Relationships between wheat yield and soil organic matter, total nitrogen, alkali-hydrolysis nitrogen, available phosphorus and available potassium in the Weibei region of Shaanxi province.

<p>*Significance level: P<0.05.</p

Map of the study area.

<p>Map of the study area.</p

Variations of soil nutrient balance on wheat and maize plots in different regions of Shaanxi province.

<p>Variations of soil nutrient balance on wheat and maize plots in different regions of Shaanxi province.</p

Variations of PFP of fertilizer on wheat and maize in the different regions (kg kg⁻¹).

<p>Variations of PFP of fertilizer on wheat and maize in the different regions (kg kg⁻¹).</p

Relationships between N rates and total nitrogen, N rates and alkali-hydrolysis nitrogen, P₂O₅ rates and available phosphorus and K₂O rates and available potassium on wheat plots in the Weibei region of Shaanxi province.

<p>**Significance level: P<0.01.</p

Variations of soil organic matter, total nitrogen, alkali-hydrolysis nitrogen, available phosphorus and available potassium in different regions of Shaanxi province (error bars show standard deviations).

<p>Variations of soil organic matter, total nitrogen, alkali-hydrolysis nitrogen, available phosphorus and available potassium in different regions of Shaanxi province (error bars show standard deviations).</p

The screening process and results for literature from the 1970s to the 1990s.

<p>The screening process and results for literature from the 1970s to the 1990s.</p

Variations of yields for wheat and maize at the farmers' level in different regions of Shaanxi province (error bars show standard deviations).

<p>Variations of yields for wheat and maize at the farmers' level in different regions of Shaanxi province (error bars show standard deviations).</p

Average yield components, dry matter and nitrogen accumulation in different growth stages, and correlative coefficient (r) between grain yield and these parameters for all samples (n = 413).

**<p><i>p</i><0.01.</p

Total dry matter (A) and nitrogen (B) accumulation dynamics with N-0 (n = 79), N-opt (n = 126) and N-over (n = 154) treatments.

<p>(GS25, GS30, GS60, and GS100 are the regreening, stem elongation, anthesis, and maturity stages, respectively.).</p