Cables de fibra óptica

In this section we describe the steps taken to re-design field-level maize cropping systems. Since the objective of the study focused on alternatives to current systems for the short term, we concentrated on existing technologies or technologies that could be mobilized without major research effort.

Design criteria

We used three sources of information to select design criteria, i.e. attributes distinguishing the different alternative production systems (Hengsdijk and van Ittersum, 2003): the state government fertilizer subsidy scheme, the recommendations of the national extension service, and results from our own experiments and surveys.

We did not find other sources of information that were locally relevant. The resulting design criteria and the associated variants are listed in Table 3.

The design criteria comprised the origin of fertilization strategies, sources of nutrients, use of canavalia and level of residue retention. Cropping systems were constructed by combining variants of the various criteria. Not all combinations resulted in cropping systems that were parameterized. In particular, information on the effect of combinations of organic and mineral sources of nitrogen is still limited, and information on canavalia only existed from the on-farm experiments. In total 14 maize-based cropping systems (MBCS) were parameterized (Table 4). For each

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MBCS all relevant inputs and outputs were defined as described in the next section.

Quantification of outputs and inputs of MBCS

Outputs and inputs of the cropping systems were quantified to be able to evaluate their performance at farm level in the next stage using the FarmDESIGN model. Marketable outputs comprised maize grain and roselle calyx yields. Non-marketable outputs comprised changes in the soil OM balance resulting from application and

Table 2. Land characteristics of the eight case study farms. Ranges refer to variation among fields. Soil erosion was calculated using RUSLE (Renard et al., 1997). Data summarized from Flores-Sanchez et al. (2011).

Table 3. Criteria used to design alternative maize-based cropping systems (MBCS) for smallholders in the Costa Chica, Mexico.

Design criterion Variants and their labels

Origin of the strategy • Current farm-specific use (Cu)

• Current farm-specific use plus K (Cu+K)

• Subsidy scheme (S)

• Subsidy scheme plus K (S+K)

• Agronomic recommendation (R)

• On-farm experiments (E) Source of external nutrients • Mineral fertilizer (F)

• Vermicompost (V)

• Combination of mineral fertilizer and vermicompost (FV)

Canavalia • Not used (c)

• Intercropped with maize (C) Level and destination of residue

retention

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Table 4. Design criteria used to create maize-based cropping systems (MBCS) for smallholder farming systems in the Costa Chica, the abbreviations of the variants, their use in scenarios during exploration and the information sources used in their quantification.

1 Scenario S4 comprises the MBCS of S3 and number of animals as decision variables

decomposition of OM. Inputs included seeds of maize, roselle and canavalia, mineral and organic fertilizer, herbicide, and labour. For each field, crop products were characterized in terms of biomass and yield(see below), and N, P, K and ash contents using on-farm measurements (Flores-Sanchez et al., 2011), complemented with

Design criteria with addition of K according to Gómez et al. (2007)

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information from the literature (Mitra and Shanker, 1957; Burgess et al., 2002;

Colunga et al., 2005; Harrington et al., 2006).

Using the design criteria outlined in Table 3 soil fertility strategies were created (Table 4). Farm-specific current fertilizer use (Cu) served as a reference. The simplest change comprised application of K at the same rate as N to compensate for the lack of K in current strategies and in the soils (Flores-Sanchez et al., 2011). Also for the subsidized fertilizer package (69-30-00 kg ha^-1 N-P-K) an alternative which included 25 kg ha^-1K was created based on INIFAP recommendations (Gómez et al., 2007). Finally, a system with a fertilizer rate of 135-39-83 (kg ha^-1 N-P-K) was included corresponding to the agronomic recommendation (R) for maize – roselle systems (Navarro et al., 2002). Other soil fertility strategies were based on experimental trials (E), which included mineral fertilizers at a rate of 55-5-46, vermicompost at a rate of 2.5 Mg DM ha^-1, equivalent to 23-6-20 (kg ha^-1 N-P-K), and a combination of both equivalent to 78-11-66 (kg ha^-1 N-P-K).

Maize production levels for each cropping system and each farm were calculated in an input-oriented manner using the model QUEFTS (Janssen et al., 1990), which was evaluated for the region by Flores-Sanchez et al. (2011). The model uses soil chemical properties as inputs, including organic carbon (g kg^-1) assuming 58% C in soil OM, total N (g kg^-1), P-Bray-1 (mg kg^-1) (B.H. Janssen; personal communication), K-exchangeable (cmol kg^-1), pH (H2O) and cropping system-specific rates of fertilizer. The model first calculates crop uptake rates of N, P and K based on the potential supply by the soil, the applied amounts of fertilizer, and an estimated nutrient recovery of applied nutrients. Next, three intermediate yield estimates are made, one for each of the nutrient pairs based on the uptake of N, P and K, taking into account for each nutrient values for maximum accumulation (i.e. the nutrient is not yield-limiting) and maximum dilution (i.e. the nutrient is yield-limiting). In the final step, yield is predicted based on the smaller of the three yield estimates.

