Evaluation of Soil Quality in Arid Western Fringes of the Nile Delta for Sustainable Agriculture

Table 1

Soil quality scoring functions (SSFs) and thresholds values for soil and terrain quality indicators.

Indicator	SSF	Thresholds		B	O	L1	U1	S	Sources
		L	U
Sand	SSF5	0	60	—	35	30	50	0.440	[89]
Silt	SSF3	0	25	10	—	—	—	0.249	[89]
Clay	SSF3	0	30	15	—	—	—	0.268	[89]
pH	SSF5	4.5	9.5	—	7.00	6.5	7.7	1.301	[3, 75, 83, 84, 90, 96, 97]
EC^a,b	SSF5	0.0	2	—	1	0.25	1.75	2.234	[84, 90, 96, 97]
OM^a,b	SSF3	0.2	2	1	—	—	—	1.049	[36, 86, 96–98]
ESP	SSF9	2	15	5	—	—	—	2.50	[15, 39, 66, 99–101]
CEC^a	SSF3	0	21	10.5	—	—	—	0.245	[36, 82, 89, 96, 102, 103]
CaCO3^b	SSF9	1	8	3	—	—	—	2.50	NE, EO
FC	SSF3	15	25	20	—	—	—	−2.50	NE, EO
AWHC^a,b	SSF3	2	10	4	—	—	—	0.198	[80, 85]; NE
BD	SSF9	1.00	2.0	1.50	—	—	—	−2.62; –0.323	[104, 105]
PD^b	SSF9	1.00	1.50	1.2	—	—	—	2.50	[81, 97, 106, 107]
Slp^a	SSF9	2.00	4.00	3.00	—	—	—	2.50	NE, EO
Rlf	SSF9	3	10	5	—	—	—	2.50	NE, EO
TWI^b	SSF9	5	15	10	—	—	—	2.50	NE, EO

^aSelected soil and terrain indicators based on the minimum dataset (MDS) from factor analysis. ^bSelected soil and terrain indicators chosen by expert opinion based on the natural ecosystem. NE: natural ecosystem, EO: expert opinion. For SSF₃: L, lower threshold, at which or below the score is 0; B, baseline, at which score is 0.5; U, upper threshold, at which or above score is 1.0. For SSF₅: L, lower threshold, at which or below the score is 0; L₁, lower baseline is 0.5 with bell-shaped relationship; O, optimum level, at which score is 1.0; U₁, upper baseline is 0.5 with bell-shaped relationship; and U, upper threshold, at which or above score is 0. For SSF₉: L, lower threshold, at which or below the score is 1; B, baseline, at which score is 0.5; and U, upper threshold, at which or above score is 0. S, slope at baseline for nonlinear scoring functions.