Changes in Biological Soil Health Properties in Response to Increased Crop Diversity in a Dryland Wheat-Based Cropping System

Figures & data

Table 1. Enzyme substrates, reagents, and reaction conditions used in enzyme assays.

Enzyme	Substrate	Reaction conditions	Reaction stop
N-acetyl-β-d-glucosaminidase	ρ-nitrophenyl-N- acetyl-β-D-glucosaminide	0.1 M acetate buffer	0.5 M CaCl2 0.5 M NaOH
β-glucosidase	p-Nitrophenyl-β-D-glucopyranoside	Toluene MUB buffer	0.5 M CaCl2 0.1 M THAM

Table 2. Soil chemical properties at the experimental site measured in the final year of the project. Mean value ± sd. Differences were not significant between treatment.

			Treatment
Measurement		Unit	SW-WW	SP-MIL-SAF-SW
pH			7.4 ± 0.2	7.6 ± 0.2
OM		g kg^−1	37.6 ± 2	37.1 ± 1
Organic C*		g kg^−1	18.2 ± 1	18.5 ± 2
Total C		g kg^−1	20.0 ± 3	20.1 ± 2
Total N		mg kg^−1	1944 ± 122	1916 ± 109
Phosphate (Mehlich p-III)		mg kg^−1	36.4 ± 6.8	29.9 ± 2.2
Potassium		mg kg^−1	264 ± 28	236 ± 28
Sulfate		mg kg^−1	23.0 ± 2.8	22.1 ± 3.2
CEC		cmolc kg^−1	26.7 ± 4.2	29.2 ± 0.9

*Note: soils were calcareous and samples were not pretreated to account for carbonates. This may have resulted in an overestimation of organic C.

Figure 1. Soil respiration as a function of soil water content and temperature. Respiration increased significantly (p < .001) with increasing soil water content in both cropping systems (A). Respiration increased significantly (p < .001) with increasing temperature under the diverse crop sequence but not in the SW-WW sequence.

Table 3. Effect of cropping system on soil respiration. Mean soil (± standard deviation) respiration fluxes are shown for pre-planting, vegetative phase, and post-harvest. Differences were significant (p < .001) between treatments in the pre-planting and post-harvest intervals.

	Mean respiration
Time period	WW-SW (μmol m^−2 s^−1)	Diverse (μmol m^−2 s^−1)
Pre-planting	0.76 ± 0.01	0.82 ± 0.01
Growing season	1.52 ± 0.02	1.53 ± 0.02
Post-harvest	0.61 ± 0.01	0.74 ± 0.01

Table 4. Model statistics for soil respiration, for pre-planting, growing season, and post-harvest. Statistically significant differences were determined by type III analysis of variance with satterthwaite’s method.

Pre-planting
	Type III SS	Mean Square	DenDF	F-value	p-value
Crop Sequence (CS)	25.111	25.111	471	42.600	<0.001***
Tsoil	4.943	4.943	470	8.385	0.004**
Msoil	31.326	31.326	470	53.143	<0.001***
CS:Tsoil	0.063	0.063	470	0.107	0.744
CS:Msoil	10.467	10.467	471	17.756	<0.001***
Tsoil:Msoil	1.425	1.425	469	2.417	0.121
CS:Tsoil:Msoil	1.709	1.709	470	2.899	0.089
Growing season
	Type III SS	Mean Square	DF	F-value	p-value
CS	3.177	3.177	871	9.851	0.002**
Tsoil	1.278	1.278	869	3.964	0.047*
Msoil	7.015	7.015	871	21.752	<0.001***
CS:Tsoil	6.276	6.276	871	19.462	<0.001***
CS:Msoil	2.875	2.875	870	8.914	0.003**
Tsoil:Msoil	25.528	25.528	870	79.159	<0.001***
CS:Tsoil:Msoil	2.650	2.650	871	8.217	0.004**
Post-harvest
	Type III SS	Mean Square	DF	F-value	p-value
CS	14.882	14.882	591	27.535	<0.001***
Tsoil	14.562	14.562	592	26.943	<0.001***
Msoil	1.320	1.320	591	2.443	0.119
CS:Tsoil	6.142	6.142	593	11.363	<0.001***
CS:Msoil	0.751	0.751	593	1.390	0.239
Tsoil:Msoil	6.731	6.731	591	12.453	<0.001***
CS:Tsoil:Msoil	0.092	0.092	593	0.171	0.680

Figure 2. Average enzyme activities for N-acyl-β-D-glucosidase (A) and β-glucosidase (B) under diverse and SW-WW crop sequences. Letters indicate significant differences (p < .05) between treatments.

Figure 3. Enzyme activity as a function of soil NO₃-N. N-acyl-B-D-glucosaminidase activity had a significant negative correlation with soil NO₃-N while β-glucosidase activity was not significantly correlated to soil NO₃-N. No significant differences were observed between diverse (●) and SW-WW (▲) crop sequences.

Figure 4. Chao1 measure of alpha diversity of (A) bacterial and (B) fungal communities for SW-WW and diverse crop sequences. Treatments with different letters are significant at p < .05.

Figure 5. Beta diversity of (A) bacterial and (B) fungal communities for SW-WW and diverse crop sequences.

Table 5. Mean net N mineralized comparing in situ columns to mineralized N as measured by laboratory column incubation experiments. Differences in mineralized N were not significantly different (p > .05) between treatments.

			Mean N mineralized (kg ha^−1)
Method		N	SP-MIL-SAF-SW	SW-WW
In situ column		12	35.1 ± 3.1	31.2 ± 1.9
Laboratory column incubation		12	323 ± 9.4	334 ± 8.0

Data availability statement

The DNA sequencing data generated and analyzed in this study are available in the NCBI BioProject repository, https://www.ncbi.nlm.nih.gov/bioproject/PRJNA833079