Weed management was assumed to be conventional with herbicide applications at maize sowing and three weeks later, resulting in same biomass of weeds as found for current practices (Flores-Sanchez et al., 2011). In all land use activities, roselle yield was assumed to be similar to that found currently on the farms, as roselle was found to show little response to different rates of fertilizer (Chapter 4).

A number of fertilization strategies included canavalia as cover crop (Table 4), which was assumed to be sown 4 weeks after sowing maize. Experimental results did not reveal direct effects of canavalia on maize grain yield (Flores-Sanchez et al., 2013), but did demonstrate a substantial reduction of weed biomass. Assuming similar conditions as in the experiments for those MBCS that included canavalia, weed biomass was reduced by 66% compared to current practices. Except for those strategies in which

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fields were assumed to be fenced resulting in 100% residue retention, 70% of the biomass of crop residues, weeds and canavalia was assumed to be removed by roaming animals (on farms without animals) or fed to the own farm animals (Flores-Sanchez et al., 2011). Input from N2 fixation by canavalia was set at 6 kg ha^-1 y^-1 in a maize – roselle intercrop, and 16 kg ha^-1 y^-1 in a maize monocrop, similar to field estimates (Flores-Sanchez et al., unpublished data).

Quantification of labour input was based on current labour use observed on each of the case study farms. A fixed amount (2 labour-days = 16 hours) of additional labour was added to account for the time needed to cover the fertilizer and compost after application to the plant base. This technique was assumed to be a ‘best technical means’ (van Ittersum and Rabbinge, 1997) to maximize use efficiency by avoiding washing off. Labour was hired outside the farm to deal with labour peaks; the remainder was supplied by the farmer and his family (Table 5). We denote the former as casual labour and the latter as regular labour.

Table 5. Regular and casual labour (hr ha^-1) for each MBCS variant and for each farm.

1Variants as described by their labels (Table 3).

For each cropping system production costs were estimated based on quantities and prices of inputs: mineral and organic fertilizers, herbicides, seeds and labour. Cost of inputs per MBCS and variation among farms are presented in Table 6. Prices of crop products (maize grains and roselle calyces) and animal products (meat) were obtained from the databases Sistema Nacional de Información Agroalimentaria y de Consulta (SIACON) and Sistema Nacional de Información e Integración de Mercados (SNIIM) using data of 2003. Both family and hired labour were valued at 50 MX$ hr^-1.

MBCS

Farm Current All Cu and R

variants¹ All others

Regular Casual Regular Casual Regular Casual

A1 128 208 144 240 160 256

A2 176 256 200 280 224 288

A3 96 176 112 208 128 224

A4 180 244 196 276 212 292

X1 120 232 136 264 152 280

X2 144 288 152 312 160 336

X3 168 264 192 288 216 296

X4 144 288 171 250 184 274

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Table 6. Average costs per ha (in Mexican pesos (MX$) for each maize-based cropping system. Ranges are due to differences in amounts used per farm. For abbreviations of the MBCS see Table 4.

MBCS Casual

labour Regular labour

Fertilizers

herbicides and Seeds^a Fences Total cost

Cu(Fcr) 3961 1580 1189 0 0 6730

Cu+k(Fcr) 4063 1703 2004 0 0 7770

S(Fcr) 4150 1703 1233 0 0 7086

S+K(Fcr) 4063 1703 1502 0 0 7268

R(Fcr) 4078 1703 2304 0 0 8085

E(Fcr) 4063 1703 1023 0 0 6788

E(Vcr) 4063 1703 2812 0 0 8578

E(F-Vcr) 4063 1703 3508 0 0 9274

E(FCr) 4161 1802 1023 350 0 7336

E(VCr) 4161 1802 2812 350 0 9125

E(F-VCr) 4155 1802 3508 350 0 9815

E(FCR) 3442 1838 1092 350 181 6644

E(VCR) 3442 1838 2893 350 181 8444

E(F-VCR) 3442 1838 3570 350 181 9122

aCost of canavalia seed. Farmers used own or exchanged seeds of maize and roselle.