Maize Cannot Be Grown in Xiengkhouang Province?

During a 2005 visit with National Agricultural and Forestry Institute (NAFRI) Director, Dr. Kouang Doungsila issued a challenge to these authors to determine if it was true that crops could not be grown in the extensive uplands of Xiengkhouang Province, Laos PDR. In response, a two-phase series of experiments was proposed and implemented. The Phase I experiment was to bring soil from the Xiengkhouang province uplands to a NAFRI greenhouse near Vientiane to assess possible nutrient requirements using a nutrient omission experiment. Simultaneously, soils were collected and analyzed from seven recognized agricultural regions of Laos. The initial Vientiane greenhouse experiment indicated that maize did grow, but there were multiple issues of extreme soil acidity and clear deficiencies of phosphorus and other nutrients. Phase II of the study included field studies on the site of soil selected for the greenhouse study. Field experiments were carried out for two years at the site with yields of maize exceeding 5500 kg∙ha in the first year and exceeding 6250 kg∙ha in a subsequent year. Intense symptoms of nutrient zinc (Zn) deficiency were observed, however. In 2008 another experiment was designed and carried out that included a Zn variable. The results from that experiment confirmed that maize yields nearing 6000 kg∙ha were indeed possible. Substantial amounts of lime were needed to correct the strong soil acidity, and a series of other nutrients including N, P, K, and Zn were also required. Ongoing issues are where to obtain the extensive amounts of limestone needed as well as an evaluation of the residual effect of the limestone The finely ground, very reactive burnt lime residual effect was, as expected, short-lived. The reHow to cite this paper: Souliyavongsa, X., Sipaseuth, N., Dounphady, K., Attanandana, T., Kanghae, P., Yost, R., Yampracha, S. and Kunaporn, S. (2019) Maize Cannot Be Grown in Xiengkhouang Province? Agricultural Sciences, 10, 1359-1369. https://doi.org/10.4236/as.2019.1010099 Received: October 1, 2019 Accepted: October 22, 2019 Published: October 25, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access X. Souliyavongsa et al. DOI: 10.4236/as.2019.1010099 1360 Agricultural Sciences sults clearly demonstrated that, indeed, it was possible for maize to be produced in the extensive uplands of Xiengkhouang province, in answer to Director Khouang’s challenging question.


Introduction
According to the World Food Program's Comprehensive Food Security and Vulnerability Analysis of Laos, food insecurity is widespread throughout the country and alarmingly high in rural areas [1]. While Lao PDR has reduced the proportion of hungry poor to 23 percent, the 2015 Global Hunger Index still rates hunger levels as "serious". Climate change is expected to further worsen this situation [1]. The 2019 report further states that, 35.6% of children between 6 and 59 months suffer from chronic malnutrition and stunting [1]. One of the contributing factors is the insufficient production of food. Other researchers in Laos have previously identified soil phosphorus (P) as being among the nutrients that most limiting growth of rice in both uplands soils of Laos [3] [4] as well as in lowland soils [5]. A subsequent study also carried out by the senior author of this manuscript confirmed and quantified the extensive P deficiency in Lao uplands [6].
The plains of Xiengkhouang province of Laos are located in the northeast part of Laos and represent high potential for production of food and industrial crops such as maize. As of 2005, only 5% of the plains were cultivated [7]. In the vicinity of the provincial capital of Xiengkhouang, it is estimated that more than 60,000 ha of acid, infertile savanna grassland was under-utilized by smallholders [8].
Limitations to food crop production by phosphorus are well-known in the tropics and a large number of technologies are available to diagnose and solve this pervasive problem [9]. -Assess yield potential of maize in a site representative of upland soils and estimate amendments necessary to achieve maximum yield. [10], available P was extracted by Bray 2 [11], Mehlich 1 [12], and by the Fe-strip Pi [13] methods. Exchangeable K, Ca, Mg, Na were extracted by NH 4 OAc, pH 7 [14], and cation exchange capacity (CEC) was measured by NH 4 OAc, pH 7 [14].

