E. Marten

You need to use WordPress SEO by Yoast (Props to him!)
Adds “More Sitemaps” to your WordPress SEO Settings. If you are using a second WordPress-Installation in a subdirectory, you can now easily add the second Sitemap into the main one.
If you are using a second WordPress-installation in a subdirectory and want it to be fully integrated it into your main site to prevend struggeling with two or more Sitemaps in your Webmastertools, 
you can easily integrate more sitemaps into your main one. (sitemap_index.xml) 
The Plugin adds your second and third (aso) sitemap into the main sitemap and tooks care about the modification date automatically!
Thanks to Joost de Valk!

IsSiY (Include second Sitemap into Yoast) WordPress SEO Extension

Adds "More Sitemaps" to your Wordpress SEO Settings. Include differen sitemaps to your sitemap_index.xml

Sunil Kumar Sharma

The Better India

Hey buddy, 
If you’re looking for a plugin that helps you create a news sitemap and automatically ping your website’s sitemap to Google Webmaster, you’re in the right place! 
The WP News Sitemap plugin provides a seamless solution for dynamically updating news sitemaps and automatically pinging them to Google Webmaster for better SEO and indexing of news content.
<h4>Features</h4>
<ul>
<li>Create a dynamic news sitemap for your site. </li>
<li>Automatically ping Google Webmaster with updated sitemaps. </li>
<li>Customize settings to suit your site’s requirements. </li>
<li>Compatible with multiple post types and custom date ranges.</li>
</ul>

WP News Sitemap

This plugin is used to create a news sitemap and auto ping sitemaps to Google Webmaster.

IsSiY (Include second Sitemap into Yoast) WordPress SEO Extension vs WP News Sitemap