Equations for Calculating N-Fertilizer Rates for Khaw Dauk Mali-105 Rice from Soil Analysis

ABSTRACT Comparisons were made to assess the reliability of 10 chemical methods for evaluating the availability of N in soils to Khaw Dauk Mali-105 rice and for calculating rates of N-fertilizer for rice. The methods studied were: (1) measuring soil organic matter by Walkley and Black's method, (2) measuring total soil N by Kjeldahl's method, (3) extracting soil N with acidified K 2 Cr 2 O 7 solution, (4) extracting soil N with basified KMnO 4 solution, (5) extracting soil N with acidified KMnO 4 solution, (6) extracting soil N with solution of CaCl 2 and K 2 SO 4 , (7) extracting soil nitrate according to Only the indices from the methods (9) and (10) gave significant relationships (at 95% confidence level) with the relative paddy yields, with Method (10) showing slight superiority over the method (9). None of the chemical methods gave significant relationships among the index and the relative dry matter and amount of N in plants. The equations for calculating rates of N fertilizer required for desired paddy yields were: (a) log (100 -y) = 2 -0.0226b -0.0374x for method (9) and (b) log (100-y) = 2 -0.00533b -0.0584x for method (10); where y is the desired grain yield (as % of maximum yield), b availability index value for soil N (in ppm N), and x rate of fertilizer N required (as kg N/rai, 6.25 rais = 1 ha). Both of the two equations gave highly significant correlation between the actual paddy yields and the predicted paddy yields. However, method (10) was more recommended than method (9) for it was more reliable than method (9) in prediction of the yield

Rainfed lowland rice breeding strategies for Northeast Thailand. II. Comparison of intrastation and interstation selection

There has been limited progress for grain yield of rainfed lowland rice in Northeast Thailand since the 1960s. The current breeding strategy operates as a series of six semi-independent pedigree programs, each at a different site. Each program has three major phases of selection: (1) intrastation selection, (2) interstation selection, and (3) on-farm selection. The expected selection response for grain yield based on intrastation and interstation selection was examined using a combination of experimental results, prediction equation theory and computer simulation. Experiments were conducted to estimate genetic, genotype-by-environment interaction and error components of variance as inputs for estimation of heritability on a number of bases and also to obtain estimates of realised response from selection. Estimates of line-mean heritability for grain yield based on intrastation evaluation of lines suggest that it is low, ranging from 0.07 to 0.13, for one to four replicates, respectively, at a single site in 1 year. Line-mean heritability for intrastation evaluation based on two replicates and 2 years was estimated to be 0.18, only slightly higher than for 1 year and four replicates. In contrast, estimates of line-mean heritability for interstation testing were intermediate, e.g. 0.32 and 0.48 for two replicates at six sites for 1 year and 2 years, respectively. Estimates of realised selection response for grain yield from intrastation and interstation selection were consistent with the low to intermediate heritability estimates. Interstation selection, based on two replicates, eight sites and 1 year, showed an advantage over intrastation selection, based on two replicates and 1 year, when response was measured as the mean yield of selected lines across environments. The present breeding strategy applies intense selection during the intrastation phase of the breeding programs. Consequently, only a small number of lines (ca. 70 lines from all stations) are advanced from the intrastation selection phase to the interstation selection phase. Therefore, for most lines generated by the breeding program there is limited opportunity to evaluate the contributions of broad and specific adaptation to higher yield. The presence of large genotype-by-environment interactions, in combination with limited yield evaluation of lines in multi-environment trials (until the final stages of testing), is identified as a major factor contributing to the slow genetic progress for grain yield. The proposed breeding strategy replaces the intrastation testing phase with a coordinated early generation interstation testing based on F bulks. Evaluation of the proposed breeding strategy by computer simulation demonstrated an advantage from modifying the current breeding strategy to give greater emphasis to interstation selection in place of intrastation selection

Behavior of chlorpyrifos and its major metabolite TCP (3,5,6-trichloro-2-pyridinol) in agricultural soils amended with drinking water treatment residuals

Purpose: Chlorpyrifos can be effectively adsorbed by drinking water treatment residuals (WTR), ubiquitous and non-hazardous by-products of potable water production. The major metabolite 3,5,6-trichloro-2-pyridinol (TCP) was found to be much more mobile and toxic than its parent chlorpyrifos. To assess the feasibility of WTR amendment for attenuation of chlorpyrifos and TCP pollution, the sorption/desorption and degradation behavior of chlorpyrifos and TCP in WTR-amended agricultural soils was examined in the present study. Materials and methods: Two representative agricultural soils were sampled from southern and northern China, respectively. The soils were amended with WTR at the rates of 0, 2, 5, and 10 % (w/w). Batch sorption/desorption test were applied to investigate the sorption/desorption characteristics of chlorpyrifos and TCP in WTR-amended soils. The influence of WTR amendment on chlorpyrifos degradation and TCP formation was evaluated using the incubation test, and its effect on the soil bacterial abundance was further studied through DNA extraction and PCR amplification. Results and discussion: Results showed that WTR amendment (0–10 %, w/w) significantly enhanced the retention capacity of chlorpyrifos and TCP in both soils examined (P &lt; 0.05). Fractionation analyses further demonstrated that the bioavailability of chlorpyrifos was considerably reduced by WTR amendment, resulting in a decreased chlorpyrifos degradation rate. The WTR amendment also significantly reduced the mobility of TCP formed in chlorpyrifos-contaminated soils (P &lt; 0.001). The chlorpyrifos toxicity to soil bacteria community was largely mitigated following WTR amendment, resulting in increased total bacterial abundance. Conclusions: Results obtained in the present study indicate a great deal of potential for the beneficial reuse of WTR as soil amendments for chlorpyrifos and TCP pollution control.</p