Materials and Methods
Organic matter (OM) was determined by the method of Walkley and Black [15].
Iron, Mn, and Zn were extracted by the DTPA pH 7.3 method [16]. Extractable Al and Fe were measured by two methods-acid ammonium oxalate pH 3 and the citrate bicarbonate dithionite method [17].
The taxonomic classification of the soils was determined using Soil Taxonomy [18].
Maize variety (Zea mays, L. "LVN10"), which was extensively grown in the Vientiane province was selected for the greenhouse study. The greenhouse study was conducted at the Dong Dok Station, Vientiane, during the late summer of 2006.

Phase 2. Field studies
A field experiment was begun in 2006 by Dounphady on the grasslands near Mee village, Pek district, Xiengkhouang Province [2]. The soil of this area was that used in the Phase 1 experiment at the Dong Dok Station, Vientiane. The soil was tentatively classified as a fine, kaolinitic, isohyperthermic, Typic Paleustult. Nutrient and chemical analysis is shown in Table 1. This soil was very acid, high in Al and Fe oxides and also extremely P deficient. Lime, 3500 kg•ha −1 of Ca(OH) 2 , was applied two weeks prior to planting of the first crop (2006) and incorporated to a depth of 20 cm [2]. The field study of 2006 (data not shown) revealed that maize responded to P applications up to 56 kg•P 2 O 5 •ha −1 but plants still appeared P deficient and zinc (Zn) deficiency symptoms were also observed.
In 2007, an additional 300 kg•ha −1 of burnt limestone was added.

Grain and Stover Yield Collection
Grain and Stover data were collected from the middle two rows in subplots of Zn and without Zn applied treatments. The two rows of plants and two plants of the beginning and the end of row were used as guard plants. The harvest area of grain and stover was 6 m 2 .

Statistical Analysis
Grain yields as affected by levels of P and Zn were analyzed using a strip-plot analysis with SAS [20] since the Zn was applied as a stripped factor. Yields of grain in 2008 were plotted versus P applied in 2008 to assess whether maximum response to added P had been obtained.
Grain yields for 2008 versus P additions in 2008 were also analyzed using a linear-plateau model [21], which is an implementation of the linear response model presented by Anderson and Nelson [22].

Discussion
Phase 1. Results from both the soil analyses (Table 1) and the nutrient omission experiment ( Table 2 and Figure 1), indicate that both soil pH and nutrient levels were extremely low and clearly were growth limiting for most food crops.
The nutrient omission experiment clearly demonstrated that among nutrient limitations, the P deficiency limitation was one of the most growth limiting. At  Measurements taken 55 days after planting (see also Figure 1).   (Table 3). Of particular interest was the result that yields increased with the additional application of P ( Figure 2). The application of Zn confirming earlier observations that it might be limiting. It was also interesting that the response to the addition of Zn was even greater at high levels of applied P. Maize response as measured by stover yields also increased markedly as well.
A soil analysis taken subsequent to the 2008 harvest pointed out several additional issues with growing crops on such acid soils ( Table 4). The limestone initially added was burnt limestone, CaO, and as such it was extremely fine powder, which neutralized the soil acidity very rapidly, but does not typically have a

Conclusions and Recommendations
The utility of classifying the soils can be illustrated by pointing out that the soil at the site of the experiment; Pek, was classified as a Typic Paleustult, indicating a highly weathered, acid, low nutrient capacity soil as well as low nutrient containing. The results show that these soils were both infertile and acid and will require substantial lime and fertilizer inputs, but can become highly productive if properly managed. Similar soils are highly productive elsewhere in the tropics.
It was observed that the soils had become acid again (pH 4.6) suggesting that the quick-acting burnt lime had a residual effect of approximately 2 to 3 years.
The expected productivity of LVN10 variety of maize was about 6 -7 t•ha −1 .
The field experiment results suggested that the P requirement of this area was 71 kg•P 2 O 5 •ha −1 . Besides the lime and P applications, it was shown that Zn was necessary for maize production in Xiengkhouang province.
The results of this study indicate that high yields of food crops were possible with proper management. The soil pH should be increased to be 5.5 -6 with local liming materials and adequate amounts of P and Zn fertilizer applied. Moreover, planting with native legumes or other acid tolerant plants during the dry season and the incorporation of the residues into the soil is also recommended, especially when maize is to be grown. Gradually, the soil will be improved to better physical and chemical properties. These results suggest that the region has enormous potential to support food crops and to improve food security of the region.