Jeremy Landon Darilek

Major nutrient balances in small-scale vegetable farming systems in peri-urban areas in China

Balances of major nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in small-scale farming systems are of critical importance to nutrient management and sustainable agricultural development. Mass balances of N, P, and K and some of their influencing factors were studied for two years from July 2003 to July 2005 on small-scale vegetable-farming systems in two contrasting peri-urban areas (Nanjing and Wuxi) of the Yangtze river delta region of China. This balance approach considered organic fertilizer inputs (cow manure, pig manure, and human biosolids), inorganic fertilizer inputs (urea, composite fertilizer, and phosphates), irrigation water, and atmospheric deposition; and considered outputs by vegetables. Input via organic fertilizers was significant for all element balances in the Nanjing area. Inorganic and organic fertilizer, particularly inorganic fertilizer, contributed major nutrient inputs to the system in the Wuxi area. Compared with nutrient output by vegetables, there were significant surpluses of N and P on two vegetable farm systems. Furthermore, N surplus in the Nanjing area was higher than that in the Wuxi area with an inverse relationship to P surplus. In contrast, the general trend of K balances was negative on both sites; hence, the nutrient use efficiency was significantly lower for N and P than K. The nutrient imbalance may be attributed to the differences between fertilizer types and management modes driven by social economic status differences among farmer households. The large N and P net excess creates an environmental threat because of potential losses to ground or surface waters, whereas negative K balance creates soil fertility risks. The results highlight researchers’ and farmers’ need to develop rational fertilization technology to optimize nutrient management on vegetable farmlands to promote sustainable agricultural development in peri-urban areas.

Effect of Land Use Conversion from Rice Paddies to Vegetable Fields on Soil Phosphorus Fractions

Abstract Excess phosphorus (P) from agricultural soils contributes to eutrophication in water bodies. Samples ( n = 60) were taken from sites where rice paddies have been converted to vegetable fields for 0, 20 years and analyzed for five inorganic P (P i ) fractions, three organic P (P o ) fractions, and several soil parameters to investigate how land use conversion affects P i and P o fractions in a peri-urban area of China with soils characteristic of many agricultural areas of Asia. Significant increases of 33, 281, 293, and 438 mg kg −1 were found for soluble and loosely bound P i (SL-P i ), aluminum-bound P i (Al-P i ), calcium-bound P i (Ca-P i ), and iron-bound P i (Fe-P i ), respectively, after conversion from rice paddies to vegetable fields. Most of the increase in P i was in the form of Fe-P i , which increased from 8% of total P (TP) on paddy soil to 31% on the soil with > 20-year vegetable cultivation, followed by Al-P i , which increased from 2% to 19% of TP. For P o fractions, there was no significant change in P concentrations. The conversion of land use from paddy fields to high intensity vegetable fields was causing significant changes in soil P fractions. Management practices were causing a buildup of soil P, primarily in the Fe-P i fraction, followed by Ca-P i and Al-P i fractions. If current trends continue, a 30%–70% increase in TP could be expected in the next 20 years. Farmers in the area should reduce P application and use to maximize P uptake.

Spectral data mining for rapid measurement of organic matter in unsieved moist compost

Fifty-five compost samples were collected and scanned as received by visible and near-IR (VisNIR, 350-2500 nm) diffuse reflectance spectroscopy. The raw reflectance and first-derivative spectra were used to predict log(10)-transformed organic matter (OM) using partial least squares (PLS) regression, penalized spline regression (PSR), and boosted regression trees (BRTs). Incorporating compost pH, moisture percentage, and electrical conductivity as auxiliary predictors along with reflectance, both PLS and PSR models showed comparable cross-validation r(2) and validation root-mean-square deviation (RMSD). The BRT-reflectance model exhibited best predictability (residual prediction deviation=1.61, cross-validation r(2)=0.65, and RMSD=0.09 log(10)%). These results proved that the VisNIR-BRT model, along with easy-to-measure auxiliary variables, has the potential to quantify compost OM with reasonable accuracy.

