase of crop yields during the last decades in China but it has also increased P flows in food production and consumption. The relationship between P use efficiency and P flow is not well quantified at national level. In present paper we report on P flows and P use efficiencies in rice, wheat, and maize production in China using the NUFER model. Conservation strategies for P utilization and the impact of these strategies on P use efficiency have been evaluated. Total amounts of P input to wheat, rice, and maize fields were 1095, 1240, and 1128 Gg, respectively, in China, approximately 80% of which was in chemical fertilizers. The accumulation of P annually in the fields of wheat, rice, and maize was 29.4, 13.6, and 21.3 kg ha(-1), respectively. Phosphorus recovered in the food products of wheat, rice, and maize accounted for only 12.5%, 13.5%, and 3.8% of the total P input, or 3.2%, 2.6%, and 0.9% of the applied fertilizer P, respectively. The present study shows that optimizing phosphorus flows and decreasing phosphorus losses in crop production and utilization through improved nutrient management must be considered as an important issue in the development of agriculture in China.

WATER-SOLUBLE P AS AFFECTED BY FRESHLY APPLIED AND RESIDUAL P AND P FRACTIONS OF SOIL

Water-soluble P content of soils is not regularly investigated in Hungary, but we need to understand its dynamics as influenced by previous and recent fertilization in order to predict dissolved P load from agricultural areas at the watershed of Lake Balaton, Hungary. Two sites were selected from a long-term fertilization trial representing characteristic soils around the lake. Soil samples from plots with different P fertilization were investigated in an incubation experiment in which fresh P was applied in a single dose or split and water-soluble P was measured. Available P, water-soluble P and modified Hedley P fractions were determined on the original samples. The soil at Keszthely has lower total P content, but higher rates of available (ammonium-lactate-soluble) P and mineralizable Hedley P fractions than the soil at Bicsérd. Because of these “light” fractions, the incubation produced temporarily high-water soluble P content even in the unfertilized soil. Initial quick fixation of freshly applied P has been higher in the soil at Bicsérd (65–75%) than at Keszthely (55–70%). Further, the soil at Bicsérd has additional capacity to fix P (approximately 1% per week) and that property was only slightly influenced by the fertilization history. However, only the soil from unfertilized plot at Keszthely has shown this ability. Soils like we have collected at Keszthely pose higher risk to pollute Lake Balaton with P than soils from Bicsérd. Regulations in order to reduce P load should be focused more on the previous soils.

Assessment of Short‐Term and Long‐Term Phosphorus Dynamics in Four Soils in the Watershed of Lake Balaton

Each horizon of four soils was sampled in the watershed of Lake Balaton, Hungary. The soils have been under natural vegetation, and they represent a litho‐sequence between sand and silty clay loam. Samples from the upper three horizons were analyzed with the phosphorus (P) fractionation method of Hedley, White, and Nye (1982) modified by Sharpley. The same samples were used for an incubation experiment according to the method of Waugh and Fitts (1966). Treatments were the following: control (no P added), 100 mg kg−1 P, and 50 mg kg−1 P at the beginning of the incubation, and 10 × 5 mg kg−1 P and 10 × 10 mg kg−1 P as weekly treatments. Incubated soils were analyzed for water‐soluble P after weeks 1, 2, 4, and 10. Decrease in water‐soluble P level was described as an exponential curve, linear equation, or as a constant. Prompt fixation of the P varied between 43 and 88%, slow fixation varied between 0 and 34%, and the percentage of the P remaining water‐soluble for a longer time varied between 3 and 30% for the different soils. Organic matter and organic P forms strongly contributed to the high level of water soluble P.

Application of Digital Soil Mapping Techniques to Refine Soil Map of Baringo District, Rift Valley Province, Kenya

Detailed and precise description of soil information is important for both developed and developing countries. Africa is highlighted as the most soil data-challenged land surface in the world and it is the area most in need of improved soil information. Our objective was to compile a detailed soilscape class map for the Baringo area in Kenya by using auxiliary variables (digital elevation model, satellite images, and climate maps). In the first step, we extracted landscape–soil relationships based on soil classes from KENSOTER database. We applied soil spatial prediction based on nine standardized predictor variables: x and y coordinates of the sampling points, two principal components from the seven bands of satellite images explaining 83 % of the total variance, three principal components from the 42 variables of climate database explaining 96 % of the total variance, and slope and elevation from digital elevation model. In the first phase (rule extraction), explanatory and target maps were sampled at 999 random points. In the next phase (prediction), 14 major combined soil classes were predicted based on randomly placed 10,000 points. Distances between point values and centroids of the soil classes were calculated, and the closest were scored with 1 and the others with 0. The scores were kriged to obtain continuous probability estimates. Final map was derived based upon the highest probabilities. Our approach had the clear advantage that real-world variability was represented by stacked layers of smooth probability estimates for the soil classes instead of blurred outputs where neighboring pixels can be differently allocated. Our method is suitable to update old and less detailed soil maps or predict new ones for similar environments in the presence of fine resolution auxiliary information. Validity of the prediction should be appropriately tested.