Multiple linear regressions are concerned with studying and analyzing the relationship between the dependent variable and a set of explanatory variables. From this relationship the values of variables are predicted. In this paper the multiple linear regression model and three covariates were studied in the presence of the problem of auto-correlation of errors when the random error distributed the distribution of exponential. Three methods were compared (general least squares, M robust, and Laplace robust method). We have employed the simulation studies and calculated the statistical standard mean squares error with sample sizes (15, 30, 60, 100). Further we applied the best method on the real experiment data representing the varieties of

Cover crops (CC) improve soil quality, including soil microbial enzymatic activities and soil chemical parameters. Scientific studies conducted in research centers have shown positive effects of CC on soil enzymatic activities; however, studies conducted in farmer fields are lacking in the literature. The objective of this study was to quantify CC effects on soil microbial enzymatic activities (β-glucosidase, β-glucosaminidase, fluorescein diacetate hydrolase, and dehydrogenase) under a corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation. The study was conducted in 2016 and 2018 in Chariton County, Missouri, where CC were first established in 2012. All tested soil enzyme levels were significantly different between 2016 and 2018

Semi-parametric models analysis is one of the most interesting subjects in recent studies due to give an efficient model estimation. The problem when the response variable has one of two values either 0 ( no response) or one – with response which is called the logistic regression model.

We compare two methods Bayesian and . Then the results were compared using MSe criteria.

A simulation had been used to study the empirical behavior for the Logistic model , with  different sample sizes and variances. The results using represent that the Bayesian method is better than the   at small samples sizes.

Different formula of bioagents (Rhizobium cicceri cp-93, Azospirillum sp.,
Pseudomonas fluorescence, Trichoderma harzianum ) used in this study as a
biofertilizer on wheat crop with two level of chemical fertilizer (0 and 12.5
kg/donm Dap) compared to 50kg/donm Dap (standard amount).the study carried out
in Iraq/Diyala –Alkhales during November 2014,results showed significant increase
in no. of spikes, no. of spikelet’s, length of spike ,Weight of 1000 seed and yield of
one m2 when adding (Rhizobium cicceri cp-93,Azospirillumsp+ Trichoderma
harzianum +12.5 kg/donm Dap) in comparison with the 50kg/donm Dap. Other
formulas recorded same results with the treatment 50kg/Donm Dap with not
significant differences