Effect of Moisture Conditions in Rice Paddies on Phosphorus Fractionation in Agriculture Soils of Rapidly Developing Regions of China

Moisture conditions in rice paddies play an important role in phosphorus (P) cycling and may affect P loss to nearby water bodies. This study seeks to identify factors that contribute to P-fraction transformations in flooded rice paddies on Cambosols and Anthrosols using Zhangjiagang County of the Yangtze River delta region, China, as a study area. Soil samples preserved under flooded and aerobic conditions (n = 60) were collected, and P fractions and soil properties were measured. Under flooded conditions, soluble and loosely bound P significantly decreased to half of aerobic levels, aluminum/iron-bound P increased by 66%, and organic-bound P decreased by 64%. Soil organic matter, cation exchange capacity, pH, and active iron were well correlated with soil P fractions under both moisture conditions across two soil orders despite a disparity in soil properties. Further research goals that would aid in specific fertilizer recommendations and management strategies are identified.

Effect of Drying on Heavy Metal Fraction Distribution in Rice Paddy Soil

An understanding of how redox conditions affect soil heavy metal fractions in rice paddies is important due to its implications for heavy metal mobility and plant uptake. Rice paddy soil samples routinely undergo oxidation prior to heavy metal analysis. Fraction distribution of Cu, Pb, Ni, and Cd from paddy soil with a wide pH range was investigated. Samples were both dried according to standard protocols and also preserved under anaerobic conditions through the sampling and analysis process and heavy metals were then sequentially extracted for the exchangeable and carbonate bound fraction (acid soluble fraction), iron and manganese oxide bound fraction (reducible fraction), organic bound fraction (oxidizable fraction), and residual fraction. Fractions were affected by redox conditions across all pH ranges. Drying decreased reducible fraction of all heavy metals. Curesidual fraction, Pboxidizable fraction, Cdresidual fraction, and Niresidual fraction increased by 25%, 33%, 35%, and >60%, respectively. Pbresidual fraction, Niacid soluble fraction, and Cdoxidizable fraction decreased 33%, 25%, and 15%, respectively. Drying paddy soil prior to heavy metal analysis overestimated Pb and underestimated Cu, Ni, and Cd. In future studies, samples should be stored after injecting N2 gas to maintain the redox potential of soil prior to heavy metal analysis, and investigate the correlation between heavy metal fraction distribution under field conditions and air-dried samples.

Impacts of agricultural land management on soil quality after 24 years: a case study in Zhangjiagang County, China

Agricultural soil quality is drastically affected in modern societies by human activities. This paper evaluates the anthropogenic influence on agricultural soil quality variation in Zhangjiagang County, China from 1980 to 2004 based on indicator selection and standard scoring function (SSF). The results indicated that after 24 years of anthropogenic influence, soil organic matter (SOM), total nitrogen (TN), cation exchange capacity (CEC) and available phosphorus (av-P) increased significantly and total phosphorus (TP) and available potassium (av-K) decreased slightly. Soil pH increased slightly for Cambosols and decreased significantly for Anthrosols. According to analysis of an integrated soil quality index (SQI), both Cambosol and Anthrosol soil quality have improved. For Cambosols, class II and III soil increased by 4.4% and 5.7%, respectively; class IV soil decreased by 10.1%. For Anthrosols, Class II soil increased in area by 74.6%; class III soil decreased to 8.1%. ΔSQI showed the same variation trend for Cambosols and Anthrosols. Among the total selected indicators, SOM was the main driving factor and pH was the limiting factor of soil quality base on path analysis. Current anthropogenic influence on soil quality variation was double-edged, stakeholders must pay close attention to this tendency and closely monitor not only agricultural production yields but also crop safety, long-term soil quality and environmental quality indicators, and timely direct agricultural and economic activities to achieve the best economic performance while protecting natural resources.